Objetivou-se com este estudo avaliar os impactos ambientais causados por um sistema de cultivo de camarões marinhos em tanque-rede sobre a qualidade da água e sobre a estrutura da comunidade zooplanctônica. O estudo foi realizado na Baía de Guaratuba, onde os cultivos eram realizados em 300 tanques-rede (3,6 m de comprimento, 3,6 m de largura e 2 m de profundidade) distribuídos em uma área de 4.200 m², em densidade de 720 camarões/m². As concentrações de amônia, nitrito e fosfato na água foram monitoradas e amostras de zooplâncton foram coletadas no local dos cultivos (ponto 1) e em outros três pontos localizados a aproximadamente 200 m para oeste, noroeste e sudeste dos tanques. O ponto 5, usado como controle, localizava-se a aproximadamente 1.000 m a sudoeste da área de produção. As concentrações de nitrogênio amoniacal, nitrito e fosfato não diferiram entre os pontos amostrados, assim como a estrutura da comunidade zooplanctônica, que foi semelhante entre os pontos amostrados. Não foram evidenciados impactos significativos do empreendimento sobre a qualidade da água ou sobre estrutura das comunidades zooplanctônicas no local do cultivo e em áreas adjacentes, durante o período em que a investigação foi conduzida.

The objective of the present study was to evaluate environmental impacts caused by a system of shrimp farming in net-pen on water quality and on the structure of zooplanktonic community. The study was carried out in Baía de Guaratuba, were the cultivations were conducted in 300 net-pens (3.6 m in length, 3.6 m in width, and 2 m in depth), distributed in an area of approximately 4,200 m² in 720 shrimp/m² density. Concentrations of ammonia, nitrite and phosphate in the water were monitored and zooplankton samples were collected from cultivation sites (point 1) and from three other sites located approximately 200 m to the west, northeast and southeast from the tanks. Point 5, used as control, was at approximately 1,000 m southwest from the production site. Concentrations of amoniacal nitrogen, nitrite and phosphate did not differ among sampled points as well as the structure of zoopplantonic community, which was similar among the sampled points. No significant impacts of the enterprise on the quality of the water and on the structure of the zooplankton communities in the cultivation site and in adjacent areas was evidenced during the period in which the investigation was carried out.

Fish predation is thought to exert an important influence on the demographical dynamics of larvae and juveniles of estuarine brachyuran crabs but few studies have investigated this phenomenon in nature. In this study, fishes were captured during full moons (in January and February 2005), when many brachyuran species are known to release their larvae. Samples were carried out in the Pinheiros river, Guaratuba Bay, Paraná, Brazil. The stomach contents of collected fishes were surveyed to determine the species that are most likely to prey on brachyuran immature forms in this location. Two techniques were used to capture fishes: manual samplings, using a 5-mm mesh size net (1.8m depth), and bottom trawling with a 20-mm mesh size net. The collected specimens were fixed using 10% formaldehyde and preserved in 70% ethanol. A total of 2941 fishes of 43 different species were collected and the stomach contents of 962 individuals were analyzed in laboratory. Food items were identified and quantified. The fish species captured using manual nets that showed the highest number of preyed zoeae per stomach was the clupeid Platanichthys platana (Regan, 1917). Sphoeroides testudineus (Linnaeus, 1758) and Centropomus parallelus Poey, 1860 showed the highest levels of predation on megalopae. Of the fish species captured using trawl nets, Genidens genidens (Cuvier, 1829) showed the highest average number of zoeae per analyzed stomach and Bairdiella ronchus (Cuvier, 1830) was the most important predator on brachyuran megalopae and on young juveniles. The obtained data indicate that brachyuran crab restocking efforts performed in the Guaratuba Bay should include strategies to avoid or, at least, reduce the access of fishes to the released early juvenile stages, given the potential substantial losses caused by fish predation. Considering that, in general, predation potential was 8.5 times lower in juveniles than in megalopae, releasing immature forms produced in laboratory in the juvenile phase or releasing megalopae into tethered areas and maintaining than under this condition until they reach the juvenile phase may be tested as a method to reduce losses given to fish predation.