Ecosystem characteristics and ecological carrying capacity of a subtropical marine ranch in the pearl river estuary: an ecopath modeling approach

Marine ranching has been widely promoted as an ecosystem-based approach to restore degraded coastal ecosystems and enhance fishery resources, particularly in heavily impacted estuarine regions. The National Marine Ranch Demonstration Zone of Wailingding Island, located in the Pearl River Estuary of the northern South China Sea, represents a typical subtropical coastal system influenced by intensive anthropogenic activities and ecological restoration efforts. Based on continuous bottom trawl surveys in April and September 2020 from the Wailingding Island marine ranch (WIMR) area, this study employed an Ecopath model to evaluate the ecosystem characteristics of the study area. The model systematically analyzed energy flows, structural characteristics, and the ecological carrying capacity of major functional groups. Seventeen functional groups were defined, representing the key energy transfer pathways in the study area. Their trophic levels (TLs) ranged from 1.000 to 3.737, with marine mammals occupying the highest level. The overall energy transfer efficiency of the ecosystem was 3.873%, and the total system throughput reached 10,536.750 t/(km²·year), with 49% derived from detritus. The ratios of total primary production to total respiration (TPP/TR) was 7.431. Finn’s cycling index (FCI) and Finn’s mean path length (FML) were 2.529% and 2.198. These results suggest that the Wailingding Island marine ranch ecosystem is characterized by low maturity and stability and a relatively simple food web structure. Model simulations further indicated that under ecologically balanced conditions, the ecological carrying capacities of major functional groups could increase up to 3.8 times their current biomass levels.