Characteristics Of Invertebrate Community In The Yangtze Estuary And Its Relationship With Environmental Factors

Based on the bottom trawl surveys in the Yangtze River Estuary and its adjacent waters in May and November from 2013 to 2017,we discussed the variation characteristics of resources and community structure of invertebrates and their relationship with environmental factors in order to grasp the changes of invertebrate resources in the Yangtze Estuary in recent years and the influence mechanism of environmental factors on community structure.The main results were as follows:A total of 33 species were collected in five spring voyages belonging to 2phylums 4 classes,7 orders,and 15 families.With 19,25,20,17,and 13 species collected from 2013 to 2017 respectively,crustaceans were dominant in every year.The dominant species was determined by Index of relative importance(IRI),including Loliolus japonica,Portunus trituberculatus,Ovalipes punctatus?Acetes chinensis and Palaemon gravieri,of which,the Portunus trituberculatus had the highest IRI in every year.All Margalef's species richness index(D),Shannon-Wiener diversity index(H')and Pielou's evenness index(J')reached the lowest value in 2015,but only J'had significant annual variations.Both invertebrate abundance(66.87kN/km~2)and biomass(205.41kg/km~2)peaked in 2014 which were also significantly higher than other years.ANOSIM analysis showed that the annual variation of invertebrate community was significant,and the significance level of sample statistic between each year was higher than 70%.The characteristic species according to the SIMPER analysis included Portunus trituberculatus,Loliolus japonica,Trachypenaeus curvirostris,Charybdis bimaculata,Crangon affinis,Acetes chinensis,Sepiola birostrata,Ovalipes punctatus and Palaemon gravieri,of which,Portunus trituberculatus and Loliolus japonica were typical species with high contribution of average similarity in each year.The results of Canonical correlation analysis(CCA)showed that depth,dissolved oxygen,temperature and salinity were key environmental factors structuring the invertebrate community in spring.The spatial difference is mainly driven by the depth,while the temporal difference is mainly driven by dissolved oxygen,temperature and salinity.Invertebrate community was separated into two distinct assemblages,stratified by depth,corresponding to the shallow assemblage and deep assemblage.The invertebrate biodiversity,abundance and biomass were different between two assemblages but without significant difference,while the environmental factors showed significant spatial difference.In autumn,26 species were collected belonging to 2 phylums,2 classes,5 orders and 11 families,of which 22,15,15,14 and 18 species were collected in five years respectively and crustaceans were dominant with 19 species.Dominant species included Oratosquilla oratoria,Portunus trituberculatus,Charybdis bimaculata,Solenocera melantho,Palaemon gravieri,Metapenaeopsis dalei,Loliolus japonica and Trachypenaeus curvirostris.All Margalef's species richness index(D),Shannon-Wiener diversity index(H')and Pielou's evenness index(J')with significant annual variations reached the lowest and the highest value in 2015 and 2017 respectively.Invertebrate abundance and biomass were had the highest value in 2013 and were significantly higher than the other years with 19.7 kN/km~2 and 526.88 kg/km~2 respectively,the lowest value were found in 2017 with 0.88 kN/km~2 and 22.24 kg/km~2 respectively.ANOSIM analysis showed that the annual variation of invertebrate community in autumn was significant,and the significance level of sample statistic between each year was higher than 65%.The characteristic species included Oratosquilla oratoria,Portunus trituberculatus,Charybdis bimaculata,Solenocera melantho,Palaemon gravieri,Loliolus japonica and Trachypenaeus curvirostris,of which Portunus trituberculatus became the typical species in every year.Dissolved oxygen,temperature and salinity were key environmental factors shaping the invertebrate community in autumn as revealed by CCA analysis.Among them,the time variation is mainly driven by dissolved oxygen,temperature and salinity,the spatial differences in invertebrate communities in 2014 were mainly driven by dissolved oxygen and salinity,while the spatial differences in other years were mainly driven by temperature.According to the ANOSIM analysis,invertebrate community was separated into two distinct assemblages in each year,corresponding to the northern assemblage and southern assemblage.The invertebrate biodiversity,abundance and biomass were different between two assemblages but without significant difference,which was same as the characteristics in spring.The spatial variation of invertebrate biodiversity,abundance and biomass,as well as environmental factors between two assemblages had similar characteristics with spring investigation.A significant temporal and spatial changes existed in the composition of invertebrate species.The number of species in autumn was higher in spring in 2013and 2017,which was higher in spring from 2014 to 2017.Except for 2013,the number of species in the shallow waters in spring is higher from 2014 to 2017,which was higher in autumn in the northern seas.The highest values of invertebrate abundance and biomass in spring and autumn were in 2014 and 2013,respectively,with the lowest values occurring in 2017.As is revealed by CCA analysis,the spatial differences in community structure was significant with a significant difference between the deep waters and the shallow waters in spring and a significant difference between the northern area and the southern area in autumn which were consistent with the results of NMDS analysis.Invertebrate communities were significantly affected by temperature,salinity and dissolved oxygen in the Yangtze Estuary.