REPRODUCTIVE ECOLOGY OF THE VELVET SWIMMING CRAB, NECORA-PUBER (BRACHYURA, PORTUNIDAE), AT PLYMOUTH

Monthly samples of intertidal and near-shore Necora puber were collected over two years from a commercially unfished area around Plymouth (south-west England). A clear reproductive cycle, consistent between the two years, was observed, and relatively high numbers of ovigerous females were found from January to June. Zoeal release was estimated to occur from April to June. Ovigerous females had developing ovaries, indicating that sequential broods occur. During embryonic development, egg volume increased by 109%, and egg loss was significant, accounting for between 14 and 18.5% of initial brood number. Females suffering limb loss showed a further reduced brood size compared to females with a full limb complement. The sex ratio of immature crabs was 1:1, whereas the ratio for mature crabs was biased to males (1.46:1). Two sperm plugs were observed in 90% of early postmoult mature females, but 10% had only one or no plug intact, suggesting their failure to mate successfully. These results are reviewed in relation to the biogeography of N. puber and with reference to the developing fishery in the United Kingdom.