The Effect of Ontogenetic Dietary Shifts on the Trophic Structure of Fish Communities Based on the Trophic Spectrum

The trophic spectrum provides a useful method to investigate the trophic structure of fish communities. However, ontogenetic shifts in diet can cause variations in the trophic level with body size, thereby influencing the trophic structure of fish communities. In this study, we investigated the effect of ontogenetic dietary shifts on the trophic structure of fish communities in Haizhou Bay based on trophic spectra and trophic indicators calculated under different scenarios of functional group classification. The results showed that the size threshold of ontogenetic dietary shifts was a viable basis for functional group classification. The biomass of fishes at trophic levels 3.4–3.8 was lower when ontogenetic dietary shifts were considered, which can influence the intensity of top–down control and hinder the formulation of harvest strategies. Ontogenetic dietary shifts can also redistribute the biomass of fishes across trophic levels, thereby regulating the trophic structure of fish communities. Different responses of trophic indicators to ontogenetic dietary shifts were identified, with high trophic indicator (HTI) being the most appropriate indicator reflecting the effect of ontogenetic dietary shifts in the trophic structure. This study provides a feasible way to optimize the trophic spectrum for elucidating the trophic structure of fish communities. And we recommend that ontogenetic dietary shifts should be considered and valued in fishery management.