Temporal Changes of Structure and Functioning of the Bohai Sea Ecosystem: Insights from Ecopath Models

The marginal semi-enclosed Bohai Sea is an important ecosystem for many commercial as well as ecologically important species. At the same time, the Bohai Sea increasingly facing various anthropogenic disturbances which have been reported to affect the functioning of this ecosystem in many ways. Using Ecopath and Ecosim modeling suite (ver 6.5), this study examined the temporal changes in the ecological status of the Bohai Sea ecosystem. The present model comprises a total of 23 functional groups based on a year-round trawl survey conducted in 2016. The results of the present study showed that the mean trophic level of the commercial species as well as the overall fisheries species declined during the last few decades. The fundamental source of biomass flows within the Bohai Sea food web generated from the lower trophic levels. Primary producers (phytoplankton) and detritus contributed about 52.77% and 47.23%, respectively of the total energy flows originated from the base of the food web in 2016. Estimation of the ecological parameters during the decadal-scale suggests that the Bohai Sea ecosystem is at an immature stage. The niche overlap indices showed intermediate overlaps between prey species rather than predator species overlapping. The mixed trophic impacts indicated that the lower trophic levels had positive influences on most of the groups in the higher trophic levels, indicating the strong bottom-up ecosystem dynamics. Increased biomass of jellyfish and cephalopod had moderate adverse effects on other groups. This comparative analysis provides an important platform by increasing our understanding of the several food web properties that can be integrated within a future management plan of the Bohai Sea fisheries resources.