Food web structure in a Salix subfragilis dominated wetland in Hangang estuary using stable isotopes and fatty acid biomarkers

Abstract

We investigated food webs of a Salix subfragilis-dominated wetland in the Janghang wetland in the Hangang estuary, which is very close to the Demilitarized Zone, along the west coast of Korea. Our study focused on understanding sesarmine crab (Sesarma dehaani)-related food webs in a S. subfragilis forest. For our study, we used carbon and nitrogen stable isotopes and fatty acid biomarkers. We collected samples of plants, animals, and detrital sediment from four quadrats (5 x 5 m(2)) set in the S. subfragilis community. Samples were collected from September 2006 to June 2009, except during the winter hibernation period of S. dehaani. In the wet season, the sediment showed relatively high delta C-13 and low delta N-15 signatures compared with relatively low delta C-13 and high delta N-15 signatures in the dry season. Mature S. dehaani appeared to feed on fresh leaves and other carbon sources, such as immature individuals or fish, in addition to detrital sediment, which appeared to be the main carbon source for immature crabs. Principal component analysis of fatty acid biomarkers of S. dehaani showed a clear difference between immature individuals (10-30 mm) and mature ones (larger than 30 mm), indicating that the main food source for immature crabs was detrital sediment, whereas mature crabs foraged plants in addition to consuming detrital sediment. On the basis of our results from stable isotope and fatty acid analyses, mature S. dehaani appeared to feed on detrital sediment and fresh leaves of S. subfragilis in summer in addition to engaging in cannibalism of immature individuals.