Research On The Marine Ecological Environment And Fishery Resources Carrying Capacity Of Dachen Islands

The 21st century is the marine century,the oceans have been of major strategic importance to the economic and social development.With the rapid development of urbanization and industrialization,the marine environmental pollution problem has become a new constraint on the process of Chinese modernization.Marine carrying capacity refers to the limits of the self-regulation and self-maintenance,which can support the coordinated development among different subsystems(economy,society and environment).It is of great practical significance to improve the marine carrying capacity at the levels of resource,structural,economic and technical,and to establish and perfect evaluation system.Based on the background investigation of Dachen Islands from 2019 to 2021,we conducted comprehensive evaluations of the ecological environment.Then,comprehensive index method and fuzzy comprehensive evaluation method were used to evaluate the marine ecological environment carrying capacity,and the indicators of marine fishing and mariculture were selected to calculate the carrying capacity of fishery resources.Finally,we used the coupling coordination degree model to analyze the coupling coordination relationships between the fishery resources and environment in Dachen Islands.The results showed that:(1)The water quality of the Dachen Islands has a high degree of eutrophication,with moderate eutrophication in surface seawater during spring and autumn voyages,and mild eutrophication in other voyages.The eutrophication degree in autumn was significantly higher than that in other voyages(p<0.05).The output result of neural network showed that summer and spring reached Class II water quality,while autumn and winter were Class III.The Nemerow comprehensive index method showed that the sedimentary environment was clean or still clean.The potential ecological risk assessment method showed that Cd and Hg elements had ecological risks,and survey area generally belonged to the slight ecological risk level.The phytoplankton and zooplankton diversity indices had significant seasonal differences(p<0.01),the differences of benthic biodiversity indices were not significant(p>0.05),and the stability of community structure was unhealthy in spring and winter.(2)The calculation results of the comprehensive index method showed that the scores of the water environment quality,sediment quality and ecological health subsystem were 0.536,0.854 and 0.467 respectively,which were critical overload,loadable and critical overload.The marine ecological environment carrying capacity was the highest in summer(0.599±0.055),followed by spring(0.563±0.035)and autumn(0.541±0.031),whereas the winter voyage was the lowest(0.469±0.030).The carrying capacity had spatial heterogeneity,with an average value of 0.543(critical overload).(3)Based on the calculation results of fuzzy comprehensive evaluation,the comprehensive score value of the ecological environment carrying capacity was summer(70.003)> autumn(63.840)> spring(62.262)> winter(55.720),the difference between seasons was extremely significant(p<0.01),and the corresponding carrying capacity ratings were 1.422,1.694,1.796 and 2.179,respectively.(4)The evaluation results of relevant indicators of swimming animals in Dachen Islands were fine,but the unit output value of marine capture was low,and the fish eggs and juvenile of the spring and autumn voyages were in a low density state due to the disturbance of human activities and the non-spawning period.The output yield and value per unit area of mariculture were at a high level,however the structure index was critically overloaded.The average score of the marine fishing subsystem was 0.651,which were excellent in the autumn,but the proliferation rate of fishery resources in the spring of 2021 lagged behind the fishing intensity.The mariculture subsystem got 0.549,showing a slight downward trend.In the autumn of 2019,2020 and spring of 2021,the fishery resource carrying indexes were 0.692,0.679,and 0.507,respectively,which were at a good level.(5)The ecological environment and fishery resource system in Dachen Islands were highly coupled,and the two developed well in autumn of 2020,and moderately in autumn of 2019 and spring of 2021.The ecological environment order parameters have changed from backward to ahead of the fishery resources.Specifically,in the autumn of2019,the ecological environment lagged behind,in the autumn of 2020,the two were synchronized,and in the spring of 2021,the fishery resources lagged behind the ecological environment.The correlation degree of the environmental pollution factor to the fishery resource system was higher than that of the ecological response factor,and the aquaculture subsystem to the ecological environment system was higher than that of the marine fishing.The comprehensive pollution index of heavy metals in sediments and the Shannon’s diversity index of catchs were highly correlated with the coupling coordination degree.