Impact assessment related to an oyster farming on the benthic environment

Abstract

The oyster farming has attracted attention in the Northeastern region of Brazil. This activity is considered to cause less damages to the environment compared to other cultures, once oysters are filter feeders. However, there is a lack of knowledge related to its environmental impacts. It is important to investigate such impacts in order to permit the maintenance of the activity with low environmental risk and high sustainability. The present study was carried out in an estuarine region of the São Francisco river, where two transects were delimited: 10 meters far from de farm (CONTROL) and just below farming structures (CULTIVE). In each transect three points with three sediment replicates each were sampled to the analysis of nematodes. Abiotic factors were also measured (temperature, salinity, pH, dissolved oxygen and organic matter and granulometry of the sediments). Multivariate and univariate statistical analyses were applied such as: indices of diversity and of evenness, T tests, ordination (MDS) and analysis of similarity. There were no significant differences among all the environmental parameters measured. It was observed that the oyster farm structures changes sediment characteristics and hence those of meiofauna and nematofauna community structure, mainly regarded to density and diversity values, which were always higher in CONTROL than in CULTIVE (from 2,086 to 776 ind 10 cm^-2 and from 0.8 to 0.7 for density and diversity, respectively). It seems that the farm has no effects on nematode trophic guilds. The impact was considered moderate.