WILLEMSTAD - 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. Until now, these animals were not known in the Caribbean. The discovery raises questions about the threats invasive species can pose to coral reefs.
Worm snails are small, tubular snails found in tropical or subtropical waters. Some are known to form reef-like aggregations. Others live with corals, where they often cause damage from the poisonous slime the snails secrete to hunt prey. Because of their shape, and as their name suggests, worm snails are often confused with true worms, such as the Christmas tree worm (Spirobranchus giganteus), which also lives with corals. However, these worms do not secrete slime nets, but have colorful tentacles with which they catch prey.
Old material, new discoveries
The Curaçao snail appears to be of the genus Petaloconchus, but the exact species is still unknown. Future research into the snail's appearance and DNA may reveal its real identity, says lead author Bert Hoeksema, of the University of Groningen and Naturalis. “With this article I hope to create awareness,” he explains. "I'm curious if colleagues elsewhere in the Caribbean also find this phenomenon, because nobody seemed to have noticed it before."
The genus is mainly known in the Indian Ocean, with some populations on islands in the Pacific Ocean. A coral-dwelling worm snail in the Caribbean was a bit of a surprise. But after the discovery of the snail in Curaçao, researchers searched more thoroughly, and eventually saw it in photos of previous fieldwork. Worm snails appear in photos taken in Curaçao as early as 2014, but also in photos of the neighboring island of Bonaire. This suggests that the snail is not widespread in the Caribbean and may have been introduced to the southern Caribbean islands. However, the possibility that the species also appears elsewhere cannot be ruled out, says Hoeksema.
A cryptogenic snail
Still, the researchers don't know how the snail ended up in the Caribbean. The Caribbean worm populations are what ecologists call cryptogenic: from the Greek kryptos, meaning hidden, and genesis, meaning origin – their origin is unknown or untraceable. The snail appears to be an invasive species, and Hoeksema says he personally considers it "very likely invasive". But it's too early for such labels, as the route that brought the species here is still unclear. The researchers speculate that the snail could be from the Pacific Ocean, where a similar snail has been observed.
Corals in danger?
Given the damage worm snails do to corals, are there any potential negative impacts on coral reefs? Hoeksema thinks not yet, because the snail is not very numerous. But he adds: “I'm not a conservationist. I just want to make colleagues and managers of marine parks aware of the snail.” In combination with factors such as climate change and eutrophication, parasites such as worm snails and the above-mentioned Christmas tree worm can generally become more prevalent. All in all, they can therefore very well be harmful to coral reefs.
Photo: A worm snail from Curaçao on a host coral, Porites astreoides, with remains of a mucous membrane (Credit: Bert W. Hoeksema)