Invasion of coral reefs of Lakshadweep atolls by a central Indo-Pacific corallimorph

Abstract Worldwide, coral reefs are in decline due to mass bleaching, natural calamities, diseases, and anthropogenic stressors that expose large swathe of unutilized substratum which is later occupied by other benthic organisms like corallimorpharians, anemones, macroalgae etc. In the current work, we describe for the first time, the competitive interaction between a corallimorph and hard corals, observed in Kavaratti and Chetlat atolls in the tropical Indian Ocean, which is the first reported instance of an invasion of corallimorpharian in the entire Lakshadweep islands. The corallimorph, Rhodactis bryoides Haddon & Shackleton, 1893, is identified by morphological and molecular analysis. It is found that the species has no previous records from the western Indian Ocean region. Since the competitive interaction among reef organisms for space will have significant repercussions on the entire reef ecosystem in the future, we observed the pace of invasion for six months and calculated the relative abundance of the corallimorph using transects. None of the previous factors causing a corallimorpharia outbreak viz., external disturbances and nutrient enrichment were observed in this region. However, these tropical atolls are prone to occasional bleaching during the summer seasons. Further investigation needs to be conducted on the biology of this species, the interaction with other benthic groups and the environmental descriptors promoting the invasion.