THERMAL STRESS AGGRAVATES THE EFFECT OF OCEAN ACIDIFICATION ON FOUR CARIBBEAN REEF-BUILDING CORALS
Climate change leads to rising sea surface temperatures and changes in carbon chemistry that result in decreasing ocean pH and aragonite saturation state. Low pH has been shown to reduce calcification rates of symbiotic corals, but its impact under conditions of elevated light stress during thermal stress events is not known yet. Light absorbed in excess and increased photodamage is the main cause of the loss of photosynthetic activity during thermal stress, so the role of the light stress in this response should not be ignored. In this study we exposed four species of Caribbean reef-building corals Pseudodiploria strigosa, Orbicella faveolata, Montastraea cavernosa and O. annularis to heat stress conditions (pH8.1-32 °C); low pH (pH7.9-30 °C); and their combined effect (pH7.9-32 °C) for 10 days under natural light. Exposure to +2 °C in summer induced a loss of pigmentation, symbionts and photosynthetic activity and calcification due to increased accumulation of damage in Symbiodinium (decline in Fv/Fm). Low pH did not adversely affect coral photosynthesis and pigmentation, and only a slight decrease in the calcification rates was observed in P. strigosa. However, the combined effect of thermal stress and low pH significantly exacerbated the loss of calcification in P. strigosa and O. annularis, but not in the other two species. Considering the predicted changes for the ocean in the different global change scenarios, coral reefs are seriously threatened due to their adverse impact on the physiology of this symbiosis and carbon production, even prior to undergoing bleaching.
Krämer, W. E., Universidad Nacional Autónoma de México, Mexico, firstname.lastname@example.org
Iglesias-Prieto, R., Universidad Nacional Autónoma de México, Mexico, email@example.com
Enríquez, S., Universidad Nacional Autónoma de México, Mexico, firstname.lastname@example.org
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