Spatial and seasonal variations in the trophic spectrum of demersal fish assemblages in Jiaozhou Bay, China

Trophic structure offish communities is fundamental for ecosystem-based fisheries management, and trophic spectrum classifies fishes by their positions in food web, which provides a simple summary on the trophic structure and ecosystem function. In this study, both fish biomass and abundance trophic spectra were constructed to study the spatial and seasonal variations in the trophic structure of demersal fish assemblages in Jiaozhou Bay, China. Data were collected from four seasonal bottom trawl surveys in Jiaozhou Bay from February to November in 2011. Trophic levels （TLs） of fishes were determined by nitrogen stable isotope analysis. This study indicated that most of these trophic spectra had a single peak at trophic level （TL） of 3.4-3.7, suggesting that demersal fish assemblages of Jiaozhou Bay were dominated by secondary consumers （eg. Pholisfangi and Amblychaeturichthys hexanema）. The spatial and seasonal variations of trophic spectra of Jiaozhou Bay reflected the influence of fish reproduction, fishing pressure and migration of fishes. Two-way analysis of variance （ANOVA） showed that seasonal variations in trophic spectra in Jiaozhou Bay were significant （P〈0.05）, but variations among different areas were not significant （P〉0.05）. The trophic spectrum has been proved to be a useful tool to monitor the trophic structure of fish assemblages. This study highlighted the comprehensive application of fish biomass and abundance trophic spectra in the study on trophic structure offish assemblages.