#ocean observatories

[juicetrump2]

Dismay as Trump officials to dismantle key ocean monitoring system

Ocean Observatories Initiative, $368m network that has provided crucial climate data, latest victim of Trump cuts

[juniperpublishersoceanography]

Progress to Date and Future Perspective of Ocean Research- Juniper Publishers

Abstract

Most recently signed economic, political, and social agreements such as the Paris Agreement, the 2030 Agenda for Sustainable Development, or the FAO’s Blue Growth Initiative have as common objective the strengthening of the global response to the threat of climate change holding the increase in the global average temperature well below 2 °C above pre-industrial levels. Aside of the implementation of ambitious plans on adaptation and mitigation, our ability to contain climate change within safe limits depends largely on the evolution of the ocean circulation and state. The increased awareness of the rapid degradation of the ocean and its importance to the future of humanity is the result of decades of ocean research that has finally been embodied by the proclamation of a Decade of Ocean Science for Sustainable Development (2021–2030) by the United Nations General Assembly. In the framework of this program, there is an extraordinary opportunity to connect ocean sciences more directly with policy-makers, business, and civil society around a program of joint research and technological innovation [1].

Present Situation

Decades of marine research have provided clear evidence of the crucial role of the ocean in the past, present and future climate and in the origin and maintenance of life. Now, we know that the oceans cover more than seventy percent of the Earth surface and due to its large volume and its thermal inertia -about 4000 times greater than that of the air- the ocean accumulates 93% of the energy in the Earth Climate System, being the main driver of climate regulation and acting as a heat buffer for climate warming [2]. Besides, the global ocean not only absorbs, stores, and redistributes vast amounts of heat but also of carbon. The ocean contains 50 times more carbon than the atmosphere and it is actively absorbing about 30% of the emitted anthropogenic carbon dioxide (CANT) [3]. 50% of the oxygen in Earth’s atmosphere is produced in the upper layers of the ocean by phytoplankton [4]. The regulation of atmospheric and marine carbon dioxide (CO2) concentrations and the provision of oxygen are just some of the services that marine ecosystems and marine biodiversity provide for human well-being. Obviously, they also provide fish and shellfish, representing the primary source of animal protein in the diets of approximately 1 billion people (mostly in developing countries) [5].

However, in the last decades an important question has arisen influencing irremediably the scientific progress: Is the climate on Earth changing and is that change induced by the human being? Due to its crucial role in the Earth’s climate, contributing to answer this question has also determined oceanographic research. As greenhouse gases increase the Earth radiative imbalance (the energy that we receive from the sun exceeds the energy that leaves the atmosphere back to the space), the oceans sequester up to 93% of the extra heat in the climate system [1], and as a result, the ocean is warming [6,7]. The drastic surge in anthropogenic CO2 emissions since the industrialisation not only results in ocean warming but is also the cause of ocean acidification (progressive increase in ocean inorganic carbon concentrations and decreased water pH and calcium carbonate saturation) and a significant decrease in the dissolved oxygen content [3]. In parallel with these changes, the human population has been introducing an increasing level of nutrients into coastal waters, leading to problems of eutrophication and severe oxygen deficits in coastal waters [8]. In 2011, 28.8% of the fish stocks were overexploited; 61.3% fully exploited; and 9.9% underexploited [5]. Next, this review briefly outlines a range of critical consequences of ocean warming, acidification and deoxygenation and future challenges of marine research.

Ocean Warming

Over the period from 1971 to 2010, the ocean warmed at average rates of 0.1 °C/decade in the upper 75 metres (m) of the water column and 0.015 °C/decade in the first 2000m [6]. Although these temperature increases may seem small, they should be seen in relation to the large body of water that has been heated. If the same amount of heat that had been buried in the upper 2000m of the ocean would had been accumulated in the atmosphere, the surface of the Earth would have warmed up to 36 °C instead of 1 °C for the past 40 years.

Ocean surface warming is commonly associated with a more stratified, less productive, and less oxygenated ocean. Such an assertion is mainly based on consistent projections of increased near surface stratification and shallower mixed layers under global warming scenarios [9,10]. However, as shown in [11] this statement cannot be considered globally applicable and outcomes may differ by region. Ocean warming is causing fish, birds, sea turtles, and other species to change their behavior and habitat. All organisms specialize in a limited range of ambient temperatures for optimal performance. An organism under climatic conditions exceeding these limits can see affected its immune system, growth, body size, and behavior [12]. Species are moving into deeper waters and towards higher and cooler latitudes at a speed that is up to five times faster than the displacements observed by species on land. In the composition of the fisheries’ catches, a shift of 30 to 130km towards the poles of the species captured in North Atlantic, Antarctic and Arctic waters and 3.5m/decade into deeper waters has been observed [13,14].

The thermal expansion of the ocean and the melting of glaciers are the main factors responsible for the rise in mean sea level in the 20th century. Sea level rise introduces saline water into the deltas and estuaries, where aquaculture is commonly carried out, forcing the facilities to move upstream. The spread of infectious diseases in a warmer ocean also represents a major threat to aquaculture, as observed for example in oyster and abalone aquaculture [15].

Ocean Acidification

Ocean acidification represents one of the major drivers of ocean physical and biological changes. The pH value of ocean surface water has decreased by 0.1 pH units since the pre-industrial period [16]. Excess of CO2 in seawater reduces the availability of carbonate ions which are necessary for marine calcifying organisms with shells and calcareous skeletons consisting of aragonite (CaCO3), such as corals, molluscs, echinoderms and crustaceans [17]. This leads to reductions in survival, calcification, growth, development and abundance for these marine organisms with implications for aquaculture. Regarding fisheries, it is rather the interactive effects of pH decrease with other stressors, such as warming or eutrophication, that may potentially lead to long-term changes in species composition [18].

Deoxygenation

The decrease in the concentration of oxygen in the ocean is the result of the decrease in the solubility of oxygen due to the heating of the ocean, the decrease in its ventilation [4], and changes in respiration rates. Ocean deoxygenation is causing the expansion and shoaling of oxygen minimum zones (OMZs), which are expected to cause a decrease in demersal fish diversity and alteration of trophic networks [18]. Hypoxia intolerant and high oxygen-demand species are expected to undergo habitat compression, making them more susceptible to overfishing. It is likely that demersal fisheries will be adversely affected by the expansion of OMZs [19]. OMZs are found in the subtropical and tropical zones of the Atlantic, Pacific and Indian Oceans.

Future perspective of Ocean Research

The most prominent advances in physical oceanography in the last 20 years have been summarized in the recognition that ocean variability at meso- and submesoscales and ocean– topography interactions are crucial in shaping the elementary features of ocean circulation [20]. Satellite measurements and mesoscale eddy-permitting global general circulation models have revealed the ocean -far from behaving according to linear approximations- to be intrinsically turbulent [21]. This recognition that the mean state of the ocean is largely determined by turbulent aspects of the flow and interactions with topography has significantly change the way the oceanographic community approaches the study of ocean circulation. In the WOCE-era, it was expected to obtain a meaningful estimate of the time-mean ocean circulation through standard oceanographic sections and using quasi-steady-state inverse estimation techniques. This approach has been replaced by observation efforts including a wide range of measurements (oceanographic sections, Argo buoys, gliders, drift buoys, autonomous profilers, etc.) and models that assimilate such data to estimate the evolving state of a turbulent ocean.

The situation for biogeochemistry and marine ecology is substantially different. Currently, the factors that force marine ecosystems and biogeochemical cycles are not fully understood, nor the response to these stressors or the synergy between them [22]. Fisheries research with the objective of knowing the state of the stocks of fish, molluscs and crustaceans is possibly even more deficient of a deep knowledge of how the abiotic factors affect the species and the fishing activity. Besides, a transition in the way of approaching the study of the mean state of the ocean has not yet taken place for marine ecology and biogeochemical studies. The need of samples for analytical determinations hinders this progress. However, the information that can be obtained from optical sensors has not been exploited to its full potential, and the use of state-of-the-art autonomous ocean technology to study marine ecosystems and biogeochemical cycles is the area of biogeochemical oceanography where major advances are to be expected in the coming decades. Concerning physical oceanography, the role of the circulation in the coupled climate and the dissipative processes for having received less attention until recently due to the difficulties in observing and modelling flows on the smallest length scales and shortest time scales of the circulation are the areas where major advances are to be expected in the coming decades [20,21].

Apart from the expected advances in each of these areas, the proclamation of a Decade of Ocean Science for Sustainable Development (2021–2030) by the United Nations General Assembly gives an extraordinary opportunity to the scientific community for multilateral cooperation with policy-makers and civil society with the capacity to transform the field of Ocean Sciences [1].

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[juniperpublishersoceanography]

An Acoustic Archival Tag for Long-Range Tracking Of Small Fishes- Juniper Publishers

Abstract

This mini review describes the development of an acoustic tag for long-range (tens to hundreds of kilometers) tracking of small fishes or other marine animals. Tracking is achieved by standard RAFOS triangulation using the arrival times of unique sound signals emitted by moored sources. The tag also records temperature and pressure. All functions of the tag are controlled by an application specific microchip. The collected acoustic and sensor data are stored in a non-volatile memory. A cylindrical hydrophone of 25.4mm length and 10.7mm diameter also serves as housing for all electronic components. Power is provided by 2 button cell batteries, which enable an active tag lifetime of approximately two years.

Introduction

Much has been learned about the behavior of fishes during the past few decades through various kinds of data storage tags (DSTs), which were attached either externally to the back of the fish, or subcutaneously (e.g. Metcalfe [1], Block [2]). By recording in-situ physical parameters such as temperature, depth and light intensity, the geographical position can be inferred on the basis of retrospective analysis of known hydrographic features of the animal's environment or light level for surface species. However, such retrospective positioning is invariably imprecise because physical features may vary only slightly (horizontally, and vertically in higher latitudes) or be poorly known (at least for purposes of retrospective positioning). During the first decade of the new millennium, a new technology emerged, which allowed equipping the tags with compact high frequency acoustic transmitters, each transmitting a unique ID code. When a fish tagged with such a transmitter passed within the acoustic range of a moored stationary receiver, a record of that event was kept. While fish cannot be tracked continuously this way, this widely used technology provided valuable insight into the overall range and timing of their movements [3].

To track submerged objects over much longer distances, Rossby [4] pioneered a new approach more than 30 years ago with his SOFAR floats, that passively listened for scheduled acoustic transmissions from anchored sound sources (Rossby [5], whose narrow-band emissions, centered at 260Hz, could be detected tens to hundreds of kilometers away depending on the physical conditions of the sound channel. The selected 260Hz range renders signal absorption insignificant and avoids most of the low- frequency ambient noise Urick [6], Wenz [7]. Each RAFOS float keeps a record of the arrival times of the precisely timed sound signatures. The source distance can then retroactively be inferred by multiplying the travel time of each sound signature by its known propagation speed.

The Fish Tag

Thanks to the continuing reduction of the transistor dimensions in microelectronic circuits (Moore's Law), it is now possible to implement the complex acoustic arrival time detector of a RAFOS float on a tiny microchip. While in its most active mode when the tag is searching for sound signatures, the chip dissipates approximately 70|iW, but the stand-by power is not more than 4|iW. Assuming a realistic duty cycle of 10% (e.g. searching for sound signatures for 6 minutes every hour), the average power dissipation amounts to just 10-11|iW. Two 1.5-volt button cell batteries of 80mAh capacity can thus keep the system running for more than 2 years. The microchip also houses a thermal sensor as well as a pressure sensor interface to assess depth. The sensors utilized in the fish tag yield a resolution of 0.05 °C and approximately 0.7 PSI (~0.5m), respectively. If so desired, pressure and temperature can be sampled more frequently than searching for sound signatures. A more detailed description of the chip's features and its design can be found in reference Fischer [8].

Accurate timing is critically important in any time-of-flight based positioning system. Since the fish tag’s energy capacity is severely limited, it uses a low power commercial watch crystal oscillator circuit as the clock source. To avoid severe clock deviations, the fish tag timer employs a digital correction unit, which allows adjusting for offset errors stemming from the manufacturing process and compensating for the expected temperature deviations. The 6-bit digital correction scheme limits timing errors to ±0.95ppm or ±0.6 seconds per week. The remaining clock deviations can be mitigated by utilizing the travel time differences from three source to determine the position hyperbolically. One can then retroactively determine the clock correction needed to obtain the right travel time [9].

The assembly of the tag is a relatively straightforward matter. The custom microchip is surface mounted on a tiny printed circuit board (PCB) together will all other electronic components, i.e., the watch crystal oscillator, the nonvolatile memory chips and 3 filter capacitors. This PCB is only 8mm wide and fits tightly inside the hydrophone cylinder, which also serves as the tag's housing. The circular pressure sensor board is attached perpendicular to the PCB and forms one of the two end plates of the cylindrical tag. Figure 1 depicts a RAFOS sound source together with one of the 4 cm long prototype tags without its final polyurethane coat.

