Distribution and density of the bivalve Anomalocardia brasiliana in Rio Grande do Norte beaches during an atypical rainfall period

The aim of this study was to evaluate the distribution and density of Anomalocardia brasiliana along a 22 km stretch of beaches in the western region of Rio Grande do Norte during and after periods of unusual rainfall related to the La Ni a phenomenon. Four samples were taken every six months between April 2009 and October 2010, where imaginary lines were made perpendicular to the beach, along a spatial gradient of distance from the estuary, to collect organisms, sediments and temperature and salinity water data. There were no significant differences in A. brasiliana density between the different seasons, and the average density was 218 ind/m2 in April 2009, 198 ind/m2 in October 2009, 233 ind/m2 in April 2010 and 200 ind/m2 in October 2010. A. brasiliana showed a well-defined pattern of distribution, with its occurrence restricted mainly to the Apodi/Mossoró River estuary, where the organic matter content of the sediment was higher. Thus, this species has low resilience, since it could not regain the density it displayed prior to March 2008, before the heavy rains caused by the La Ni a phenomenon.