Estimating secondary production of Uca uruguayensis (Decapoda, Brachyura, Ocypodidae) from Samborombón Bay, Argentina

Abstract

Specimens of Uca uruguayensis were collected (n = 1200, 216 megalopae, 984 undifferentiated and adults), counted and classified as males, females or undifferentiated individuals. Each was measured (total carapace width, CW) and weighed (dry weight, DW). The crabs were analyzed and separated into cohorts by the conversion of polymodal width-frequency distributions into normal curves. Six cohorts were recruited during the study period. Two cohorts coexisted in September and December 2001, and April and October 2002, and three in March and June 2001, December 2002, and February 2003. Ovigerous females were captured in December 2001 and 2002, and February 2003; on this last date, megalopal settlement was registered at all the sampling sites. The correlation between CW and DW was analyzed and the growth pattern was modelled by applying the power function (DW = a CWb). Males, females and undifferentiated individuals were examined separately and all together as a group. The data were fitted, indicating a positive allometry for DW, males showing the highest allometric values. To estimate the annual production we used a size-frequency method. Mature individuals, in particular those included in the 10–11.99 mm size class, contributed most to production. On the other hand, few individuals belonged to the size class prior to puberty. Total biomass (expressed in DW) varied between 20 and 611 mg m–2 and the highest values were recorded during summer.