Preliminary data on the impact of fish farming facilities on Posidonia oceanica meadows in the Mediterranean

Abstract

While the extension of aquaculture along the coasts of the Mediterranean islands is today an economic priority, no data is available on the impact of these facilities on the littoral environment in general, and in particular on the Posidonia oceanica meadows that are responsible for the richness and diversity of these biotopes. The impact of fish farming facilities in the marine littoral environment is assessed at three Mediterranean sites in Corsica and Sardinia. Various parameters are considered: (i) the amount of light available, (ii) the nature of the sediment, and (iii) the vitality of the Posidonia oceanica beds. The findings confirm the impact of the aquaculture facilities within the water column (increase in turbidity, enrichment of the sediment in organic matter and nutrients), and it would appear that the Posidonia oceanica beds also undergo significant alterations. The decline in density of the meadows in the area influenced by aquaculture farming and their total disappearance beneath the facilities is particularly disturbing, even if the areas affected are not very extensive, at least for the smaller farms (a few hundred square metres), and if certain beneficial effects may be recorded (increase in benthic primary production). Because of its ability to record environmental alterations caused by these facilities (light, nutrients, trace metals), the Posidonia oceanica meadow is a good bioindicator for use in monitoring studies.