DIMENSIONING OF A MASS ALGAL CULTURE FACILITY FOR THE TEMPERATE ZONE NURSERY CULTURE OF BIVALVE MOLLUSCS

Aquacultural Research Corporation (ARC) has operated a continuous mass algal culture facility for the nursery culture of the hard clam (Mercenaria mercenaria) for twenty years. Procedures have been developed for the mass culture of selected species of microalgae that are of proven nutritional value for rearing bivalve spat. Within the past three years a 60% increase in algal yield has been achieved by selection of small centric diatoms for mass culture and by empirical determination of optimum depths and seasonal dilution rates for the light limited 40 m3 continuous cultures. Cell densities of the diatoms Thalassiosira pseudonana (3H) and Skeletonema sp. have averaged over 109 cells/liter from March through November. The algal pond surface area necessary to support a hypothetical nursery with a monthly average clam biomass of 8 kg dry meat weight (ca 13 × lo6 clam seed) was calculated for latitude 41°N during the four seasons of the year. These calculations were based on 1982–1983 algal yields and an assumed food chain efficiency of 10%. The required minimum algal pond surface area ranged from 192 m2 in summer to 750 m2 in winter. The current ARC nursery operation is compared with this hypothetical model. Costs of nursery seed production and a proposed strategy for minimizing the seasonal algal areal requirements of a temperate zone bivalve nursery are discussed.