Effects of CO sub(2) and the harmful alga Aureococcus anophagefferens on growth and survival of oyster and scallop larvae

Globally, the frequency of harmful algal blooms is increasing and CO sub(2) concentrations are rising. These factors represent serious challenges to a multitude of estuarine organisms as well as to efforts to restore depleted stocks of filter-feeding bivalves. In this study, we compared the responses of larval bivalves Crassostrea virginica and Argopecten irradians to the brown tide alga Aureococcus anophagefferens (250 X 10 super(6) cells l super(-1) and 1 X 10 super(9) cells l super(-1), respectively) and a gradient of CO sub(2) concentrations ( similar to 240, similar to 390, and similar to 850 ppm). Results indicated that A. anophagefferens and higher levels of CO sub(2) significantly depressed rates of survival, development, growth, and lipid synthesis of A. irradians larvae with the combination of both factors having the largest effects. C. virginica larvae were also negatively impacted by the harmful alga and elevated CO sub(2), but displayed a higher overall survival rate when exposed to these combined stressors. For both species, high densities of A. anophagefferens (10 super(9) cells l super(-1)) elicited a stronger negative effect on larval survival than high levels of CO sub(2) concentrations ( similar to 850 ppm). Collectively, these results demonstrate that the concurrent occurrence of harmful algal blooms and high CO sub(2) concentrations will have negative consequences for bivalve populations and further demonstrate that some species of larval bivalves are more resistant to these stressors than others.