Magazine article Oceanus

Diel Vertical Migration in Zooplankton: Trade-Offs between Predators and Food

Magazine article Oceanus

Diel Vertical Migration in Zooplankton: Trade-Offs between Predators and Food

Article excerpt

Why do so many aquatic organisms, including zooplankton, undertake vertical migrations of tens to hundreds of meters between deep, darker waters during the day and surface waters at night? The answer to this question has long eluded scientists, despite the fact that this behavior, known as diel vertical migration, has been recognized for over a century as one of the most conspicuous and important types of animal migration on earth. Recent experiments undertaken with collaborators at the University of Washington and the Max Planck Institute of Limnology shed new light on this enigmatic phenomenon.

We borrowed from a theory developed primarily by terrestrial ecologists that predicts individual animals should select a habitat or set of habitats (or depths, in the case of zooplankton) that allows them to maximize energy gain via feeding (such as on algae) while minimizing the probability of death via predators (such as fish). To test this intuitively appealing theory, we designed two experiments. The first test was based in a marine lagoon in 1994 on San Juan Island, Washington, where large (3-cubic-meter) plastic enclosures contained the marine copepod Acartia hudsonica. More recently we worked with the freshwater cladoceran Daphnia hyalina in the 11-meter-tall "Plankton Towers" at the Max Planck Institute in Germany. US funding for this work was provided by the National Science Foundation and the Office of Naval Research. In both systems the abundances of algae and predatory fish - which could be quantitatively related to feeding gains and the probability of predation mortality, respectively - were manipulated in the experimental containers. …

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