Department of Physics, Chemistry and Biology (IFM)

Invertebrate grazing efficiencies on epiphyton were measured and used as an indicator to determine an aspect of the functional role of species in subemerged vegetation. Aiming to compare the use of algae as food source among different mesograzer species in Lake Täkern, near Linköping, Sweden, Lymnaea columella, Asellus aquaticus and Gammarus pulex were used to test two hypotheses that: (a) mesograzer species under controlled laboratory conditions, will consume epiphyton biomass at the same grazing rates; (b) mesograzer species feeding rates on epiphyton biomass is proportional to the rate of feeding on dead leaves. Grazing on algal biomass was calculated as a function of three parameters of measurement; actual food consumption (F), food consumption at varying density (FC) & weight-specific consumption (WSC); while feeding effects on dead leaf alternative food source was calculated as a function of one parameter of measurement: consumption rate (CR). A one-way analysis of variance (ANOVA) followed by a Tukey HSD post hoc comparison test of the parameters of measurement indicated highly significant differences (P<0.0001) among mesograzers in their individual abilities to significantly reduce algal biomass while grazing on it. Similarly, there was a significant difference (P<0.0001) in the feeding efficiencies of mesograzers on dead leaf biomass. However, the significant feeding effects of mesograzers on both epiphyton and dead leaf food sources increased with an increase in species densities. Lymnaea columella demonstrated the highest grazing efficiency on epiphyton biomass; while Gammarus pulex had the least grazing effect on epiphyton.   Asellus aquaticus exhibited the highest feeding impact on dead leaf; while the feeding efficiencies of Lymnaea columella and Gammarus pulex on dead leaf biomass were even. Invertebrate species consumed more of the algae food than the dead leaf alternative food source. Differences in grazing and feeding rates on epiphyton and dead leaf food sources among invertebrate species can be attributed to the influence of some underlying natural factors such as species body size, food selection, feeding mechanism etc.