Liu Jiashou

Status and historical changes in the fish community in Erhai Lake

Erhai Lake is the second largest freshwater lake on the Yunnan Plateau, Southwest China. In recent decades, a number of exotic fish species have been introduced into the lake and the fish community has changed considerably. We evaluated the status of the fish community based on surveys with multimesh gillnet, trap net, and benthic fyke-net between May 2009 and April 2012. In addition, we evaluated the change in the community using historical data (1952–2010) describing the fish community and fishery harvest. The current fish community is dominated by small-sized fishes, including Pseudorasbora parva, Rhinogobius giurinus, Micropercops swinhonis, Hemiculter leucisculus, and Rhinogobius cliffordpopei. These accounted for 87.7% of the 22 546 total specimens collected. Omnivorous and carnivorous species dominated the community. A canonical correspondence analysis (CCA) plot revealed that the distribution of fishes in the lake is influenced by aquatic plants, water temperature, pH, and season. The abundance of indigenous species has declined sharply, and a majority of endemic species have been extirpated from the lake (a decrease from seven to two species). In contrast, the number of exotic species has increased since the 1960s to a total of 22 at present. The fishery harvest decreased initially following the 1960s, but has since increased due to the introduction of non-native fish and stocking of native fish. The fishery harvest was significantly correlated with total nitrogen, not total phosphorus, during the past 20 years. Based on our results, we discuss recommendations for the restoration and conservation of the fish resources in Erhai Lake.

Response of rotifer community to environmental changes in five shallow lakes in the middle reach of Changjiang River, China

We evaluated the response of a rotifer community to environmental changes in five shallow lakes in the middle reach of the Changjiang (Yangtze) River in summer and autumn 2010. These five lakes differed in trophic status and rotifer community structure. Twenty-nine rotifer species were collected, of which Keratella cochlearis, Polyarthra dolichoptera, and Trichocerca elongate were dominant. The mean density, Shannon-Wiener diversity, and equitability among the five lakes differed significantly (P<0.05). The mean rotifer density was positively correlated with trophic state. The diversity was higher in lakes with high macrophyte coverage. The composition of rotifer species was closely associated with the trophic gradient. Five environmental variables, Secchi depth, conductivity, TN, NH4-N, and TP, significantly affected the composition of rotifer species. Keratella quadrata, Brachionus calyciflorus, and B. forficula were more common in eutrophic conditions. Our results suggest that eutrophication has a significant influence on the rotifer community structure and highlight the potential for using rotifer community structure as an indicator of trophic status in subtropical lakes.

Community structure of rotifers in relation to environmental factors in Lake Hongze

The spatial-temporal changes in rotifer species composition and community structure and their relationship with key environmental factors were investigated seasonally from May 2010( spring) to February 2011( winter) in a shallow freshwater lake,Lake Hongze,China.Totally 34 species of rotifer,belonging to 17 genera,were identified during the seasonal sampling.Keratella cochlearis,Asplanchna priodonta,Polyarthra dolichoptera,Brachionus calyciflorus and Keratella valga were the dominant species.Lake Hongze has three main areas that are Chengzihu,southwest and east area.The rotifer distribution in the three main areas was significantly different.There were 27,26 and 19 species in Chengzihu,southwest,east area,respectively.Meanwhile,the maximum density and biomass of rotifers was found in the southwest area of Lake Hongze while the minimum was found in the east area.In terms of seasonal variation,the density and biomass of rotifer was highest in spring,with higher values in autumn.The density and biomass in summer was lowest in the four seasons.Their relationship with environmental factors was analyzed using canonical correspondence analysis( CCA).From the result of CCA,environmental factors such as water temperature,dissolved oxygen and chlorophyll-a that representing seasonal variations of water quality were significantly correlated with the Axis 1 and affected the composition and the density of rotifer community.Moreover,environmental factors related to nutrient concentrations such as total phosphorus,total nitrogen and dissolved inorganic nitrogen were also important nutrient factors which influenced the community structure of rotifer of Lake Hongze.