In Situ and Theoretical Analysis of Zooplankton Patch Dynamics

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Davis 9818661In-situ and Theoretical Analysis of Zooplankton Patch DynamicsZooplankton patchiness is a well-known phenomenon. Although patch spatial structure and its corre-lation with environmental variation has been well described, and theoretical explanations for it have been proposed, direct measurement of how patches form and persist has not been possible to date because of technological limitations. The investigators will conduct a focused field and modeling study to quantify the struc-ture, dynamics, and controlling mechanisms of dense copepod patches in eastern Cape Cod Bay. Using a combination of numerical modeling, high resolution biological and physical mapping, and in-situ behav-ioral observations, they will directly test the hypothesis that the patches form in a three-step process: 1) upward swimming enhances near-surface abundance, 2) surface convergence together with increased up-ward swimming rate further enhances abundance, and 3) high abundance in the convergence zone increases interneighbor detection rates which lead to increased aggregation behavior. During the field program, mea-surements will be made during different phases of the tidal cycle to examine formation of the patches due to the tidally driven convergence. Measurements of patch persistence after the convergence has dissipated will be indicative of the role of biological aggregation behavior in maintaining the patches. Direct in-situ observations of various components of copepod swimming behavior will be used together with environmental (CTD, fluorescence, attenuation, downwelling light) and fluid velocity data to determine parameter values for patch formation models. Patch formation in convergent flow will be modeled using a combination of two approaches: 1) high resolution 3-D numerical models of the region to quantify tidal and subtidal flow and convergence and 2) process models of patch formation and swarming that incorporate convergent flows. These calculations will be compared with the actual measurements of how the 3-D patch structure varies over time. The proposed work will shed new light on mechanisms of patch formation and maintenance in zooplankton.