MEPS 334:131-143 (2007)  -  doi:10.3354/meps334131

ABSTRACT: The trophic importance of different primary organic matter sources to macroinvertebrates was studied in the intertidal salt marsh (Scirpus triqueter) habitat of the Nakdong River estuary (Korea) using carbon and nitrogen stable isotope ratios. δ¹³C and δ¹⁵N values of primary producers and dominant invertebrates, along with their biomass or abundance, were monitored monthly from December 2004 to November 2005. S. triqueter flourished from spring to summer and vanished in late fall to winter. Biomass of microphytobenthos peaked in late spring to summer. Of 25 taxa of macrozoobenthos collected, 7 were found throughout the year. Despite a dramatic seasonal fluctuation in the marsh club-rush S. triqueter biomass, the expected seasonal change in the isotopic signatures of the 7 dominant macroinvertebrates was not found. A large gap (3.5 to 12.3‰) in the δ¹³C signature between S. triqueter (–27.9 ± 1.0‰) and the marsh-dwelling macroinvertebrates (means from –24.4 to –15.6‰) indicates little utilization of this marsh-derived organic matter by the animals. Surface grazers and deposit feeders (e.g. Hediste japonica, Heteromastus filiformis, Angustassiminea castanea, Ilyoplax pusilla and Paranthura sp.) had δ¹³C similar to δ¹⁵N and about 4‰ higher than those (–16.5 ± 2.1 and 8.7 ± 1.1‰, respectively) of microphytobenthos, revealing that mainly microphytobenthos-derived carbon contributed to their diets. Two suspension-feeding bivalves (e.g. Laternula marilina and Corbicula sp.) showed a similar δ¹³C to that of suspended particulate organic matter (POM) in the channel (–23.0 ± 0.7‰) and the Nakdong River (–24.5 ± 1.9‰). However, their δ¹⁵N values are about 4‰ higher than that of channel POM (5.7 ± 0.6‰), but lower compared to that of river POM (–11.6 ± 2.3‰), suggesting that organic matter derived from coastal phytoplankton, not river discharge, is a major nutritional source for these bivalves. Overall, our isotopic data suggest that the S. triqueter-marsh invertebrates are generally more dependent on organic matter derived from algal sources than on S. triqueter or terrestrial sources.

KEY WORDS: Scirpus triqueter · Salt marsh · Stable isotopes · Food source · Macroinvertebrate · Microphytobenthos