Laboratory experiments revealed different bleaching susceptibilities to heat stress in eight species of subtropical urban corals

Understanding species' susceptibility to environmental stressors is crucial for conservation planning, but such data are unavailable for many subtropical corals. We therefore conducted 1-month laboratory experiments to determine the heat stress susceptibility of eight species from subtropical areas by exposing them to 32 °C (treatment) or 25 °C (control). Four species (Dipsastraea rotumana, Echinophyllia aspera, Pavona decussata, and Platygyra carnosa) survived the whole experiment, although bleaching occurred after one to two weeks of exposure. The heat exposure caused total mortality in the other four species: on day 2 in Acropora solitaryensis, day 7 in Acropora digitifera, day 9 in Acropora pruinosa, and day 17 in Montipora peltiformis. These results suggest that repeated heatwaves may cause changes in coral communities by causing disproportionally high mortality of heat-sensitive species. Coral species tested in this study, collected from subtropical reefs previously thought to be refuges for coral reefs under global warming, demonstrated greater susceptibility to heat stress than their tropical counterparts. This raises concerns about the persistence of coral reefs as sea surface temperatures continue to rise.