Global climate change has aggravated the severity of space competition put up by marine sponges in the tropical coral reef ecosystems. We report here an outbreak of coral-killing sponge Clathria (Microciona) aceratoobtusa (Carter, 1887) over live coral colonies of the genus Turbinaria in an unprotected reef (mainland patch reef) in the Gulf of Mannar in India. An outbreak of this orange-reddish sponge was observed during an explorative dive in April 2020. Live coral cover in the reef was 62.06% (SD±3.36), which was dominated by the genus Turbinaria with 82.31%. Among the total of 549 Turbinaria colonies counted in five transects, 21.86% (n = 120) of colonies were found infested by the sponge. As the mainland patch reef lies outside the boundary of marine protected area, it is exposed to human-induced threats, apart from climate change implications. This report would serve as an evidence to indicate the intensity of the space competition waged by sponges in a disturbed reef ecosystem.
