Response of a temperate coral to temperature stress: A comparison of populations across sites

Abstract

The negative effects of warming temperatures on coral physiology are well-documented. However, research increasingly suggests that these effects are variable and that the degree to which corals are impacted by higher temperatures are dependent on a range of environmental and physiological variables. In tropical corals, which live near their upper thermal limits, these disparities have led to significant differences in bleaching and other negative health effects even over relatively small spatial scales. However, the response of temperate corals across small spatial scales is less well understood despite their occurrence in areas with larger temperature ranges than their tropical counterpart. To determine whether responses to thermal stress (27.4 versus 29 °C) differed in a common temperate coral species across a small geographic area, as has been documented in tropical corals, we evaluated coral growth and photosynthetic efficiency (Fv/Fm) of the coral Oculina arbuscula over the course of eight weeks when grown at differing temperatures. When measured as buoyant mass (calcification), growth of O. arbuscula did not differ as a function of temperature or site of collection. In contrast, when measured as change in tissue mass or total wet mass, elevated temperature suppressed growth. Change in total wet mass also varied significantly by collection site, corals from some sites experiencing little if any growth and those from other sites experiencing negative growth. Photosynthetic efficiency (Fv/Fm) was significantly lower at 29 °C than at 27.4 °C. Analyses of symbionts showed that sequence variants related to the genus Breviolum made up ∼98% of all Symbiondiniaceae across all sites and temperature treatments with one variant (100% sequence identity to Breviolum psygmophilum) being 91% of the total community. Only one Symbiodiniaceae, with a 99.28% sequence identity to Breviolum psygmophilum, differed significantly as a function of temperature. It also comprised only 1–3% of the community. Bacterial microbiome variance increased during our experiment, but there were no significant effects of temperature or collection site. For O. arbuscula from these collection sites, location did not impact the coral's ability to withstand the effects of temperature stress.