LARVAL DEVELOPMENT OF THE CRAB CANCER-MAGISTER IN TEMPERATURE REGIMESSIMULATING OUTER-COAST AND INLAND-WATER HABITATS

Postlarval megalopae of the Dungeness crab Cancer magister inhabiting offshore coastal waters along the west coast of North America are larg er and settle earlier than do those occupying the inland waters of the Puget Sound basin (Washington, USA, and British Columbia, Canada). Th e Puget Sound habitat is characterized by low initial temperatures tha t steadily increase during the course of zoeal development, while offs hore temperatures are more moderate and stable. Larvae were raised ill the laboratory from hatching to megalopa in three temperature treatme nts: (1) constant 10 degrees C (CO); (2) a regime that temporally simu lated temperatures found off the central California coast during the l arval season (CA); and (3) a regime simulating temperatures found with in the Puget Sound basin (PS). Zoeal duration was 44% longer in the PS treatment than in the other two, at least partially accounting for ob served differences between outer-coast and inland-water settlement tim es. Although differences were measured in megalopal weights and carapa ce lengths among treatments, results do not explain differences in meg alopal size observed between outer-coast and inland-water individuals. Survival to megalopa was highest in the PS treatment, with the differ ence due to significantly lower mortality than ill CO and CA treatment s during the terminal zoeal stage. Daily instantaneous mortality rates were lower in the PS than in CO or CA treatments, indicating that ext ended larval duration will not necessarily result in reduced settlemen t success.