TEMPORAL VARIATION OF FISH BIODIVERSITY IN POYANG LAKE

Biodiversity serves as an important index in reflecting the impact of environmental changes on ecological communities. It is also essential in evaluating the health and integrity of ecosystems, providing insights into management and conservation initiatives. The river-lake complex ecosystem in the middle and lower Yangtze River are one of the most threatened areas subjected to anthropogenic activities. However, there is still a lack of research on taxonomic diversity and general understanding of fish community and diversity changes in the Poyang Lake over a long time span. Based on data derived from fish resources investigation in 9 regions of the Poyang Lake area in April and July 2010, August 2018 and May 2019, we analyzed the temporal changes of species diversity, functional diversity and taxonomic diversity of fish communities in the Poyang Lake as well as the relationship between biodiversity and environmental factors. The results showed that 74 and 93 species of fish were collected in 2010 and 2018—2019, respectively. There were significant differences in community structure, with Coilia brachygnathus, Pseudobrama simoni, Carassius auratus, Pelteobaggrus nitidus and Cyprinus carpio contributed the most variance. There were also significant differences in environmental factors between different years and seasons (P<0.05). Although the species diversity and functional diversity in 2018—2019 were higher than those in 2010, the variations in functional diversity and taxonomic distinctness (Λ⁺) were insignificant, suggesting the taxonomic range has narrowed albeit the fish species has increased in the past decade. The randomization test of the average taxonomic distinctness index (Δ⁺) and the variation in taxonomic distinctness (Λ⁺) showed that the number of sampling localities below the 95% probability confidence funnel from 2018 to 2019 increased compared with 2010, indicating that the degree of interference in the Poyang Lake area increased. The fish biodiversity in the Poyang Lake area was significantly correlated with water temperature, chlorophyll and total suspended solids concentration (P<0.05). The biodiversity of fish community was positively correlated with water temperature. However, the average taxonomic distinctness index (Δ⁺) and the variation in taxonomic distinctness (Λ⁺) were negatively correlated with the chlorophyll and total suspended solids. The results showed that the number of fish species in the Poyang Lake has increased under the periodic fishing ban of the Yangtze River, breeding and releasing project and ecological regulations. However, the small-sized fishes were still the dominant species in fish communities in the Poyang Lake during the past decade. This could be attributed to over-exploitation. Besides, anthropogenic disturbance compromised habitat heterogeneity. In particular, regions that located far from the Yangtze mainstream like the Poyang county, Xinjian county and Yugan county were more impacted by human activities. In order to protect and restore fish diversity in the Poyang Lake as well as the flood plain habitats in the middle and lower reaches of the Yangtze River, we suggest to take a series of measures in complementary to the ten-year fishing ban, such as demolition of small hydro power plants, reduction of reclamation and restoration of natural habitats.