Comparações da ictiofauna entre diferentes sistemas costeiros do estado do Rio de Janeiro: relações com invertebrados bentônicos, diversidade beta e distinção taxonômica

Abstract

Shallow coastal marine systems are highly productive and widely recognized by their roles as important habitats for several bottom dwelling or water column fish and invertebrate species. Several mechanisms can influence fish distribution among the coastal marine systems, such as biotic interaction (e.g. predation, competition) and abiotic influences (e.g. type of sediment, turbidity). This study was carried out in sandy beaches of coastal systems that included unsheltered oceanic beaches and sandy beaches in two large embayment (Sepetiba and Ilha Grande). Quarterly samplings were performed to collect fishes, sediment and to measure environmental variables in three sandy beaches of each system during 2014 and 2015. The aim were: 1) to determine and compare the relationship fish and benthic invertebrate among the three systems, and to detect eventual influences of environmental variables on the structure of these two biotic communities and, 2) to compare the ichthyofauna in relation to beta diversity, taxonomic distinctiveness and environmental heterogeneity, to test the hypothesis that systems with high environmental heterogeneity have higher beta diversity. Granulometric composition and environmental variables differed among the systems, with comparatively higher turbidity in the Sepetiba Bay, lower nutrient concentrations in the Ilha Grande Bay and higher salinity in the Oceanic Beaches. The highest abundance of benthic invertebrate was found in the bays, whereas the Oceanic Beaches have the lowest numbers, which can be associated to physical dynamic of wave action in the this latter system that can the potentiality to remove invertebrate from the sediments, resulting in their exposure to predation. Fish and benthic invertebrate were influenced by environmental variables but no significant correlation was found between fish and invertebrate communities. However, some specific strong relationship was found between particular species of fish and invertebrate. For example, the flatfish Citharichthys spilopterus was positively related to representant of the Crustacean from Amphipoda and Tanaidacea orders, and from Polychaeta of Opheliida and Polygordiida orders, suggesting a dependence relationship between fish and invertebrates that can be used as fish feeding prey. The coastal systems did not differ in environmental heterogeneity, whereas the beta diversity was highest in the Ilha Grande Bay, which is probably associated to better preservation of their beaches. We did not detect significant relationship between beta diversity and environmental heterogeneity, which can be attributed to the examined environmental variables that did not influence markedly fish distribution. Taxonomic distinctiveness had positive correlation with species richness, thus the higher the richness the higher the taxonomic distinctiveness that can be associated to interspecific relationship, since species closely related tend to compete for similar resources. Thus, the addition of new phylogenetically distant species will occupy different niches. We suggest that fish turnover (beta diversity) should be included in environmental management plans, as a tool to supply the basis to selection size of areas to be priorized for conservation, aiming to protect the maximum of biological diversity.