Field Test Results

A series of field tests have been conducted during the course of this project to validate the performance of the tag in its various stages. The first was a preliminary test designed to evaluate the critically important analog preamplifier and the potential tracking range. In this experiment, source and receiver were kept below the surface mixed layer at ~40 and 30m, respectively, on the New England shelf south of Nantucket. At a distance of 70km from the acoustic source, the records revealed a robust in-band signal-to- noise ratio of approximately 6dB [10].

Encouraged by the positive early test results, the project continued. But it was not until this past summer that first complete prototype tags became available. This paved the way for a more comprehensive test conducted approximately 50km south of the Mississippi delta in the Gulf of Mexico. The logistics of this experiment were simple. The tags were attached to the ends of two 30m long ropes, which in turn were tied to 2 surface drifters equipped with GPS trackers. The sound source was kept on the host vessel, the Endeavor, and lowered repeatedly to a depth of approximately 25m from the Starboard side at various distances starting at ~130km.

The submerged tags recorded an almost uniform water temperature around 27 °C during the 40-hour test period. This warm surface layer provided for less than ideal acoustic conditions, since it bends the acoustic energy away from the surface. But a thin fresh water lens of Mississippi origin created a shallow surface sound channel such that transmissions could be detected as far as 60km away. The source level was measured with a calibrated hydrophone to be 180dB re 1μPa at 1m. It was therefore no surprise that none of the tags detected a signal emitted from any of the three farthest source sites located 72 -130km away.

4-8 sound signatures were emitted at each source site. The recordings revealed a remarkably small spread in signal propagation times, 0.053-0.132 seconds. This corresponds to a spatial uncertainty range of not more than 200m.

Conclusion

The presented fish tag, with a length of approximately 4cm similar in size to other archival tags, operates according to standard RAFOS tracking principles: it detects and records the arrival times of signals transmitted from moored sound sources. Navigational accuracy is determined by how well clock errors in the tag can be controlled, but can be kept quite small thanks to knowing total drift error and temperature of the crystal clock during mission. The two main drawbacks of the presented tagging technology are the cost for the sound infrastructure and the need to retrieve the tag to upload the archived data. At a future time, we will explore how to avoid the second drawback by adapting the tag to a miniature satellite transmitter and a release mechanism, which allows the device to float to the surface at the end of mission. The added bulk means this technology will be best suited to larger species.

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[juniperpublishersoceanography]

Voluntary Commitments (VCs) under the UN Oceans Conference- Are VCs Advancing the Implementation of SDG 14?- Juniper Publishers

Introduction

The high-level United Nations Conference to Support the Implementation of Sustainable Development Goal 14: Conserve and sustainable use the oceans, seas and marine resources for sustainable development took place in New York in June 2017. While promising to be solutions-focused with engagement from all, it aimed at slowing down the decline in the health of the oceans, for the people, the planet and prosperity; and its outcome document "Our Ocean, Our Future: Call for Action" and the approximate 1,400 registered voluntary commitments (VCs) have been praised by the UN as a "global breakthrough on the path for the health of our oceans and seas"

While SDG 14 focuses on actions where there seems to be a lack of willingness, capability and cooperation from governments to reach agreements [1], VCs are a tool often used alongside official agreements and declarations in sustainable development efforts since the 2002 World Summit on Sustainable Development [2]. However, their effectiveness seems debatable as they also represent a scheme for avoiding obligations, they fail to engage all, and seldom deliver what was promised; moreover, their use in multiple forums distracts efforts towards taking decisive actions to ensure the sustainable conservation of the oceans. Consequently, the question of whether or not VCs constitute a solutions-focused approach is raised, together with the need to examine the Conference's achievement in connection with an engagement for all and lastly, their contribution towards the implementation of SDG 14.

Are VCs A Proper Solution-Focused Mechanism?

The rationale behind VCs lies in the insufficiency or incapacity of Member States to take "mandatory" or "required" decisions in sustainable development or climate forums, hence the need for new forms of non-legally binding instruments to ensure actions are taken within a given time frame, which in turn allows countries to agree on a course of action and engage wider audiences beyond their national governments. The element of flexibility in such non-negotiated, collaborative projects and partnerships often backfires as the lack of rigid constraints leaves actors free to choose the areas on which they are interested in committing. As an example, the fewest VCs are found in one of the most critical targets of SDG 14, overfishing and illegal, unreported and unregulated fishing. Due to their voluntary and complementary character, it is difficult to state that VCs are proper solution-focused mechanisms. I think they are complementary tools to enhance sustainable development efforts instead.

Have VCs Been Able to Engage us All After the Conference? Are there Gaps in Participation?

The idea behind VCs is to encourage stakeholder's engagement by ensuring the community participates in sustainable development programs. VCs have the capability to involve multiple stakeholders, intergovernmental and non-governmental organizations, multinational and national corporations, and innumerable networks, many of whom may make use of new technologies to support their causes [3]. As a result, VCs are also capable of leading initiatives where a commitment beyond compliance could be within reach, with the added benefit of potentially mobilizing or accessing additional founding.

The main contributors of VCs globally are governmental entities, with significant differences across all geographic regions. An analysis made at the VCs of the Oceans Conference showed that Eastern Europe's actions are led exclusively by governmental entities, while North America's main contributors are NGOs. The private sector is absent in VCs in the African Continent, the Middle East, Eastern Europe and Central America. In addition, it is important to point out that the sectors making the fewest contributions are academia (3%), the scientific community (2%) and philanthropic organizations (1%) [4]. As we can see, the presence of gaps in global participation opens spaces for questioning the engagement of all.

Do VCs Really Represent Advantages?

It can be said that VCs embody a «nothing-to-lose» approach. Even when failing, there is always a net gain, because nothing would have happened if there had not been a VC in the first place. A successful example is the Partnership for Clean Fuels and Vehicles that helped national ministries, agencies, groups from civil societies and UN agencies to work together in helping developing countries reduce air pollution by adopting clean fuels in vehicles [4]. In spite of their potential for achieving solutions to global problems, VCs also allow governments to circumvent their responsibilities and unfortunately are used by companies to enhance their reputation and for avoiding stricter regulations. If we look at «green washing” and "blue washing» practices by companies around UN Global Compact, there is a controversy regarding their social corporate responsibilities being undermined by their own VCs.

How Many VCs Aimed at Achieving the Sustainable Use of the Oceans are Registered?

Currently a growing number of UN and government-related initiatives have requested and published VCs. In addition to the 1406 VCs made at the Oceans Conference, other ocean forums have registered their own VCs as well, for example the Our Ocean Conference hosted by the European Union with its 437 generated commitments, and those from Our Oceans Conferences in 2016, 2015 and 2014. Similarly, commitments related to the oceans have been registered in Conferences on climate change or biodiversity, such as the Aichi Biodiversity targets in 2010. At the moment, the degree of overlap of these commitments is unknown; it is also difficult to determine whether VCs have been registered in more than one forum. Besides helping quantify current VCs, experience sharing should also be an important aim of the registry, which could help transfer knowledge among participants to help towards engaging all.

Conclusion

As shown above, VCs need to be looked upon more closely, considering that they seem to accomplish less than they set out to do as proper solution-focused mechanisms. Their flexibility is not necessarily a synonym of success; and advantages and disadvantages from previous experiences need to be kept in mind in order to be able to profit from these initiatives, which are also distorted by organizations wanting to evade their obligations.

The practice of registering VCs in different oceans forums will make it difficult to come to real figures for an overall assessment of the efficiency of the mechanism, which also raises issues of accountability. This new parallel system that was put in place somehow replicates the problems of oceans governance, but in a smaller scale, with duplication of VCs (mandates) in different forums, without a global registry and lacking an authority to monitor or manage all of them. An assessment of what VCs have achieved is critical also in order to assess their efficiency in the implementation of SDG 14. For all these reasons, there are doubts in relation to the contribution of VCs towards a real advancement in the implementation of SDG 14.

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[juniperpublishersoceanography]

Effect of Different Water Sources on Survival Rate (%) Growth Performance, Feed Utilization, Fish Yield, and Economic Evaluation on Nile Tilapia (Oreochromis niloticus) Monosex Reared in Earthen Ponds- Juniper Publishers

Abstract

The aim of the present study was to investigate the effect of water source on survival rate %, growth performance, feed utilization, fish yield, economic evaluation and production of Nile tilapia (Oreochromis niloticus) monosex reared in earthen ponds. Nine earthen ponds were used and divided into three categories of three earthen ponds each. The average size of each pond was approximately 5200m2, 6000 monosex all male Nile tilapia were used in each pond and were stocked for 192 days. The fingerlings average weight was 4.38±0.03g/ fish, the fish were fed using a floating feed 25% crude protein, and were fed at a daily rate of 3% of their body weight. Results showed that body weight was increased significantly (P<0.05) with well water to 472.33g/fish. While were 354.17 and 320.17g/fish for fresh and agricultural drainage water, respectively. Specific growth rates (SGR%) increased with well water compared to both fresh and drainage water. Feed conversion ratio (FCR) and protein efficiency ratio (PER) were improved with Agriculture drainage water. Survival rates with fresh and well water were 98.53% and 98.31% respectively, however, was 95.05% with Agriculture drainage water. Total fish yield were affected significantly by treatments. It was 2128, 1921.8, and 2837.7kg at fresh, drainage and well water respectively. Net return arrived to 12996 for well water source when it was 6784LE for agricultural drainage water and 9158LE for fresh water.

Keywords: Water resources; Nile tilapia; Growth per

Introduction

Nile tilapia, Oreochromis niloticus (Linnaeus) is one of the most important freshwater fish in world aquaculture [1]. It is widely cultured in many tropical and subtropical countries of the world [2]. Rapid growth rates, high tolerance to adverse environmental conditions, efficient feed conversion, ease of spawning, resistance to disease and good consumer acceptance make it a suitable fish for culture [3]. Farmed tilapia production increased semi dramatically in recent years, increasing from 383,654mt in 1990 to 2,326,413mt in 2006 [4]. Tilapia has established a secure position in a number of water impoundments of India. But, its performance in open water ponds of the country has been discouraging over the years [5]. For tilapia aquaculture is excessive reproduction and the resulting small size of the fish produced.

Egypt has suitable natural conditions for desert aquaculture. Egypt has vast resources of groundwater [6]. Fresh groundwater resources in Egypt contribute 20% to the potential water resources in Egypt. One of the groundwater resources is the Nile Valley and Delta system with the storage capacities of 200 billion m3 and 300 billion m3, respectively. Oasis water in the west desert, Bahariya, Farafra, Dakhla, Kharga, and Siwa, were established from underground natural wells and springs.

With the prohibition of the establishment of fish farms on agricultural land, with the prohibition of the use of Nile water for fish farming, with increased competition for spaces adjacent to the lakes and sources of agricultural drainage water, despite its disadvantages, has caused the possession of new fish farm in the Nile [7]. Valley of the most difficult things and out of reach. Hence the search for an alternative to invade the desert, especially with the development of methods of fish farming and providing the requirements of education and with the provision of underground water of the highest purity with different salinity (fresh & brackish & marine) and where the trained professionals are available [8]. In the hope to produce clean fish with improved quality and cheaper than other animal proteins we conducted the present research in a private fish farm located in the desert belonging to Noubaria Agricultural Development company (Ragab Farms) aiming to study the effect of water source on survival rate (%) growth performances, feed conversion ratio, protein efficiency ratio, annul fish yield and profitability Nile tilapia (Oreochromis niloticus) monosex commercial farming.

Materials and Methods

Water Source

Three types of water sources: fresh water, agricultural drainage water, and well water were compared in the present experiment. Water supplies were replaced three times during the experimental period (192 days).

Experimental design

Nine earthen ponds (5200m2) were used in these experiment were divided into three categories of earthen ponds even three ponds represent one treatment (fresh water, drainage water and well water.

Stocking density

6000 monosex all male Nile tilapia (Oreochromis niloticus) fingerlings of average weight (4.38±0.03g/ fish) were stoked in each pond on April 11, 2007 and observed through October 19, 2007. The area of each pond 5200m2.

Experimental Fish

Fingerlings of all male Nile tilapia (Oreochromis niloticus) monosex were collected from Noubaria Agricultural Development Company (Ragab Fish Hatchery) and were over wintered in earthen ponds to provide suitable fingerlings for the beginning of the growing season. All ponds in this experiment were sampled monthly using a cast net method. Sample sizes were 1% of the stocked numbers and the average individual fish weight was calculated to determine growth rates. Then, with these calculations, the feed amounts were adjusted for the following month.

Experimental diet

The floating commercial diet used in this experiment was fed at a daily rate of 3% of the fish body weight by using self feeders The ingredients of the commercial diet used in the experiment is presented in (Table 1). The dietary composition of vitamin and mineral premix is listed in. Fish were fed a floating ration for 6 days per week. Feeding rate was adjusted monthly based upon the calculated biomass of fish obtained through the monthly sampling and assumption of 100% survival.

Water quality

Physical parameters: Water temperature °C was determined at every days in the experiment.

