| An Ecopath model is constructed with comprehensive assessments of accuracy and sensitivity,based on the quarterly survey of the Yangtze estuary and its adjacent waters in February,May,August and November 2014.Noteworthy aspects are analyzed,including trophic structure,energy flow characteristics and overall ecosystem status of the estuarine ecosystems in 2014;The dynamic evolution of taxa groups'structure and their energy flow networks in the three periods?1985-1986,2004 and 2014?are compared and analyzed.The interactions between taxa groups and overall ecosystem status in the three historical periods of the sea area are discussed,as follows.?1?Taxa groups is divided based on the niche characteristics of different species,meanwhile referring to the economic value and research focus of fishery resources.The entire community are divided into a total of 23 taxa groups.More specifically,there are9 fish groups,3 benthic groups,seabirds,sharks,turtles,cephalopods,shrimps,crabs,jellyfish,zooplankton,phytoplankton,benthic producers and detritus.Exploring the nutritional relationship between different taxa groups through the hierarchical cluster of the diet composition matrix to;Using the“rules of thumb”to run the overall test of the model input parameters;Analyzing the sensitivity of estimate parameters to input parameters;based on six parameters of ecological principles,mass conservation,and thermodynamic laws to balance the model.?2?In 2014,the trophic level of each taxa group of the Yangtze estuary and its adjacent waters ecosystem was between 1-4.361;the trophic level of the nine fish functional groups was 3.046-4.361,and the average trophic level was 3.515.The average ecotrophic efficiency of the fishery functional group was 0.845.The total energy flow of the ecosystem was 12217.660 t?km-2?a-1,and the net production of the ecosystem was 1332.859 t?km-2?a-1.Total biomass without detritus was 94.336 t?km-2?a-1.Fishing had a significant negative impact on demersal mix-feeding fish and benthopelagic fish.Jellyfish and zooplankton had obvious predation and competition with each other,and Jellyfish had a certain retention effect on energy flow.Primary production from detritus had a significant supporting effect on benthopelagic and demersal fish.The EcoTroph model illustrated the strong negative impact of fishing on functional groups with a trophic level greater than 3.1.?3?The study compared the energy flow networks and the correspondence between various parameters among different functional groups of the Yangtze estuary and its adjacent waters in the three periods of 1985-1986,2004 and 2014.The results shows that the taxa groups,whose biomass rose first then fell or biomass declined consistently,were usually facing a collapse.The ever-increasing biomass of the functional group often indicates the occurrence of ecological disasters.The catch in 2004 was the highest in the three periods,which was several times higher than that in 1985-1986.In 2014,the catch was significantly reduced,except that the catch of demersal mix-feeding fish was still higher than the level of 1985-1986.In 2014,the overall Omnivory increased,and the prey trophic level of benthopelagic and demersal fish decreased,shifting from the fourth trophic level to the third trophic level in general.?4?Zooplankton was included in the taxa groups with high keystone index in 1985,2004,and 2014.In 2004,the criticalities of crabs and demersal fish were reduced,and that of pelagic planktonic fish was increased.In 2014,pelagic planktonic fish were still highly critical,however shrimps and crabs were reduced,and the role of benthos in energy flow conversion was also highlighted.Among the total system flows in each period of the estuarine area,consumption accounted for the highest in 2014 and lowest in 2004.In 2004,the huge fishing pressure faced by the marine ecosystem caused great changes in the ecosystem structure,the ecosystem became immature,and the ability to resist external disturbances declined.In 2014,the situation was relieved compared with2004.The ecosystem maturity had recovered,the energy flow network was more redundant,nevertheless the fishery output capacity was far lower than the previous level. |
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