The Non-marine Ostracods Quantitative Study Of Ecological Information In The Lakes Of The Middle And Lower Reaches Of The Yangtze River

Due to its well-preserved fossil records and sensitivity to environmental changes, etc, one of the microscopic crustaceans- ostracods were used to indicate the changes of paleoenvironment and paleoclimate in the globe. In this study, it was aimed to establish the ostracods ecological information database by investigating the information of the modern ostracods and environmental factors in the middle and lower reaches of the Yangtze River. Based on this database, we analyzed the relationship between ostracods and environmental factors and established an ostracod-based water temperture transfer function in this study. On the other hand, Yuandang lake and Dishui lake were also surveyed to analyze the response of ostracods to environmental change. The main conclusions have been summarized as follows:1. Ecological analysis of non-marine ostracods in the middle and lower reaches of the Yangtze RiverFourteen ostracod species were recorded from eleven lakes in the middle and lower reaches of the Yangtze River. They were:Cypria kraepelini、Ilyocypris salebrosa、Fabaeformiscandona sp.、Dolerocypria taalensis、Fabaeformiscandona myllaina、Cypris subglobosa、Vestalenula cylindrica、Fabaeformiscandona subacuta、 Darwinula stevensoni、Cypridopsis vidua、Fabaeformiscandona fabaeformis. Dolerocypris sinensis、Ilyocypris dentifera and Limnocythere inopinata. Among them, the dominant species were Cypria kraepelini and Fabaeformiscandona sp.. The results of canonical correspondence analysis showed that water temperture (Tw) played a most important role in ostracod distribution. A transfer function which was based on weighted averaging partial least squares regression (WA-PLS) was developed for water temperture (R2 jack=0.36325, root-mean-square-error of prediction [RMSEPjack]=1.6722, as assessed by leaveone-out cross-validation). Also, ostracods were sensitive to the change of total phosphorus (TP)、total nitrogen(TN)、 Transparency(SD) and Chlorophylla(Chla), so it could be excellent bioindicators of water quality.2. Ecological analysis of ostracods in the Yuandang lakeNine ostracod species (Cypria kraepelini、Fabaeformiscandona myllaina、Cypris subglobosa、Dolerocypria taalensis、Fabaeformiscandona subacuta、Bradleycypris vittata、Ilyocypris salebrosa、Cypretta turgida and Fabaeformiscandona sp.) were recorded from eight sampling points in the Yuandnag Lake during the period from December 2013 to November 2014. All over the year, the dominant species were Cypria kraepelini and Fabaeformiscandona sp.. Cluster Analysis and MDS Analysis showed the ostracod species were different in four seasons. Due to the change of water temperture, ostracod species could be divided into three main species assemblages. Among nine environmental factors, water depth(Dw) played a most important role in ostracods distribution.3. Canonical correspondence analysis of modern ostracods and environmental factors in the Dishui LakeDishui Lake, a new artificial lake with a low salinity of 1.4‰ to 2.0‰, can play an important role in reconstructing the evolution of the eastern Chinese Lakes by tracking its ecosystem. Living ostracods were studied in surface samples collected from this lake in order to investigate the relationship between ostracods and environmental factors. Thirteen ostracod species were found including 2 non-marine species and 11 marine species. They were:Cypridopsis vidua、Cypria kraepelini、 Albileberis sinensis、Dolerocypria mukaishimensis、Leptocythere ventriclivosa、 Neomonoceratina dongtaiensis、Neosinocythere elongata、Paradoxostoma nitida、 Sinocytheridea impressa、Sinopontocythere elongata、Spinileberis pulchra、Tanella opima and Spinileberis furuyaensis. The results of canonical correspondence analysis show an obvious correlation between ostracods and environmental factors. Among nine factors investigated, chlorophylla (Chla), total phosphorus (TP) and Electrical Conductivity (EC) played a most important role in ostracod distribution. The species with higher frequency of occurrence were more tolerant to environmental changes than that with lower frequency, while C. kraepelini and Neomonoceratina dongtaiensis are sensitive species in the Dishui Lake. Combined with historical data, we suggested that not only the natural environmental factors (conductivity, temperature, etc.), but also human-caused disturbance factors (including TP, TN) are playing an important role in the ostracods distribution.