| In this study,the Southwestern Yellow Sea ecosystem was taken as the research object,and the amount of offshore marine fishing in Jiangsu Province since 198 was analyzed.The nutrient structure of ecosystem was studied based on stable isotope analysis and ecological channel model,and the feasibility of the two methods was cross-validated.Among them,the analysis of long-term offshore marine fishing data can provide basic information for the change of key ecosystem populations.On this basis,by constructing two Ecopath models of the SYSE in different periods(2000 and 2008),and on the premise of the ecosystem structure and energy flow process in the basic coverage study area,the ecological network of the study area is analyzed,and the main conclusions are as follows.① Modelling results showed that the trophic level of all functional groups lies between 1-3.976 and 1-4.509 while the range of those functional groups.System energy was distributed into 7 integrated trophic levels.There were functional groups in the high,medium and low trophic levels of the SYSE during the two periods,and the structure of the trophic level was relatively complete.In 2000,the integrated trophic levels I and II accounted for 71.87%and 25.40%of the total flow debris,respectively.In 2008,the integrated trophic levels Ⅰ and Ⅱ accounted for 81.22%and 16.28%of the total flow debris,respectively.The results showed that the energy utilization of trophic level Ⅰ was weakened,while the utilization of trophic level Ⅱ was enhanced,the middle and high trophic levels of trophic level III and above were fully utilized,and the phenomenon of energy transfer obstruction should exist between the low trophic levelⅠ and Ⅱ of the system.In 2000 and 2008,the overall energy flow distribution of the S YSE presented a typical pyramid type,and the lower trophic level composed of debris and primary producers(phytoplankton)was the main source of system energy.It can be seen that the proportion of high trophic level in the system should be increased appropriately to make the ecosystem more mature and stable.② In 2000,the total conversion efficiency of the SYSE was 9.101%,which was lower than Linderman’s 1 to 10 conversion efficiency.The energy conversion efficiency between trophic level I to II and II to III was also lower than Linderman’s 1 to 10 conversion efficiency.In 2008,the total conversion efficiency of the SYSE was.13.22%,and the energy conversion efficiency between trophic levels was higher tha n Linderman’s 1 to 10 conversion efficiency.The conversion efficiency between low trophic levels was generally lower than that between high trophic levels in the SYSE during the two periods,which indicated that the energy of low trophic levels Ⅰ and Ⅱ in the SYSE was surplus and could not be fully utilized.③ In 2000,the total primary production to total respiration value was 1.979,and the total primary production to total biomass value was 44.964;in 2008,the total primary production to total respiration value was 2.541,and the total primary production to total biomass value was 50.326.The ecosystem maturity of the Southwest Yellow Sea in 2008 was lower than that in 2000,but both of them were at a lower level.Comparisons with other similar ecosystem parameters show that the functional groups of the SYSE are closely related,and the structure of food web is relatively complex,but it is still in a fragile,unstable and immature stage.④ Carbon and nitrogen stable isotope data of 56 species of marine organisms from 16 functional groups based on the experimental data of the Southwestern Yellow Sea and related research data of predecessors show that compared with the estimation of trophic level by Ecopath model,the nutrient level estimated by the Ecopath model was slightly higher in the low trophic functional group than in the stable isotope analysis,and slightly lower in the high trophic functional group than in the stable isotope analysis.The nutrient level of ecosystem functional group estimated by the Ecopath model is highly positively correlated with that estimated by the stable isotope 815N value of biological samples.Compared with the 2000,the linear correlation between the nutrient level of ecosystem functional group and that of stable isotope analysis is higher in 2008,which conforms to the principle of timeliness.The results show that both the Ecopath model and the stable isotope analysis method can determine the nutritional level of food web through cross-validation.This also proves that the food composition information of each functional group used in the Ecopath model is relatively accurate,and the stable isotope data of the ecosystem in this study can be used to simulate other similar ecosystems in the future.⑤Changes in offshore marine fishing volume in Jiangsu Province during 1985-2017,with 1997 and 2003 as the boundary,the total offshore marine fishing output in Jiangsu Province showed an obvious trend of first increasing and then decreasing.Fish is the main body of marine fishing in Jiangsu Province.The change trend of fishing output from 1985 to 2017 has a strong correlation with the total yield,showing a clear trend of first increasing and then decreasing.The annual output of shrimp and crab fishing showed a steady growth trend.In view of all economic fishing species,except for shrimp and crab species,since 2010,the annual marine fishing output has been stable in a certain range,and the annual variation of marine fishing output is very small compared with the previous.This indicates that the impacts of human activities on the marine ecosystem in Jiangsu offshore have been sustained for 33 years,and may affect or change the biological composition of the ecosystem to some extent. |
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