SEX-SPECIFIC LIFE-HISTORY PATTERN OF EMERITA-PORTORICENSIS (SCHMITT)

The mole crab, Emerita portoricensis, often inhabits the intertidal zone of West Indian sandy beaches. Life history characteristics of this species were investigated for 2 years at four sites within the Mayaguez and Anasco bays, Puerto Rico. Survivorship (S(x)) for all age classes was based on size frequency distributions. Female age-specific reproductive effort (M(x)) was largely determined by carapace length and the proportion of ovigerous individuals. Male fecundity schedules were calculated assuming random mating; these were constant for all size classes but varied among months. The mean generation time of males was shorter than that of females. Thc number of eggs produced by adult females (S(x)M(x)) had a tendency to increase with age initially with a later decrease. The male contribution to offspring (S(x)N(x)) decreased with age. Fisher's reproductive value (V(x)) was used to determine age specific contribution to population growth rates. V(x) of females tended to increase with age but started to decrease at older age intervals. Reproductive values (V(x)) of males decreased from the age of first reproduction to the age of last reproduction. These results suggest that young adult males and older females should have a selective advantage over other age (size) classes. These contribute most to population growth rates.