INFLUENCE OF CHEMICAL COMPOSITION OF ALGAL FOOD SOURCES ON GROWTH OF JUVENILE OYSTERS, CRASSOSTREA VIRGINICA

¹ National Marine Fisheries Service, Northeast Fisheries Center, Milford Laboratory, Milford, Connecticut 06460

Two algal flagellates, Dunaliella tertiolecta Butcher and Tetraselmis maculata Butcher, harvested in the stationary phase from a semi-continuous carboy culture apparatus, were analyzed for dry weight, total carbohydrate, total protein, and total lipid. Each species was cultured in three different growth media. The growth response of D. tertiolecta was similar in all three formulations but populations of T. maculata were considerably limited in the reduced-nutrient medium, X₁. Both algal species cultured in the X₁ medium had significantly greater dry weights and contained more carbohydrate and less protein than cells cultured in the standard formulation (E). A third formulation (N/P), in which all medium components were reduced except nitrate and phosphate, produced algae with reduced carbohydrate and increased protein as compared with E medium. The total lipid content of D. tertiolecta was significantly less than that of T. maculata regardless of the culture medium.

Algae cultured in the three formulations were fed to juvenile oysters, Crassostrea virginica. T. maculata was a consistently better food source than D. tertiolecta, indicating a probable causal relationship between algal lipid content and oyster growth. Growth of oysters fed algae cultured in X₁ medium was increased as compared with oysters fed algae cultured in E or N/P medium, suggesting a nutritional requirement for relatively more carbohydrate than protein as well. Results indicate that differences in growth media affect the gross chemical composition of algal food sources which alone can account for differences in algal nutritional value to C. virginica.