Variation in the Distribution Characteristics of Nemopilema nomurai in Relation to Marine Environmental Conditions

In this study, we examined the interannual distribution patterns of the giant jellyfish Nemopilema nomurai and their relationship with marine environmental factors using field survey data collected from the East China Sea from 2020 to 2024. Acoustic surveys and jellyfish-specific trawl sampling were conducted to analyze their vertical distribution characteristics in relation to water temperature, salinity, seawater density, and chlorophyll-a concentrations. The results revealed that N. nomurai were mainly distributed in the mid-to-lower water layers at depths of 40-60 m, particularly in areas with strong stratification between the surface and bottom waters. Temperatures and salinity at these depths were relatively stable, and jellyfish were concentrated within high-density layers (1024.6-1025.0 kg·m^-3). Correlation analysis revealed significant positive relationships between jellyfish occurrence frequency and salinity and seawater density, whereas no significant relationship was observed with water temperature. The chlorophyll-a concentrations varied between the years but did not directly correspond to the primary habitat depths of jellyfish, although synchronous variations in jellyfish abundance occurred in some years. These results indicate that the vertical distribution of N. nomurai is primarily controlled by physical oceanographic factors rather than by chlorophyll-a concentrations, reflecting an ecological adaptation for efficient energy use.