Effects of seagrass canopy removal on fish in shallow Mediterranean seagrass (Cymodocea nodosa and Zostera noltii) meadows: A local-scale approach

Abstract

The importance of the canopy of small-sized seagrasses (Cymodocea nodosa and Zostera noltii) to fish assemblages was investigated in experimental plots at three shallow sites in NE Sardinia (Italy, western Mediterranean). Fish were assessed by underwater visual census in four habitats: (1) seagrass in its natural state, (2) cut seagrass, (3) uncut seagrass (with a simulation in time and effort equivalent to those spent at the treated patches) and (4) unvegetated sand. The disturbance associated with removing seagrass canopies was not found to affect fish. Multivariate analyses showed that fish assemblages from seagrass habitats, with seagrass patches removed and unvegetated sand differed significantly among each other. Univariate analyses revealed that species richness, total fish abundance, and densities of Atherinidae, Diplodus sargus and Sarpa salpa were unaffected by the habitat type. The seagrass leaf canopy was most important for Symphodus ocellatus, Labrus viridis, Diplodus annularis and Sparus aurata, the last three species being chiefly represented by small-sized fishes. Gobiids were most abundant in habitats devoid of seagrass vegetation (i.e. sand and removed patches), while Coris julis and Diplodus vulgaris appeared to prefer unvegetated sand, even compared with the removed patches. Other species, such as Symphodus cinereus, Symphodus tinca and Mullus surmuletus, did not display any distinct distribution patterns attributable to the habitat type. For a number of littoral fish species, including some of commercial importance (e.g. S. aurata), small-sized seagrasses in NE Sardinia were thus demonstrated to exert an ecological role, which involves important implications for the protection and management of these coastal habitats and suggests the need for further research at larger spatial scales.