There have been many efforts to appraise the extent to which artificial reefs affect the surrounding community, but few studies addressed whether benthic assemblages change with distance from the reef. We experimentally assessed the relationship between infauna abundance and richness with increased distance (0, 5, 25, 50, 100 and 300 m) from reefballs deployed on a flat and homogeneous bottom, 9-m deep, on the north coast of Rio de Janeiro, south-eastern Brazil. Benthic taxon richness and abundance varied significantly between surveys with higher values in February 2007. Both numerical indicators changed similarly with distance, but more noticeably between 300 m and the other distance treatments where abundance was highest. A non-metric multidimensional scaling ordination revealed that macrobenthic assemblages were very heterogeneous with significant differences between surveys but not among sampling distances. A canonical correspondence analysis including species, distances and sediment variables showed that the distances 5, 25 and 100 m were related to organic matter and mud (fine sediment), while 0 and 300 m distances were more related to the non-organic variables, such as the percentage of gravel, sand and calcium carbonate. Spatial variations in the parameters of the sediment alone did not explain the distribution of the associated infauna, given the similarity of the community at different distances. It is suggested that the influence of artificial reefs is quickly dissipated due to strong bottom sea currents, indicating a reduced impact or influence of these reefs on the surrounding infauna.
Macrobenthic assemblages in an artificial reef in central-west Portugal: Preliminary results