Zebra mussels screw everything up

This study documented changes in the overall density and composition of benthic invertebrate communities in South Bay associated with the invasion of zebra mussels (D. polymorpha). The quagga mussel, D. bugensis, had not invaded South Bay at the time of this study.



Fig 3. Interaction of year and depth zone on log(x+1) mean density of organisms (one standard error is shown but is not visible on log scale) for various taxonomic groups. Depth zones 1, 2, and 3 correspond to shallow, intermediate and deep respectively. For clarity, depth zone values are offset for each group.

Figure 3 shows density changes in four ecologically important macroinvertebrate species in South Bay pre- and post zebra mussel invasion. Overall, you can see there is a general decline in densities over the three depth zones. The most significant decline is seen in Diporeia, which is a main dietary component of a commercially important fish, Lake Whitefish.

Fig. 5 Interaction of year and depth zone on the mean relative abundance of organisms (one standard error of the mean is shown) for various taxonomic groups. Depth zones 1, 2, and 3 correspond to shallow, intermediate and deep, respectively.



Variety of macroinvertebrates commonly
found in North American freshwater
systems.



Figure 5 perfectly illustrates the changes in relative abundance of four ecologically important macroinvertebrates in the South Bay ecosystem. Diporeia decline in the deep zones, where as oligochaeta and chironomidae appear to increase in this zone. There are drastic decreases in chironomidae in the shallow and intermediate zones and slight increases in oligochaeta in these zones. Figure 5 suggests there a potential restructuring of the benthic community resulting from the establishment of zebra mussels.



This study did a great job at illustrating changes in the benthic community, and the implications of these changes on native species, after the invasion of zebra mussels.

 

One of the limitations of this study was the lack of information necessary to make biomass estimates. Looking at biomass instead of abundance may influence the results of this study.

Reference:

McNickle, G.G., Rennie, M.D., Sprules, W.G. (2006) Changes in benthic invertebrate communities of South Bay, Lake Huron following invasion by zebra mussels (Dreissena polymorpha), and potential effects on lake whitefish (Coregonus clupeaformis) diet and growth. Journal of Great Lakes Research 32: 180-193.