Do mucous aggregates affect macro-zoobenthic community and mussel culture? A study in a coastal area of the Northwestern Adriatic Sea

In June 2000 and July 2002, two mucous aggregation events of large proportion occurred in the Adriatic Sea. In order to assess the possible effects that the events had on the macrofauna, we studied macro-zoobenthic assemblages and mussel culture (Mytilus galloprovincialis). Structural parameters of macro-zoobenthos and growth parameters of mussels were recorded. The study area was a mussel farm located 5 nautical miles off Porto Caleri (Rovigo, Italy) in the Northern Adriatic Sea. Between May 2000 and August 2002, two sites were sampled in this area and univariate and multivariate techniques were used to describe the macrobenthic community. Two-way ANOVA showed that mean values of species number, density (individuals m 2) and Shannon–Wiener’s diversity were significantly influenced ( p b0.01) by site and period of sampling and by the interactions of these factors. The Pielou’s J averages were significantly influenced only by period ( p b0.01). Application of Tuckey’s HSD test ( p b0.05) to factors detected to be significant by ANOVA did not show significant differences between samples collected after the mucous aggregation events and the other periods. Cluster analysis and MDS ordination did not allow a clear distinction between the samples. Concerning mussels, one-way ANOVA showed that mean values of the shell length and the condition index (dry weight/shell weight) were significantly influenced ( p b0.001) by the months. The mean values both for shell length and condition index were higher in 2001. The shell length trend revealed a slowing down of growth in June–July 2000 and July–August 2002, and the condition index trend showed a significant fall in samples of June 2000 and July 2002. The growth of M. galloprovincialis might be influenced negatively by mucous aggregates, whereas the soft-bottom macro-zoobenthos seems not to be directly affected by the event.