Population structure, maturity and relative growth of the porcelain crab Pachycheles laevidactylus Ortmann, 1892 (Decapoda, Porcellanidae) in a temperate zone

Abstract

The porcelain crab Pachycheles laevidactylus is the most frequent crustacean decapod in the polychaeta sandbanks in some Brazilian locations; however, the only populational data available for this species are from Argentina. Here, we analysed the population structure, sex ratio, reproductive period, size at sexual maturity (functional and morphological) and relative growth of this species from two locations in southern Brazil. The crabs were collected seasonally during one year, sexed, counted and measured. A total of 1534 individuals were sampled, 943 in Torres and 591 in Tramandaí. There was no difference in cheliped size between sexes, while females were larger and had larger pleons than males, and this difference is related to reproduction. The sex ratio was 1:1 in both locations throughout the year. Ovigerous females were found in all seasons, with a higher frequency in the coldest seasons, but the presence of megalopae occurred exclusively in spring. The morphological sexual maturity for females was larger than the size of the smallest ovigerous female collected, as already reported for other decapods. Overall, the species starts reproducing at smaller sizes at locations closer to the edges of its distribution (northern Brazil and northern Argentina). Some differences in relative growth were found between males and females, adults and juveniles, and the implications of these differences are discussed. This study brings the first populational data of P. laevidactylus from Brazil over a year, which was compared with available studies of Porcellanidae and will be useful for comparison with future studies in tropical areas, to better understand how the biological aspects of this species vary along its wide distribution in the south-western Atlantic.