2025 Volume 89 Issue 3 Pages 151-162
To investigate the effects of topographical differences on biological communities and production of the planktonic food web in surf zones, we conducted monthly surveys from November 2022 to October 2023 at 17 sandy beaches on Obama and Takahama Bays. Water temperature, salinity, nutrient (dissolved inorganic nitrogen: DIN and phosphorus: DIP), and chlorophyll-a concentrations, copepod density, and larval and juvenile fish communities were measured. In Obama Bay, compared to Takahama Bay, water temperatures tended to be lower in winter and higher in summer, and salinity was generally lower throughout the year. A generalized linear model analysis was conducted using four explanatory variables: temperature, salinity, distance from the bay mouth, and bay (Obama or Takahama). In the best models, three or four of the explanatory variables were included. Salinity had a negative effect on DIN and DIP concentrations, and a positive effect on densities of copepod nauplii and copepods (including copepodids and adults). Distance from the bay mouth had a negative effect on fish density and number of fish species. These results suggest that the main factors determining densities and production processes differ among biological communities belonging to different trophic levels, and that the interactions between the lower and higher trophic levels are not clear.
