| Daya Bay is an important economic region which located in the eastern part of Guangdong Province.Human activities such as fishing and waterway transportation change its ecological structure and function.Therefore,making assessment and utilization of fishery resources sustainably require researching interactions between ecosystem and functional groups.study on the food web structure and its energy cycle will be benecial to understand the fisheries ecosystem status,changes and trend of fishery resources in Daya Bay,will be provide the necessary basic data and technical support for the sustainable utilization of fishery resources and ecosystem protection.(1)Ecopath with Ecosim(Ew E 6.4)software was applied to study energy flow,general characteristics and food web structure in the whole ecosystem.Daya Bay ecosystem was divided into 18 functional groups and 1 detritus group based on the 2012 survey data of fishery resources and eco-environment.The results showed that trophic levels in Daya Bay ecosystem rendered the pyramid structure,and the trophic levels of the functional groups varied from 1 to 3.29.There were two main channels of the food chain.One was the grazing food chain,and the other was the detritus food chain.The conversion efficiency among trophic levels in Daya Bay ecosystem was low,with the total energy transfer efficiency being just 8%.The total system throughput of the ecosystem was 6 249.573 t?km-2?year-1.The total production was 2 827.584 t?km-2?year-1.The total net primary production was 2 468.36 t?km-2?year-1.The ratio of total primary productivity to total respiration(TPP/TR)was 2.185.Finn’s cycling index and the mean path length of the energy flow were 4.8% and 3.53,respectively.Connectance Index and System Omnivory Index were 0.324 and 0.174,respectively.In a word,the Daya Bay ecosystem is at an immature stage which has simple food web,low maturity and poor stability.Urgent need to increase environmental protection and fishing restrictions.(2)To find out the trophic relationships among main biological groups in the offshore foodweb of Daya Bay,this study stable isotope analyses were employed to explore the trophic spectrum of the food web in Daya Bay based on the data collected from four surveys of 2015~2016.Results showed that there was no significant correlation between different seasons of the swimming animals and δ13C values andδ15N values(P>0.05).There was no significant correlation between different seasons of the shellfish andδ15N values(P>0.05)and there was significant correlation between different seasons of the shellfish andδ13C values(P<0.05).There was no significant correlation between different station of the shellfish andδ13C values and δ15N values(P>0.05).There was correlation between the ratios of δ13C and δ15N(r=0.16,P=0.022).Cluster analysis showed that the major species in the food web of Daya Bay were classified into four trophic groups: suspended matter,primary producers and primary consumers,secondary consumers and top predator.According to the species partition of the Daya Bay major biological trophic levels,the fishes ranged from 2.45(Trachurus japonicas)~ 3.98(Gerres lucidus);The shrimp and crabs ranged from 3.55(Charybdis feriatus)~2.55(Portunus pelagicus);The shellfishs ranged from 3.72(Trochus maculatus)~ 1.61(Nerita costata Gmelin);The seaweeds ranged from 1.97(Dilophus okamurae)~0.84(Amphiroa dilatata).(3)This study stable isotope analyses were employed to explore the trophic spectrum of the food web in Daya Bay based on the data collected from four surveys of 2015~2016.Results showed that there was no significant correlation between different seasons of the swimming animals and δ13C values and δ15N values(P>0.05).There was no significant correlation between different seasons of the shellfish and δ15N values(P>0.05)and there was significant correlation between different seasons of the shellfish and δ13C values(P<0.05).There was no significant correlation between different station of the shellfish and δ13Cvalues and δ15N values(P>0.05).There was correlation between the ratios of δ13C and δ15N(r=0.16,P=0.022).Cluster analysis showed that the major species in the food web of Daya Bay were classified into four trophic groups: suspended matter,primary producers and primary consumers,secondary consumers and top predator.The fishes in different quarter are basically on the top predator.The trophic level of Mauritia Arabica changes in large scale.On account of reducation of fish trophic levels,Mauritia Arabica is on the top predator during the March.Due to seasonal changes in the cycle,there are obvious changes in Phytoplankton;Zooplankton;Bacillariophyceae;Sargassum;SOM;POM.According to the species partition of the Daya Bay major biological trophic levels,the fishes ranged from 2.45(Trachurus japonicas)~ 3.98(Gerres lucidus);The shrimp and crabs ranged from 3.55(Charybdis feriatus)~2.55(Portunus pelagicus);The shellfishs ranged from 3.72(Trochus maculatus)~ 1.61(Nerita costata Gmelin);The seaweeds ranged from 1.97(Dilophus okamurae)~0.84(Amphiroa dilatata).(4)In this study,we investigated the fatty acid compositions and stable isotope of primary producer and Anthocidaris crassispina in Daya Bay,which showed that δ15N value of Anthocidaris crassispina was stabilization and δ13C value was changes greatly.In addition,the composition of fatty acids in Anthocidaris crassispina was not significant in different season,and saturated fatty acid and poiyunsaturated fatty acids were very nearly the same and few differences from season to season.Anthocidaris crassispina is mainly feeding large seaweed in February and May and feeding POM and benthic diatoms in August and November,but basically not feeding zooplankton.Cluster analysis and MDS analysis showed that the purple sea urchins were self-contained and the same type of algae stable isotope ratio and fatty acid characteristics were not correlated. |
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