Extreme environmental conditions reduce coral reef fish biodiversity and productivity

Tropical ectotherms are hypothesized to be vulnerable to environmental changes, but cascading effects of organismal tolerances on the assembly and functioning of reef fish communities are largely unknown. This study examines differences in organismal traits, assemblage structure, and productivity of cryptobenthic reef fishes between the world’s hottest, most extreme coral reefs in the southern Arabian Gulf and the nearby, but more environmentally benign, Gulf of Oman. Assemblages in the Arabian Gulf are significantly less diverse and abundant than in the Gulf of Oman, despite comparable benthic composition and live coral cover. This pattern is attributed to energetic deficiencies caused by responses to environmental extremes and distinct prey resource availability, rather than absolute thermal tolerances. Consequently, biomass production, transfer, and replenishment through cryptobenthic fish assemblages are greatly reduced on Earth’s hottest coral reefs. Extreme environmental conditions, as predicted for the end of the 21st century, could thus disrupt the community structure and productivity of a critical functional group, independent of live coral loss.

Simon J. Brandl, Jacob L. Johansen, Jordan M. Casey, Luke Tornabene, Renato A. Morais, John A. Burt