Trophic importance of meiofauna to polychaetes in a seagrass ( Zostera marina) bed as traced by stable isotopes

Stable carbon and nitrogen isotope ratios of benthic invertebrates and their potential food sources, such as suspended particulate organic matter (POM), benthic microalgae, attached algae and seagrass, were identified in Dong-dae Bay during the winter. The carbon stable isotope ratios demonstrate that filter feeders, such as oysters (-19.5 +/- 1.0 parts per thousand), use benthic microalgae (-21.2 +/- 0.2 parts per thousand) as a major food, and polychaetes such as Glycera spp. (-14.0 +/- 0.6 parts per thousand) preferentially use meiofauna, such as nematodes (-14.0 +/- 0.4 parts per thousand) and copepods (-13.3 +/- 1.0 parts per thousand). These meiofauna may feed on mixed resources (including bacteria) with the isotope ratios between benthic microalgae (-21.2 +/- 0.2 parts per thousand) and seagrass (-9.3 +/- 01.0 parts per thousand). These findings are consistent with the trophic enrichment in the nitrogen isotope ratios (by 3-4 parts per thousand) between consumers and food sources. Moreover, the results of the MixSIR model based on the observed isotope ratios suggest a large seagrass contribution to the food sources of benthic organisms such as meiofauna (similar to 53.7-62.6%) and macrobenthos (similar to 41.1-68%) through the food web. This model additionally suggests a relatively large contribution of benthic microalgae to the food sources of filter feeders (i.e. 26.4% for oysters).