THE LIFE-HISTORY OF THE LITHODID CRAB, PARALOMIS-GRANULOSA, IN THE FALKLAND-ISLANDS

The life history of the lithodid crab, Paralomis granulosa, is investigated from a 16-month time series of commercial catches and scientific samples from the Falkland Islands, in the South Atlantic. The mean size at morphological maturity of male crabs is estimated from chelae allomelry to be 52 mm carapace length (CL) and the size at 50% functional maturity of females is found to be 46 mm CL. Adult P. granulosa live in sheltered inshore waters mostly between 10 and 40 ni deep, juvenile crabs inhabit the dense kelp beds in the shallowest part of this range. The percentages of the total stock in each combination of moult stage and reproductive condition are estimated for each month. The moult seasons are thus shown to be cued by the warming of the inshore waters in the austral spring with adult males moulting about a month before the females. After moulting, female crabs release new clutches of uneyed eggs, which become eyed during the austral autumn and hatch in winter. A proportion of the female crabs, increasing in the largest sizes, moult without ovulating. At all limes of year, large numbers of females also exist in intermoull condition, still with uneyed eggs, suggesting that the reproductive cycle takes longer than I year to complete. Juvenile crabs moult at least annually, along with the smaller adult males. A biennial moult cycle is proposed for most adults of both sexes. The spatial organization of the life cycle is examined by using cluster analysis to define a few relatively homogenous communities of crabs, in terms of the sex ratio, the proportions moulting in each sex. and the reproductive condition of the females. Three mam communities occur in each of the moulting and non-moulting seasons. The most central community, in the deepest water, on a soft, muddy substratum, forms the main mating aggregation of the Choiseul Sound stock, containing moulting females and the largest non-moulting males. Incubating females, mid-wav through their 2-year cycle, migrate off the spawning ground to more peripheral areas. The majority of adult males in moulting condition (along with a few large, apparently non-mating, females) occur on the shallowest coastal grounds. It is proposed that adult males alternate between moulting and feeding on warmer shallow grounds in some years, and attending the centra! malingaggregation, without moulting, in others. © 1993 Conseil International pour l’Exploration de la Mer.