Stock estimate of brown mussel Perna perna and invasive bivalve Isognomon bicolor of a natural beds from Santos bay, São Paulo State, Brazil

Abstract

The aim of this study was to estimate the stock of the populations of bivalve Perna perna and Isognomon bicolor inhabiting Santos bay rocky shores and the biomass of P. perna extracted annually from this environment. From December 2006 to February 2008 individuals were sampled on a bimonthly basis at the area occupied by both species. The stock of each bed was estimated by the method of partial count, being the quantified number of individuals sampled in the plots multiplied by the total area calculated for the respective bed. The total area available was calculated from the rocky shore of 11.20 ha in the East Bay and of 12.06 ha in the West, but the occupation of mussel beds P. perna was only 5.02% and 2.98% respectively. The densities were significantly different (ANOVA: P<0.05) among species and months, but not for the bay side and intertidal and subtidal zones. At 65,074,096 and 6,906,112 individuals of P. perna and I. bicolor, respectively, from Santos bay populations were estimated. The total biomass of P. perna available for extraction was estimated at 58.27 ton. The results indicate that the natural stocks of the mussel P. perna decreased compared to previous studies.