Diversity and Distribution of Sea Slugs (Gastropods: Heterobranchia) in Sempu Strait, Indonesia

Abstract

The heterobranch sea slugs are one of the most under-studied marine lifeforms found around the Sempu Strait Area. Currently, the records of their occurrences around this area are only known from the underwater macrophotography enthusiast's collection and have not been published on a scientific article. We conducted underwater surveys spanning from October 2017 to June 2019 at eleven dive sites of Sempu Strait and yielded 45 different species of heterobranch sea slugs, including 35 species of Nudibranchia, 6 Aplysiida (Anaspidea), 2 Cephalaspidea, and 2 Sacoglossa. The analysis of the sea slugs occurrence on Sempu Strait reveals that the areas around the Western Sempu Strait, including Rumah Apung, Kondang Buntung, Tiga Warna, and Stumbut have the most diverse sea slugs species, even though the majority of the species have a low sighting frequency. The analysis also revealed that roughly a third of the sea slugs encountered on the Sempu Strait areas are found on the coral rubble substrate. This study revealed that Sempu Strait has slightly lower sea slug species diversity than another nearby studied site. The records provided here hopefully could help to encourage macro-photography recreational dive activities to further develop the ecotourism sector around this area.