Raikow, D. F. 2002. How the feeding ecology of native and exotic mussels affects freshwater ecosystems. PhD Dissertation, Michigan State University, East Lansing, Michigan.

As zebra mussels expand their range in North America new ecosystems become invaded. Beginning with the Great Lakes and continuing through the Mississippi River drainage network, the zebra mussel invasion is currently spreading among small inland lakes. Due to the swiftness and magnitude of this invasion and the effects zebra mussels have had on previously invaded ecosystems, it is imperative that the effects of zebra mussels on inland lakes be investigated. In addition, the zebra mussel invasion represents the functional replacement of the multispecies assemblage of native bivalves which typically disappears after invasion. This dissertation examined the ecology of native unionid bivalves (Unionoidae) and exotic zebra mussels (Dreissena polymorpha) in order to learn what North American freshwater ecosystems are losing and gaining.

I examined a community of unionids in a stream by using both natural and experimentally enriched stable isotopes of nitrogen as a spin-off project of the Lotic Intersite Nitrogen eXperiment (LINX). This is the first and only isotopic enrichment of this taxon. The evidence suggests, contrary to conventional wisdom, that native freshwater mussels they may not be exclusively suspension feeders as adults.

The potential effects of zebra mussels on fish are poorly understood. I examined how larval bluegill growth and survival could be affected by zebra mussels in an experimental mesocosm setting. The hypothesized mechanism of competition between mussels and bluegill for food in the form of microzooplankton was supported. Competition between zebra mussels and obligate planktivores may contribute to ecological harm done to small inland lakes as zebra mussels spread throughout North America. The effects of zebra mussels on microzooplankton reproduction was studied as part of a large mesosoem ZEbra mussel EXperiment (ZMEX), in order to evaluate the relative importance of direct predation on microzooplankton by zebra mussels and indirect competition for resources (phytoplankton as food) causing reduced fecundity.

Another anticipated impact of zebra mussels is the alteration of phytoplankton community structure, including the promotion of the toxic alga Microcystis. I surveyed 60 lakes in the lower peninsula of Michigan to see whether the phytoplankton community has changed in the presence of zebra mussels. Standing stocks of phytoplankton have clearly been reduced in the presence of zebra mussels. While the relative abundance of Microcystis appears to have increased in the presence of zebra mussels there has been little effect on overall phytoplankton community structure.

Nutrient regeneration and benthic-pelagic coupling are important issues concerning zebra mussels. I measured ammonium (NH4), soluble reactive phosphorus (SRP), and dissolved organic carbon (DOC) concentrations, and the composition of biodeposits in the mesocosm experiment and survey. While increased SRP was detected in the mesocosm experiment, no evidence of increased SRP was found in natural systems. Zebra mussels have, however, evidently reduced the concentrations of DOC in lakes. This is important because DOC attenuates UV-B radiation, and thus invaded systems may be more susceptible.

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