Comparative Study On Ecosystem Structure And Energy Flow Of Closed Bay And Open Bay Based On Ecopath Model

The gulf ecosystem,as the closest marine ecosystem,can provide all kinds of resources and services for human begins' life and production.The bay is in a zone where oceans and lands are interlaced.So,the gulf is under the double impacts of human activities and natural environment changes which had led to a decline in the environmental quality and an increasingly fragile of the gulf ecosystem.Therefore,exploring the structure,function and state of the gulf ecosystem is important to achieve the protection and sustainable development of the bay ecosystem.In this study,two bays' mass balance models by Ecopath with Ecosim was made to assess the maturity and stability of the ecosystems.The mian results were showed as follow:(1)The Sansha Bay's Ecopath model consisted 19 function groups,and the effective trophic levels of the 19 function groups in ecosystem was in the range of 1.00 to 3.58.The values of ecotrophic efficiency(EE)of many functional groups such as Tonguefish,Platycephalidae,Mugilidae were higher,but the functional groups of Phytoplankton and Benthic mussels had a low EE.The energy flow of Sansha Bay ecosystem had two main passways:the grazing food chain from phytoplankton and the detritus food chain.49%of the total flow in the ecosystem was from phytoplankton,and 51%was from detritus.The average transfer efficiency of Sansha Bay ecosystem was 7.05%.The total system throughput was 2620.508 t/km-y.The value of TTP/TR,TB/TT,CI,SOI,FCI and MPL were 3,825,0.008,0.368,0.161,4.503 and 2.433 respectively.For Sansha Bay the value of indexes showed low energy and matter recycling and shot flow pathway,suggesting that the Sanshan Bay ecosystem was unmaturity and unstability.And it was in a phase of resource declining.(2)The Dacheng Bay's mass-balanced model contained 18 function groups,including phytoplankto,zooplankton,gobiidae,shrimp,crab,detritus and so on.The effective trophic levels of the 18 function groups in ecosystem ranged from 1.00 to 3.57.The values of EE of functional groups such as Tonguefish,Platycephalidae;Mugilidae,and so on were higher,however,the functional groups,which had a lower trophic level,had a low EE.The grazing food chain from phytoplankton and the detritus food chain were two main flow passways of Dacheng Bay ecosystem.48%of the total flow in the ecosystem was from phytoplankton,and 52%was from detritus.The value of the average energy transfer efficiency of Dacheng Bay area was 6.74%.The ecosystem total throughp.ut was 2110.798 t/km2·y.The value of TTP/TR,TB/TT,CI,SOI,FCI and MPL were 3.780,0.010,0.409,0.169,4.588 and 2.414 respectively.These indicators showed that the stability and maturity of the Dacheng Bay ecosystem is low.(3)The main activities of fishery in Sansha Bay include cage culture,shellfish farming,macroalgae culture and stock enhancement.The fishing activities in Dacheng Bay include macroalgea farming,shellfish farming,and less cage culture and stock enhancement.Cage culture should pay attention to controlling a reasonable number and density of cages.And the bay ecosystem should construct a multi-culture complex ecosystem for fish,shrimp,shellfish and algae.Macroalgae culture should implement a method of rotation cultivation and build a vertical cultivation system.Stock enhancement should take the foodwed structure and energy folw characteristics of ecosystem into account.(4)The overall characteristics of the Sansha Bay and Dacheng Bay ecosystems are similar.According to the differences in the characteristics of the nutrient structure and energy flow in different periods of the ecosystem,different species should be released at different stages.In the primary stage,stock enhancement activity should increase the kinds and biomass of species which feeding with phytoplankton and detritus.In the middle stage,we recommended that choose to species which feeding with benthonic organisms as stock enhancement species.Therefore,the energy can transmit to higher trophic levels.In the last stage,through a comprehensive analysis of the interactions between functional groups,piscivorous fishes and higher economic value species should be conducted to release,in order to improving the ecological environment and achieving the goal of restoring fishery resources of the gulf ecosystem.