Aquatic Sciences Meeting, Albuquerque 2001

SS15 Biomechanics: Making the Connection Between Physics and Biology at the Organismal Level (Disciplinary Connections)

Date: Thursday, February 15, 2001, Time: 10:15:00 AM

Location: Mesilla

Genin, A, , The Hebrew Univ. and InterUniversity Inst., Eilat, Israel, amatzia@vms.huji.ac.il

Jaffe, J, , MPL, Scripps Inst. Oceanography, La Jolla, USA, jules@mpl.ucsd.edu

Richter, C, , Center for Tropical Marine Ecology, Bremen, Germany, crichter@zmt.uni-bremen.de

Ahmed, A, A, National Inst. Fisheries & Oceanography, Cairo, Egypt,

Ohevia, M, , IUI, Eilat, Israel, moty@vms.huji.ac.il

Ayalon, I, , IUI, Eilat, Israel, inbal@vms.huji.ac.il

McGehee, D, , BAE Systems, San Diego, USA, duncan.mcgehee@baesystems.com

THE BEHAVIORAL RESPONSE OF ZOOPLANKTON TO DOWNWELLING: SIR ALISTER HARDY'S PLANKTON WHEEL REVISITED

Numerous observations indicate that zooplankton become aggregated in downwelling zones. Examples include oceanic fronts, Langmuir cells and internal waves. Surface aggregations were explained, long ago, as resulting from the buoyancy of floating organisms. However, to aggregate at depth, zooplankters need to actively swim against vertical currents, a mechanism for which no direct evidence has been obtained. In order to investigate this mechanism, we studied two coastal sites in the Red Sea where downwelling is commonly observed, primarily during winter when the upper column is not stratified. Here, zooplankton aggregations are greater by a factor of 2 to 10, compared with background (off-shore) densities. To test for depth-retention, we used FishTV-jr, a multi-beam 1.6 MHz sonar, designed to track in situ individual micro-zooplankton in 3-D. Preliminary results showed that zooplankters retained their depth under downwelling currents of 1-2 cm/s (as measured with injected flourescein dye). Unlike this response in the vertical, the animals were passively swept with the horizontal currents. The depth retention mechanism has far-reaching implications for trophic subsidy in both coastal and oceanic ecosystems.

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Aquatic Sciences Meeting, Albuquerque 2001

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