Chemical Parameters: Samples for determination of dissolved oxygen (DO) were immediately fixed after sampling and DO concentration was determined according to Winkler's technique. Methods described by Golterman et al. [9] were used in determination of ammonia. Also pH was measured by digital pH meter (Orion model 720 A, s /No 13602) in all experiments.

Chemical Analysis of the commercial of Diet: Chemical analysis of the commercial diet used in the experiment was done according to AOAC (2000) as shown in Table 1.

Growth parameters and Statistical analysis: Data on growth, feed utilization, survival rate and proximate and chemical composition of whole fish body were subjected to one-way ANOVA [10]. To locate significant differences between fish size within different water resources of pond. Duncan's multiple rang test [11] was done. All percentages and ratio were transformed to arcsine values prior to analysis [12].

Results and Discussion

Experimental diet

The commercial diet used in the present experiment contained 25% CP and 4.3kcal/g gross energy (Table 1). Although there are large variations in the data available about the optimum protein level for tilapias which range between 20 and 40% crude protein [13-15] practical diets as low as 25% protein was successfully used for rearing monosex tilapia [3].

Vit. A 8000 I.U. Vit. D3 4000 I.U.; vit. E 50mg; Vit. k3 19mg;

Vit. B1 40mg; vit. B2 25 mg; Vit. B6 125mg; vit B12 69mg;

Pantothenic acid 40mg; Nicotinic acid 125mg; Folic acid 400mg;

Water quality

Collected data on water temperature and dissolved oxygen (DO), pH and ammonia are summarized in Tables 2-4. Water temperature throughout the present experiments ranged between 24.13±0.53 and 30.26±0.45 °C in fresh water experiment, 24.23±0.53 and 30.65±0.53 °C in drainage water experiment and between 29.94±0.12 and 33.63±0.43 in well water experiment which was the high temperature and closely related to the average of optimal value for tilapia (28-30 °C). Our results were agreement with Broussard [16] reported that tilapia as a warm water fish that dominate African lakes, are known to grow well in high temperature. The fluctuation of water temperature are reached its maximum values during August, however its minimum were during April and November.

*Each value was on average of four sub samples

Biotin 20mg; cholin chloride 80 mg; copper 400mg; Iodine 40mg;

Iron 120mg; Manganese 220mg; Zink 22mg; Selenium 4mg

Means in the same column having different letters are significantly different (P<0.05).

Overall means of water dissolved oxygen (DO) throughout the present experiment were 7.20±0.37mg DO/I for fresh water, 7.19±0.36mg DO/I for drainage water and 6.33±0.36mg DO/I for well water. The fluctuation of water dissolved oxygen (DO) showed that the maximum values of DO were obtained in November for the fresh and drainage water and August in well water, however, the lowest values were in April. In general, dissolved oxygen levels were within the high standards and higher than cited by Boyd [18] for good production of tilapia (4.20 to 5.90mg DO/I) in aquaculture ponds. One of the most important environmental factors is dissolved oxygen. It is considered a limiting factor for success or failure in intensive culture. An excellent aquaculture attribute of tilapia is their tolerance to low dissolved oxygen concentration [16]. The dissolved oxygen content in earthen ponds depends on the pond water temperature, fish biomass and rate of water exchange [18]. Chervinski [19] reported that O. niloticus survived short term exposure to 0.1mg DO/ l. However, Collins [20] observed in a review on oxygen concentration of various studies, that growth rate of non-salmonid fish was increasingly depressed as dissolved oxygen fall below 50% saturation. Rappaport et al. [21] reported that growth of carp was reduced by predawn dissolved oxygen less that 25% saturation. Tichert-C & Green [22] compared the growth of tilapia monosex in earthen ponds aerated or unaerated at 10 or 30% saturation of dissolved oxygen. They found that tilapia production and final weight were significantly greater in aerated ponds than unaerated ponds.

The water pH values throughout the present experiments ranged between 8.00±0.13and 8.10±0.13 with an overall mean of 8.04±0.13 in fresh water and ranged between 8.01±0.13 and 8.10±0.13 with an overall mean of 8.05±0.13 in drainage water and ranged between 7.98±0.13and 8.01±0.13 with an overall mean of 8.00±0.13 in well water. The fluctuations of pH reach the highest value of 8.10+0.13 during August in fresh and drainage water and 8.01+0.13 in well water. The results showed that the present pH values are suitable. For rearing tilapia monosex in earthen ponds. Johnson [23] recommended the range of pH 6.5 to 9.0 for most of freshwater fish species.

The water un-ionized ammonia (NH3) throughout the present experiments ranged between 0.09±0.01 and 0.12±0.01 with an overall mean of 0.11±0.01 in fresh water and ranged between 0.10±0.01 and 0.13±0.01 with an overall mean of 0.11±0.01 in drainage water and ranged between 0.06±0.01 and 0.10±0.01 with an overall mean of 0.077±0.01 in well water. The fluctuations of un-ionized ammonia reach the highest values of 0.13mg/ l during August. Unionized ammonia concentrations in the experimental ponds generally remained below levels which would cause chronic toxicity problems in tilapia. Tilapia is more tolerant to elevated levels of ammonia than more other sensitive species such as salmonids [23]. Some tilapias have been shown to acclimate to higher levels of ammonia after chronic exposure to low levels [24]. Johnson [23] showed that levels of un-ionized ammonia which may adversely affect growth in tilapia range from 1mg/ l to 2mg/ l ammonia where temperature and pH are within normal range.

Growth performance of tilapia monosex

Mean weight: Results of the present study showed that the mean weights at all rearing intervals different significantly (P<0.05) during all the experimental periods (Table 5 & Figure 1). Averages of fish body weights for fresh water, drainage water and well water were found to be 23.16, 18.66 and 25.16g, respectively after the 1st month of stocking. The statistical evaluation of results indicated that live weights at this period increased significantly (P<0.05) with using well water. A similar trend was also observed in fish body weights during the other growing periods. At harvest average body weight of fish stocked at well water was significantly (P<0.05) higher than that of fish stocked in fresh or drainage water, which indicates that weights fish were decreased in fresh and drainage water with increasing for used well water at harvest were 354.17g, 320.17g and 472.33g for fresh, drainage and well water, respectively. This significant advancement in fish body weights with increasing at higher temperature of water advocated by Azaze et al. [25] reported that the final mean weight was significantly higher at 26 and 30 °C than at 22 and 34 °C. This finding agrees with our results.

Average daily gain (ADG g/day): Results presented in Table 5 revealed that water sources, affected significantly (P<0.05) ADG during all experimental periods tested (30, 60, 90.120.150.180 and 210 days after start). In general these results indicated that the well water favored significantly ADG of the tilapia monosex in intensive culture system. The results of this point were in agreement with those found by [17] who grew O. niloticus from 49g to 271g in 122 days (1.4%/day). Siddiqui et al. [15] found that ADG of tilapia O. niloticus reared for 98 days at different water exchange in outdoor concrete tanks was 1.06g / day at 30% dietary crude protein. In the present study the average daily gain was higher with 25% crude protein at all treatments. However, the optimal feeding rate depends on fish size and Specific Growth Rate (SGR %): Results presented in Table 5, revealed that water sources, affected significantly (P<0.05) SGR% during all experimental periods tested (30, 60, 90.120.150.180 and 205 days after start). In general these results indicated that the well water, favored significantly (P<0.05) SGR% of the tilapia monosex in intensive culture system.

During all tested experimental periods tested (30, 60, 90.120.150.180 and 205 days after start) SGR% increased significantly (P<0.05) in almost linear manner in the well water than fresh and drainage water In the present study SGR% values in case of well water continuously higher than fresh or drainage water in all experimental periods. This may be due to the higher temperature of the well water (average 31.94 °C) compared to 27.47 and 27.81 °C for fresh and drainage water, respectively. The results obtained in SGR% are in agreement with those found by Eid & El Denasoury [27] who indicated that increasing temperature from 16 °C to 27 °C improve growth rate of Nile tilapia, which using well water.

Feed conversion ratio (FCR): Results presented in Table 5, show that there were significant (P<0.05) effects of water sources on FCR, feed conversion ratio was observed at harvest was 2.87 at fresh water, followed by 2.83 at well water and 2.80 at drainage water and 2.94 for 1700m2 followed by 2.89 for 4000m2 followed by 2.75 for 5200m2 and was 2.57 for 6000 fish/ acre, 2.75 for 8000 fish/ acre and 2.78 for 10000 fish/ acre. The analyses of variance of the FCR values are presented in Table 5. The FCR is affected by the physiological state of the fish, environmental condition, [28]. Lovshin et al. [29] found that FCR for all male tilapia in earthen ponds was higher (4.3) than when compared with all male and female tilapia in earthen ponds (FCR=7.2). while, fish growth is affected by the amount of feed consumed and the efficiency of assimilation [30].

Protein efficiency ratio (PER): Results of protein efficiency ratio (PER) are presented in Table 5, There were significant (P<0.05) effects of water sources, on PER, it improved significantly (P<0.05) with each increase in pond sizes and decrease stocking density throughout the experimental periods. The best PER observed at harvest was 1.42 with drainage water, followed by 1.40 at well water and 1.38 at fresh water Nyina-W et al. [31] confirmed that when protein supply is appropriate (400500g protein/kg feed for percid fish), different lipid contents in feeds do not have an impact on the rearing results of pikeperch.

Fish survival rate: Results in Table 6 showed that survival rates were changed significantly (P<0.05) by water resources, in fresh and well water were insignificantly (P<0.05) different but survival of the fish in drainage water was 95.05% which was less than survival rates in both fresh water and well water indicating the probable effect of some faction of water quality.

Fish yield: Results of Table 4 show fish yield (kg) per acre as affected by water sources,. Results revealed that total yield increased significantly (P<0.05) with well water. The total production was found to be 133.34% and 90.31% for well water and drainage water, respectively, while it was found to be 76.33% and 68.84% for 4000m2 and 5200m2.

The results of the present experiment were similar to those of Tal & Ziv [32] who showed that the net yield of tilapia monosex in earthen ponds was 16750Kg /ha (7035.0kg/ acre) after 100 days of stocking of 80.000 fish/ha, (33600 fish/acre, 8 fish/m2) on the other hand Eid & Denasoury [27] indicated that increasing temperature from 16 °C to 27 °C improved growth rate of Nile tilapia. Watanabe et al. [33] found that growth rates generally increase with increasing temperature and where markedly lower at 22 °C and well water is the best because the temperature constant through the year and the best quality of the water. [34] found the higher yield obtained in small pond sizes because the bigger ponds with greater surface area were more difficult to manage and often resulted in lower fish yields.

All fish species are characterized by an ideal range of temperature in which they show their maximum growth [3537]. Several studies have been reported that the specific water temperature range showed the faster growth in Pikeperch, Sander lucioperca at 20 °C to 25 °C [38-40]. Low temperature causes sluggishness by retarding the digestion speeding of fish [41]. Some researchers have found that the digestion rate has been increased as the temperature increases [42]. Environmental temperature is one of the most important ecological factor which also influence the behavior and physiological process of aquatic animals [43].

One of the major advantages of groundwater sources is their constant temperature throughout the year. Shallow sources of groundwater approximate the mean air temperature of the area. The chemistry of groundwater is directly dependent on the geology of the area surrounding the source. In limestone areas, groundwater is hard, and high in calcium and carbon dioxide [44]. In areas of granite formation, the groundwater tends to be soft, low in dissolved minerals and carbon dioxide. As will be discussed later, there are advantages and disadvantages to both, emphasizing the need for early extensive water quality testing.

Water temperature has substantial effect on fish metabolism. In response to decreasing of water temperature the enzyme activity of tissues have been increased [45]. Velmurugan et al. [46] have investigated that histopathological and tissue enzyme changes of C. gariepinus exposed to nitrite when water temperatures changes from 27 °C to 35 °C. In a stressful and unfavorable environmental condition GPT and GOT may increase in blood serum. In the present study serum GPT and GOT level were affected by different water temperature. Serum GPT and GOT amount in different fish fed at 20 °C are comparatively lower than those of fish fed at 16 °C and 24 °C experiments (Tables 1-3). These results indicated that 20 °C may be a favorable water temperature for better growth of 16g juvenile Korean rockfish [47,48].

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New Records of Sea Level Changes in the Fiji Islands- Juniper Publishers

Abstract

New sea level records from the Yasawa Islands in Fiji are presented. Beachrock occurs frequently on the beaches in the zone between mean and high tide levels on most of the islands. They date to the last 4200 years. The present sea level has produced distinct shore marks in the form of under-cut notches, rock-cut platforms and sea-caves in the bedrock, as well as sand accumulations with a clear mean high tide level (HTL). The fieldwork was concentrated in 10 sites. Elevation was measured with a high-precision instrument with respect to HTL. Ages were determined by 17 C14-dates. A +70cm higher sea level was observed, sampled and dated at AD 1530-1673. It was followed by a significant regression of about 1.7-1.8m, killing coral reefs and cutting a new rock-cut platform some 20-30cm above present mean low tide level (LTL). Then sea level rose again to its present position, or slightly above, a level, which remained fairly constant over the last 150200 years. In the last 60 years corals were killed due to a sea level lowering or a severe bleaching episode. After that very stable sea level conditions must have prevailed for the last decades, forcing corals at several sites to grow laterally into microatolls.

