From the surface, the ocean appears to be vast and uniform. But beneath the surface, tiny animals called zooplankton are swept into clusters and patches by ocean currents. The very survival of many zooplankton predators--from invertebrates to whales--and the success of fishermen catches can depend on their success at finding those patches.

For almost a century ocean scientists have suspected that these patches form when the zooplankton swim against the ocean currents. In all those years, however, an understanding of zooplankton swimming response to ocean currents has remained elusive, mainly due to the lack of technology to track the motions of the miniscule animals in the sea.

Now, an international team of scientists from Israel, the United States and Germany led by Amatzia Genin of the Hebrew University of Jerusalem has provided, for the first time, evidence of the remarkable dynamics responsible for the formation of zooplankton aggregations. The new findings indicate that zooplankton are passively drifting with the current, as their name implies ("planktos" translates to "drifting" in Greek), but only in the horizontal direction, not in the vertical.

The recent development of a 3-dimensional acoustic imaging system by Jules Jaffe of Scripps Institution of Oceanography at the University of California, San Diego, has opened the door for a team of researchers to track several hundred thousand individual zooplankton at two coastal sites in the Red Sea. The team includes Genin and his student Ruth Reef from the Hebrew University; Jaffe and Peter Franks from Scripps Institution of Oceanography at the University of California, San Diego; and Claudio Richter from the Center for Tropical Marine Ecology in Bremen, Germany.

Their findings, reported in the May 6 issue of the journal Science, show that these small animals effectively keep their depth by "treadmilling" against upwelling and downwelling currents at speeds of up to
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Contact: Mario Aguilera or Cindy Clark
scrippsnews@ucsd.edu
858-534-3624
University of California - San Diego
5-May-2005

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