| Summary: | Ocean acidification (OA), a result of increased atmospheric CO2, is predicted to decrease the surface ocean pH by a value of 0.4 units by the year 2100. Decreases in pH have been shown to cause deleterious effects on many calcifying marine organisms, which may negatively affect ecosystem functions. Few studies, however, have investigated OA impacts on fertilization success of free-spawning marine organisms. This study focuses on the effects of OA on fertilization success in the sand dollar Dendraster excentricus. The goal of this study is to experimentally determine whether decreases in pH values lower fertilization success in D. excentricus. The two-pH treatments chosen for this experiment reflect the present day pH value (8.1) and the predicted pH value by the IPPC for the year 2100 (7.7). Gametes from adult D. excentricus collected from Crescent Bay, East Sound, Orcas Island, WA, were fertilized in filtered seawater with pH 8.1 and 7.7. Fertilization success was determined by the percentage of 2 and 4-cell cleaving embryos. A numerical model of reproductive success as a function of adult density and current conditions will be used to assess potential population-level effects of observed changes in fertilization success. Results of this investigation will aid future studies on the effects of climate change on marine organisms and ecological stability of marine communities.
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