Keywords: Relative sea level changes; Regional eustasy; Rotational eustasy; Yasawa Islands; Fiji

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Introduction

Before addressing our research project, it seems appropriate to review the regional background with respect to plate tectonics, regional geography, the interaction of changes in land and sea levels, and especially previous research achievements in Fiji with respect to sea level changes. It seems surprising to note that all previous work has been addressed to interglacial and Holocene sea level change older than the last millennium, because it is the sea level of the last 500-1000 years that have the potential to act as a key to our understanding of what is actually going in present time.

Plate tectonic setting

Fiji is positioned between plates of complex geodynamic force and motion (Figure 1). According to the Fijian Ministry of Land and Mineral Resources [1], the Lau-Colville Ridge and Fiji represent an old dormant island arc ridge (Figure 2). However, this area is still seismically active [2-4]. For example, Suva experienced a M 6.8 earthquake in 1953 and a M 7.1 earthquake in 2009. In the Yasawa Islands area, the subject of this paper, a M 6.8 earthquake occurred in 1902 and a M 6.1 earthquake in 1984 [2].

Geography of the Fiji Islands

The nation of Fiji consists of about 330 separate islands (Figure 3). The main island is Viti Levu with Vanua Levu the second largest. The sea level changes and archaeology of Viti Levu have been studied by [5,6]. The eastern island group known as the Vanuabalavu Islands have been investigated by [7]. Kadavu Island has been studied by [8]. The Yasawa Islands were the target of our own investigations with respect to sea level changes. The Mamanuca Islands have been studied by [9,10].

Changes in land and sea levels

The tide-gauges at Lautoka and Suva on Viti Levu (Figure 3) provide records of the relative sea level changes since 1992 and 1972, respectively. In the vicinity of the tide-gauge stations there are GPS stations measuring the changes in crustal level. Both tide-gauge stations seem very unfortunately placed on heavy harbour constructions resting on soft marine sediments susceptible to significant compaction, and can hardly be used to decipher the present trend of sea level changes [11].

Several authors have tried to apply a seismotectonic zonation of the Fiji Islands (e.g. [12-16]). According to [16] only the Ovalau-Moturiki Islands (just east of Viti Levu) represent stable tectonic conditions, however.

Previous sea level research

As far as we know, there have been no studies of sea level changes conducted in the Yasawa Islands, except for a few notes (e.g. [14]). In this case our investigation brings forward new material. On Viti Levu, the Ovalau-Moturiki Islands, the Vanuabalavu Islands, the Karavu Island and the Mamanucas Islands, there are previous investigations to consider. Before addressing those papers, there are a few general problems to consider.

Radiocarbon dates of marine material need to be calibrated with the so-called reservoir effect satisfactorily well determined. Petchey et al. [17] reports the ages of four modern shell and coral samples. The reservoir ages were around 450 years, a value we adopted and used as 450±30 years in our marine radiocarbon calibration via OxCalv4.2.4 [18]. This makes direct comparisons complicated as, for example, [5] used a reservoir value of 370 years and an old calibration curve [19], and [7] used 438 years and an older calibration technique [20].

The use of datum level is another subject of great difference. Both [5,7] use the lowest astronomical tide (LAT) as their zero- level. This is quite surprising as this level is a theoretic level [21,22] not recognizable in the field. The unfortunate choice of LAT as their zero-level generates problems with respect to the identification of past sea level index points.

Past sea level data can only be referred to MSL (usually more or less arbitrary, however), HTL (morphological features like notches, sea caves, rock-cut platforms and some beach structures) or LTL (microatolls). This implies that sea level graphs with a datum set at LAT become misleading as they show data points above the chosen LAT-datum, which in fact may not represent any higher sea level position.

It seems natural that the nautical charts are referenced to the low-tide level. But geological and biological associations to shore structures, corals in situ or marine shells and corals in shore deposits are all much better related to the high-tide level, which in most cases is very easily identifiable. Therefore the HTL was selected as the ideal datum. The mean-tide level is usually also easy to identify on a beach, as a minor break in slope and concentration of larger particles like coarse sand and gravel [23].

The present tidal range is given as 1.30m by NOAA [21] and maximum 1.84 for Suva and 1.82 for Nadi according to [24]. In the field, a tidal range of 1.51m was measured. The conversion to LAT is not obvious (and we have no information of what value previous authors have used), but it seems that LTL should be about +30cm, MTL about +100cm and HTL about +170cm with respect to the LAT-datum [25].

Finally, it is interesting to note that all the previous papers are devoted to Mid and Late Holocene sea level data, and that there is a general lack of data for the last millennium. This is why the study, being focused on the last 500-600 years' field evidence on sea level changes, will fill a gap in the sea level history of the Fiji Islands [26-27].

Viti Levu: Nunn & Peltier [16] listed 32 C14-dated samples from 11 sites on Viti Levu. Additional dates come from [9,28,29], and our dates from Maui Bay (below). The data are plotted in Figure 4.

From Rove Peninsula (SW Viti Levu), [28,29] have reposted a stratigraphical record spanning the entire Holocene. At around 8000cal.yrs BP marine influence is recorded at the -3m (MSL) level. At 8000 BP, global eustatic sea level was at about -10m [30], suggesting that the Rove Peninsula has been uplifted by about 7m since 8000 BP; i.e. at a mean rate of 0.875mm/yr. Therefore, there are good reasons to dismiss their maximum sea level of about +2.1m dated 4055±575cal.yrs BP (suggesting a mean uplift of 0.525mm/yr).

From Vuda Point, between Nadi & Lautoka, [9] describes microatolls of Porites sp. at 16cm below MTL dated at 6460±70 and 6350±60cal.yrs BP, which corresponds to a sea level position at about +0.8-1.0m. If eustatic sea level at that time was at about -2.0m, the Vuda Point area is likely to have gone up by 2.0m; i.e., at a mean rate of 0.312mm/yr.

Bloom [31] reports the finding of a submarine peat-bed in a drowned valley tributary to the Rewa River east of Suva dated at a depth of -4.5m with a C14-age of 5500±110 BP, corresponding to 6295±111cal.yrs BP. If we assume a eustatic position at that time of about -1.5m, the site would have gone down by 3.0m or at a mean rate of 0.476mm/yr, which seems reasonable for a delta area. Wood at -0.2m in the Rewa River delta has been dated at 4165±245cal.yrs BP. Even this date is likely to represent subsidence, and has therefore been ignored in the sea level graph of Figure 4.

Obviously, there must be differential tectonics involved; uplift of Rove Point, uplift of Vuda Point and subsidence of the Rewa River delta. All the other sites seem to provide a reasonably congruent picture (i.e. stability); viz. sea level at about +0.3m from 5600 to 4900cal.yrs BP, at about±0.0m 4150-3950cal.yrs BP, at about +0.3m around 3350cal.yrs BP and at about -0.5m from 2900 to 1500cal.yrs BP (as illustrated in Figure 4).

Ash [5] investigated three sites along the northeast coast of Viti Levu and had 7 samples radiocarbon dated. He concluded that sea level rose to about +0.45m by 5300 BP and "has since declined at a constant rate". He also claimed: "sea level has not been significantly raised since 1630±250 years BP". The last statement is seriously contradicted by the present findings in the Yasawa Islands, however (below).

The earliest inhabitants of the Fiji Islands were the Lapita people. Kumar et al. [6] reported the finding of charcoal dated at 2583±233cal. BP. Nunn [32] gives an age of the Lapita settlement of "approximately 1350-750BC" (i.e., 3300-2700BP). This is in good agreement with the general Lapita immigration according to [33] and the stratigraphic records from Tavua Island, west of Nadi, by [10].

We investigated a section at Maui Bay on the south-coast including a piece of pottery and shells dated at 4019±103cal. yrs BP (below), suggesting that people might have been present significantly earlier, however

The Ovalau-Moturiki Islands: The Ovalau Island lies just east of Vitu Levi with Moturiki Island close by. They were studied by [34]. According to [34] the islands "have been subsiding very slowly for most of the past few thousand years". According to [16], however, these islands represent stable tectonic conditions, and would hence record regional eustatic changes in sea level.

There are 10 C 14-dates from Ovalau Island and 7 from Moturiki Island [16]. When plotted against time, the data suggest that sea level was at around +0.5m (MSL) in the period 6500-4500cal.yrs BP and at about +0.4 to +0.7m (MSL) in the period 3500-2900cal.yrs BP. Two dates from +1.6m (LAT) of about 5700cal.yrs BP and from +1.5m (LAT) of about 3700cal. yrs BP are problematic [34].

The Vanuabalavu Islands: Nunn et al. [7] undertook an extensive survey of past Holocene and Pleistocene sea levels as recorded by shore notches and marine deposits. The story is backed up by 4 C 14-dates of Holocene deposits (below recalibrated according to the methods used) and 3 Th/U-dates of Last Interglacial material. As mentioned before, they use a theoretical LAT as their zero-datum, which poses problems with respect to the identification of morphological sea level criteria, according to [7] here "typically marked by shore platforms, notches, marine caves and, less commonly, fossil corals and beach deposits". In the text they often talk about elevation with respect to "its modern analogue" (which is to be recommended) and some drawings give elevation with respect to mean sea level (which implies a new zero level about 70cm above LAT).

Nunn et al. [7] observed 3 different shorelines in the Vanuabalavu Islands; an upper +9-10m level of unknown Pleistocene age, a +5m Last Interglacial Level, and a +1-2m Holocene level. Their records have been combined into a shoreline diagram in Figure 5, and supplied with some additional information. The Last Interglacial level (red) seems to go through all sites at a fairly uniform level of about +5m above MTL. The Holocene level (blue) is by no means uniform, varying between around +1m and +2m. Because of the uniform Last Interglacial level, the Holocene irregularities cannot be interpreted in terms of differential tectonics, but have to be from field interpretation; the +2-3m levels on Mago Island are far from clear, on Kaibu Island there are no such levels recorded, on Yacata Island the +2-3m levels are unclear, and this is also the case with the +2m level of Vatuvara Island. Much better and more conclusive are the +1m levels of Vanuabalavu and Namalata Islands. The data presented suggest an elevation of +0.9m to +1.3m and an age of 3540±170cal.yrs BP to 3959±180cal. BP (overlapping at 3745±69 years). Therefore, a +1.1±0.2m level with an age of about 3750cal.yrs. BP is proposed. The microatoll (Porites) at +0.2m on Avea Island is indicative of sea level stability around 4178±180cal.yrs BP at about +0.6m.

On the south tip of the Vanuabalavu Island, there is a big cave named the Qaranilaca Cave. Its floor is given as "approximately 2.1-2.5m above mean low-water spring tide" [35]. This datum is not very useful, but corresponds to 0.8-1.2m above HTL and 1.5-1.8m above MTL. The stratigraphy is interesting [7,35,36]. The top 70cm is a bed indicating human habitation. According to Nunn et al. [7], it represents a significant regression at about 300BP (AD 1788±114cal. yrs). Then follows a 7cm marine bed (with sharp boundaries below and above) at +0.25-0.30cm above HTL. Below that are two beds with human habitation material dated at AD cal. 660 to 1160. At the base, 50cm below HTL and 10cm above MTL, there is a second marine bed of sand and beachrock.

Kadavu Island: Nunn & Omura [8] studied the Quaternary sea level changes on Kadavu Island. Their tectonic interpretation seems hardly tenable. The structural observations, on the other hand, seem quite straightforward; a "reef limestone" reaching +7.1m and dated to the Penultima Interglacial around 210Ka BP (3 Th/U-dates given), an undated "predominant erosional bench" at +2.6-3.4m of assumed Last Interglacial age, and an absence of emerged Holocene levels. This is illustrated in Figure 6.

There is a clear difference in elevation of the three shorelines in Figure 4 (Vanuabalavu) and Figure 6 (Kadavu): The Penultima Interglacial level of +7.5-8.0m on Kadavu seems to correspond to the +9-10m shoreline (green) on Vanuabalavu, The Last Interglacial level at +3m corresponds to the +5m level in Vanuabalavu (red), and the absence of emerged Holocene levels on Kadavu correspond to the +1m level in Vanabalavu (blue). A Penultima Interglacial sea level at +7.5m calls for some tectonic uplift. At the same time, however, the Last Interglacial and Holocene sea levels are indicative of predominant stability. Therefore, it seems to represent an episodic uplift of at least 5m in pre-Last Interglacial time.

Mamanucas Islands: Morrison et al. [10], studied nine cay islands of the Mamanucas Islands, located between Vita Levu and the Yasawa Islands. Cay islands are small sandy islands of low elevation formed on top of coral reefs by the erosional debris of corals, mixed with other marine organisms. They reported C14-ages from 3 cay sand islands. The subsurface ages go back to about 2200cal.yrs BP. All the surface dates belong to the last 600 years. The study has little to contribute to sea level changes. It just supports the notion that sea level had changed from a general rise to a general stability (or fall as proposed by [16]) well before 2200BP.

