Morphological and genetic characterization of Stylophora madagascarensis, Pocillopora acuta, and Pocillopora verrucosa in Mauritius and their thermal photophysiological stress responses

Increasing frequency and intensity of marine heatwaves worldwide warrant characterizing and understanding variation in thermal response among reef coralsthroughinsituandexsituexperimentationtoultimately help with coral conservation and management strategies. This study first characterized species of Pocilloporidae, including two morphs of Stylophora and Pocillopora spp., from the Mauritian waters using morphology and genetics. The photophysiological responses and bleaching sensitivity were then examined when exposed to experimental and natural thermal stress. Pocillopora acuta and Pocillopora verrucosa were identified from Grand Gaube (GG) and harbored a species of Cladocopium (clade C) as their symbiont. The two morphs of Stylophora madagascarensis from Amber Island (AI) and GG were genetically similar and harbored a unique species of Durusdinium (clade D). These pocilloporid taxa exhibited differential bleaching responses during warm water events that occurred in March 2016 and again in 2019. The latter year was characterized by narrower daily variations in sea surface temperature allowing for minimal acclimatization, and possibly explains why bleaching was more severe. Coral nubbins subjected to 28, 30 and 32 °C, and 170 and 10 μ mol quanta m⁻² s^–1 light levels for a period of 55 hrs revealed variable thermal photophysiological responses. These findings indicate that the regionally endemic morphotypes of S. madagascarensis are thermally robust and P. acuta tended to be more heat tolerant than P. verrucosa. These results indicate how increasing episodes of thermal stress are likely to affect coral populations in the region and have implications for coral conservation.