História de vida do caranguejo Goniopis Cruentata(Latreille, 1803) em um manguezal do nordeste brasileiro

Abstract

The life history traits of an organism are the result of trade-offs between maintenance, growth and reproduction. This theory aims to explain the variations in the population aspects of a given species in function of the conditions and available resources in the environment, being the theoretical basis for studies dealing on the dependence of density. The density is a factor regulating the population dynamics since it promotes the competition for resources and, thus, it influences the attributes of life history. The present study aims to answer the following questions: does density influence size and sexual maturity in a population of the crab Goniopsis cruentata? Do the environmental conditions influence the biological aspects and increase the density effects on this species? Field work was conducted from January to November 2011, in the Municipalities of Aracati and Fortim (Ceará, Brazil). The crabs were manually collected in two sampling stations, Alfredo and Caldeleiro, in an area of 400m² for each station, during 40 minutes. The individuals collected were sexed and measured at the carapace width, gonopod length (males) and abdomen width (females). Ten individuals from each station were submitted to a histological procedure to determine the stage of gonad development. Density was calculated as the number of individuals per area (ind/m²). The individuals collected were distributed in size classes, by station and by sex. Morphological and physiological maturities were also calculated. Abiotic factors such as rainfall, pH and salinity of the soil were measured and correlated to the density of each station. The density of the Alfredo station was higher than the Caldeleiro station one, which may occur due to the greater availability of nutrients at this area, due to the lower pH than the Caldeleiro station. The rainfall was correlated to the density at Caldeleiro, due to the fact that this station presented a lower topography, suffering a greater influence of the level of the river. The salinity of the soil did not show differences between the stations. Males mean size did not differ between the stations, contrary to what occurred in females, with larger mean size at the highest density local. In both sexes, the larger maximum sizes were observed in the station with higher density, showing lower mortality between adults and, thus, allowing a delay in maturation at this local. The size class distribution did not differ between the stations, but presented a tendency to be bimodal at the station with higher density and unimodal at the station with lower density. This result may indicate the influence of the density in the distribution by size classes. The sexual maturity was anticipated in the lowest density local and delayed in the highest density local, as predicted by the life history theory. This pattern may be a result of higher mortality rates in juveniles at the highest density local and higher mortality rates between adults at the less dense area. The larger proportion of females observed at the highest density area may provide a spermatic limitation. Males, copulating with a higher number of females, do not have the capacity to produce spermatozoids to fertilize all of them. The results of the present study corroborate the predictions of the life history theory: (1) in populations with lower density, sexual maturity is anticipated and organisms attain smaller sizes, and in populations with higher density maturity is delayed and organisms attain larger sizes; (2) the distribution in size classes was different between the sampling areas, showing the influence of the population density.