Stable isotope analyses of benthic organisms in Lake Baikal

Abstract

Stable isotope ratios of carbon and nitrogen were used successfully to elucidate the biogeochemical and ecological frameworks of the trophic structure of benthic organisms in Lake Baikal, Siberia. Analysis of the benthic animals showed a considerable variance in both carbon and nitrogen stable isotope ratios. Two main primary producers of benthic plants and planktonic organic matter were clearly differentiated by δ13C, and thus the diets of these two primary producers' groups could be analyzed with the use of a two source mixing model. The trophic position of each benthic animal was estimated by the analysis of δ15N. Contrasting characteristics between food webs in shallow and deep benthic areas were clearly observed on the δ13C – δ15N map. Food webs in shallow benthic areas were complex, and many primary producers and various animals were present with diverse isotope distributions. In contrast, food webs in deep benthic areas were composed of single organic matter origin exhibiting simple predator and prey relationships. Both δ13C and δ15N values of benthic gammarids were correlated with the sampling water depth. A trend of δ13C decrease and δ15N enrichment was observed with increasing water depth. The stable isotope ratios of the benthic animals indicated that the complexity of the food web structure in their ecosystem decreased as the depth of the water increased.