Investigating the Efficacy of Alkalinity Addition in Mitigating the Effects of Ocean Acidification on Commercial Shellfish

Lead PI: Justin Ries, Northeastern University

To conduct controlled experiments to quantify the efficacy of different types of alkalinity addition (Na2CO3, CaCO3, Mg(OH)2, Ca(OH)2) in mitigating the impacts of future ocean acidification (OA) on juvenile specimens of four commercially important shellfish species (eastern oyster Crassostrea virginica, bay scallop Argopecten irradians, quahog Mercenaria mercenaria, softshell clam Mya arenaria). To conduct trials at collaborating shellfish hatcheries investigating the efficacy of different types of alkalinity addition on larval specimens of a subset of the commercially important shellfish species investigated in the controlled laboratory experiments. To convey results of experiments to stakeholders, including scientists, resource managers, shellfish industry, and policymakers.

Juvenile specimens of commercially important shellfish will be grown under present-day and future pCO2 conditions with and without different types of alkalinity addition. These different types of alkalinity will also be added to shellfish hatchery waters to investigate impacts on larval stage development. Seawater carbonate chemistry will be calculated from total alkalinity and dissolved inorganic carbon, with temperature, pH, and salinity measured daily. Calcification rates will be determined via buoyant weighing for juvenile specimens and by photomicroscopy for larvae, with shell polymorph mineralogy quantified by powder xray diffraction. Basic physiological conditions will be assessed at completion of experiments.

Shellfish aquaculturists increase seawater pH and alkalinity through the dissolution of Na2CO3—a process termed ‘buffering’. However, there are other low-cost alkaline minerals that may offer advantages over Na2CO3. Buffering with Ca(OH)2 or CaCO3 should increase the availability of Ca2+ ions, in addition to CO32- ions, for calcification. Mg(OH)2 and Ca(OH)2 can also be used to modify seawater Mg/Ca in support of bivalve shell mineralogy, with Mg/Ca<2 favoring calcite and Mg/Ca>2 favoring aragonite. The goal of the proposed research is to conduct a systematic evaluation of the efficacy of different alkalinizing agents at mitigating ocean acidification for various commercial shellfish.