Morrison et al. [10] studied Tuvua Island in the same island group with respect to sediment stratigraphy and archaeological material. Coral fragments without morphological relation to any beach structure were dated; one at +1.9m (MSL) at 2816±20BP and one at 1.75(MSL) at 3294±21BP, suggesting that sea level was at about the present level, or even somewhat higher. The archaeological remains have ages in full agreement with the age of Lapita immigration according to [32].

Methods

Before going to Fiji, we carefully scanned suitable coastal segments of the Yasawa Islands as recorded on Google Earth images. After that we selected our spots and formulated our fieldwork program. Sometimes, this was not easy because we were not sure how to arrange local transport. In the field, we investigated the morphological characteristics and decided about how to work with respect to levelling, photo documentation and sampling for C14-dating.

We used the mean high-tide level (HTL) as our datum because it was morphologically easily identified. This level is about 70cm above mean-tide level (MTL) or mean sea level (MSL), and about 170m above the lowest astronomical tidal level (LAT). Levelling was performed with a high-precision Kern instrument, implying a measurement accuracy of better than 1.0cm. Microatolls were observed and their upper top surface was measured with respect to the sea level at low tide to the minute of its lowest position. The photo documentation includes several hundreds of images taken by different cameras, including one under-water camera.

Radiocarbon AMS dates were performed by Professor Goran Possnert at the Ångström Laboratory at Uppsala University. The marine calibration was done according to OxCal v4.2.4, with a reservoir effect of 450±30 years applied [36].

Results from Fiji Island

Because the Fiji Islands were going to be the center piece at the UN conference in June 2017 [37] and at the COP23 conference in Bonn in November 2017 [38], there suddenly became an urgent need of a careful sea level investigation in Fiji with respect to present trends and recent to sub-recent changes in sea level. Therefore, we initiated a new sea level project in the Fiji [26]. After studies of coastal segments on Google Earth, we selected the Yasawa Islands as our main target.

Our field studies spanned 3 weeks in March 2017. The locations of our investigation sites are shown in Figure 7, and include four sites on Viti Levu (coastal observations at Denarau west of Nadi and at Maui Bay east of Sigatoka, and the locations of the tide-gauge stations Lautoka and Suva). However, our main investigation concentrated on 10 sites in the Yasawa Islands.

Studies on Viti Levu

The investigations on Viti Levu will be described as shorter notes under this section. The main report on our results from the Yasawa Islands will follow below.

The Lautoka and Suva tide-gauge stations

The study of the two tide-gauge stations at Lautoka and Suva has already been reported on [11]. Our main conclusion was: "Any application of mean trends would produce meaningless values rather misguiding than assisting in the handling of estimation of on-going absolute sea level changes".

This is important, and implies that we must seek other means of establishing the present trend in regional ocean level changes. Consequently, this was our main target in our fieldwork in the Yasawa Islands, besides recording sub-recent to Late Holocene sea level changes.

The Denerau Site

Our first contact with the shores of the Fiji Islands occurred at Denarau. The first observation was that there are absolutely no indications of the shore advancing inland due to sea level rise, on the contrary sea level seems to remain quite stable (Figure 8).

A second observation was that there was an upper limit of dead Patella shells, and a lower limit of living Patella shells (Figure 9). The difference in elevation is 10-20cm, and may suggest that there has been a lowering of sea level in sub-recent time.

The Maui Bay site

At Maui Bay Public Park, on the south coast some 21km east of Sigatoka, the accidental find of an interesting site of past sea level changes led to some important discoveries. There is a thick beachrock deposit outcropping in the intertidal zone of the present beach. Also, there is clear evidence of a somewhat higher sea level. In an erosional depression of a small brook, we found a stratigraphic section, documented in Figure 10. Three generations of shore deposits can be distinguished.

An extensive beachrock deposit has its surface planed into a rock-cut platform (RCP). The high water level was found in direct association only 5cm higher (HTL). The present beach sand deposition, unit III, goes up 110cm above HTL (zero in Figure 10). An older over-grown sand unit (II) goes up 90cm above the top of unit I, indicating that sea level at one time must have been higher than today by about 90cm or a bit less.

Underneath these sand units, there is a third unit (I). It has a 30cm-deep soil at its top, indicating considerable age. A piece of pottery was found at a depth of 10cm (sample 20 in Figure 10), indicating that the soil and sand unit has to be of Late Holocene age. Shells and corals at a depth of 20cm (sample 19) were C14- dated at 4244±26 BP, or 4345±100cal.yrs. BP. A 10cm thick bed of flint-hard beachrock occurs close by. Corals from this bed (sample 17) were C14 dated at 4005±26 BP, or 4019±103cal.yrs. BP. This means that shore unit I has an age of about 4182cal. yrs BP (the mean of the two samples). Obviously, sea level had reached the present level, but hardly above this level (at least not more than 0.5m).

A sea level at about ±0.0m at about 4200 BP is in minor contrast to the results of [5], who has a Holocene sea level maximum at +0.45m at 5300cal.yrs BP. Ash and Ash [39] demonstrated that a proposed +1.6m Holocene maximum [40], in fact, was only at a +0.48m level (MTL). A sea level at about +0.4-0.5m would agree with all three records, however, but strongly contradict a +2m level as suggested by [16].

The piece of pottery found in the soil (sample 20) with a date of 4019±105cal.yrs. BP implies that Lapita people are likely to have already arrived on Fiji by 4000 BP. As this is earlier than considered before (e.g. [10,33,35], it seems necessary to show the piece of pottery (Figure 11).

Results from the Yasawa Islands

The Yasawa Islands is a chain of six main islands and numerous smaller islets spanning 80km in a SW-NE direction (Figure 12). The islands were not charted until 1840. All islands consist of volcanic bedrock (Figure 13). Erosional products generate coastal sand beaches. We undertook detailed sea level studies in 10 separate places. In addition, we made important observations of the coast from the ferryboat as well as the small boats we used for local transportation. As part of our planning for this investigation, we studied all of the islands on Google Earth images.

At Viwa Island 25km to the west of the main Yasawa Islands, three coral samples have been Th/U-dated at the Last Interglacial [8], viz. 126±7ka BP from +2.1m, 128.7±1.6ka BP from 2.85m, and 136±12ka BP from +3.1m. According to [14] "no relatively emerged features of certain Holocene age are known from the Yasawa and Mamanuca Islands". This statement seems valid even today (except for the +70cm level described below).

The present shore forms a distinct line all around the islands of rock-notches, sea-caves and rock-cut platforms, as well as sandy beaches (Figure 14). These morphological elements are closely tied to mean HTL, and therefore constitute an ideal datum for our investigations. Levelling was undertaken with a high-precision Kern instrument with rod-readings of up to 0.51.0cm accuracy.

General coastal observations

All the way from Kuata Island in the south to Bukama Village in the north, we observed very distinct shore morphological elements indicating the HTL; i.e., bedrock notches, under-cut notches, rock-cut platforms, and sandy shore HTL marks.

A few examples of the distinct high-tide shore markers are given in Figure 15a-c. At some coastal segments it seems evident that the coastal sand is also graded to a somewhat higher level (+1m or less), now overgrown and not reached by the waves at the present sea level. This seems to indicate that there was, in sub-recent time, a higher sea level on the order of +0.5 to +1.0m (Figure 16a-b).

There seems to be a general lack of higher shore marks, either from a Late Holocene sea level maximum (as proposed by [16]) or from a Last Interglacial level (as found on Viwa Island to the west).

Bukama Village

We spotted the coast at Bukama Village on the Google Earth images and were attracted by sandy beaches disappearing against rock cliffs and a tombolo spit (Figure 17), both structures of which had a potential for recording changes in present sea level. We accessed the site via a 25km long boat ride from Nabua lodge. This ride provided excellent coastal views of distinct shore morphological features indicating the HTL (under-cut notches and sea caves) and sand beaches with the present HTL clearly visible and an older, overgrown, higher surface from a somewhat higher sea level at about +0.5-1.0m.

An extensive beachrock at point 1 (Figure 18) was C14-dated at AD 611±82cal.yrs. This implies that sea level at that time was at about the same level as today. Judging from the Qaranilaca Cave section on Vanuabalavu Island (section 1.4.2, above), this level was followed by a lower level lasting from about AD 660 to 1160 [35].

The tombolo spit is built out between the mainland and a small island (Figure 17). Figure 19 gives a view from the bedrock hill seawards. The tombolo is built out from the north to the south by converging long-shore drift. The crest, the washing (swash) limit (WL), and the HTL on both sides were leveled with our high-precision instrument (Figure 19 & 20). The vegetated part is no longer reached by normal waves, and was partly formed at a somewhat higher sea level. The crest is successively falling off to the south and there is a total lack of any signs of present rise in sea level, on the contrary stability is evident. At the foot of the rock hill, there is an old, inactive under-cut notch, now filled by sand (Figure 21a). It must have been cut at a former sea level somewhat higher than today. The leveling indicates that the former sea level must have been about 70cm higher than today (Figure 20). Besides the +70cm notch, there are erosional marks in the bedrock at +2.4-2.6m and at +5.5m (Figure 21b). Those marks perhaps represent former sea level notches. We are not sure how to classify them, and leave the question open by assigning them "possible higher sea level notches". No other site with higher notches was observed between Naisisili and Bukama (Figure 22). At Naisisili, there might be one (Figure 31).

Nabua Lodge and Naisisili Village

This site was selected because the Google Earth image showed a long coastalspur (Figure 23), which by precise leveling might provide insight into the present trend of sea level; whether rising, stable or falling. Naisisili Village lies on a sandy flat between the sea and a small brook running parallel to the shore for about 600m. Today, the area of the village is not reached by the normal waves. The sandy ground of the village represents littoral swash deposits at a former sea level in the order of 0.5- 1. 0m higher than today's sea level. The shore spur to the south is graded to a lower level. The situation is illustrated in Figure 24.

The shore spur (spit) was subjected to precise levelling with 7 sections crossing the spit, identifying the present HTL, the sand/vegetation limit, the crest on the seaside, and the lagoonal HTL both the inner side and the foot of the back-side escarpments (Figure 26).

Figure 26 gives the main levels identified along and across the shore spur. The crest falls off from around +2m in the north to +1.5m in the south. The shore spur is 155m long. A C14-date of shells 30cm below surface gave an age of 532±23BP, which in calendar years is AD cal. 1866±82. Assuming an age of about 150 years for the spur to form, it would have been built out to the south at a speed of about 1.0m per year, which seems quite reasonable.

It has taken quite some time and checking of photos at both high- and low-tide to decipher the genetic origin of the red, purple and light blue levels in Figure 26. The foot of the undercut notches (red crosses) forming a perfectly straight level (Figure 26) are neither cut at present HTL nor MTL, but at HTL of a former sea level lower that the present one. In the field, we noted that there was a wide rock-cut platform 20-30cm above low tide level (LTL). Subsequent observations at White Sandy Beach (below) revealed a similar rock-cut episode at a low-stand prior to the building out of the shore spur here discussed.

Figures 27&28 give the sequence of under-cut notches along the bedrock just south of the shore spur and the brook outlet. Present HTL corresponds to the top of the notch, where the flat or concave surface starts to bend out again (yellow line in Figure 28). The leveled base of the notches (red crosses) in Figure 27 corresponds to a former HTL (present MTL lies above).

In summary, we document a former, lower sea level with its HTL about 100cm below the present HTL (Figure 26). The foot of the cliff (Figure 29) and the notches (Figure 27) goes over into an extensive rock-cut platform extending about 20-30cm above present LTL. This former, lower sea level must have preceded the formation of the shore spur. The shore spur, on the other hand, seems to have been built out during a more or less constant sea level during the last 150, maybe 200, years. Therefore, it seems likely that the low sea level stage belongs to the 18th century. This story is built on the observational facts observed at Naisisili, but the full interpretation is admittedly influenced by observations and C14-dates to be discussed later in this paper (especially sections Goat Island, and White Sandy Beach).

Comparing pictures taken at low-tide and high-tide respectively, clearly indicate that present day HTL lies well above the major sea level marks in the form of the foot of cliffs, the base of notches, the floor of sea caves and the top of rock-cut platforms (Figure 30). At Bukama Village, we had some bedrock structures that might represent sea notches at +2.6m and + 5.5m (Figure 21). For the rest of the 25km between Bukama and Naisisili no such levels were recorded, however (Figure 22). At the southeastern tip of the peninsula south of Naisisili Village (Figure 31), there is a very clear bedrock bench that might represent a former sea level at about +2-3m (Figure 31). At Wiva Island, [8] reviewed three coral samples collected at elevations ranging from +2.1 to +3.1m and dated at the Last Interglacial. Our Figure 23 notch may therefore represent a Last Interglacial sea level position at about +2-3m; i.e. the same level as recorded on Wiva Island and Kadawa Island (Figure 6), but about 2m lower than recorded on the Vanuabalavu Islands (Figure 5) Figure 31.

