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Endangered mussel species found in Thames River
The discovery of live Rayed Bean mussels marks only the second time the species has been found in the Thames, and represents only the second population of live specimens in Canada. According to Fisheries and Oceans Canada, the Rayed Bean mussel once ranged from western Lake Erie to rivers in the Lake St. Clair drainage. Until this most recent discovery along a north reach of the Thames, the Canadian population of the Rayed Bean was found only in the middle reach of the Sydenham River—its population struggling with the environmental pressures of pollution and the invasive Zebra mussel. The Rayed Bean is a tiny mussel and often easy to overlook at just under 40 mm long and 19 mm high. It takes its name from the wavy green rays that mark its elliptical body. The inside of its shell is silver-white and iridescent. In Canada, the Rayed Beans host fish is the Greenside darter. Scientists believe a lack of habitat is most likely the main limiting factor for Rayed Bean mussel. The species thrives in shallow, silt-free riffle habitat which is being impacted through siltation caused by agricultural and forestry practices. This siltation buries the Rayed Bean mussel, interferes with their feeding and exposes the species to pollution. "The Rayed Bean may be more directly exposed to sediment-associated contaminants than most other species of freshwater mussels because it buries relatively deeply. It is also susceptible to negative effects from exposure to agricultural chemicals such as fertilizers and pesticides," said Fisheries and Oceans officials. In the Thames, Rayed Beans were found while UTRCA staff and volunteers were assisting an American researcher, Dr. Dave Zanatta of Central Michigan University, who was conducting research on the genetics of another endangered mussel species, the Wavy-rayed Lampmussel. "An enthusiastic crew assisted Dave with a search for (Wavy-rayed Lampmussels) along a reach of the North Thames between London and St. Marys," said UTRCA officials in a media release. "Despite being a rare species with a very limited range in Canada, we found over 60 live and apparently healthy Wavy-rayed Lampmussels, from which Dave was able to extract genetic samples. All specimens were then carefully returned to the streambed." Like all freshwater mussels, the larvae of Wavy-rayed Lampmussels start off life as parasites, in their case attached to the gills of suitable fish species. Like expert fishers, several mussel species use a unique technique to attract a potential larval host – they present a "lure." The lure of the adult Wavy-rayed Lampmussel closely resembles a small fish, complete with realistic looking eyespots. When the host species (usually a smallmouth bass) attacks the lure, the mussel releases its larvae, called glochidia, which attach to the fish's gills. After a short time the larvae drop off the host fish. If they happen to fall in a suitable location, they burrow into the stream bottom, commence filter feeding and continue development. The parasites have little impact on the host species, but because the host fish is much more mobile, the mussels use this adaptation as a mechanism for dispersing the larvae.
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| Actually, I'm a Canadian biologist who happens to be faculty at an American university. |
| By: David Zanatta on 10/27/2009 |
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