Assembleia de peixes recifais da Baía da Ilha Grande: fatores influenciadores e uso de Índices Multimétricos para avaliação da condição ambiental

Abstract

different approaches were used to assess the ecological condition and factors structuring rocky coastal fish assemblage under different anthropogenic influences in the Ilha Grande Bay. The first approach aimed to detect biological, physical and anthropogenic predictors of fish assemblage structure, richness, abundance and biomass. The second approach was used to develop a multimetric index to assess ecological condition with reference to two types of disturbance (thermal effluent and urban influence) between control and impacted sites. Biological and ecological characteristics of species were used to metric selection. The third approach was to assess the efficiency of a Marine Protected Area - MPA inside the bay (Ecological Tamoios Station) by comparing sites inside and outside of MPA. To do so, the developed multimetric index, abundance-biomass curves and functional groups were used. We found that depth and the distance from the coastline were the main predictors for the fish assemblage structure. Species richness was positively associated with a Physical Structure Index (PEI) and depth, and negatively with occurrence of zoantids. Fish density was positively related to PEI and distance from the coastline, whereas the biomass was positively related to the distance of the coastline, only. Areas near to the coastline had comparatively lower richness, density and biomass, whereas the farthest sites had an inverse situation for these fish assemblage parameters. Both, the thermal disturbance and the urban influence had differences for the metrics. Eight metrics were selected for the thermal impact, of the whole of 41 candidate metrics: “total number of species”, “number of criptical species”, “number of water column species”, “number of residents species”, “density of individuals with low resilience”, “density of omnivores”, “density of herbivores” and “density of carnivores”. For the urban impact: “total abundance”, “the ratio number of rare species/total number of species”, “density of individuals with heavy fishing pressure”, “number of criptical species”, number of dependent species and “density of herbivores”. The best ecological condition was detected for the control sites compared with the impacted sites. Concerning the evaluation of the MPA efficiency, no significant differences were found between the sites inside and outside the MPA using the three tools to assess ecological condition (multimetric index, ABC curves and functional groups). Both areas (inside and outside the MPA) were characterized as moderately disturbed. However, when the species dominant were excluded from the analyses, the sites outside the MPA were classified as not impacted. The multimetric index did not show significant difference between the areas and important metrics such as “density of individual with high fisheries pressure”, “total number of species” and “density of herbivorous” had low scores for both sites, inside and outside de MPA. We also did not find significant difference between these areas using the functional groups, suggesting thea the MPA have no influence in protecting rocky coastal fish species in the Ilha Grande Bay.