Distribuição espaço-temporal e densidade anomalocardia brasiliana (Bivalvia Veveridae): em um estuário hipersalino (Rio Grande do Norte, NE Brasil)

Abstract

Anomalocardia brasiliana is a bivalve mollusk widely found from the Caribbean to Uruguay. Although A. brasiliana is widely studied in several estuaries along the Brazilian coast, information about this species in hypersaline habitats are still lacking. In this context, this study evaluates spatiotemporal variation of this species in the estuary of the hypersaline Rio Tubarão, northern coast of Rio Grande do Norte state. It also verifies whether abiotic factors such as temperature, salinity and substrate characteristics may be influencing the distribution of the species. Specimens collection occurred monthly between July/2005 and June/2006 in six sampling sites distributed from the mouth to the upper portions of the estuary. At each sampling site, two samples collected with a sampler of 0.25 x 0.25 m randomly placed along a transect of 25 m in length. The specimens were sorted, measured and weighed. Abiotic data (e.g. salinity, temperature, substrate grain and precipitation) were also obtained. The density of A. brasiliana (ind/0.0625 m

2 ) exhibited spatial variations during the studied period. The average density was higher in the points located farthest from the mouth of Rio Tubarão, the same was observed for biomass. In relation to the hydrological cycle, there was no significant difference in the density of A. brasiliana (F = 1.081 and p = 0.302). Temporally, the highest biomass of the species was recorded during the rainy season. Statistically, no significant spatial difference in biomass (F = 1.314 and p = 0.269) were observed. The presence of individuals in shell length <15 mm and 15-20 mm suggests that recruitment of young is occurring throughout the year. An evident peak of recruitment was not observed. Among the abiotic parameters analyzed, salinity was the only one who had a slight influence on the distribution and density of Anomalocardia brasiliana. The seasons had no influence on the occurrence and density of A. brasiliana in an annual cycle. The data presented here may support programs to fisheries management in the studied area. It also provides relevant information about the distribution, density and biomass of Anomalocardia brasiliana in hypersaline habitats.