The co-occurrence of the demosponge Hymeniacidon perlevis and the edible mussel Mytilus galloprovincialis as a new tool for bacterial load mitigation in aquaculture.

Pollutants in marine coastal areas are mainly a consequence of anthropogenic inputs, and microorganisms often play a major role in determining the extent of this pollution. Thus, practical and eco-friendly techniques are urgently required in order to control or minimise the pathogenic bacterial problem. The bacterial accumulation of Mytilus galloprovincialis (Lamarck 1919) in the presence or absence of another filter feeder, the demosponge Hymeniacidon perlevis (Montagu 1818) on sewage flowing into the Northern Ionian Sea has been estimated in a laboratory study. On account of the interesting results obtained, we also evaluated the bioremediation capability of the sponges when reared in co-culture with mussels. Specimens of M. galloprovincialis and H. perlevis were collected from the Mar Grande and from the Second Inlet of the Mar Piccolo of Taranto (Northern Ionian Sea, Italy), respectively. In the laboratory, we detected the bacterial abundances in the sewage, in sponge homogenates (both sponges alone and sponges that have been added to sewage with mussels) and in mussel homogenates (both mussels alone and mussels that have been added to sewage with sponges). In the field, we estimated the bacterial concentration in both the seawater within the mussels culture and the seawater collected where mussels were reared in co-culture with sponges. The bacteriological analyses were performed analysing the following parameters: the density of culturable heterotrophic bacteria by spread plate on marine agar, total culturable bacteria at 37 °C on plate count agar and vibrios on thiosulphate-citrate-bile-sucrose-salt (TCBS) agar. Total coliforms, Escherichia coli and intestinal streptococci concentrations were detected by the MPN method. The study demonstrates a higher efficiency of the sponges in removing all the considered bacterial groups compared to the mussels. Due to the conspicuous bacterial accumulation by the sponge, we can conclude that the co-occurrence of the filter-feeder H. perlevis with M. galloprovincialis is a powerful tool in reducing the bacterial load in shellfish culture areas thus playing a role in mitigating the health hazard related to the consumption of edible mussels.