The Structure And Function Of The Typical Semi-enclosed Bay Ecosystem Based On Ecopath Model

As an important area of land sea interaction,a Gulf is rich in fishery resources,which is significantly affected by human activities such as fishing.In recent decades,with the decline of offshore fishery resources,semi-enclosed bays,which are spawning and breeding grounds for fishery resources,are attracting more and more attention.In order to analyze the current status and development trend of China's inshore bays based on ecosystem structure and function,this study selected two typical semi-enclosed bays respectively in China's temperate and subtropical zones,the Jiaozhou Bay and Daya Bay,whose ecosystems are significantly affected by human activities and which basic data have been accumulated.The Ecopath with Ecosim 6.5(Ew E6.5)software was used to construct the Ecopath models for the Jiaozhou Bay in 1980 and 2015,and for the Daya Bay in 1985 and 2015.Using the Ecopath model,we evaluated the trophic structure,energy flow and system attributes of the Jiaozhou Bay in 2015.Based on the Ecopath models,we compared and analyzed the differences in ecosystem structures,functions and attributes in different periods of the Jiaozhou Bay and Daya Bay respectively.We also compared the differences between the Jiaozhou Bay and Daya Bay ecosystems in various aspects.Based on these analyses,we try to draw the universal characteristics of the inshore semi-enclosed bays.The main results were described as follows:Based on the survey data of fishery resources and ecological environment in the Jiaozhou Bay during 2015-2016,we developed a mass-balance model using Ecopath with Ecosim software for the Jiaozhou Bay.The Jiaozhou Bay model consists of 21 functional groups,and the fractional trophic levels ranged from 1 to 4.383.The mean trophic level of fishery catch is 2.023,mainly in Manila Clam(Ruditapes philippinarum).The energy flow of the Jiaozhou Bay ecosystem is dominated by grazing food chain,which accounts for 59% of the energy source.Using network analysis,the system network was mapped into a linear food chain and six discrete trophic levels were found with a mean transfer efficiency of 16.53%,16.22% from primary producer and 15.76% from detritus within the ecosystem.In addition,the ratio of total primary production to total respiration(TPP/TR)was 2.518,which suggests the Jiaozhou Bay system is in an immature state.Based on the survey data of fishery resources and ecological environment in the Jiaozhou Bay during 1980(1980-1982),we constructed the model of the Jiaozhou Bay in 1980 using Ecopath with Ecosim 6.5 software.The models of the Jiaozhou Bay consist of 21 functional groups.Based on the two models,we compared and analyzed the differences in ecosystem structures,functions and attributes.The trophic structure of the Jiaozhou Bay ecosystem in 2015 has changed with a decrease in the biomass proportion of top predator and an increase in Ruditapes philippinarum biomass proportion.The main products of catch are the Ruditapes philippinarum,and the mean trophic level of fishery catch has reduced nowadays.The energy flow of the Jiaozhou Bay ecosystem was dominated by grazing food chain,and the system energy transfer efficiency increased from 15.83% in 1980 to 16.35% in 2015.Analyses on the keystones species for Jiaozhou bay ecosystem indicated that Ruditapes philippinarum are a keystones species in the 1980 and 2015.Compared with the 1980 ecosystem,the system scale of the Jiaozhou Bay has increased and the net system production increased by 5 times in 2015.The parameters of the ratio of total primary production to total respiration increased from 1.267 in 1980 to 2.518 in 2015 also.In addition,the connectance index,system omnivory index and Finn's cycling index decreased from 1980 to 2015.In conclusion,the maturity and stability of the Jiaozhou Bay ecosystem have been reduced in the past 30 years,and the system has the trend from maturity stage to immaturity stage.In short,the Jiaozhou Bay ecosystem is currently in an unstable young stage.Based on the survey data of fishery resources and ecological environment in the Daya Bay during 2015(2015-2016)and 1985(1985-1986),we constructed two periods ecosystem models of the Daya Bay using Ecopath with Ecosim 6.5 software.The models of the Daya Bay consist of 26 functional groups.In the Daya Bay ecosystem,the fractional trophic levels ranged from 1 to 4.025 in 1985 and from 1 to 3.987 in 2015.Compared with the 1985 ecosystem,the biomass,production,flow to detritus and throughput of the Daya Bay ecosystem have increased in 2015.In the two periods,the trophic structure of Daya Bay ecosystem is like a pyramid,and the energy flow was dominated by grazing food chain.The system energy transfer efficiency in 1985 was higher than that of 2015,which was 12.673% and 9.470% respectively.The total system throughput was 3828.963 t·km-2 in 1985 and 8255.895 t·km-2 in 2015.The parameters of the ratio of total primary production to total respiration increases from 1.351 in 1985 to 2.970 in 2015 also.In addition,the connectance index,system omnivory index and Finn's cycling index have decreased in the past 30 years.In conclusion,the Daya Bay ecosystem is currently in an unstable young stage.Through horizontal comparison of Jiaozhou Bay and Daya Bay ecosystems,it was found that the two Gulf fisheries resources declined more seriously.At the same time,the important economic species decreased significantly,and the trophic level of most species has showed a declining trend.The energy flow of Jiaozhou Bay and Daya Bay was mainly dominated by grazing food chain.The system energy transfer efficiency of Jiaozhou Bay was higher than that of Daya Bay.From the 1980 to 2015,the mean trophic level of fishery catch has reduced in both ecosystems,and the Jiaozhou bay is particularly obvious.In terms of the evolution trend of the two ecosystems,the parameters of the ratio of total primary production to total respiration in Jiaozhou Bay and Daya Bay increased,and the maturity and stability of the both ecosystem decreased.