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Della Ripa, L. A., Univ. California, San Diego, La Jolla, USA, ldellari@ucsd.edu
Landry, M. R., Scripps Institution of Oceanography, UCSD, La Jolla, USA, mlandry@ucsd.edu
Décima, M. ., Scripps Institution of Oceanography, UCSD, La Jolla, USA, mdecima@ucsd.edu
Bradley, C. J., University of Hawaii at Manoa, Honolulu, USA, cjbradle@hawaii.edu
Popp, B. N., University of Hawaii at Manoa, Honolulu, USA, popp@hawaii.edu

PREDATOR:PREY SIZE RELATIONSHIPS IN PELAGIC ECOSYSTEMS: TESTING THE 10:1 HYPOTHESIS WITH MESOZOOPLANKTON FROM THREE REGIONS

Size-based theories of energy flow in pelagic marine ecosystems, as well as numerous conceptual models, assume that predators and prey are linked, on average, by a body length ratio of 10:1. We tested this hypothesis using bulk N and Compound-Specific Isotope Analyses (CSIA) on zooplankton in the 0.2 to 5 mm size range collected from three biogeochemical systems: the California Current Ecosystem (CCE), the Costa Rica Dome (CRD) and the subtropical North Pacific (Stn. ALOHA). Bulk δ15N values reflect substantial regional differences in the dominant N cycling processes, which vary from N2 fixation (Stn. ALOHA) to denitrification (CRD). However, the slopes of bulk δ15N versus size suggest that a 10-fold size difference corresponds to ≈½ of a trophic level, implying a mean predator:prey size ratio in natural systems ≈100:1. CSIA corrects for source N differences among regions and size classes, but does not markedly alter this conclusion. CSIA assessments of trophic position versus size strongly overlap for the three regions. If these results are generalizable, energy transfer to higher trophic levels of ocean systems may be substantially more efficient than previously considered.

Session #:123
Date: 2/23/2012
Time: 08:45
Location: Ballroom A

Presentation is given by student: No