Abundance, relative growth and fecundity of Emerita rathbunae Schmitt, 1935 (Decapoda, Anomura, Hippidae) in the S.E. Gulf of California, Mexico

Abstract

Specimens of the mole crabEmerita rathbunaeSchmitt, 1935, were collected during a one-year period along two sandy beaches in the S.E. Gulf of California, Mexico. A total of 2171 specimens were examined. Only 8% of the collected females were ovigerous. The large majority of males (95%) were collected in the sand as “free living” males, while the rest (39 individuals) were “dwarf males”, with developed genital papilla, 95% of which were found attached to females. Density for pooled samples reached an overall maximum of 309.8 orgs/m2in February and a minimum in April (65.0 orgs/m2). Females always outnumbered males, except in February. Ovigerous females were observed in the first half of the study period (February to September). Proportions of males were very similar throughout the study period, while indeterminate specimens were proportionally more abundant in its second half. Relationships between CW and CL for both males and females were highly correlated and isometric. Relationships between size and weight were highly correlated in both males and non-ovigerous females for pooled samples or for each sampling zone, and in each case growth was isometric. The number of eggs per ovigerous female varied considerably, from 910 to 22 866, and the relationship between number of eggs per batch and body size was poorly correlated. In the study area,E. rathbunaeappears to have a rather restricted reproduction period. A larger series of data combined with the analysis of other environmental factors, such as beach profiles, current patterns and primary productivity, might bring some additional information on this species biology and ecology. Due to the key role that mole crabs play in the food web of sandy beaches, special attention should be provided to this particular habitat.