Seawater carbonate chemistry and coral (Acropora digitifera and Acropora tenuis) algal infection rate, survival and surface area of plyps during experiments, 2009

Ocean acidification, caused by increased atmospheric carbon dioxide (CO2) concentrations, is currently an important environmental problem. It is therefore necessary to investigate the effects of ocean acidification on all life stages of a wide range of marine organisms. However, few studies have examined the effects of increased CO2 on early life stages of organisms, including corals. Using a range of pH values (pH 7.3, 7.6, and 8.0) in manipulative duplicate aquarium experiments, we have evaluated the effects of increased CO2 on early life stages (larval and polyp stages) of Acropora spp. with the aim of estimating CO2 tolerance thresholds at these stages. Larval survival rates did not differ significantly between the reduced pH and control conditions. In contrast, polyp growth and algal infection rates were significantly decreased at reduced pH levels compared to control conditions. These results suggest that future ocean acidification may lead to reduced primary polyp growth and delayed establishment of symbiosis. Stress exposure experiments using longer experimental time scales and lower levels of CO2 concentrations than those used in this study are needed to establish the threshold of CO2 emissions required to sustain coral reef ecosystems.

(Table 1) Near surface water chemistry of south Patagonian waters during spring and winter

Both the biomass of autotrophic dinoflagellates and its contribution to total chlorophyll were found to increase significantly with seawater temperature and the level of stratification in southern Patagonian waters during spring and winter. The highest peak of biomass corresponded to a single species, Prorocentrum minimum (Pavillard) Schiller, and was detected in middle shelf waters, coinciding with the primary productivity and CO2 uptake maxima reported for the area under spring conditions.