Temporal And Spatial Variation Characteristics Of Invertebrates In Yangtze River Estuary And The Relationship With Environmental Factors

The invertebrate community characteristics and the relationship between theinvertebrate community and the environmental factors in the Yangtze River Estuary andits adjacent waters were discussed using t-test, ANOVA, community ordination such asHierachical Cluster, non-metric Multi-Dimensional Scaling(NMDS), DetrendedCorrespondence Analysis (DCA), Canonical Correspondence Analysis(CCA) orRedundancy Analysis (RDA) according to the data from the invertebrate surveyscarried out during1998-2012in both spring and autumn.Invertebrates species captured in spring during1999-2012were identified to41species, belonging to6classes,10orders, and23families. The species number ofCrustacean was the largest (26species), followed by Molluscs (13species). Dominantinvertebrates included Loligo japonica, Portunus trituberculatus, Palaemon gravieri,and Trachypenaeus curvirostris, etc, taking at least80%from the total abundance.Significant inter-annual variations in invertebrate species abundance and diversity wereobvious in the estuary. Species abundance peaked in1999and2001, and showed a trendof decrease-to-increase after2004. There were2or3assemblage groups of invertebratein the estuary, which was formed by spatial distribution variations of indicator species.The variation in the invertebrate diversity can be divided into three periods.1999-2001featured high diversity, in2004-2007the diversity plunged to the bottom, and thediversity bounced back in2009-2012but still below the level of the1999-2001. Themain environmental factors affecting the invertebrate community were the bottomdissolved oxygen (1999-2001), the bottom chemical oxygen demand, the surface pH,the surface total nitrogen, the bottom total nitrogen (2004-2007), the surface totalnitrogen, the bottom temperature, the bottom salinity and the surface pH (2009-2012).Invertebrates species captured in autumn during1998-2012were identified to52species, belonging to5classes,10orders, and25families. Resembling to the results inspring, the species number of Crustacean was the largest (34species), followed byMolluscs (17species). Portunus trituberculatus, Loligo japonica, Charybdisbimaculata, and Trachypenaeus curvirostris, etc, taking at least70%from the totalabundance. Species abundance peaked in1998, decreased to the bottom in2004. Beingsimilar with the results in spring, there were also2or3assemblage groups ofinvertebrate in the estuary in autumn, different groups having different indicator species. The variation in the invertebrate diversity can be divided into three periods.1998-2002featured high diversity, in2004-2007the diversity plunged to the bottom, and thediversity bounced back in2009-2012but the Shannon-Wiener index (H’n) was stillsignificantly below the level of the1998-2002. The main environmental factorsaffecting the invertebrate community in autumn were the bottom total suspended matter,the bottom dissolved oxygen, the surface chemical oxygen demand, the surface totalnitrogen, the bottom total phosphorus (1998-2002)，the bottom pH (2003-2007), thesurface total suspended matter (2009-2012).Comparing the spring invertebrate community characteristics and environmentalfactors to the autumn, we found that (1) The number of species in autumn was higherthan in spring; Crustacean and Molluscs were the main invertebrate species in theYangtze River Estuary and its adjacent waters.(2) The dominant species are consistentin spring and autumn. The main dominant invertebrates included Loligo japonica,Portunus trituberculatus, and Trachypenaeus curvirostris, etc, which had a greatcontribution to the cummunity abundance. The annual variation trends of abundance inspring and autumn are relatively consistent, and2004had the lowest abundance.(3)There were2or3assemblage groups of invertebrate in the estuary in both spring andautumn.(4) The temporal variation in the invertebrate diversity successions can bedivided into three periods in both spring and autumn which had the time consistency.(5) There were great differences in the environmental factors of the Yangtze RiverEstuary and its adjacent waters at different periods and different seasons, whichindicated great environmental fluctuations.