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Sources and sinks of pelagic zooplankton near the coast: The coral reef example

Amatzia Genin, Ph.D.
Stanford University

Wednesday, January 10, 2001
3:00 p.m.—Pacific Forum

Zooplankton constitutes a major component of fish diet in coastal habitats such as coral reefs and kelp forests. Where fish abound, the density of zooplankton sharply decreases from the open water shoreward; where fish are rare, an opposite gradient of a shoreward increase in zooplankton abundance is commonly observed. Using various in situ techniques, including the FishTV (a high-frequency 1.6 MHz multi-beam sonar), we were able to quantify predation rates by individual and schools of coral-reef fishes and to track small (1-5 mm) zooplankters in 3-D. Our results indicate that the coastal zone is frequently exposed to vertical flows in the range of 1-2 cm/s and that small zooplankton, mostly copepods, are able to retain their depth against such flows, thereby increasing their abundance near the coast. The fish readily harvest these zooplankton aggregations. This dynamic trophic subsidy can play a major role in fish-zooplankton interactions in many coastal regions and oceanic fronts.

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