ALKALINITY ENRICHMENT ENHANCES GROWTH OF THE LARVAL BLUE MUSSEL Mytilus edulis  

The seawater saturation state with respect to calcium carbonate mineral phases  (Ω aragonite or Ω calcite) is an important factor in the shell growth of marine bivalves, including the Pacific oyster, Crassostrea gigas, and the Mediterranean mussel, Mytilus galloprovincialis. Seawater that is less strongly supersaturated with respect to aragonite leads to slower development during key early-life stages; related chemical changes, such as elevated carbon dioxide partial pressure and lower pH, seem less directly tied to larval growth. While many studies have examined the negative effects of decreased saturation state on calcifying organisms, there has been little work on the effects of increasing alkalinity (and thus saturation state), as could be done in an aquaculture setting. To determine whether or not chemically elevating seawater alkalinity above natural levels could be advantageous to blue mussel (Mytilus edulis) aquaculture, larval rearing experiments were conducted starting with newly fertilized embryos, grown for 8 days under 3 increased aragonite saturation states (1.5, 2.5 and 3.5 times that of the control); the alkalinity enrichments were achieved using sodium bicarbonate additions. Shell length was greater with each enriched aragonite saturation state, and was greatest at the highest saturation state (Ω 7, 3.5 times control). We are currently examining larvae from the different treatment groups with a scanning electron microscope, in order to analyze saturation state effects on shell integrity and structural mutations at early development stages. Our findings so far suggest that sodium bicarbonate enrichment could be a good option in East Coast shellfish hatcheries, particularly in the face of rising ocean acidity.