Study On The Quantity Long-term Variation Of Macrobenthos In Daya Bay Of South China Sea

Daya bay is a semi-enclosed bay,being adjacent to Dapeng Bay to the west and Honghai Bay to the east,which is located in the northern South China Sea.Daya Bay has the excellent natural environment and rich biological resources,and it has been one of the main fishery germplasm resource.In the 1980 s,Daya bay can maintain high productivity with high quality of water and poor nutritional status.In recent 30 years,the economic development of this bay in surrounding area was rapid,and human disturbance continued to increase.At present,the ecosystem of Daya Bay is undergoing a rapid deterioration.The macrobenthos community are main part of marine ecosystem,and play an important role in maintaining the healthy and stable development of the ecosystem.Because of the low abilities of mobility and avoiding adverse environment,high sensitive to environment changes,and the long lifecycle,the macrobenhos are severely affected by the envionment.Therefore,the quantity fluctuation of macrobenthos can relate to the long-term changes in enviromental conditions,the studies on the change characteristics of macrobenthos are important in maintaining the stable development of ecosystem and sustainable utilization of biological resources.In this study,the quantity variation characteristics of macrobenthos will be analysed,outcome of this study will provide basic materials for the further researches and support on the restoration and protection of the Daya Bay ecosystem.Based on the 32 cruises survey data collected from 414 sampling station in Daya Bay of South China Sea from October 1982 to December 2015,the horizontal distribution characteristics,the trend of quantity fluctuation,the relationship with environmental factors of the abundance,biomasss and secondary production were analysed.1.Horizontal distribution characteristics of macrobenthos quantityFrom the horizontal distribution,we can know that the obvious varation areas of macrobenthos abundance,biomass and secondary production are the west top bay,south-central top bay and Dapengao Bay,the eastern part of the cental bay and outer bay formed two new high-value areas.2.The trend of macrobenthos quantity fluctuation.We simulated the fluctuated trend of macrobenthos abundance,biomass and secondadry production in different times,different groups and different regions based on the non-linear regression model,y(28)a(10)b?t(10)c?cos[2p/T ?(t(10)d)].According to the results,temporally,the abundance,biomass and secondary production of macrobrnthos population,Mollusca,Polychaeta and Echinoderm all decreased in 1982-2015.The abundance,biomass and secondary production of whole macrobrnthos,Mollusca,Polychaeta and Crustacean except the biomass of Echinoderm all increased in 1982-2000,and the abundance,biomass and secondary production of whole macrobrnthos,Mollusca,Polychaeta,Crustacean and Echinoderm decreased in 2000-2015.Spatially,the abundance,biomass and secondary production of macrobenthos population and main groups were decreased gradually at the top area of the bay,except for the increases of the abundance of Crustacean.At the central bay,the abundance,biomass and secondary production of macrobenthoos population and main groups showed a decreasing trend.There were more complicated for the fluctuated trend of the abundance,biomass and the secondary production of macrobenthoos population and main groups at the outer area of the bay.The abundance and secondary production of whole macrobrnthos showed an increasing trend,howeerver,the biomass exhibited an opposite trend.The abundance and biomass of the main group were consistent with the whole macrobenthos.The secondary production of Mollusca,Echinoderm and Crustacean decreased in recent 30 years,while those of Polychaeta showed an increasing trend.3.The relationship between the quantity of macrobenthos and environmental fatorsBased on generalized additive model and generalized linear model,we analyzed the relationship between the abundance,biomass and secondary production of macrobenthos and environmental factors in Daya Bay.The results showed that the generalized additive model(GAM)is better than the generalized linear model(GLM),which can more effectively explain the relationship between quantity of macrobenthos and environmental factors.According to the results,the abundance,biomass and secondary production of macrobenthos were significantly influenced by the transparency,temperature,salinity,offshore distance,the content of dissolved oxygen and chlorophyll a in the water,the content of sulfide and petroleum in the sediment.