MEPS 346:127-141 (2007)  -  DOI: https://doi.org/10.3354/meps07010

ABSTRACT: To evaluate the relative importance for the macrobenthos of possible food sources, including riverine particulate organic matter, reeds, benthic microalgae, seaweeds, coastal phytoplankton and aquaculture-derived matter, over 194 macrofaunal species were collected from 9 intertidal and subtidal stations along the axis of Gokasho Bay, Japan, and their isotopic compositions analyzed. The δ¹³C values for terrestrial organic matter were very different from those of the consumers (>5‰), suggesting a negligible trophic role for this source. Differences in δ¹⁵ N between seaweeds and primary consumers were small, suggesting a minor contribution of seaweeds. The δ¹³C values of the majority of consumers fell between coastal phytoplankton and benthic microalgae, allowing the calculation of the relative contribution of these microalgae to the diets of consumers. The estimated contribution ratios and the between-site comparison of the δ¹³C value for the same species along the bay axis suggest a shift of the main food source from benthic microalgae on the mudflat to coastal phytoplankton at the subtidal seaward stations. Several consumers collected from the fish-farm area had enriched δ¹⁵N and depleted δ¹³C values relative to samples of the same species that occurred outside of the farm area. The δ¹³C values of the consumers at the fish farm were significantly more depleted than those at the other stations. These findings suggest that the consumers inhabiting the farming area incorporate ¹⁵ N-enriched fish meal and ¹³C-reduced cereals that are major constituents of fish feed.

KEY WORDS: stable isotopes · Macrobenthos · Benthic microalgae · Phytoplankton · Tidal flat · Fish farm