Determination of trophic relationships within a Bohai Bay food web using stable δ15N and δ13C analysis

This study measured stable carbon and nitrogen isotope ratios in phytoplankton, zooplankton, five invertebrates species, eight fishes species and three seabirds species collected in Bohai Bay. delta C-13 ranged from -25.38 parts per thousand to -11.08 parts per thousand showing a relative low enrichment in the food web from Bohai Bay. The mean delta C-13 of mullet is higher than that of other organisms, and this might be due to that mullet is migration fish and feeds mainly on inshore sources. delta N-15 ranged from 4.08 parts per thousand to 13.98 parts per thousand, and showed a step-wise enrichment with trophic level of 3.8 parts per thousand. The delta N-15 enrichment factor was used to construct an isotopic food web model to establish trophic relationships within this marine food web. According to this model, exact trophic levels of all organisms were estimated as 1.46-2.10, 1.91-3.32, 2.55-4.23 and 2.98-4.28 for plankton, invertebrates, fishes, and seabirds.