Species inventory of sea slugs (Gastropoda: Heterobranchia) for Koh Tao, Thailand, with 25 first records for Thai waters

A combination of benthic surveys and photographic records was used to evaluate the abundance and diversity of sea slugs around the island of Koh Tao, Thailand. Observations and records spanning over 14 years yielded 87 different species, including seven Sacoglossa, four Cephalaspidea, three Anaspidea, one Pleurobranchomorpha, and 72 species of Nudibranchia. Of these, seven records are claimed to be first for the Gulf of Thailand, and a further 25 species are found to be first records for Thailand, according to current literature. Analysis of the relative abundance based on estimated frequency of sightings, and geographic distribution based on number of different dive sites, was carried out. Analyses revealed that although the diversity of species for an island of its size was relatively high, a majority of species had a low frequency of sightings. Furthermore, a number of records had limited geographic ranges or were isolated to specific ecological niches. Analysis of preferred substrate type for the different species showed that a significant proportion of species were isolated outside the coral reef areas and are, therefore, unlikely to be observed by the diving community. These records indicate a greater wealth of biodiversity of charismatic organisms in non-reef areas than previously thought, which can help to encourage non-coral reef tourism in an area where coral reefs are under threat in part due to over-use by SCUBA diving.