The Impact of Ocean Acidification on Larval Sea Scallops (Placopecten magellanicus) and Possible Mitigation by Feeding- An Initial Experimental Study

Dan McCorkle, Woods Hole Oceanographic Institution

Abstract

Laboratory CO2 manipulation experiments conducted by ourselves and others demonstrate
that early life stages of some of the region’s most lucrative fisheries – oysters, bay scallops and surf clams – are vulnerable to ocean acidification (OA), and that reduced growth and elevated mortality occur at aragonite saturation state (Ωar) values less than 1. However our recent results also suggest that the response of larval shellfish growth to aragonite undersaturation may be modulated by the availability of food. The study proposed here will provide the first experimental data for the combined impacts of OA and food supply on sea scallops (Placopecten magellanicus, a >$550M/yr fishery); if we find that sea scallops experience OA and feeding rate effects similar to those we have seen in other shellfish species, the implication is that future impacts of ocean acidification on sea scallops must be considered within a framework that includes the impact of global change on ocean circulation, stratification and productivity.

We propose an experimental study at WHOI, in collaboration with colleagues at the NOAANMFS Milford CT lab, to quantify the impact of ocean acidification on the early development of the sea scallop, and to assess the influence of food availability on this OA impact. We will build on our previous work with other species, and test two hypotheses for P. magellanicus:
1. Lower pH and aragonite saturation state will elevate mortality, and reduce the growth rate of surviving larvae, and
2. Well-fed larvae in low-pH, low-Ωar conditions will experience reduced mortality and
elevated growth rates compared with less well-fed larvae reared in the same CO2 conditions. The experiment will run for approximately 2 weeks, and will use two CO2 levels (ambient and enriched, targeting Ωar values of 2.2 and 0.8, to span the saturation state levels observed in sea scallop habitat today and projected levels in the coming decades), and three feeding levels.

Today, the P. magellanicus habitat underlying outer continental shelf waters north of the
mid-Atlantic bight is characterized by Ωar values less than 2, but these low-Ωar waters are also highly productive, which may sustain high scallop recruitment despite chemical conditions less than optimal for shell growth. However, at least one recent climate model projects that productivity in this region will decline in response to global warming. If this projection is realized and our feeding hypothesis is correct, the combination of ocean acidification and declining productivity could threaten the most valuable US fishery in the Atlantic.