THE EFFECTS OF ALTERING SEAGRASS CANOPY HEIGHT ON SMALL, MOTILE INVERTEBRATES OF SHALLOW MEDITERRANEAN EMBAYMENTS

The height of seagrass canopy was manipulated in experimental plots in meadows of the fine-leaves seagrass Cymodocea nodosa at two sites in the Mediterranean Sea, la Lagune du Brusc, lies des Embiez near Toulon , and l'Etang de Diana on Corsica. Epifauna (small motile invertebrate s associated with the seagrass canopy or sediment surface), was collec ted al night at both sites, and during the day at Diana only, from thr ee treatments: full seagrass canopy, reduced canopy, and canopy remove d entirely. Although epifaunal assemblages from the two sites were dif ferent, treatment modification had the same effect at both sites when analysed using multivariate ordinations. Abundance and biomass of tota l epifauna and of key taxa were all reduced in line with decreasing se agrass cover at both sites at night. The effects of treatment modifica tion on epifauna during the day showed the same trend but were of grea ter magnitude, both for assemblages and for total abundance and biomas s. At both sites and at both times, the fauna of plots from which seag rass had been cut tended to be dominated by animals of higher biomass than the fauna of plots with full canopy. Epifauna form the major diet ary component of small fish inhabiting shallow, sheltered embayments. These results are therefore consistent with a model in which reduced a bundance of fish associated with reduced seagrass canopy is explained by a reduction in food availability.