Are plant beds in streams hot spots of macroinvertebrate diversity, abundance and biomass?

Abstract

ARE PLANT BEDS IN STREAMS HOT SPOTS OF MACROINVERTEBRATE DIVERSITY, ABUNDANCE AND BIOMASS?

By Michael P. Shupryt

Macroinvertebrates are known to exhibit habitat preferences for macrophytes in lakes and large rivers where macrophyte beds are abundant. It is less understood if these preferences will hold true in low order streams where macrophyte beds are less abundant and sporadic. I examined the ability of small sporadic macrophyte beds to be hot spots of macroinvertebrate diversity, abundance and biomass in a Central Wisconsin sand plain stream. I sampled eight discrete macrophyte beds and 4 sand\gravel patches monthly from March through October 2007. Overall mean invertebrate diversity (Shannon-Weiner Index), abundance and biomass in the macrophyte beds was significantly greater than in sand\gravel patches (paired t-test p < 0.05). Mean invertebrate diversity in the macrophyte beds had a non-significant time (Repeated Measures ANOVA p=0.057) and a significant bed effect (p<0.05). Although there was a significant difference in mean diversity the difference was small and not a likely indication of a biodiversity hot spot. Mean invertebrate abundance and biomass had significant time (p<0.001) and bed effects (p<0.01). I scaled the results of the summer invertebrate abundance and biomass results using a substrate survey in a 400m stream reach. Although sand\gravel outnumbered macrophytes as a habitat nearly 3:1 they contributed equally to macroinvertebrate abundance and biomass and the whole reach level. I concluded that macrophyte beds were hot spots of macroinvertebrate abundance and biomass. These results show that even when macrophyte beds are isolated and sporadic in small streams they may be major contributors to invertebrate biomass and production at the whole stream level.