At Nabua lodge, an extensive layer of beachrock occurs all along the shore between MTL and HTL. Shells from the beachrock just outside Nabua lodge (Figure 32; with + marking sample) were sampled and C14-dated at 2799±25BP or 2501±101cal. yrs BP. Beachrock is usually formed just above MTL (but may occasionally even form below mean sea level). Therefore, the age obtained indicates that sea level at about 2500cal.yrs BP was at about the same position as today.

Nanuya Lailai Lodge

A coral reef just off the coast was investigated. A coral colony measured as 130x140cm consists of four minor units. All of those have reached a level so close to LTL that they are now growing laterally instead of upwards; i.e. they are "microatolls", with dead centres. The central part of one of the miniatolls (20x35cm wide) was sampled and C14-dated as "younger than 1955" (i.e., after the bomb effect, and hence not dateable).

Close by, there were two corals grown into columnar "chimneys"; one had a flat surface and was dead, while the other was still alive and growing. The difference in elevation between the top of the dead column and the living column was only 5 cm, indicating the very high sensitivity to depth below LTL. The occurrence of microatolls indicates present sea level stability.

Navutu Stars Resort

At this site, the under-cut notches and rock-cut platforms are closely tied to HTL, as evidenced by Figures 33 & 34.

Beachrock deposits occur at several places around the islands (viz. at Navutu, Yageta, Goat Island and Long Sandy Beach). The beachrock on the shore of Navutu Stars consist of a lower sandy beachrock with occasional shells covered by a conglomeratic gravel unit (Figure 35). Shells from the lower unit were dated at 4331±60 BP or 4479±180 cal.yrs BP (2529±180cal.yrs BC).

Yageta Village

The shore of Yageta Village has been heavily eroded over the past ten years. This has nothing to do with sea level changes, but is the effect of the removal of thousands of sea cucumbers as further discussed in [41].

The village is located on a flat sand plane, which seems to represent littoral deposits from a time when sea level was about 0.5-1.0m higher than today. A sandy beachrock with shells occurs on the present shore (between MTL and HTL). A sample of shells was collected but not dated.

Goat Island

This site was chosen because of its easy access to the strait between Goat Island and Long Sandy Beach. Here Google Earth images showed strong currents and re-deposition of sand, which might record the trend in present sea level; whether rising, falling or remaining virtually stable (Figure 36).

Most of the coast consists of bedrock with a distinct HTL marked by notches and sea caves, which, on a straight line, grade over into the HTL along the sandy shores (Figure 37). In the northeast, the shore projects a sand wedge into the sea. Here, the present beach has a clearly identified HTL and washing limit (WL) as illustrated in Figure 38. We rapidly made two important discoveries, viz. the presence of a former (fossil) shore 30m inland, and the occurrence of a coral microatoll off the shore.

The old shoreline found inland has morphology almost identical to that of the present shore (Figure 38). There is a difference of 70cm between the present and old WL levels (68cm measured), as well as between the present HTL level and the old HTL limit (71cm measured). Therefore, it was safely assume that a +70cm former sea level was documented.

Corals from the old +70cm beach were collected and C14- dated at 815±26BP or cal. AD 1601±143. This implies a time within the period of the Little Ice Age climatic conditions. A high level at that time might, therefore, be surprising. It fits very well, however, with the findings in the Indian Ocean with a +50-60cm higher sea level within the period AD 1550-1700 followed by a low level in the 18th century [42].

Within the big sea cave in Figure 37, it seems that there, in fact, are two levels; the present level in full agreement with surrounding shore marks, and an older level at a higher and deeper level in the cave, which is now overgrown and hence inactive and "fossil" (Figure 39).

In the strait adjacent to the leveled section, we observed a large coral microatoll when passing over it by boat (Figure 40). From Navutu Stars lodge, we had the time of the next low-tide the following morning within a 1-minute precision. Despite thunderstorms and heavy rain we were at the site just in time for the LTL. The distance between the top of the microatoll and the sea level at low tide was measured at 40cm (Figure 41). This is, of course, a very critical depth, preventing vertical coral growth and forcing it to grow horizontally into a microatoll (Figure 42).

We returned the next day, photographed the microatoll under water (Figure 42), measured it, sampled it and tied it into the leveled section (Figure 41). The coral has grown like a pinnacle with a height of about 2m and a diameter of 110x130cm. The surface of the dead coral in the centre of the microatoll was sampled and C14-dated at "106.4±0.3pmC", implying that it was too young to be dated; i.e. AD<1955.

This seems to imply that the coral had been growing upward in columnar form until, in the mid-to-late 20th century, came so close to the low-tide level that it was forced to change growth habit, growing laterally rather than vertically, thus becoming a "microatoll" with a dead centre. This gives evidence of a stable sea level during the last 50-70 years.

The death of the coral top and centre may be an effect of the 1998 coral bleaching event, or a sub-recent lowering in sea level (cf. Figure 9). At any rate, the occurrence of microatolls at Goat Island provides strong indication of a stable sea level over the last decades to half a century. Microatolls were also observed NW of Goat Island.

Long Sandy Beach Lodge

A part of the shore at Long Sandy Beach is subjected to coastal erosion. The erosion has nothing to do with changes in sea level, but is an effect of misplaced seawall and jetties, as further discussed in [43].

Gunu Village

The Google Earth image of the coast at Gunu Village documents a sea level history of 3-4 steps, and a present shore with the building out of double shore spurs (Figure 43). The spurs were subjected to precise leveling in order to see if there were any changes in sea level to be documented (Figure 44).

Both shore spurs were leveled, in eight crossing sections. Figure 44 shows the HTL, used as local zero level, the MTL and the level of the crest of spur-1 and spur 2. The HTL keeps a constant level across the profile. The MTL level lies about 60cm below, which agrees well with the half tidal amplitude at Suva tide-gauge station on Viti Levu. The levels of the crests of spur-1 and spur-2 are almost identical, showing that the change from one level to the other is related entirely to shore dynamics, and not to any change in sea level. The crest of spur-2 is slowly rising from +32cm at 47m to +56cm at 138m. This might be interpreted as a slowly rising sea level trend. The last 15m are characterized by a distinct lowering in the crest level (the leveling reads 19cm). Under no circumstances, however, is there any indications of a current trend for sea level rise.

Shells were collected in a pit dug at the crest of spur-1 at a depth of 40-50cm below the surface. They were C14-dated at 434±23BP or AD cal. 1910±40. This seems to suggest that the spur system has built out during the last century, at a mean speed of about 1to 1.5m per year

Gunu Village itself is located on littoral sand sediments originating from a time when sea level was 0.5-1.0 m higher than today (marked 3a on Figure 43). On Google Earth images there seems to be two additional sea level positions further inland (marked as shores 1 and 2 on Figure 43). They are likely to represent the +0.3m sea level peaks recorded in Viti Levu at about 5300 and 3350cal.yrs BP (Figure 4). The submarine part may perhaps record an additional low sea level (marked 4? in Figure 43). It might be the remains of the 18th century low level, recorded in White Sandy Beach (below).

White Sandy Beach Lodge

White Sandy Beach turned out to become one of our key sites (Figure 45). A short overview report has been presented (Mörner et al., 2017). The various observations will be described below with references to points 1-8 in Figure 45. The present HTL is very well expressed as under-cut bedrock notches and rock-cut platforms at points 1, 3, 4 and 8. The HTL is also well expressed along the sandy shores. The HTL level was used as our zero level. MTL is well expressed in a break in slope of the shore profile, and the accumulation of coarser sand grains and fine gravel grains.

The LTL is marked by the emergence of an extensive shore flat (tan colour in Figure 45), in its outer zone consisting of dead corals. It represents a former rock/reef-cut platform at about 20cm above present LTL. Outside the LTL the depth increases (blue colour in Figure 45) and corals occur, including microatolls with its top 40cm below LTL.

At points 1-4 and at point 8 (Figure 44), there are extensive rocks-cut platforms and under-cut notches, which are closely tied to present HTL and merge over into the active HTL of the long sandy beach. At point 8, this is especially clear (Figure 46). Because of the clear relationship between present HTL and the shore morphology (under-cut notches and rock-cut platforms at the rocky coasts, the HTL marks on the sandy beaches, and the observed tidal cycle), we chose the HTL as our zero level.

Inside the present-day sandy shore, there is a somewhat higher level of littoral sand, upon which the present houses are constructed. These elevated littoral deposits must represent a former sea level position higher than the present one. At points 1 and 3, we found bedrock notches above the present HTL. At point 3, the notch was leveled at 70cm above present HTL (Figure 47).

A former HTL, now 70cm above the present HTL, is identical to the records at Goat Island (Figure 41). In association with the +70cm notch, there is an accumulation of corals, now partly covered by downfallen blocks (Figure 48). A C14-date of a coral dug out from a position under a big block gave 847±24BP or AD cal. 1576±71. This is very close to the age of the +70cm beach on Goat Island dated at AD 1601±143. We may therefore, assume that sea level was 70cm higher than at present within the period AD 1500-1700, without specifying the beginning and end of this period. This fits well with a higher littoral level inside the calls for a corresponding sea level, at least, 25cm higher than present sandy beach in sub-recent time (Figure 48). today when the coral lived (Figure 51).

The episode of downfallen blocks must post-date the age of the corals underneath; i.e., 1601±143cal. yrs AD. It seems likely that the block-fall was triggered by an earthquake. At many sites along the shores of the Yasawa Islands, we observed faults, fractures and collapsed block indicative of seismic activity.

At point 1, there are remains of an old rock-cut platform with under-cut blocks and pillar at an elevation of about 20cm above LTL (Figure 49, Figure 50).

The low sea level following the +70cm high level at about 1500-1700, also trimmed the coral reef and littoral deposits off White Sandy Beach (point 6 in Figure 45) into a rock-cut platform to just above present LTL, with some coral remains emerging 15cm above LTL (Figure 50). A sample from a dead coral now at +15cm above LTL was C14-dated at 388±23BP or AD cal. 1901±29. Another sample 15cm below LTL (Figure 51) was C14 dated at AD <1955 (107.0±0.3pmC). This implies that the dead corals at present LTL are only about 100 and 50 years old, respectively. This seems surprisingly young with respect to the fact that the corals need a minimum depth of 40-60cm. This would fit well with the +70cm sea level. The C14-dates are younger, however. Because present day contamination could not be excluded, a second sample of the -15cm coral was dated. The date 105.1±0.7pmC confirmed the recent date, however. This calls for a corresponding sea level, at least, 25cm higher than today when the coral lived (Figure 51).

The rock-cut platform at present LTL is likely to have been cut at a former HTL when sea level was 110-130cm lower than today. The edge of the dead coral reef is steep, erosive and rapidly falls off to several meters depth. Coral rubble covers the trenches and sea floor outside (Figure 52). This is indicative of erosion at a former lower sea level. Despite available C14-dates, it seems reasonable that this low level occurred in the 18th century.

The main reef body consists of dead corals (Figure 50). Today, it also contains some living corals at depths exceeding 50cm below present LTL. We also observed a number of corals grown into microatolls (Figure 53). The depth at LTL to the surface of the microatoll was measured at 40cm (Figure 50). Samples from the centre of dead corals in two microatolls were C14-dated as <1955 AD (105.4±0.3pmC and 106±0.3pmC). This implies that the coral centra died within the last 60 years, and that the microatoll growth is less than 60 years old and has occurred under stable sea level conditions.

The death of the corals may be due to a sea level lowering or a severe coral bleaching episode (like the one in 1998). The re-establishment of new corals, and the sea level forcing some of them to grow into microatolls (Figure 53) is indicative of stable sea level conditions for, at least, the last 15-20 years.

Figure 53, [42] summarises the records of latest Holocene sea level changes at White Sandy Beach:

I. A +70cm dated at about AD 1500-1700.

II. A low sea level in the 18th century its HTL 20cm above present LTL, and

III. A rise to a sea level position at around the present one, which quite stable sea level conditions (formation of miniatolls) during the last 15-20 years.

Older beachrock deposits occur at points 3, 5 and 7 (Figure 45). They usually occur in the zone between MTL and HTL. The beachrock at point 7 has its surface cut into a rock-cut platform at present HTL. The beachrock at point 5 is a typical intertidal deposit. The beachrock at point 3 is a strongly cemented deposit including large coral fragments (Figure 55). It was C14-dated at 3030±25BP or 2765±82cal.yrs BP. This implies that sea level was at or closely below present sea level at about 2700cal.yrsBP.

Discussion

In the previous section all the field data were presented. Below follow a discussion and synthesis of those data.

General views

The study of sea level changes must be performed in nature itself. This may be a painstaking work, but this is how it must be done. Tempting shortcuts must be avoided. All observations and samples must be referred to a specific benchmark. In our case, we used the present HTL, which was easy to identify in the field. All our elevation values were obtained with a high-precision leveling instrument. Our studies were geographically spread over ten sites in the Yasawa Islands (with a few additional sites on Viti Levu). Chronology was obtained by 17 radiocarbon dates (Table 1).

