THE WATER-SEDIMENT REGULATION SCHEME ON THE COMMUNITY STRUCTURE OF ICHTHYOPLANKTON IN THE YELLOW RIVER ESTUARY

The rapid transfer of large amounts of water and sand to the Yellow River basin during the implementation of the Water-Sediment Regulation Scheme (WSRS) can significantly alter the physicochemical environment of the ecosystem in the Yellow River estuary and its surrounding sea areas. In order to understand the effects of WSRS on the community structure and spatial and temporal distribution patterns in the Yellow River estuary, a survey of ichthyoplankton was conducted in June and July of 2017 (a non-WSRS year) and 2018 (a WSRS year) using horizontal trawl methods. The results showed that a total of 6212 eggs and 431 larvae belonging to 14 genera and 12 families in 8 orders were collected during the six surveys. Cynoglossus joyeri was the main species controlling the succession pattern of ichthyoplankton community during the summer in the Yellow River estuary. WSRS exerted its influence on the ichthyoplankton community structure by changing the runoff, salinity and water temperature in the estuary. The dominant species, quantity, and diversity index of ichthyoplankton displayed fluctuations during the process of WSRS. The spatial distribution of fish eggs varied among investigation stages due to the combined effects of circulation and WSRS, with larvae tending to be distributed in nearshore waters of the estuary. The northeastern and southeastern part of the estuary, near Laizhou Bay, were the main aggregation areas of the ichthyoplankton community in the Yellow River estuary. In 2018, there was a significant increase in the number of ichthyoplankton and demersal fish eggs compared to 2017, as the abundant runoff and sediment brought by the water and sand transfer were favorable to replenish the fishery resources in the waters of the Yellow River estuary. The community structure of ichthyoplankton in the study area is closely related to salinity, water temperature, water depth, and plankton abundance. The environmental conditions played a crucial role in determining the habitat preferences of fish. The abundant freshwater and sediment transported by the Yellow River water and sand transfer constituted a close response relationship with the marine ecological environment and marine biological resources in its neighboring waters. With the accumulation of practical experience in water and sand transfer, it is suggested that we should further strengthen the attention to the optimization of water transfer and sand transfer in terms of its target, time and frequency in our future work.