Microphytobenthic response to mussel farm biodeposition in coastal sediments of the northern Adriatic Sea

The effects of long-line mussel farming on microphytobenthos were investigated in a coastal area of theGulf of Trieste. Sediment grain-size, organic matter content, microalgal abundance and community structurewere analysed in September 2008 and March 2009. Four areas were sampled: a twenty-year farm, afour-year farm, a disused farm and a reference site. Principal component analysis (PCA) highlighted adecreasing gradient of organic matter content from the twenty-year farm to the control. Mussel farmingseemed to influence microphytobenthic abundance with higher densities in the oldest farm. Three generawere dominant; Navicula and Gyrosigma seemed to be stimulated by the organic load under the activefarms while we infer that Nitzschia proliferation was limited by shade caused by mussel ropes. In thePCA, samplings of the disused farm were placed in-between the still active farms and the control, indicatingthe partial recovery occurred in this site.