Swimming Against the Flow: A Mechanism of Zooplankton Aggregation

by Genin, Jaffe, Reef, Richter, and Franks
appearing in the 6 May 2005 issue of SCIENCE, vol 308, issue 5723, pg 860


Zooplankton reside in a constantly flowing environment. However, information about their response to ambient flow has remained elusive, because of the difficulties of following the individual motions of these minute, nearly transparent animals in the ocean. Using a three-dimensional acoustic imaging system, we tracked >375,000 zooplankters at two coastal sites in the Red Sea. Resolution of their motion from that of the water showed that the animals effectively maintained their depth by swimming against upwelling and downwelling currents moving at rates of up to tens of body lengths per second, causing their accumulation at frontal zones. This mechanism explains how oceanic fronts become major feeding grounds for predators and targets for fishermen.

They used a high frequency multi-beam sonar to track individual animals.

You can go to the Science site and look at back issues. Abstracts are free, and if the article is a year old you can get the full text.