Analysis of carbon flow characteristics of an offshore ecosystem based on mass balance model

This study evaluated the characteristics of carbon flow among high-trophic level organisms in a coastal ecosystem. Based on comprehensive data collected from the field fishery survey in 2023 and literature information, a carbon-based mass balance model was constructed to represent the southern coastal area of Zhejiang (SCZ), China. The model included 19 functional groups, ranging from primary producers to top predators. Bacteria were also considered in this ecosystem model. The results indicated that the trophic level of the SCZ ecosystem ranged from 1.000 to 4.820, with a mean trophic level of 3.743. The variation in carbon transfer efficiency between different trophic levels ranged from 0.071 to 0.950. The total carbon flow of the SCZ ecosystem was 590.238 gC/m2/year, with detrital flow accounting for 35.67 % of the total carbon flow, while 9.28 % of the total carbon flow was attributed to fisheries. In the SCZ ecosystem, carbon fixed by phytoplankton through photosynthesis contributed 31 % of the total carbon sources in the carbon cycle, and 69 % came from detritus in water bodies. We found that bacteria played a key role in the carbon cycle of the SCZ ecosystem by contributing 80.47 %, 68.56 %, 37.34 % and 65.11 % of the total carbon consumption, total carbon respiration, carbon flow into detritus, and total ingested carbon of the ecosystem, respectively. Furthermore, as key species of the SCZ ecosystem, zooplankton, pelagic fish and shrimp played a significant role in the carbon cycle by contributing to the demand for primary production required (PPR), accounting for 33.30 %, 24.32 % and 10.23 % of the total PPR of SCZ ecosystem, respectively. In addition, the general characteristic parameters of the SCZ ecosystem indicated low ecosystem stability and relatively simple food web. This study provides a reference for the analysis biological carbon cycle and carbon sink function of higher trophic marine organism in the SCZ ecosystem.