2001, by the American Society of Limnology and Oceanography, Inc. Detecting food search in Daphnia in the field

From laboratory experiments, it has been suggested that visually guided feeding, chemical and mechanical per-ception of increased ingestion rate (including perception of hunger and satiation), and odors associated with algae help Daphnia in tracking food gradients. To test the ability of Daphnia to find food in the field, suspended yeast, suspended clay, or control water was pumped into a localized point in the littoral zone of Lake Myravann (Bergen, Norway). Daphnia longispina and Daphnia pulex, the most numerous zooplankton species in the experimental area, aggregated in areas of yeast input but not when adding suspended clay or control water. Thus, Daphnia is able to evaluate the patches both quantitatively and qualitatively, possibly through perception of increased ingestion rate and odor, while light scattering is indicated to be unimportant. This is the first experiment to demonstrate that Daphnia is able to find patches of food under natural conditions. In the laboratory, zooplankton express a capacity to track gradients in food availability (e.g., Jakobsen and Johnse