The mode of sea level changes

The sea level change may follow main long-term trend as suggested by Nunn & Peltier (16), or occur in an oscillatory trend (like observed in the Maldives by [44], and in Goa, India, by [42]). When evaluating and systemising the field observations, one should start from scratch and try to build up the most accurate interpretation, regardless of any outside models.

Evaluating and systemising the field observations

It is well-accepted that sea level was successively rising from the Last Glaciation Maximum low level at about 24ka ago. By about 5500 sea level had reached the present position (Figure 4) . Minor sea level peaks seem to have occurred at 5300 (+0.300.45m), 4100 (±0.0m) and 3350 (+0.30m) cal.yrs BP (Figure 4).

Our records include five sites of pre-historical sea level changes. The Maui Bay site (p. 5-6) records a former sea level position at about ±0.0m, dated at about 4182±163cal. BP. This seems to represent a minor sea level peak (Figure 4). This is in good agreement with the Avea Island date of 4178±180cal.yrs BP and in reasonable agreement with the age of the elevated shoreline by [7] on the Vanuabalavu Islands (above). The beachrock at Navutu Star was C14 dated at 4479±180cal.yrs BP (p. 11). This age is close to the age of the beachrock at Maui Bay on Viti Levu of 4345±100 cal.yrs BP. At White Sandy Beach and Nabua there are beachrock deposits dated at 2765±82cal.yrs BP, and 2501±101cal.yrs BP, respectively. Both dates are indicative of a sea level at or shortly below the present level in the period 2500-2750cal.yrs BP, which fits well with a sea level at about -0.5m as given in Figure 4. At Bukama, there is a beachrock dated at 1339±82cal.yrs BP (AD cal. 611±82). It implies that sea level was at about its present position or shortly below at that time. It seems to have been followed by a regression, judging from the chronostratigraphy of the Qaranilaca Cave on Vanuabalavu Island [35] dating a habitation layer at about present sea level at AD cal. 660-1160. In Figure 56, the dates of the beachrock deposits are plotted with respect to the graph of proposed sea level changes. They all represent periods when sea level was slightly below present sea level. The former shores 1 and 2 at Gunu Village (Figure 43) are likely to represent the 5300 and 3350cal.yrs BP sea level peaks in Figure 56.

Our main sea level story from Yasawa Islands refers to the last 500 years, including

a. A +70cm higher sea level dated at the 16th and 17th centuries,

b. A sea level lowering in the 18th century by about 180200cm (i.e., at -110-130cm),

c. A sea level rise to about its present position during the last 200 years,

d. Some coral environmental changes in the last 60 years, and

e. Quite stable sea level in the last 15-20 years (with formation of microatolls).

The +70cm level is defined with high precision on Goat Island (Figure 39) and at White Sandy Beach (Figure 46). At Goat Island, we have a date of 1530-1673, and at White Sandy Beach of 1501-1646. At Bukama (Figure 20 & 21), there is an old undercut notch at +70cm. At Maui Bay (Figure 10) sand unit II goes 90cm higher than the corresponding sand unit of the present beach. At Nabula, Yageta, Gunu, White sandy Beach and others sites observed from the sea, we noted littoral deposits at a former higher level, estimated between +0.5 and +1.0m.

The subsequent regression is well documented at White Sandy Beach in a rock-cut platform (Figure 50) and under-cut rocks (Figure 49) now about 20cm above the LTL. At Naisisili, there is a similar rock-cut platform 20-30cm above present LTL and very prominent under-cut notches (Figures 28-30), located 100cm below present HTL (Figure 26). Obviously, it is correlating to the layer in the Qaranilaca Cave section, which according to [7] represents a significant regression at about 300BP or with our calibration ADcal. 1788±114 (above).

The subsequent sea level rise brought sea level up to about its present position. At Naisisili there is a 155m long shore spur, which we leveled in details (Figure 25). The building out of the spur is continual for about 150 years (dated at ADcal. 1866±82 at the beginning of the spur). The crest is about 30cm higher in the first part. This might suggest a somewhat higher sea level at the beginning. This might perhaps be relevant in view of the uppermost marine layer in the Qaranilaca Cave section located 0.25-0.30cm above the present HTL (above). At Gunu Village, there is a double shore spur (Figure 43 & 44), built out in quite stable coastal conditions, with a date from the inner spur of AD cal. 1910±40.

Microatolls were recorded and sampled at Nanuya Lailai, Goat Island (Figure 41 & 42) and White Sandy Beach (Figure 53). They were sampled in their dead centre. The C 14-dates are all too young to be dated; i.e., <1955AD. This implies that the corals died in the last 60 years due to a sea level lowering or an extensive coral bleaching episode. A 15-20cm sea level lowering might perhaps be recorded in the Kings Wharf old tide-gauge in the late 1970s [11]. It may be significant that at Denarau (Figure 9) we recorded a 10-20cm sea level lowering in sub-recent time. A major coral bleaching episode occurred at the ENSO event in 1998, and it might, at least theoretically, have generated extensive coral death, too. The present growing microatolls with their surfaces 40cm below present LTL indicate quite stable sea level conditions during the last 15-20 years. This is also indicated by several under-cut notches and rock-cut platforms that exhibit stable morphological conditions.

Summary

The data are combined and summarized in a general sea level curve of the last 7000 years (Figure 56) and a specific sea level curve of the last 500 years (Figure 57), which compiles our findings from the Yasawa Islands. It should be noted that the sea level changes of last 500 years have not been covered by any previous investigations (which were all confined to the Mid and Late Holocene data).

In the graph of sea level change during the last 7000 years (Figure 56) we compare our beachrock data with the new sea level curve of Viti Levu (Figure 4). The dates from White Sandy Beach and Nabua of 2500-2975cal.yrs BP fall in the sea level low of about -0.5m in Viti Levu. The sea level regression at around 3000cal.yrs BP exposed sandy material and led to ground water lowering, both factors of which may have led to beach-rock formation. The date from Bukama of 1340cal.yrs BP also falls within a period where the Vitu Levu data suggest a sea level at around -0.5m.

Figure 56 suggests that sea level peaked at around 5300cal. yrs BP at +0.3m or +0.45 as suggested by Ash [5] with later peats at about 4100cal.yrs BP at ±0.0m and at about 3350cal.yrs BP at +0.3m. This is quite different from the graphs by [9,10,16]. Undoubtedly, the Fiji Islands have suffered partly episodic differential tectonics (e.g., the level of the Penultima Interglacial level on Kadavu Island, Figure 6, is indicative of uplift), and partly differential tectonics within the main island of Viti Levu (Figure 4).

Our main findings are the sea level records of the last 500 years in the Yasawa Islands (Figure 57). This curve seems to apply also for most of the others islands of the Fiji nation. We propose it as a new sea level curve of Fiji, and believe that is predominantly recording the regional changes in eustatic sea level. It is composed of 6 elements:

a. A +70 cm level in the 16th and 17th centuries

b. A -100 cm low level in the 18th century

c. A +30 cm peak in early 19th century

d. Stable sea level condition during the last 150 years

e. Coral death in the late 20th century, due to a 10-20 cm sea level lowering or maybe due to severe coral bleaching at the 1998 ENSO event

f. Quite stable sea level conditions in, at least, the last 1520 years with forced coral growth into microatolls

This implies that high sea levels are recorded at grand solar minima with Little Ice Age climatic conditions, and low sea level at the grand solar maximum in the 18th century. This might be surprising as it is opposite to what one would expect from a glacial eustatic point of view. The sea level fluctuations documented (Figure 57) are very similar to those recorded in the Indian Ocean [42,43], which were driven by changes in Earth's rate of rotation [45]; speeding-up during grand solar minima and slowing-down at grand solar maxima thereby forcing water masses to move in a N-S pattern [27,46]. Now, this process is also documented in the Fiji Islands (which came as a surprise to us). The term applied to this factor is "rotational eustasy" [27] (Table 1).

Conclusion

Our findings are condensed and summarized in Figures 56 &57. From 5500 to 1500cal.yrs BP sea level seems to have oscillated between about +0.5 and -0.5m, with minor peaks at 5300 (+0.3 to 0.45m), 4100 (±0.0m) and 3350 (+0.3m). In the last 500 years, we record high-amplitude change: high-low-high- stable (Figure 57). Those changes were driven by rotational eustasy, not glacial eustasy. In the last 60 years coral reefs died due to a sea level lowering of about 10-20cm or due to severe coral bleaching at the 1998 ENSO event. After that, very stable sea level conditions must have prevailed forcing corals at several sites to grow laterally into microatolls.

This documentation (Figure 57) implies that there is a total lack of signs indicating a present rise in sea level; on the contrary, our results are indicative of quite stable sea level conditions. Consequently, our records may be taken as reassurance for low- laying coasts and islands that potential for flooding in the near future is unlikely.

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Linking Ocean Observation and Fisheries - Relevance to Deep Ocean Living Resources- Juniper Publishers

Abstract

Systematic ocean observation for real time data collection during the last three decades, development of sensors and tools, and ocean modelling have paved the way for better understanding of the ocean processes and better prediction of coastal hazards like cyclones, tsunami, storm surge, etc., leading to direct societal benefits globally. In particular global ARGO float data have brought in remarkable changes in ocean science studies. This paper discusses about the growing need to link ocean observation to fisheries and futuristic approach about deep ocean marine living resources

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Introduction

The goal of fisheries oceanography is to understand the oceanographic and ecological processes that affect fishery abundance, distribution, and availability and then apply this understanding to improve fisheries assessment and management. Ecophysiology is the interrelationship between the environment and an organism's physiology [1]. The future of fisheries oceanography lies in the pursuit of multiple hypotheses [2]. Using temperature as an example, a range of biological processes are related to temperature either directly or indirectly [3]. All organisms have thermal limits above and below which death is rapid. Within these limits, temperature controls a number of rate processes, including gene expression, enzyme kinetics, metabolism, activity, consumption, and growth. Organisms also respond behaviourally to temperature through migration, foraging, and resting.

Looking ahead, the core question is whether today's agriculture and food systems are capable of meeting the needs of a global population that is projected to reach more than 9 billion by mid-century and may peak at more than 11 billion by the end of the century [4]. Human activities have profound, possibility irreversible impacts on ocean health, in terms of physical state (warming, freshing, and circulation changes), its biogeochemistry (carbon uptake and acidification) and its ecosystem. The ocean influences climate by storing and transporting large amounts of heat, freshwater, and carbon, and by exchanging these properties with the atmosphere. Ocean warming dominates the global energy change inventory with warming of the upper (0 to 700m) ocean accounting for about 64% of the total. However, below 700m ocean depth, data coverage is too sparse to produce annual global ocean heat content.

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Deep Ocean Policy, Strategy and Capacity Building

The deep ocean is the single largest ecosystem on our planet. It sustains a great variety of habitats and life forms and is host to potentially valuable resources such as minerals, oil and gas and more traditionally food. Harnessing the full potential of deep ocean resources, whilst mitigating and managing environmental impacts, requires in-depth knowledge and understanding of the complexities of deep sea ecosystem and interconnection of the physical environment and the life forms within it [5].

Deep Ocean is yet to be understood and answered in the context of the role of deep ocean processes and various science questions pertaining to Earth's energy imbalance, heat budget, fluxes, and deep ocean mixing, on climate change. Industrial activities on deep sea mining, bottom trawling and oil and gas extraction need detailed study of the biogeochemical processes and impact assessment, which require systematic ocean data collection. Available reports indicate that inertial-period oscillations have been observed by numerous investigators in deep sea locations ranging from subtropical to polar latitudes [6].

Innovative technologies are a key to study ocean processes in space and time. Today's underwater exploration is supported by vessels operated by a number of skilled crew members, and underwater robots controlled from the vessel. These underwater technologies have been utilised widely by the private sector. Different robotic platforms like benthic landers, crawler, floats, glider, Autonomous Underwater Vehicle (AUV), Unmanned Airborne Vehicles (UAVs) and sensor systems are required for deep sea studies. The use of these new underwater technologies will enhance our capabilities in improving our knowledge on the effects of climate change and ocean observation [7,8].

The deep ocean is our planet's largest biome, and is under increasing pressure from human activities such as resource exploitation and pollution. The 1982 United Nations Convention on the Law of the Sea (UNCLOS) declared the seabed area beyond national jurisdiction (the Area) and its mineral resources as the "common heritage of mankind", to be administered for the benefit of mankind as a whole. All mineral exploration and exploitation activities must be sponsored by the Party to UNCLOS and approved by the International Seabed Authority (the Authority). The United Nations Environment Programme (UNEP) report states "it is important that policies guiding mineral extraction from the deep seas are rooted into adaptive management-allowing for the integration of new scientific information alongside advances in technology. Governance mechanisms for international waters and the seabed need to be strengthened". Hence there is also an unprecedented need to integrate the deep ocean into ocean science and policy. New international regulations (e.g, for mining) and treaties (e.g. for biodiversity), environmental management, and spatial planning also must incorporate climate and the role of deep processes.

