Stable isotopes: new tool for the study of aquatic food webs

Stable isotopes, in particular of nitrogen and carbon, are a new tool to study the structure of food webs in aquatic ecosystems. These isotopes show characteristic enrichment when organic material is passed from one step in the food chain to the next. Moreover, the isotopic composition of organisms provides information on the origin of their resources. Scientists in the Department of Physiological Ecology of the Max Planck Institute for Limnology used this method to show how carbon from methane produced in lake sediments is transferred through bacteria and midge larvae to spiders outside of the water. In another project, they were able to demonstrate that different morphotypes of the same fish species specialize on different habitat and food resources in a lake.