Cellular Responses of Astrangia poculata (Ellis and Solander, 1786) and Its Symbiont to Experimental Heat Stress

Climate change has had devastating effects on tropical coral reefs; however, much less is known regarding how heat stress affects temperate coral. This research focuses on Astrangia poculata (Ellis and Solander, 1786) collected from Narragansett Bay, RI, during the summer and winter seasons and understanding the effect of experimental thermal extremes (i.e., 26 °C) on seasonally different populations. Photosynthetic efficiency (Fv/Fm), symbiont density (via an inverse relationship with pixel intensity), and oxidative stress via reactive oxygen species (ROS) concentrations were measured on symbiotic and aposymbiotic A. poculata. Higher Fv/Fm rates were observed in summer- vs. winter-collected corals (p ≤ 0.05). Lower symbiont density within symbiotic and aposymbiotic A. poculata were observed at elevated temperatures, and higher intensities as well as symbiotic coral were observed in winter compared to the summer collections (p ≤ 0.05). No differences in ROS were observed in host tissue cells, suggesting that ROS produced in the algal symbionts was not translocated into host tissues. Overall, higher ROS concentrations were observed in summer- vs. winter-collected corals (p ≤ 0.05) in both symbiotic states. ROS concentrations were higher in symbiotic compared to aposymbitoic colonies (p ≤ 0.05), albeit no differences were observed between temperature treatments, suggesting that antioxidants mitigate the deleterious effects of ROS on host tissues.