Early life history response of reef building coral Orbicella faveolata to ocean warming and acidification

Guy Harvey Oceanographic Center Facility

Anthropogenic increases in atmospheric carbon dioxide (CO2) have largely altered the physical and chemical parameters of the world’s oceans, elevating oceanic temperatures and decreasing oceanic pH (ocean acidification). These two impacts of climate change are major threats to the livelihood of coral reefs and have been extensively investigated over the past few decades. While a majority of research has examined the effects on mature reef-building corals (highlighting bleaching and calcification), few studies have focused on the effects of ocean acidification and thermal stress on the earliest and potentially most vulnerable life stages of reef-building corals. The results of the limited experiments conducted to date have been contradictory, and have primarily focused on species from the Indo-Pacific. It is unknown how the early life stages of Atlantic corals cope with the combined effects of these two global environmental stressors. Coral reef recovery is critically dependent upon the success of corals throughout their early life history stages: fertilization, larval survivorship, and settlement. In order to better understand future reef health, we must consider climate change effects on all coral life stages across all oceanic regions. This research investigates the effects of thermal stress and ocean acidification throughout the early life stages of the Caribbean coral species, Orbicella faveolata. Gametes from O. faveolata were subjected to current day and future scenarios of oceanic temperatures and pH predicted by 2050 in order to quantify the effects of changing climate on fertilization, larval survivorship, and settlement. Results of this study indicate that treatment type did not significantly affect fertilization success. However, high temperature stress caused the greatest larval mortality than all other treatments and inhibited all settlement of O. faveolata. This effect was significantly mitigated by the combined ocean acidification and temperature stress treatments. This research provides insight into the complications for broadcast spawning corals to reproduce and contribute to coral reef recovery in the future. Reduced survival and settlement of O. faveloata larvae when subjected to these conditions may weaken the ability of this species to persevere when combined with disease and additional environmental stressors. Although ocean acidification reduces the impact of temperature stress in the early life stages, the well documented effects of ocean acidification that decrease accretion and growth of more mature calcified corals may drive this threatened species further into decline.