A newly found worm snail might indicate future threats to Caribbean coral reefs

Naturalis Biodiversity Center
30-APR-2022 - While studying coral reefs on Curaçao, a team of researchers from Naturalis and the University of Groningen came across what turned out to be a worm snail. Up until now, these animals had not been known in the Caribbean. Their discovery raises questions about the threats that invasive species may be posing to coral reefs.

A worm snail from Curaçao on a host coral, Porites astreoides, with remnants of a mucus netWorm snails are small, tube-dwelling snails found in tropical or subtropical waters. Some of them are known to form reef-like aggregations. Others live in association with corals, to which they often cause harm because of the toxic mucus that the snails secrete to hunt for prey (see close-up picture). Due to their shape, and as their name suggests, worm snails are often confused with actual worms, such as the Christmas tree worm (Spirobranchus giganteus), that also lives in association with corals. These worms, however, do not secrete mucus nets but have colourful tentacles with which they catch prey.

Old material, new discoveries

The snail from Curaçao seems to be from the genus Petaloconchus, but the exact species is unknown. Future research on the snail’s morphology and DNA may reveal its real identity, says lead author Bert Hoeksema. “This is an introduction article to create awareness,” he explains. “I am curious to find out if colleagues will find it elsewhere in the Caribbean, because nobody seemed to have found it before”.

The genus had mainly been recorded in the Indian Ocean with some populations on Pacific islands. A coral-dwelling worm snail in the Caribbean was a bit of a surprise. A worm snail associated with Cladopsammia manuelensis corals, which was also discovered recently in Caribbean coral reefsHowever, after the researchers found the snail on Curaçao and started to look for it more closely, they ended up noticing it in pictures from earlier fieldwork. Worm snails appear in pictures taken on Curaçao as far back as 2014, as well as on pictures from the neighbouring island Bonaire. This suggests that the snail is not widespread in the Caribbean and may have been introduced in the southern Caribbean islands. The possibility of it existing elsewhere definitely cannot be excluded though, Hoeksema states.

A cryptogenic snail

Still, we do not know how it got to the Caribbean. The Caribbean worm snail populations are what ecologists call cryptogenic: from the Greek word kryptos, meaning hidden, and genesis, meaning origin – their origins are unknown or untraceable. The snail seems like an invasive species, and Hoeksema says he personally considers it “very likely invasive.” But it is still too early for such labels as there is no confirmed invasion corridor yet. The researchers speculate that in that case the snail might have come from the Pacific, where a similar snail has been observed.

Corals in danger?

A worm snail on dead coral: the little elliptic white particles next to the snail are faecal pelletsGiven the damage worm snails do to corals, is there a possibility of negative consequences to the coral reef ecosystem? Hoeksema thinks not yet, as the snail is not very abundant. But he adds, “I’m not a conservation biologist. I just want to make colleagues and marine park managers aware of the snail.” In combination with factors like climate change and eutrophication, parasites like worm snails and the above-mentioned Christmas tree worm might generally become more abundant. All of them together may very well be harmful to coral reefs.

More information

Text: Kurt Kurat, Naturalis Biodiversity Center
Photos: Bert W. Hoeksema, Naturalis Biodiversity Center & Rijksuniversiteit Groningen