Assessment Of The Ecological Effects Of Tangshan Marine Ranching Based On The Atlantis Ecosystem Model

Atlantis is a biogeochemical ecosystem model that integrates biology,physics,chemistry and anthropogenic impacts,allowing a holistic assessment of biogeochemical processes and the impact of human activities on ecosystems.This study developed the Tangshan Marine Ranch Atlantis model based on field survey data from the Tangshan Marine Ranch waters in March2018(spring),November 2018(autumn)and August 2019(summer),combined with social research and literature,and based on the Australian Atlantis model framework.Using the main fishery species(Scomberomorus niphonius,Sebastes schlegelii,sea cucumber and abalone)in the marine pasture as research objects,the ecological effects of the marine pasture were assessed by adjusting the indicators of primary productivity growth rate and changes in invertebrate mortality caused by nutrient salt concentration and the intensity of sea currents to predict the trends of biomass and related fishery indicators.The conclusions are as follows:(1)Changes in nutrient salt concentration will have some impact on food webs and affect fishery production and ecosystem structure.An increase in nutrient salt concentration promotes the growth of phytoplankton and macroalgae,which in turn causes changes in the growth rate of primary productivity.In this study,six scenarios of changes in primary productivity were set,and the simulation results showed that with changes in primary productivity,fish grew by about 40%,invertebrates by about 30% and primary producer biomass by about 50% on average;while seabird populations were less affected by changes in nutrient salt concentration,and their total biomass only decreased by about 7%.(2)Based on the fact that increased nutrients may cause eutrophication of seawater,which can lead to harmful algal blooms and consequently alter the mortality of marine invertebrate populations.As invertebrate mortality increases,the food supply for invertebrate-feeding fishery stocks decreases,and therefore the biomass and fishery production of fishery stocks will decrease.In this study,four different mortality scenarios for marine invertebrates were developed and the simulations showed that changes in nutrient concentrations would initially increase the biomass and catches of various groups in the ecosystem,but as algal blooms continued to grow,especially red tide organisms,this would lead to a massive reduction in population size and catches due to hypoxia,and a reduction in total ecosystem biomass of approximately 40%.The total biomass of the ecosystem will be reduced by approximately 40%,with demersal fish declining by approximately 30% and invertebrates such as shellfish,shrimps and crabs declining by an average of approximately 25%,with jellyfish being the most significantly affected,declining by approximately 45-60%.The results show that the Atlantis model can simulate the impact of dynamic changes in nutrient salinity on the ecosystem,providing theoretical support for fisheries management decisions.(3)Changes in the ocean current field will have a certain impact on marine productivity.Artificial fish reefs will have a significant impact on the flow field in the sea,generating eddies on the leeward side of the reef and upwelling on the upwelling side.The upwelling will bring nutrient-rich bottom layers to the pelagic zone.The ecosystem effects of changes in nutrient concentrations have been studied.In this study,the effects of eddies generated by artificial reefs on the ecosystem were modelled.The results showed that the total biomass of primary producers in the reef area increased by about 4% compared to the control area,with microzooplankton increasing by about 2% to 3%.Among invertebrates shellfish biomass increased by about 1%and jellyfish by about 1.5%.The impact on fish is less significant.At the same time,the stronger the eddy currents generated by the artificial reefs,the more biomass they increase,which proves that the eddy currents generated by the placement of artificial reefs will directly affect some of the populations in the ecosystem.(4)The results of the simulation of the ecological effects of Tangshan Marine Ranch are: the growth of seaweeds is about 3%,the growth of micro phytoplankton is about 1.5%,the growth of micro zooplankton is about 0.4%,the growth of benthic filter feeders is about 0.4%,the growth of shellfish is about 0.3%,the growth of shrimp mayflies is about 0.02%,the growth of jellyfish is about 0.6%,the growth of Japanese sea crab is about 0.5%,the growth of carnivorous zooplankton is about 1.8%,and the growth of Otaki six-lined fish is about 1.8%.The increase in the number of six-lined fish in Otaki was about 1.28% and the increase in the number of redfish in Hsu was about 0.17%.Therefore,the artificial reefs have improved the productivity of the sea area and produced good ecological effects,which are important for the high-quality development of marine pastures.