COMPARISON OF FISH AND MOBILE MACROINVERTEBRATES ASSOCIATED WITH SEAGRASS AND ADJACENT SAND AT ST. CATHERINE BAY, JERSEY (ENGLISH CHANNEL): EMPHASIS ON COMMERCIAL SPECIES

摘要

Local-scale studies provide fishery agencies with essential information on the relative importance of seagrass beds as habitats. Combinations of dayight and low/high tide trawls within the same shallow bay were used to identify significant differences in the commercial species associated with seagrass (Zostera marina) and unvegetated sand. ANOVA revealed that species number was significantly higher in seagrass than sand, but this varied with tidal and diel conditions; there was no evidence that the seagrass bed supported higher densities of commercial species. Certain species showed significant temporal and spatial patterns of occurrence; black bream (Spondyliosoma cantharus) densities were significantly greater (P < 0.01) in seagrass (0.003 ind m~(-2)) compared to sand (0.0005 ind m~(-2)). In contrast, the highest densities of brown shrimp (Crangon crangon) were found on sand, when daytime high-tide densities (mean; 0.093 ind m~(-2)) were significantly greater than (P < 0.05) either daytime low tide (0.001 ind m~(-2)) or nighttime high tide (0.024 ind m~(-2)). Incorporation of these tidal and diel factors in future studies of sand and seagrass is important if such comparative analyses are to be used as the basis of a management strategy (for example when considering the benefits of habitat restoration).