Physiological responses to oxidative stress associated with pH variations in host tissue and zooxanthellae of hermatypic coral Pocillopora capitata

To study the adaptive mechanisms of host and symbiont in a decrease in pH, coral branches of Pocillopora capitata from La Boquita reef in the Bay of Santiago, Mexico were assigned to experimental units (n=38 per treatment) and three pH treatments were evaluated: (a) pH 8.00-8.40 (control; Treatment C-1), (b) pH 7.85-7.95 (Treatment C-2) and (c) pH 7.60-7.70 (Treatment C-3). Corals were collected at the beginning of the experiment (T-0) and at different times: T-1 (5h), T-2 (12h), T-3 (48h) and T-4 (168h). We examined malondialdehyde (MDA), antioxidant enzyme activities (SOD and CAT), antioxidant capacity and chlorophyll a (Chl a) content. The results showed a different response to the treatment between zooxanthellae and Cnidaria tissues. Initially in zooxanthellae, we observed a SOD response for the C-3 treatment; however this response did not prevent lipid degradation. In Cnidaria, the C-3 resulted in a greater SOD activity from the middle to the end of the experiment. The results improve our understanding of the effects of ocean acidification, the ability of coral to respond to environmental changes and the use of biochemical indicators related to the physiological condition for the recognition of coral communities affected by a decreases in pH.