Abstract
We analysed datasets of fish assemblages for two timescales（decadal and annual, composed of four periods: 1993-1994; 2004-2005; 2005-2006; 2006-2007）to estimate the temporal dynamics of assemblage structures and changes in estuarine use functional groups（EUFGs） along a modified shoreline. The datasets were obtained from monthly sampling using a light trap at a mooring berth site reinforced with a vertical hard structure in an estuarine canal in Tokyo, Japan. A comparison of the fish community parameters during the sampling periods showed significant decadal variation in some factors, but no significant variation across sequential annual timescales. Total species richness increased due to increased richness in fish in the marine EUFG category. The percent abundance of marine fish also significantly increased, whereas the abundance of estuarine fish（primarily Acanthogobius flavimanus predominated）decreased. Habitat degradation around the mooring berth site accompanying city planning might be responsible for the decline in estuarine fish species over several decades, whereas the increased species richness reflected a recent recovery in water quality in the Tokyo Bay. These results suggest that nowadays the study site functions as an ecological corridor between natural shore
sites rather than as a true habitat for estuarine fish species.