New knowledge is critical to climate predictions and societal impact assessments and will require the expansion of deep-water research with experimental capacities, to support the design of marine protected areas encompassing vulnerable regions in deep waters, and to inform environmental management of industrial activities and development of new policies addressing deep national and international waters.

Outreach events on advances in ocean science and technology and their role in judicious and sustainable exploitation and use of the vast resources should target groups of people including schoolchildren, people and local communities and by contributing interactive exhibits and displays for curious visitors of all ages. They can contribute directly to the country’s prosperity, benefit humanity, and many non-scientists who have little knowledge of these important issues. The public awareness of science by communicating their work widely, whether it involves explaining climate change, and/or investigating life at the bottom of the world's deepest oceans, will go a long way in knowledge enhancement among the entire cross section of the society.

The deep sea is out of sight, out of mind, and because there is no specific human society that is directly impacted by the negative consequences of extraction, it is challenging to focus attention on environmental issues of deep-ocean industrialization, including commercialisation of deep sea fisheries. It is imperative to work with industry and governance institutions to put in place progressively strong environmental regulations, even at the planning stage of the industry itself. There is a need for international agreements and multiple sources of research funding that can help provide the scientific information to protect and manage the deep sea environment and its resources. All these will require efforts that bridge several disciplines and engage different stakeholders in these tasks.

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Role of Oceanography in Sustainable Fisheries Management

Often fisheries stock assessment and management has been questioned for failing to account for oceanographic processes. It is clear from the abundant research that fisheries scientists and managers are well aware of the role that oceanographic processes play in controlling fish populations. Debate about the relative roles of fisheries versus the ocean conditions / environment in determining the abundance of fish stocks has persisted for decades. There are numerous examples of academic exercises developing methods to identify relationships between population dynamics and oceanography, to integrate oceanographic data into stock assessment and management, and to evaluate the advantages of using oceanographic data, but there is a lack of successfully implemented examples in the real terms.

Recently, the methodology adopted by USA and Australia have shown success. NOAA Fisheries oceanography program is more than 100 years old and has successfully developed methods for annual outlooks with emphasison the long-term sustainability of fish stocks. Linking ocean conditions to salmon returns using plankton species, SST and DO revealed important changes in the marine food chain and offshore ecosystem and their "red light-green light" chart has become popular among fishing industry.

Periodic research articles by Oceanographers along the Indian east and west coasts have showed the linkage of Phytoplankton survey, Oxygen Minimum Zone and Upwelling in Arabian Sea, fronts meandering in Bay of Bengal which are linked to fishing, and impact of coastal/ocean pollution to fisheries. The availability of fine spatial and temporal scale oceanographic data from remote sensing and ocean observation system like moored buoys, ARGO floats, etc., ship borne measurements, and oceanographic models allow research on more appropriate scales, which may lead to improvements in the near future, leading to better understanding of the interaction between the ocean parameters and the deep sea fisheries resources.

Unfortunately, the understanding of the mechanisms involved, the available data, or the large scale correlations are limited. In most cases, statistically significant correlations between population dynamics and population processes break down are yet to be established. This has led to advocating direct monitoring or developing management strategies that are robust to the variation rather than determining the relationships between population dynamics and oceanographic processes. The few successfully implemented examples mainly relate to predicting the spatial distribution of a fish stock. Therefore, use of oceanographic data to determine dynamic spatial closures to reduce by catch appears to be one of the most promising areas of research.

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Indian Context

Of late, in India our enhanced observing and modelling capacity is providing new opportunities to improve fisheries management at both short (e.g., weekly) and long (e.g., climatic) time scales. Indian National Centre for Ocean Information Services (INCOIS) Hyderabad under the Ministry of Earth Sciences develops Potential Fishery Zones (PFZs) advisories and issues them to the coastal fishing community through various media. INCOIS uses satellite measurements of sea surface temperature (SST) and chlorophyll generated from OCEANSAT to develop these PFZ advisories, which consist essentially of curves drawn on a map to delineate the Potential Fishing Zones. Judging by download statistics and the feedback available, the product is popular with the fishing community within India as well as in this region.

In India, there is no industrial fishing fleet operating within the EEZ. Out of 199,141 fishing craft which are presently operating in the Indian seas, non-motorised and motorized traditional fishing crafts constitute 63.41% (126,392), with the remaining 72,749 (36.59%) being the mechanised fishing boats including trawlers. Traditional fishing crafts do day fishing in east coast up to 3 to 5 NM and west coast up to 7nm. The motorized fishing crafts (fitted with Outboard motors of 10-15 HP) do fishing up to a maximum of 70-100m depth. The mechanised fishing craft including trawlers which are less than 20m Overall length (OAL) operate as either day fishing boats or multi-day fishing boats depending on their OAL and the horse power of the inboard engine and do fishing for 7-15 days in the open sea depending on their endurance. These fishing crafts are landing on an average 3.10 million metric tonnes per annum during 20042014, against the projected Maximum Sustainable Yield levels of around 4.5 million m.t. This is in spite of the fact that there had been an increase both in terms of the fishing effort in the form of increase in fishing craft and the fisher population. The existing satellite based technique often does not work close to land and hence there is a need to evolve an unique methodology supported by primary field level data on productivity, coastal ocean monitoring data and fisheries data, which could be integrated and used to supplement the sea surface temperature derived from satellite imageries and other physical and chemical oceanographic data collected from moored and floating buoys for providing information on potential fishing zones along the coastal belt within 5-10nm zone for the benefit of fishers who do fishing using traditional sail powered and motorized fishing boats.

In India pioneering work carried out in the Arabian Sea by the Indian researchers has provided a lot of opportunities for correlating the oceanographic parameters with fisheries resource abundance beyond 100-200m depth zone within the Indian Exclusive Economic Zone and areas beyond national jurisdiction. The data and information collected so far from these studies will be very useful in furthering our studies in the Bay of Bengal and parts of the Indian Ocean abutting the southern tip of the country and the Andaman and Lakshadweep areas. It is proposed to involve all the relevant Government organizations and stakeholders to make a realistic assessment of the deep sea fisheries resources/fish stock assessment and management in correlation with the oceanographic parameters.

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Issues to be Addressed in Fisheries Oceanography

I. Why do we get a certain fish in a certain region?

II. Why is the fishery pattern changing ?

III. Forcing in shelf has any influence.

IV. Early fish life history to integrate with river run off nutrients which trigger fish to bread mostly after monsoon.

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National Fisheries Outlook

There is a need to involve national outlook on fisheries and to support ecosystem based fisheries management following the example of NOAA's Fisheries oceanography program on ocean conditions to salmon returns using plankton species, SST and DO, Although traditional single-species management continues to use spawning stock biomass as the primary indicator for recruitment, recent research is being addressed on the early life history of fishes (Figure 1).

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Summary

There is growing demand from funding agencies and public on the sustained fishing practices and relevance of Oceanographic scientific finding to support the society in particular the fishing community / Industry. When a fisherman sets out to sea, he confronts a vast expanse of water and the vagaries of nature. There exist no roads to follow, no tracks to lead him to the fish, which too are not to be found all over the ocean. Fish, being migratory in nature, either tend to congregate in certain regions, or are always in motion and hence it is important for the fishermen to locate them in order that their fishing effort serves its purpose. By seeking to elucidate mechanistic relationships between fish species and their surrounding oceanic habitats, the field of fisheries oceanography will aim to provide a solid understanding of fish behaviour, population dynamics, and life history with an ecosystem perspective. In future similar weather forecasting. Science would improve to focus on prediction or forecast for fishing using a different data sets available.

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Growing Demand for High-Quality Seafood Products and Production Systems in Aquaculture- Juniper publishers

Short Communication

Aquaculture production has grown enormously in recent years worldwide especially in Asia due to their high economic value and export. Aquaculture is the fastest growing food production sector in the world, providing almost half of the global fish/shrimp supply. Global fish and shrimp production by 2030, it is estimated that aquaculture production will grow by 40% to satisfy global fish and shrimp demand. Shrimp and fishes are rich in proteins, vitamins, omega 3 fatty acids, selenium and essential minerals and is recommended for the maintenance of strong body and healthy bones. With increasing population and health awareness the demand for high quality fish and shrimp is increasing. Nowadays, shrimps/fishes are infected by numerous pathogenic microbes which caused high mortality. The excess feed and fecal matter in grow out ponds accumulating in the impoundments may result in bacterial decomposition of organic matter in the sediment and produce excess oftoxic compounds like ammonia and also pollute the environment. Very limited research has been carried out on the culture, growth performance and disease management in aquaculture using beneficial microbes. Although vaccines, medicated feeds and immunostimulants are effective in combating some pathogens in other meat-producing programmes, they are either unavailable to shrimp farmers or their efficacy is unproven. Various pond management strategies like stocking of high-health seed, reducing water exchange rate, and screening influent water have been employed to mitigate the risk of disease outbreak. To meet the growing demand for high-quality shrimp products, novel production systems must be designed to minimize the introduction and spread of pathogenic agents, as well as to protect coastal resources. Biosecure zero- exchange systems represent an emerging technology that provides a high degree of pathogen exclusion with minimal water exchange. An important ramification associated with reduced or zero water exchange is the increased importance of in situ microorganisms both in regulating biogeochemical cycles within the culture environment and in directly affecting shrimp growth and survival.

Biosecurity can be defined as the sum of all procedures in place to protect living organisms from contracting, carrying and spreading diseases and other undesirable health conditions. When designing a biosecure production facility, it is important to identify all known and potential disease vectors. For shrimp viruses, one of the most important vectors is the seed. The use of shrimp specific pathogen free (SPF) seeds of high health sources is highly recommended. Aquaculture uses resources from and interacts with the environment. Many aquaculture operations generate metabolic waste products (e.g., faeces, ammonia, uneaten food etc.) that are released into the receiving waters. In some cases, the organic particulate waste will accumulate on the seabed in the immediate vicinity of the farm, while soluble waste will eventually end up in the receiving waters. Organic enrichment of the benthic ecosystem may result in formation of anoxic conditions. Under extreme cases, reduction in macrofauna biomass, abundance and species composition may also follow. In semi-intensive and intensive pond systems, sometime up to 40% of pond volume is exchanged daily. Often on large farms, water exchange is based on a set schedule, with occasional emergency flushes, rather than as an ongoing response to changing pond conditions.

Disease outbreak is being increasingly recognized as a significant constraint on aquaculture production and trade, affecting the economic development of the sector in many countries. It is the limiting factor in the shrimp culture subsector. So far, conventional approaches, such as the use of disinfectants and antimicrobial drugs have had limited success in the prevention or cure of aquatic disease. Furthermore, there is a growing concern about the use and, particularly, the abuse of anti-microbial drugs not only in human medicine and agriculture but also in aquaculture. The massive use of antimicrobials for disease control and growth promotion in animals increases the selective pressure exerted on the microbial world and encourages the natural emergence of bacterial resistance. Not only can resistant bacteria proliferate after an antibiotic has killed off the other bacteria, but also they can transfer their resistance genes to other bacteria that have never been exposed to the antibiotic. Frequently, pond flushing removes plankton, bacteria and natural productivity that could have otherwise benefited the pond water quality and the cultured organisms. Reducing water exchange is feasible without negatively affecting the culture environment. High shrimp yield can be produced without water exchange. In semi-intensive and extensive farming, all or part of the waste is recycled into micro-algae production. A normal bacterial composition may also keep the pond healthy and reduce risks for rapid spread of pathogenic microbes. A sterile pond may increase disease risks substantially, since any microbe that enters the system might easily take over. To reduce the risk, experiment is now made to introduce probiotics that is "friendly microbes", in the farming environment to suppress and out competitive pathogenic ones.

Considering the recent success of these alternative approaches the Food and Agriculture Organization of the United Nations defined the development of affordable yet efficient vaccines, the use of immuno-modulators and nonspecific immune enhancers and the use of probiotics and bioaugmentation for the improvement of aquatic environmental quality as major areas for further research disease control in aquaculture. Microbial probiotics is a term, which in aquaculture, usually refers to a bacterial supplement of a single or mixed culture of selected bacteria. These bacteria are added to aquaculture production systems in order to modify or manipulate the microbial communities in the water and sediment to reduce or eliminate selected pathogenic species of microorganisms, and generally, to improve growth and survival of the targeted cultured aquatic species. Additionally, according to the demonstrations of manufacturers and distributors of probiotics, the products improve water quality and lower the level of the organic sludge in the aquaculture facility. The newest attempt to improve water quality in aquaculture is the application of probiotics and/or enzymes to ponds. This approach of biotechnology is known as bioremediation, which involves manipulation of microorganisms in ponds to enhance mineralization of organic matter and get rid of undesirable waste compounds. Hence, the extrapolation of beneficial microbes/enzymes as feed and/or water probiotics in shrimp culture will definitely prevent the aquaculture ponds from undergoing organic matter accumulation, ammonification, eutrophication and prevent the environment from pollution and also control the microbial diseases to the shrimps and enhance the productivity of the farms to the benefit of local economies in an ecofriendly ambience without antibiotics.

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