The Effects of Elevated Temperatures on the Reproductive Biology of a Mediterranean Coral, Oculina patagonica

Global climate change is profoundly impacting coral ecosystems. Rising sea surface temperatures, in particular, disrupt coral reproductive synchrony, cause bleaching, and mortality. Oculina patagonica, a temperate scleractinian coral abundant across the Mediterranean Sea, can grow at a temperature range of 10–31 °C. Studies conducted three decades ago documented this species bleaching during the summer months, the same time as its gonads mature. However, the Eastern Mediterranean Sea is experiencing some of the fastest-warming sea surface temperatures worldwide. This study repeated the year-round in situ assessment of the reproductive cycle and gonad development and correlation to summer bleaching. In addition, thermal performance of the holobiont was assessed in an ex situ thermal stress experiment. In situ monitoring revealed no temporal changes in gonad development compared to previous studies, despite sea surface warming and concurrent bleaching. Experimental thermal performance curves indicated that photosynthetic rate peaked at 23 °C, bleached coral area was significant at 29 °C, and peaked at 34 °C. With local sea surface temperature reaching 31 °C, O. patagonica is exposed beyond its bleaching threshold during the summer months in situ. Despite this, O. patagonica maintains gonad development and physiologically recovers at the end of summer demonstrating resilience to current warming trends.