Distributions of Dreissena in Lakes Michigan and Ontario indicate optimal zones for colonization

In many species, individuals self-organize into predictable patterns that depend on a balance of facilitation and competition. For sessile organisms, these patterns may persist for long periods of time and give insight on local environmental conditions. Dreissena are now nearly ubiquitous in the Great Lakes and their spatial distributions rely on food availability, currents, wave action, and sediment type. In some cases, Dreissena may facilitate one another through greater attachment strength in larger clusters, but clustering may also be disadvantageous where food is scarce. This suggests that self-organization in these mussels depends on, and reflects, environmental conditions. We used video survey techniques (benthic sled transects) to map distributions and self-organization patterns of Dreissena in Lakes Michigan and Ontario. In Lake Michigan, we compared Dreissena patterns with current and bottom shear stress from NOAA's Great Lakes Coastal Forecast System. We also compared distributions to chlorophyll concentration from satellite data as a proxy for food availability. Consistent with previous studies, we found a zone of optimal habitat for Dreissena at mid-depths, where mussels occupied nearly all space with no patterning evident. We found that Dreissena are not found at high abundances in areas with extremely low currents. There were no apparent effects of shear stress due to wind-waves, however, the number of stations with high shear stress were limited. Our results indicate that Dreissena self-organize in the Great Lakes in ways that reveal underlying environmental conditions in abiotic stress and resource availability.