Food quality and food choice in freshwater gastropods: Field and laboratory investigations on a key component of littoral food webs

Freshwater gastropods form a key link in the food webs of lake littoral zones. They make benthic primary production available to invertebrate and vertebrate predators. However, their community biomass is strongly influenced by the nutritional quality of periphytic algae. In this study, several factors that potentially determine the nutritional quality of periphyton for gastropod grazers (and strategies of the snails to cope with food quality constraints) were investigated both in the field and under standardised conditions in laboratory growth experiments. As food quality is patchily distributed, it should be highly adaptive for gastropod herbivores to utilise chemical cues in order to detect patches of (high quality) food. In particular, volatile organic compounds released from benthic algae can be used by the snails as foraging kairomones that indicate the presence of a food patch. These adaptations probably contribute to the extreme success of freshwater gastropods in many lake and river littoral zones.