Parasites or predators? Gastropod ectoparasites and their scleractinian host corals at Koh Tao, Gulf of Thailand, with the description of a new species

Abstract

Recent years have seen a rapid increase in the study of coral-associated gastropods. In particular, the description of several new species in conjunction with their host specificity or dietary variability, has raised questions pertaining to their impact on reef health. These corallivores have been labelled as both ‘parasite’ and ‘predator’ by different studies, due to the tendency of some species to entirely consume their ‘host’ corals. Here we present new findings of corallivory and parasitism based on surveys conducted on the reefs of Koh Tao, Gulf of Thailand. A total of 6566 corals were assessed for their tendency to host gastropods of the nudibranch genus Phestilla and the caenogastropod family Epitoniidae. Thirteen gastropod species were found to be associated with 20 scleractinian coral species, including six that do not match the original description of previously known taxa. Herein we describe one of them, the first nudibranch proven to be associated with corals of the scleractinian genus Acropora and discuss conservation implications of these coral/gastropod relationships. Additionally, we explore the complex topic of defining these relationships as parasitic versus predatory and the merits of using these labels to better understand the ecology of these relationships.