The use of algal-mat habitats by aquatic insect grazers: Effects of microalgat cues

Microalgal biomass is important for the growth and survival of aquatic insect grazers, and we hypothesized that the abundance of microalgae mediates the habitat-use behavior of aquatic insect grazers in stream ecosystems. To test this question under laboratory conditions, we prepared four types of experimental habitat in an artificial stream: untreated ceramic plates, ceramic plates with thin algal. mats, ceramic plates with thick algal mats, and natural stone with algal. mats. We compared the upstream movement forward each experimental habitat substrate by caddisfly grazer Glossosoma larvae. At day and at night, a significantly greater number of Glossosoma larvae were attracted by thin and thick algal mats as well as by natural. stones than by the untreated ceramic plate. At night, thick algal mats attached significantly more larvae than thin algal mats. Thus, Glossosoma larvae can recognize and respond to the abundance of microalgae through microalgal cues (chemical and/or algal drift), which induce the movement of Glossosoma larvae to habitats with high microalgal. biomass. We propose that cues from microalgae are recognized by grazers in stream ecosystems. (c) 2005 Gesellschaft fur Okologie. Published by Elsevier Gmbh. All rights reserved.