Effects of the 2015 marine heatwave on stony corals in the Gulf of Cazones, Caribbean Sea

Introduction: Coral reefs harbor high biodiversity and have great ecological, social, and economic importance. However, multiple local and global stressors increasingly degrade these ecosystems. Among global stressors, rising SST (Sea Surface Temperature) stands out, and studies on remote reefs provide a unique opportunity to assess its effects. Objective: This study aimed to determine the effects of the 2015 marine heatwave on coral condition at two remote reef crests in the Gulf of Cazones, southern Cuba. Methods: In October 2015, we surveyed three sites across two reef crests and used 2012 data from the same area to assess changes in reef condition. We used a 10 m linear transect for field sampling and obtained time series of SST and accumulated heat stress from 1998 to 2015. Results: The mean SST in 2015 was 0.56–0.59 °C higher than the 17-year average (i.e., 1998-2014), with 298–303 days exceeding the average SST, while maximum SST values reached 31.94–31.97 °C across the three sites. Accumulated heat stress reached approximately 11 °C-weeks, a value never previously recorded for these reef crests. Bleaching affected 56–77 % of corals in response to accumulated heat stress in 2015, with recent mortality ranging from 4.5 % to 31.3 %. The generalized linear mixed-effects model showed that coral bleaching significantly predicted the probability of recent mortality at the colony level. Between 2012 and 2015, live coral cover decreased significantly at all three sites, with losses of up to 44 %, accompanied by declines in Acropora palmata relative abundance and cover of ~ 19 % and ~ 43 %, respectively. Conclusions: Accumulated heat stress during the 2015 marine heatwave was the main driver of the intense coral bleaching event, accompanied by coral mortality and substantial losses of live coral cover, as well as declines in A. palmata relative abundance and cover at two reef crest sites, which is concerning because it is the keystone shallow reef-building species in the Caribbean Sea.