Ocean acidification (OA) from the equilibration of atmospheric CO2 with seawater is predicted to negatively affect scleractinian reef corals over the 21st century. In adult corals, OA has been reported to reduce rates of coral calcification, induce coral bleaching, and affect coral respiration and the photosynthetic productivity of the coral’s algal symbiont Symbiodinium spp. However, OA effects on the early life-history stages of corals (e.g., larvae, newly settled recruits, juveniles) are less understood. In this thesis research, I used juvenile Seriatopora caliendrum from southern Taiwan, and massive Porites spp. from Moorea, French Polynesia, to experimentally evaluate the effects of OA on three important physiological processes of scleractinians: coral bleaching, calcification, and metabolism inferred through respiration and excretion rates. In Chapter II, using S. caliendrum, results from my research indicate that OA (841 μatm pCO2) does not affect juvenile S. caliendrum corals undergoing thermal bleaching at 30.53 °C, and OA alone does not result in coral bleaching under ambient temperatures (27.65 °C). Subsequently in Chapter III, I exposed juvenile massive Porites spp. to low-pH and elevated dissolved inorganic carbon (DIC) seawater within sealed respirometers incubated in situ. I determined that low-pH (pHT 7.73, Ωarag = 2.27) at 976 μatm pCO2 had no effect on calcification, respiration, or the energetic expenditure concurrent with calcification relative to control conditions. However, elevated [DIC] (~3 mM) stimulated calcification under low-pH and low- Ωarag (pHT 7.69, Ωarag = 2.75), indicating calcification may be DIC limited under ambient [DIC] (~2 mM). These results agree with past studies identifying adult and juvenile massive Porites spp. as resistant to environmental stress, and emphasize the success and pragmatism of in situ designs for the future application of ecologically relevant OA experiments. Finally, in Chapter IV using S. caliendrum, I determined that OA (885 μatm pCO2) affected the metabolism of intact juvenile corals by increasing nitrogen excretion, however OA did not affect rates of aerobic respiration or total protein content. Finally, I present preliminary results that suggest OA (885 μatm pCO2) affects coral metabolism by increasing rates of nitrogen excretion, which has implications for amino acid and protein catabolism, as well as, the capacity for corals to regulate intracellular pH. In summation, findings presented here suggest: (1) OA does not affect or cause coral bleaching in juvenile corals; (2) certain coral taxa may be resistant to short-term exposure to OA conditions, and (3) OA may affect nitrogen metabolism in the coral-algal symbiosis.
Thesis or Dissertation
Department of Biology, CSU Northridge