Mortality, growth and regeneration following fragmentation of reef-forming corals under thermal stress

Abstract

Storms inflict damage to corals resulting in fragments that have the potential to regenerate thus contributing to the asexual reproduction of the parental colony. Extreme climatic events like these are predicted to increase in the future due to ocean warming, which is also the primary cause of coral reef bleaching and consequent coral mortality in the tropical and subtropical seas. This way it is urgent to investigate the differential effect of warming over post-fragmentation and regeneration processes among the scleractinian hermatypic coral species. This study investigated the mortality, growth and regeneration capacity of nine reef-forming coral species of the Indo-Pacific. Fragments were exposed to 26 °C, 30 °C, and 32 °C for 60 days. Half of these fragments was inflicted with one injury and the other half was used as control. Mortality, partial mortality, bleaching level, growth and regeneration of artificial injuries were assessed. Mortality increased with temperature, reaching 100% for most species after 60 days, at 32 °C, but Psammocora contigua which showed remarkably lower mortality (40%) and all coral fragments of Turbinaria reniformis and Galaxea fascicularis survived the experiment. Partial mortality was lowest for P. contigua, T. reniformis, and G. fascicularis even at 32 °C. These three coral species were also the most resistant to bleaching. Growth rates decreased with temperature, with the exception of G. fascicularis that maintained similar growth rates at 26 °C and 30 °C. Regeneration rates generally increased with temperature. It was concluded that P. contigua, T. reniformis, and G. fascicularis fragments show higher capacity to withstand higher temperatures.