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Marine Ecology Progress Series

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MEPS 216:167-179 (2001)  -  doi:10.3354/meps216167

Copepod foraging in patchy habitats and thin layers using a 2-D individual-based model

Andrew W. Leising*

University of Washington, School of Oceanography, Box 357940, Seattle, Washington 98195-7940, USA

ABSTRACT: Evidence has shown that thin, horizontally extending phytoplankton layers may be comprised of smaller high-concentration aggregations of phytoplankton, rather than a homogeneous high-concentration sheet. A 2-D (horizontal and vertical dimensions) individual-based model of copepod foraging was developed, in order to examine whether the foraging success of a copepod would be significantly affected by phytoplankton patchiness. The foraging rules for the simulated copepods were to decrease speed and increase turning angle when high food concentrations are encountered. The underlying distributions of phytoplankton used in the model were, for the patchy layer scenario, representations of raw 2-D field fluorescence obtained using the Optical Serial Section Tomography (OSST) device, and for the homogeneous layer scenario, distributions created by simulated vertical sampling of the OSST distributions with a CTD/Fluorometer. In both the patchy and homogeneous layer scenarios, the copepods always had higher net foraging efficiency than randomly behaving controls, suggesting that the simple behavioral rules adopted are advantageous for copepod-like organisms. Foraging efficiency was significantly greater for the patchy layer scenarios than for the homogeneous layer scenarios when patches were small (i.e. one step length in width) and intense (i.e. near ingestion-saturating concentrations). Ingestion was up to 30% higher in the most patchy case versus its paired homogeneous case, suggesting that the existence of patchiness is critical to copepod survival, and that sampling scales should not exceed the step length of a copepod.

KEY WORDS: Acartia · Foraging · Area-restricted search · Thin layers · Copepods · Individual-based model

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