Aquatic Sciences Meeting, Albuquerque 2001

SS36 Dealing With Scales in Aquatic Ecology: Structure and Function in Aquatic Ecosystems (Spatial and Temporal Connections)

Date: Tuesday, February 13, 2001, Time: 10:00:00 AM

Location: San Miguel

O'Reilly, C, M, University of Arizona, Tucson, USA, coreilly@geo.arizona.edu

Hecky, R, E, University of Waterloo, Waterloo, Canada, rehecky@sciborg.uwaterloo.ca

Cohen, A, S, University of Arizona, Tucson, USA, acohen@geo.arizona.edu

An upside-down food web: The problem of time-integration across trophic levels

The ease of stable isotope analysis makes them an appealing tool, but care must be taken in interpretation of the results. We examine the effect of time lags across trophic levels in the incorporation of recent production into the food web. In stable isotope ecology, the response time to an environmental perturbation depends on tissue turnover rates, which generally increase with consumer size. The pelagic food web in Lake Tanganyika, East Africa, provided an excellent example of the effect of variable time delays through the pelagic food chain. The isotopes show a slight depletion of heavy nitrogen from phytoplankton to secondary consumers instead of the expected enrichment. We interpret the isotope signatures of these lower trophic levels to be an indicator of a recent upwelling event. If such events are ephemeral, the larger, higher trophic levels will have only a muted response and will reflect the mean isotopic value of the lower food web. This study illustrates the importance of understanding temporal variation of different trophic levels and the potential effect of time lags in stable isotope ecology.

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Aquatic Sciences Meeting, Albuquerque 2001

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