Detecting food search in Daphnia in the field

From laboratory experiments, it has been suggested that visually guided fee ding, chemical and mechanical perception of increased ingestion rate (inclu ding perception of hunger and satiation), and odors associated with algae h elp Daphnia in tracking food gradients. To test the ability of Daphnia to f ind food in the field, suspended yeast, suspended clay. or control water wa s pumped into a localized point in the littoral zone of Lake Myravann (Berg en, Norway), Daphnia longispina and Daphnia pulex, the most numerous zoopla nkton 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 quatitatively, possibly thr ough perception of increased ingestion rate and odor, while light scatterin g is indicated to be unimportant. This is the first experiment to demonstra te that Daphnia is able to find patches of food under natural conditions.