Distribuição espaço-temporal das larvas de camarões (Decapoda) no estuário do Rio Marapanim, Pará, litoral norte do Brasil

Abstract

Despite the ecological and economic importance larvae of shrimp, there is no knowledge on shrimp larvae in the Marapanim estuary (Pará, Brazil). With the aim of studying the species composition, abundance and spatial-temporal distribution of these larvae in the estuary in relation to season (dry, transition and rainy), estuary zone (1, 2 and 3), sampling site (A1, A2, A3, B1, B2 and B3) and profile (A and B), monthly collections were carried out between August 2006 and July 2007. Biological samples were obtained from two horizontal drags at each sampling site at 0.5 m from the surface of the water column with the aid of a conical plankton net (aperture = 0.5 m and mesh = 200 μm). Abiotic data were a lso gathered, such as temperature, salinity and pH of the water. A total of 4644 shrimp larvae from the infra-orders Penaeidea and Caridea were collected. Among the species and/or families encountered, the most abundant were Alpheus estuariensis (302.59 larvae/m3), Palaemonidae (97.05 larvae/m3) and elaphocaris stage of Sergestidae (90.47 larvae/m3), with A. estuariensis the most frequent (76.39%). Greater abundance, diversity and richness of the shrimp larvae occurred in the dry season. Cluster analysis of the monthly abundance of larvae led to the formation of three groups with 65% similarity, in which A. estuariensis was dominant and was the species that most contributed to the similarity in the groups. The main difference among groups was due to Sergestidae, Palaemonidae and Xiphopenaeus kroyeri larvae densities. Among the abiotic factors studied, the salinity was the factor that most influenced the spatial-temporal distribution of the shrimp larvae in the Marapanim estuary, important region for larval recruitment of shrimp species.