#intertidal fauna

[uncharismatic-fauna]

Slip on the Common Slipper Limpet

The common slipper limpet, also known as the boat shell or the fornicating slipper snail (Crepidula fornicata) is a species of sea snail native to the North American coast of the Atlantic Ocean. In addition, it has been introduced to the eastern coasts of Europe and parts of the Pacific Northwest and Japan. They can reside in a variety of habitats including bays, estuaries, island shores, and rocky intertidal zones; their maximum depth tolerance is 70m (229 ft).

Fornicating slipper snails are noted for their unique mating methods. Adults typically live stacked on top of each other, with up to 12 to 14 individuals in a group. The largest, and oldest adults are at the bottom of the stack, while the younger, smaller adults are at the top. C. fornicata is a sequential hermaphrodite; new adults are all male, and will change into females as they get older or if they become the oldest in a stack of all males.

Breeding can occur between Februrary and October, although the peak season is in May or June. Unlike other marine mollusks, which are broadcast spawners, the common slipper limpet utilizes internal fertilization. The male closest to the female at the bottom extends his penis under her shell and fertilize up to 11000 eggs. These eggs hatch after about 3-4 weeks, and the planktonic larvae are released into the water. These larvae take 4-5 weeks to develop into juveniles, at which point they settle either on bare rock or on top of an established limpet chain. If it settles in isolation, the young adult immediately changes into a female; if it settles on a chain, it remains a male. Adults can live on these chains for up to 6 years.

Adult boat shells are rather small, ranging in length from 20–50 mm (0.7-1.9 in). The shell is distinctly arched, with a flat underside that gives it a slipper-like appearance. The shell can be white, pink, or yellow with red or brown streaks; older adults are often covered in algal growth.

Conservation status: The common slipper limpet has not been evaluated by the IUCN. Although they are commonly harvested for food, populations are considered stable. Outside its native range, this species is considered invasive and harmful to other limpet snails.

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Photos

Dr Keith Hiscock

Sytske Dijksen

[uncharismatic-fauna]

The Atlantic Mudskipper: A Fish Out of Water

Found only along the west African Cost, the Atlantic Mudskipper (Periophthalmus barbarus) is an incredibly unique species of fish. What makes it so special is that, unlike most other fish, the mudskipper can survive on land. It has several adaptations to make it semi-terrestrial. A layer of mucus over the surface of the body allows it to retain moisture, and when on land it can close its gill chambers and breathe through its skin. The eyes are set high on the head and can move independently 360 degrees, giving the Atlantic mudskipper a wide range of vision. Lastly, the pectoral fins that allow it to crawl, climb, and even skip on land, aided by a pair of pelvic fins.

P. Barbarus’ special adaptations allow it to occupy uncommon habitats within its range. It prefers semi-salty brackish water, especially at the mouths of rivers and in mudflats, although they are able to tolerate a range of temperatures and salinity. They can also be found in mangrove forests and lagoons, where they can climb up onto the roots of trees. Along the coast, individuals are most often visible at low tide when they climb up on the shore to feed. In these regions the Atlantic mudskipper digs burrows in which they can hide during high tide. To blend in, they are usually tan to dark brown with dark mottling along the back and bright blue spots on the cheeks.

During the day, the Atlantic mudskipper spends most of its time feeding and defending its territory. They are carnivorous fish, preying on crustaceans, insects, and small fish. The mouth of P. barbarbus is specially shaped so that it covers its prey with water, then sucks the water back up with its accompanying meal. When threatened by terrestrial predators such as shore birds, the Atlantic mudskipper lives up to its name and will ‘skip’ away. These fish also use their mouths in fights, which are quite common. Individuals typically guard of about 1m around their burrow. Males are especially territorial, and will fiercely guard burrows and mates from competitors. Despite their ferocity, Atlantic mudskippers are not very large; most only grow to be 14-16cm long.

Mating occurs year round, although peak times are between February and May. Males engage in territorial displays, after which females will select a male and enter his burrow to lay eggs. Clutches can easily number in the thousands, although few survive to adulthood. The male guards the burrow and, after a brief incubation period, floods it to induce hatching. Larvae drift for 1-2 months before metamorphosing into a juvenile stage, at which time they begin to return to land. Individuals reach sexual maturity at about 10.2-10.8 cm in length, roughly 1 year after hatching, and can live up to 5 years in the wild.

Conservation status: The IUCN rates the Atlantic mudskipper as Least Concern, although populations are declining. Their primary threats are from over-fishing and by-catch, pollution, and urban development. Some areas within their region have instituted sustainable fishing practices and established protected reserves as part of conservation efforts for this species.

Photos

Eva Mártensson

Eric Verhagen

Pedro Martins (via iNaturalist)

Rogerio Ferriera

[uncharismatic-fauna]

Superb Black Turban Snails

For beach-goers along the North American Pacific coast, the black turban snail (Tegula funebralis) is a common sight. They can be found from the northern reaches of British Columbia, Canada to southern California in the United States, almost exclusively in the intertidal zone. Although they are small, weighing only 20g and about 5 cm long, their clusters are hard to miss. Groups of hundreds of black turban snails congregate in seaweed beds, under rocks, and in the tight crevices of the rocky shoreline, and disperse only when they are covered by the sea.

    The most distinctive feature of T. funebralis is the shell. It is typically black or purple, but over time the outer layer of chiten can wear away to reveal a pearly inside. These shells are sought after by people for decoration, and by hermit crabs for shelter, although in both cases the shell is typically scavenged after it has already been emptied by predators. The rest of the snail’s body is black, soft, and can curl easily inside its shell to protect itself. As a member of the order Trochida, these snails also have an ‘operculum’; a hard trap door- like structure that the snail can close the aperture of the shell with to further protect itself. Interestingly, turban snails also have a unique organ called a bursicle that can sense chemicals released by their predators; primarily sea stars and crabs. When a threat is detected, the snail may either curl up in its shell or attempt to flee at a racing 8cm per minute. 

    Like many gastropods, black turban snails are herbivorous. Their primary food is algae, especially macroscopic algae like seaweeds and kelp. They compete with other grazers, mainly hermit crabs and urchins, for this food, although it’s not uncommon to see all three in the same area. In turn, black turban snail shells are sometimes colonized by limpets and slipper snails, which feed on the red algae that grows there. Periwinkles or other predatory snails will also sometimes attach themselves to turban snail shells and predate upon them by boring holes through the shell itself, but this is less common. 

    The main driver behind the black turban snail’s abundance is its high reproductive rates. It is a broadcast spawner, meaning that when it is covered by water, both sexes of the snail will release hundreds of thousands of gametes into the water column . Within a day or two, many of these gametes will combine and become microscopic larvae, which then disperse, metamorphose into juvenile snails, and settle in less than three weeks. Juvenile turban snails are a favorite food of sea stars, crabs, and intertidal fish, but the sheer number of young ensures that most will survive. 

    Conservation status: Although black turban snails were and still are a source of food for humans, they are extremely common and are considered of least concern. Their primary threat is ocean acidification and warming temperatures, but they are in turn a much larger threat to intertidal zone community stability when their primary predator, the sea star, is removed and their population grows unchecked.