Marine heatwaves threaten key foraging grounds of sea turtles in Southeast Asian Seas

Extreme regional ocean warming events, like marine heatwaves (MHWs), could have severe and long-lasting impacts on species and ecosystems. Extreme and persistent warming of the ocean could directly threaten survival of marine species, as exceeding their thermal tolerance often leads to massive mortality events. Similarly, MHWs could further threaten species persistence indirectly, by altering food webs, leading to cascading effects that are expected to be more pronounced for species at a lower trophic position. Green turtles, a representative species of the charismatic marine megafauna, are largely herbivorous; thus, their food availability is tightly linked to environmental conditions. Here, we explored the degree to which foraging areas of green turtles along the Southeast Asian region could be subjected to MHWs in the future. For this, we applied a series of climatic niche models to spatially delineate important foraging habitats for adult green turtles, Chelonia mydas, across the marine region of Southeast Asia. Our analysis revealed that marine sites, which could host foraging grounds for adult green turtles, cover around 37% of the Southeast Asian region, with high probability of experiencing prolonged and intense MHWs for the vast majority of these sites. The annual number of days subjected to MHWs could increase by 16-fold from the very recent past period, leading to even a permanent MHW state. These results offer some alarming messages for scientists and conservation planners, highlighting the need to improve our knowledge on the potential response of species to MHWs and design climate adaptation strategies.