Another New Species of Sea Slug, Discovered Here on Koh Tao

KORSHUNOVA et al. 2019There is a small and beautifully ornate sea slug that has mesmerized divers on Koh Tao for years, which turned out to be unknown to science. However, our familiar little sea slug has been described in a recent paper by our team, and is now known as Unidentia aliciae. This is an important update to the world of nudibranch taxonomy, as the family Unidentiidae is still in dispute, and this new species helps to solidify the family and genus amongst debating scientists. Furthermore, it is another example of the amazing diversity of sea slugs found on the coral reefs around our island, currently estimated to have over 150 species.

Why is This Nudibranch Special?

This particular species of nudibranch was first recorded in 2009 by divers working on a coral nursery project in the vicinity of Chalok Ban Kao, a bay on the southern side of the island. Since then, it has primarily been recorded on artificial reef structures, nurseries, fishing nets, and marine debris from several areas around the island, however rarely has it been observed on the natural reef. Rahul Mehrotra and Spencer Arnold, conservation instructors at the New Heaven Reef Conservation Program and among the authors of the paper, say the reason they are only found in these locations is that the artificial substrates provide a growing area for a hydroid known as Corydendrium sp. This species of hydroid seems to be the primary food source for the nudibranch, as it has only ever been found in close association with the hydroid. This observation, along with the abundance of nudibranchs on other artificial reefs, such as the Hin Fai Biorock, is an interesting story, and one that Rahul is looking into further.

It was first noticed that this was indeed an undescribed species while members of RCP were working on a project to record and identify sea slugs around the island, which was published in 2016 in the paper “Species inventory of sea slugs (Gastropoda: Heterobranchia) for Koh Tao, Thailand, with 25 first records for Thai waters.”

Where can I Find This New Sea Slug?

The species, now known as U. aliciae was named after researcher Alicia Hermosillo of the University of Guadalajara, who is a well respected researcher, and shares the responsibility for pioneering work on the family Unidentiidae. You can identify this species by its cream-yellow body color, ornate cerata containing a violet band and white tips, and violet line down the body. You will usually have to look around artificial reef structures or old fishing nets for them. Currently, this species has only been found on Koh Tao, although you may find its similar looking cousins, U. nihonrossija in Japan or a yet undescribed species of Unidentia in Australia.

This discovery, among many others that have recently been made on our island supports the claim that Koh Tao’s reefs are a unique place, in need of preservation. The biodiversity of our reefs has been shown by several papers and scientific studies to be the highest in the Gulf of Thailand. But, other studies have also shown it to be threatened by a variety of local and global impacts, such as over-use, run-off, coral predators, and thermal bleaching. These two factors imply the need to increased protection of these ecosystems and the resources they provide to sustain our island  community and economy.

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