Little Shells, Big Problems.

Now that we're able to see the ground again, here's something from the beach at North Point Marina:

Zebra Mussel (Dreissena polymorpha),
N. Pt. Marina, Lake Co, IL 2/23/14

Actually, I could have gotten this shot at just about any beach in the area -- it's a Zebra Mussel (Dreissena polymorpha). They're native to Europe, where they're quite widespread. The first discovery in North America occurred in 1988, and that initial publication predicted that they would likely spread throughout the Great Lakes. (1) They were right! The same life history traits that produced their widespread native range has allowed them to spread rapidly here, and they now are abundant throughout the Great Lakes and the Mississippi River basin. They don't get very big, just an inch or so long, but they grow in dense colonies that cover just about any hard surface. They cause economic issues by fouling water intakes and similar structures.

They also cause a host of ecological changes -- they are very efficient filter feeders, and increase water clarity by removing phytoplankton. (2) They also cover native mussels and clams, causing steep declines in many of them. (3) Given that 60% of the 297 known species of freshwater mussels in the US are considered endangered, with an additional 12% already presumed extinct, this is a serious problem. (3,4) Illinois alone has 16 species that are listed by the state, seven of them also on the Federal Endangered Species list. (5) It seems likely that we will lose all of them in the near future. (4) (Most of this work was done in the 1990's, so I don't know how many have disappeared in the meantime. The Illinois numbers are based on the most recent revisions to the Endangered Species List, in 2011, but I can't find any older versions to compare to.)

Surprisingly, finding additional research on this species published since 2000 isn't especially easy. Either they've somehow stabilized or we've mostly moved on to other crises.

There are, of course, things that eat Zebra Mussels, even here, and here's one of them:

White-winged Scoter (Melanitta fusca), Pleasant Prairie Yacht Club,
Kenosha Co, WI, 2/23/2014

This is a White-winged Scoter (Melanitta fusca). They're a large sea duck that breeds across Canada and winters mostly on the coasts, but some do spend the winter on the Great Lakes. Zebra Mussels seemingly provide an easy food source, so I would have expected an increase since the early 1990's in the state. However, CBC numbers don't back that up -- both White-winged and Surf Scoter (M. perspicillata) numbers decline rather dramatically at just about the time that the mussels were getting started here. (6) Either they prefer larger food, or there's something else entirely going on with them.

(1) Griffiths, R. W., Schloesser, D. W., Leach, J. H., & Kovalak, W. P. (1991). Distribution and dispersal of the zebra mussel (Dreissena polymorpha) in the Great Lakes region. Canadian Journal of Fisheries and Aquatic Sciences,48(8), 1381-1388.

(2) MacIsaac, H. J. (1996). Potential abiotic and biotic impacts of zebra mussels on the inland waters of North America. American Zoologist, 36(3), 287-299.

(3) Schloesser, D. W., Nalepa, T. F., & Mackie, G. L. (1996). Zebra mussel infestation of unionid bivalves (Unionidae) in North America. American Zoologist,36(3), 300-310.

(4) Ricciardi, A., Neves, R. J., & Rasmussen, J. B. (1998). Impending extinctions of North American freshwater mussels (Unionoida) following the zebra mussel (Dreissena polymorpha) invasion. Journal of Animal Ecology, 67(4), 613-619.

(5) http://www.dnr.illinois.gov/ESPB/Documents/ETChecklist2011.pdf

(6) National Audubon Society (2010). The Christmas Bird Count Historical Results [Online]. Availablehttp://www.christmasbirdcount.org [3/13/2014]