Changes Of Habitat And Fishery Biodiversity In The Yellow River Estuary And Adjacent Waters

The Yellow River flows into the Bohai Sea from Dongying city,Shandong Province.The basin is rich in nutrients and is the main breeding site,spawning ground and feeding ground of Marine biological resources.However,in recent years,due to environmental pollution,coastal development and overfishing,the biological resources in the Yellow River estuary and its adjacent waters tend to be degraded,and there is a possibility of Marine habitat fragmentation.Therefore,in May 2020,August and September respectively the bottom trawl surveys in the region,with the help of satellite remote sensing data analysis,the number of species and site survey of fishery resources CPUE spatial overlay analysis,divided fisheries habitat,study of fishery biology characteristics and distribution,proven swimming animal community structure changes and its influencing factors.Combined with relative importance index and Marine biodiversity correlation index,the composition of fishery community and biodiversity characteristics were analyzed.The specific results are as follows:In the study area,the ρ（Chl-a）of the Yellow River estuary and its adjacent area has an obvious step-change,the ρ of the near coastal area is higher than that of the far coastal area,and gradually decreases from the near shore to the middle of the sea area,showing a distribution characteristic of high in the south and low in the north,high in the east and low in the west.The average ρ（Chl-a）values of the three survey months all appear in the southern sea area.The average SST increased firstly and then decreased with the seasonal change.The average SST high value in May and August appeared in the estuary and the southern sea area（the highest value in the estuary）,and the average SST high value in September only appeared in the estuary.On the one hand,the coastal waters are shallow and full of nutrients,which is suitable for phytoplankton reproduction.On the other hand,anthropogenic pollutant discharge in coastal areas leads to the sharp increase of nitrogen,phosphorus and other elements in local sea water,the intensification of eutrophication in water and the explosion of phytoplankton,all of which can lead to the increase of ρ（Chl-a）and SST.Human activities,such as overfishing and land-based sewage,can affect the physical and chemical environmental factors of the habitats in the Yellow River Estuary and adjacent waters,resulting in the differences of habitats.The reproduction and development of fishery resources have certain requirements on the flow rate,velocity and water depth of the estuary.Salinity and water temperature are important environmental factors in the Marine environment.Based on the catch data,the ecological cluster analysis of the Yellow River Estuary and its adjacent waters was carried out.The habitats in May,August and September were divided into four habitat groups,respectively.In May,it was found that the distribution of each fishery habitat was continuous and intact,and the productivity level was relatively high.In August,the habitats were concentrated,mainly distributed from the mouth of the Yellow River to the southern area of Laizhou Bay,while the dispersal degree was high in the northern and eastern areas of Laizhou Bay.In September,the degree of habitat dispersion decreased significantly,and was more concentrated than that in August.The difference degree of fishery habitat decreased gradually,the commonness of some stations strengthened,and the overall spatial distribution of fishery habitat group improved.Four base habitats were classified based on the high similarity maintained over 55% in each group over the three survey months.They are the western area of Laizhou Bay（stations 11,13,14,15,16）,the coastal area of the Yellow River Estuary（stations 5,7）,the eastern area of Laizhou Bay（stations 17,18,21,22）,and the southern area of Laizhou Bay（stations 19,20）.The center of basic habitat was located in the southern part of Laizhou Bay,and the survey site in the southern part of Laizhou Bay was less affected by environmental factors such as temperature and salinity,thus showing a small seasonal difference.Besides,the swimming organisms were constantly adapting,adjusting and changing while the environment was changing.As a result,the basic habitat maintained a relatively stable community structure in all three months.The diversity index of swimming community in the three survey months had a smaller range,and the species diversity and richness of swimming community in September were higher than those in August,which to some extent reflected that the diversity of swimming community was stable in different seasons in the Yellow River Estuary.A total of 101 species of swimming animals were found,including 54 species of fish,38 species of crustaceans and 9 species of cephalopods,respectively.According to the habitat,61 species of benthic life were caught,followed by 31 species of bottom organisms,and 9 species of middle-upper organisms.According to the classification of temperature suitability,the caught organisms can be divided into 59 warm species,15 warm water species,4 cold water species,6 cold temperature species and 17 eurythermic species.The fishery resources near the Yellow River mouth and the southwest of Laizhou Bay were higher,and the distribution integrity and regularity were stronger.The number of biological species in the Yellow River Estuary was at a low level as a whole,and the biomass decreased significantly in spring due to the decline of major economic species resources.In September,the number of species protected by policies such as summer fishing ban,proliferation and release increased.Habitats for swimming animals were further restored and expanded.However,after the start of fishing on September 1,the population of propagating and releasing populations and the species of high economic value were heavily fished,resulting in a serious decline in the resources of the main economic species.As a result,the community composition of swimming organisms in the Yellow River Estuary and its adjacent waters changed,and the spatial distribution showed regional differences.The numbers of dominant species,important species,common species,common species and rare species in May,August and September were 3,7,8,14,10,16,21,14,23,16,16,17,25,21,20,respectively.The number of dominant species in May was significantly lower than that in August and September,and the biomass of dominant species accounted for less than 15% of the total biomass,which fully reflected the characteristics of simple community structure and single dominant species composition in the Current Yellow River estuary and its adjacent waters.