Meeting Abstract
Anthropogenic atmospheric pCO2 concentrations are increasing at unprecedented rates, resulting in declining seawater pH (ocean acidification – OA). Estimates of the global mean seawater pH indicate that pH has already decreased by 0.1 units, and is predicted to continue to decrease by another 0.4 pH units by 2100. The majority of OA research to date has focused on the effects of OA in single species experiments. To assess how OA may influence natural macroalgal-mesograzer assemblages we conducted a mesocosm experiment with a common chemically defended Antarctic brown macroalga, Desmarestia menziesii, seeded with natural densities of a D. menziesii-associated mesograzer assemblage, generally dominated by amphipods. We exposed these assemblages to three levels of pH representing present-day (pH 8.1), near future–2100 (pH 7.7) and more distant future (pH 7.3) conditions. Following a four-week exposure period, all mesograzers were collected from each mesocosm and preserved for identification. We found a modest but significant decrease in the percent species abundance in the lowest pH treatment (pH 7.3) compared to the other two pH treatments, but no significant differences between pH treatments for two standard measures of species diversity. These results suggest that benthic macroalgal-mesograzer assemblages of the WAP are likely to be resilient to near future decreases in seawater pH. This project was supported by NSF award ANT-1041022 (CDA, JBM, RAA).
