Ecologia do caranguejo Ocypode quadrata (FABRICIUS, 1787) em ecossistemas de dunas no litoral de Santa Catarina, Brasil

Abstract

The semi-terrestrial crab, Ocypode quadrata (Fabricius, 1787), popularly known as ghost crab in the world and maria-farinha in Brazil, is the most conspicuous invertebrate on sandy beaches of the western Atlantic coast. The species is extremely relevant to this ecosystem, since it´s the top-chain predator concerning to other invertebrates. However, the study about biology of this crab still exhibition a shortage of information. Therefore, the objective of this work was to evaluate the diet and population dynamics of O. quadrata in three morphodynamic beaches in southern coast of Brazil. The collections were carried out on March 2017 to February 2018, on the beaches of Lagoa de Barra Velha, Navegantes and Brava, located in coast of northern Santa Catarina. A total of 698 specimens were captured: 55.58% males, 33.52% females, 1.86% ovigerous females and 10.90% juveniles. Among these, 660 stomachs were examined and the food categories were expressed by the food index (IAi). The crab diet did not show significant differences regarding sex, ontogeny and beaches with different morphotypes. There was only variation in relation to the year, with the most representative categories being Insecta, Unidentified organic matter and Crustacea. The O. quadrata crab was classified as opportunistic with a carnivorous food habit, with a trend to insectivory. Regarding the population aspects, the densities of burrows showed no differences during the year and between the environments, and the pattern distribution of burrows was aggregated for the three beaches. Regarding sex ratio, there was a deviation in favor males at some periods in the year for the three sites. The recruiting period occurred in late summer in Navegantes and in the cold season in Barra Velha and Itajaí. Sexual dimorphism was evident for this species, males tended to invest more in body mass than females, but both presented positive allometric growth. There was also a difference in growth between the beaches of Itajaí and Navegantes. Von Bertalanffy's growth model demonstrated that the highest value L∞ (maximum width) estimated for both sexes was in the reflective beach (Barra Velha). The maximum longevity of the species was Tmax = 4.86 years for males and Tmax = 3.61 years for females. Regarding sexual maturity, the size of first gonadal maturation (L50) for the species resulted in differences between the sexes, with males ranging from 2.40 cm to 2.83 cm and females between 2.84 cm to 3.01 cm.