Effects of Artificial Zebra Mussel Druses on Macroinvertebrate Communities and Benthic Carbon Accumulation

Abstract - Dreissena polymorpha (Zebra Mussel) disrupt biological processes throughout aquatic ecosystems in which they are introduced, while simultaneously increasing benthic habitat complexity and food availability by forming druses on various substrates. Numerous studies have investigated the effects of infestation on benthic communities; however, because Zebra Mussels were already established within these systems, it is possible that results were influenced by ecosystem-wide changes in water clarity and suspended nutrient concentrations. In this study, we placed tiles with artificial Zebra Mussel druses in Lake Bemidji, which did not have a well-established Zebra Mussel population at that time, to investigate the effects of benthic habitat modification on macroinvertebrate communities and carbon accumulation. We used control (n = 0 druses) tiles as well as 3 treatment tiles—low (n = 247), medium (n = 428), or high (n = 610) number of individuals per tile—to examine how Zebra Mussel density affected macroinvertebrate communities and carbon accumulation. Macroinvertebrate abundance (ANOVA: P < 0.001) was higher on the treatments compared to the control tiles. However, macroinvertebrate density was highest on control tiles (one-way test: P = 0.002), and treatment did not influence overall community structure (NMDS: P = 0.111) or macroinvertebrate diversity (ANOVA: P = 0.630). Furthermore, organic matter ash-free dry mass (AFDM) density was highest on control tiles (one-way test: P = 0.021), while treatment did not influence invertebrate AFDM density (one-way test: P = 0.098). These results indicate that while macroinvertebrates are able to exploit the additional habitat provided by druses, biological processes such as water filtration, carbon transfer, and benthification facilitated by living Zebra Mussels were also likely crucial in restructuring benthic communities to the extent observed in previous studies.