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.
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