MEPS 259:79-92 (2003)  -  doi:10.3354/meps259079

ABSTRACT: The role of benthic microalgae as the source of primary organic matter for the macrozoobenthos community was examined in 3 bay systems of the south coast of the Korean peninsula using stable carbon and nitrogen isotope ratios ( δ¹³C and δ¹⁵N) as a dual tracer. The δ¹³C and δ¹⁵N of riverine particulate inputs, primary producers and macrozoobenthos collected from the intertidal and subtidal habitats of the bays were measured and compared with those from adjacent offshore waters. Extensive intertidal flats occurred with wide marsh plains (primarily Phragmites australis) at the uppermost part of the intertidal zone in all 3 bay systems, but different hydrologic features were exhibited among bay systems. There were no systematic variations in δ¹³C for the same plant taxa, but different producer groups were clearly separated by their δ¹³C values. Benthic microalgae and macroalgae, which had similar δ¹³C values, were separated by their δ¹⁵N values. The δ¹³C values of macrozoobenthos collected from the offshore areas were similar to those of phytoplankton. Macrozoobenthos collected from all 3 bay habitats had similar δ¹³C ranges, and their δ¹³C values (means of all consumers, feeding types and species) were less negative than those of the offshore macrozoobenthos. Isotopic linkage between sources and benthic consumers, based on the documented trophic fractionation for C and N, indicated that benthic microalgae and phytoplankton are the major sources of organic matter supporting macrobenthic consumers in the bay systems. A 2-source mixing model revealed that pelagic feeders in both the intertidal and subtidal habitats subsisted in equal shares on marine phytoplankton and benthic microalgae, whereas the food source of benthic feeders was derived predominantly from benthic microalgae. Phragmites or riverine particulate inputs appeared to have made little contribution to the diets of consumers in the bay systems. Our collective isotopic data set suggested that benthic microalgae, along with phytoplankton, constituted the organic matter that forms the trophic base of pelagic as well as benthic food webs in the coastal bays, despite differing vegetational composition and hydrology.

KEY WORDS: Stable isotope ratios · Food webs · Benthic microalgae · Tidal flat · Macrozoobenthos · Korean coast