Changes in Fish Assemblages Associated with the Deployment of an Antitrawling Reef in Seagrass Meadows

Abstract

Posidonia oceanica seagrass meadows have been degraded in the Mediterranean Sea by trawling. To reduce this impact, antitrawling artificial reefs have been deployed. The introduction of artificial structures on seagrass meadows, however, could potentially change the composition of fishes. Using visual techniques, we examined changes in fish assemblage and density of key species by comparing fish abundances at four seagrass sites with and without artificial reef blocks in El Campello (Alicante), southeastern Spain, between October 1992 and August 1995. The fish assemblage on plots with artificial reefs changed substantially a year after their installation in October 1992. Differences in fish abundance (total counts of 6,692 fish on artificial reefs and 3,565 fish on Posidonia) and in species richness (41 species on artificial reefs and 29 on Posidonia) were found. The abundance of key species were quite different between habitats. Diplodus vulgaris and Chromis chromis were most abundant in all samples, whereas Oblada melanura recruited to the artificial reefs during winter 1994. Two species, Apogon imberbis and Sciaena umbra were found at all times on artificial reefs but were not present in P. oceanica plots. The antitrawling artificial reefs influenced the spatial distribution of fishes on a scale of tens to hundreds of meters but did not affect the overall Posidonia fish assemblage. Antitrawling artificial reefs protect seagrass from trawling and had little overall effect on seagrass fish assemblages in areas away from the artificial reefs.