Food web structure of animal communities formed on seawalls of artificial islands in Osaka Bay as determined by analyses of carbon and nitrogen stable isotope ratios

Abstract

Coastal artificial structures are demanded for a consideration of environmental protection in recent years. Although gradually sloped seawalls were adopted in various parts of Japan, little is known on the food web of the community around such structures. In the present study, the food web and food source were estimated on the seawalls of artificial islands in Osaka Bay as determined by analyses of carbon and nitrogen stable isotopes. Clustering of δ¹³C and δ¹⁵N values of animals on the seawalls showed five feeding groups: fish, suspended feeders, suspended and surface deposit feeders, carnivores and herbivores. The dual isotope plot of δ¹³C and δ¹⁵N showed that the three food sources (phytoplankton, microbenthic algae and macrobenthic algae) were eaten by herbivores, suspended feeders, surface deposit feeders, and that these animals were ingested by carnivores and fish, both occupying the highest trophic levels.