Resource limitation by freshwater snail (Stagnicola vulnerata) grazing pressure: an experimental study.
Muñoz, I.; Real, M.; Guasch, H.; Navarro, E.; Sabater, S.
Archiv für Hydrobiologie Volume 148 Number 4 (2000), p. 517 - 532
published: Jun 28, 2000
ArtNo. ESP141014804003, Price: 29.00 €
The freshwater snail Stagnicola vulnerata was introduced into experimental channels at five different densities to compare the effects of increasing grazing pressure on the algal community. Net community metabolism, carbon incorporation and chlorophyll-a concentration decreased (by more than 50 %) with increasing snail density over 14 days. The relationship between periphyton parameters and snail biomass predicted that the periphyton density available for snails would decline according to a negative exponential function as snail densities increase. Cocconeis placentula, Achnanthes spp. (lanceolata, minutissima) and Mougeotia sp. filament densities decreased with grazing pressure. However, basal cells of Stigeoclonium tenue were favoured at the highest snail density. The biovolume of the algal assemblages also decreased in channels with more grazers. The dominant physiognomic classes in the pre-grazing conditions were crustose and prostrate. Filamentous forms increased in ungrazed channels and in those with the lowest and the highest densities. Snail grazing simplified both algal taxonomic and physiognomic structure but the pattern depended on grazer density. When density increases, snail interference competition may be partially responsible for changes in functional and structural responses of periphyton assemblages.