An Experimental Investigation of the Impact of Ocean Acidification on the Early Life Stages of Surf Clams, and the Interactive Effects of Feeding

Surf clams, Spisula solidissima, are a commercially important fishery species in the
United States. Surf clams have a protracted free swimming larval stage, and form their initial shells out of aragonite, a relatively soluble form of calcium carbonate. Thus, larval surf clams may be particularly vulnerable to ocean acidification, impacting recruitment to the fishery. In 2011 and 2012 we conducted experiments to investigate the effects of ocean acidification on early development and metamorphic success of surf clams, including both fed and unfed treatments in 2011, and high and low feeding rates in 2012, to more fully investigate the influence of food availability on the surf clam response to ocean acidification. In the 2012 experiments, we observed that elevated pCO2 did not decrease the 3-day or 6-day survival rate of larval surf clams. This differed from the survival data results of our 2011 experiments, which had suggested substantial decreases in survival as a function of elevated pCO2. We also observed (a) that elevated pCO2 resulted in a small but significant decrease in shell length at day 3 in lowfood cultures, but did not have a significant impact on shell length at day 3 in high-food cultures, and (b), that pCO2 impacts on shell length at day 6 were not significant in the low-food cultures,
and were significant at only one of the two elevated pCO2 levels in the day 6 high-food cultures.

Finally, shell mass did not appear to be strongly impacted by elevated pCO2 at either low or high feeding rates. These feeding rate-size observations – (a) and (b), no apparent p CO2 effect on day-6 size in low-food cultures, in contrast to a small CO2 effect in the high-food cultures – were unexpected; we had hypothesized that the energetic demands of calcification in high-CO2 treatments would result in a stronger CO2 impact on shell size in the low-food cultures than in the high-food cultures.

We propose to build on this work in fiscal year 2013 with a surf clam ocean acidification
culturing experiment that again will be carried out in collaboration with colleagues at the
NOAA-NMFS Milford Lab. We propose to run a 9 day experiment, with three pCO2 levels
(ambient and two enrichments) and two feeding rates (fed and unfed). This longer experiment will extend well beyond the time during which maternal nutrition effects may strongly influence larval energetics, enabling us to better quantify pCO2 impacts on larval surf clam growth and development. We will also add an earlier (~24 h post-fertilization) sampling time point than in the 2011 and 2012 experiments, which had the first time point at 3 days, in order to determine whether earliest developmental stages are particularly sensitive to elevated pCO2. Measures will include shell height and mass, SEM imaging, and biochemical sampling of eggs and larval surf clam tissues (protein and lipid class).