Ecologia populacional de Ocypode quadrata (Brachyura: Ocypodidae) em uma praia arenosa exposta de macromaré da costa amazônica do Brasil

Abstract

The present study analyzes the population ecology of Ocypode quadrata (Brachyura: Ocypodidae) on an exposed, macrotidal, dissipative sandy beach located on the Amazon coast, during one year. Indirect (burrow counting and measurement) and direct (burrow excavation and assessment of individuals) methods were used on population assessments. Burrow abundance variation was analyzed over time and as a function of environmental variables (sediment properties, precipitation, air and seawater temperature, salinity). Zonation was described through burrow distribution by distance from the high tide mark. Burrow diameter was used to estimate individual growth parameters of the population. Burrow occupation rate, sex ratio and relation between burrow diameter and crab measures (carapace length, width and depth) were also estimated. Abundance was higher on the rainy season (0.78 ± 0.24 burrow.m-1, against 0.37 ± 0.13 burrow.m- 1 on the dry season) and related positively to precipitation and negatively to sediment grain size. The population was practically restricted to the supralittoral zone. The estimated individual growth parameters (L∞=53.36 mm, K=0.76 yr-1, t0=0.014 yr, Φ=3.34) describe a well-adjusted curve to cohort progression over time. Burrow occupation rate varied between 12.5% and 28.7%. There was sex equilibrium during the rainy season, however, changing to male predominance on the dry season. Burrow diameter was related mainly to carapace width. These are the first data of ghost crab population behavior on Amazon macrotidal environments. These, compared to available data on other regions, also gives insight on latitudinal tendencies of population parameters.