Reference: Biol. Bull. 165: 197-208. (August, 1983) GRAZING AND PREDATION AS RELATED TO ENERGY NEEDS OF STAGE I ZOEAE OF THE TANNER CRAB CHIONOECETES BAIRDI (BRACHYURA, MAJIDAE)* LEWIS S. INCZE 1 ** AND A. J. PAUL 2 [ School of Fisheries WH-IQ, College oj Ocean and Fishery Sciences, University of Washington, Seattle, Washington 98195, and 2 Institute of Marine Science, University of Alaska, Seward Marine Center, Seward, Alaska 99664 ABSTRACT The ability of first-feeding stage I zoea larvae of Chionoecetes bairdi to obtain energy from phytoplankton was investigated using a range of phytoplankton cell sizes and cell densities. An early first stage zoea requires approximately 6.8 X 10 calories or 0.60 ^g carbon (approximately 4% body C) per day for metabolic needs at 5C. Experiments with dinoflagellates and large centric diatoms demonstrated that the larvae are capable of capturing and ingesting these cells. However, the zoeae grazed at rates which satisfied less than 15% of basal metabolic energy requirements at cell concentrations similar to those prevailing in coastal and shelf sea environ-ments where the crabs are found. Grazing on smaller cells, including chain-forming species common in nature, was not detected. In the laboratory, first-feeding zoeae were capable of consuming zooplankton prey at rates which provided up to 308% of basal metabolic requirements. INTRODUCTION Laboratory studies have demonstrated that availability and nutritional adequacy of food are among the most important factors affecting survival of crab larvae (Roberts, 1974; Sulkin, 1975, 1978; Sulkin and Epifanio, 1975; Christiansen and Yang, 1976; Sulkin and Norman, 1976; Anger and Nair, 1979). Generally, labo-ratory diets consisting primarily of zooplankton have provided the highest survival rates (Brick, 1974; Roberts, 1974; Sulkin, 1975, 1978; Bigford, 1978). There is a high degree of morphological similarity of the feeding appendages of crab larvae and numerous reports of their attacking single zooplankton prey (Sato and Tanaka, 1949; Knudsen, 1960; Herrnkind, 1968; Gonor and Conor, 1973). This evidence has led to the widely held belief that phytoplankton is of limited dietary importance. However, there is evidence that phytoplankton may be a common component of the diet of some larvae in nature (e.g., LeBour, 1922, 1927). Laboratory studies with the larvae of a brachyuran crab (Hartman and Letterman, 1978) and a pandalid shrimp (Stickney and Perkins, 1981) indicated that phytoplankton diets can signif-icantly prolong the life of these larvae compared to unfed control animals, even though both larvae showed markedly better survival on zooplankton diets. Both studies noted that specimens collected at sea contained phytoplankton in the stom-achs. Roberts (1974) and Sulkin (1975) reported that the larvae of crabs used in their experiments (an anomuran and brachyuran crab, respectively) consumed phy-Received 21 January 1983; accepted 25 May 1983. * Contribution No. 618 of the School of Fisheries, University of Washington and No. 523 of the Institute of Marine Science, University of Alaska. ** Present address: National Marine Fisheries Service, 2725 Montlake Blvd. East, Seattle, WA 98112. 197
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