Effects of fish-farm biodeposition on periphyton assemblages on artificial substrates in the southern Tyrrhenian Sea (Gulf of Castellammare, Sicily)

Abstract

An algal assemblage growing on artificial substrata of fish-farm cages was investigated. Specifically, algal response to the effects of fish-farm facilities was studied, in order to identify a possible future descriptor of biodeposition impact. Some sites were positioned upstream of the farms (at least 750 m; ‘controls’) and other sites were positioned downstream of the farms (‘impacts’). All sites were situated in the Tyrrhenian Sea. Control and impact sites differed significantly with regard to the dissolved nutrient profile. The fouling community (samples were scraped from buoys) displayed a reduction gradient in diversity which increased with the effect of fish farms. A total of 51 taxa were identified (three Cyanophyceae, three Phaeophyceae, five Bacillariophyceae, three Chlorophyceae, six Ulvophyceae and 31 Rhodophyceae), with a dominance of opportunistic species (with r strategy). A general increase in values of the Rhodophyceae by Phaeophyceae ratio (R/P) were recorded, indicating a remarkable impact of nutrient enrichment from fish culture facilities on an algal community structure.