Aquatic Sciences Meeting, Albuquerque 2001

CS34 Trophic Dynamics

Date: Friday, February 16, 2001, Time: 8:30:00 AM

Location: Mesilla

Cohen, G, M, The University of Chicago, Chicago, USA, gmcohen@midway.uchicago.edu

Wooller, M, J, Carnegie Institution of Washington, Washington, USA, wooller@gl.ciw.edu

Hines, A, , Smithsonian Environmental Research Center, Edgewater, USA, hines@serc.si.edu

Fogel, M, L, Carnegie Institution of Washington, Washington, USA, fogel@gl.ciw.edu

ISOTOPIC INVESTIGATION OF TEMPORAL VARIABILITY IN AN ESTUARINE FOOD WEB.

Trophic interactions regulate carbon and nitrogen transfer in ecosystems, yet temporal variation in food web structure remains poorly understood. Stable isotope ratios of C and N were analyzed from Chesapeake Bay estuarine benthic and pelagic organisms on a weekly basis to determine how trophic structure varies temporally. Isotope data (d15N, d13C) were used to identify a classic phytoplankton (8.7, -25.2) zooplankton (11.1, -24.1) fish (14.3, -22.4) food chain. The clam Macoma balthica (11.7, -16.9) derived C from alternate sources. Isotopic fractionation between trophic levels varied significantly on a weekly time scale (e.g., fish d15N values spanned two trophic levels, from 13.2 to 15.4 during the study). Relative trophic structure remained fairly constant, however, over a ten-week period. Variations in stable isotope composition were correlated between trophic components (study organisms, muscle tissue, and gut contents), which is indicative of rapid integration of dietary C and N into body tissue. Because d13C and d15N fluctuate on short time scales, trophic studies with stable isotopes might be useful for detecting migrant fish species, bloom events, or other episodic ecosystem perturbations.

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Aquatic Sciences Meeting, Albuquerque 2001

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