Grazing and Predation as Related to Energy Needs of Stage I Zoeae of the Tanner Crabchionoecetes Bairdi(brachyura, Majidae)

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 l0-3 calories or 0.60 µg carbon (approximately 4% body C) per day for metabolic needs at 5°C. 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 environments 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.