Heterotrophic bacteria community and pollution indicators of mussel - farmimpact in the Gulf of Gaeta (Tyrrhenian Sea)

Field studies were carried out to determine and compare the impact of organ ic loads due to the biodeposition of a mussel farm on the water quality and sediment in a coastal area of the Tyrrhenian Sea (Western Mediterranean). A total of five environmental and five microbial parameters were examined f rom March, 1997 to February, 1998 on a monthly basis at three stations: the first was located under the mussel farm, the second located at about 40 m away from the mussel farm, while the third designed as a control was at abo ut 1-km. No clear changes in the physical characteristics of the water mass es were observed, comparing the three sampling sites and the water column g enerally showed homogeneous conditions (in terms of temperature and salinit y). Changes in density of aerobic heterotrophic bacteria, Escherichia coli and Enterococci in the water column are apparently independent from changes in environmental parameters. At all stations a constant significant correl ation between temperature and presumptive Vibrio parahaemolyticus was repor ted suggesting that this abiotic factor exerted a major control on this bac terial group and its distribution in the water column is not related to the biodeposition of the mussel farm. The major impact identified was on the s ediment where variations in bacterial abundance was observed. In the Mussel station sediment enrichment of organic compounds, and the consequent modif ication of the characteristics of the benthic environment, determined an in crease in aerobic heterotrophic bacteria, and particularly of vibrios densi ty (on average about 60%), suggesting that these bacteria are good indicato rs of organic enrichment. (C) 2001 Elsevier Science Ltd. All rights reserve d.