Environmental Factors Influencing the Species Composition of Larvae and Juvenile Fish at Geum River Estuary in the West Sea During Spring and Summer

This study investigated seasonal variations in species composition and abundance of fish larvae at six stations in the Geum River Estuary during spring and summer from 2019 to 2021, and examined the environmental factors influencing these variations. Water temperature, salinity, dissolved oxygen, precipitation, freshwater discharge, chlorophyll a, zooplankton density, and egg density were analyzed concurrently. In spring, egg density increased with higher salinity, while larval abundance was greater at stations with lower salinity. Larval abundance also showed a significant positive correlation with water temperature. In contrast, no significant relationships between larval or egg density and environmental factors were observed in summer, likely due to increased environmental variability caused by freshwater discharge and rainfall. Gobiidae dominated the larval assemblage throughout the study period, exhibiting extreme dominance in spring, whereas dominant taxa varied among years in summer. These results indicate that the Geum River Estuary functions as a relatively stable nursery ground in spring, but becomes environmentally unstable in summer under strong freshwater discharge effects. This study provides integrated information on the influence of freshwater discharge and seasonal environmental variability on larval fish assemblages.