Wednesday, November 02, 2011

Invasive Mussels and Birds

Quagga Mussel / USGS Photo
Zebra mussels first appeared in the Great Lakes in 1988, mostly likely carried in a ship's ballast. They multiplied rapidly and disrupted the lakes' ecosystems. More recently, zebra mussels have been pushed out by another invasive species, the quagga mussel, which has similarly disruptive effects on the underwater ecosystem. The changes caused by the invasive mussels seem likely to affect bird life around the lakes.

One way is through food availability:
Gary Montz, an aquatic invertebrate biologist with the Minnesota Department of Natural Resources, said, "If we see a disruption in the base of the food chain by extremely high densities of zebra mussels, this could impact food for larval fish. That in turn could impact other aquatic life that depend on such fish."

That includes fish-eating birds -- loons, mergansers, grebes, cormorants, scoters and gulls.
Zebra Mussel / USGS Photo
There also seems to be a connection with disease and toxicity:
"Zebra mussels have a connection with avian botulism," said Carrol Henderson, superintendent of non-game wildlife for the DNR. Botulism is a byproduct of mussel waste. The waste is eaten by fish, which then can infect fish-eating birds.

Thousands of birds in the eastern Great Lakes have died of botulism poisoning since 1999. Species again include loons, mergansers, grebes, cormorants, scoters and gulls.

Some species of diving ducks eat the mussels. Zebra mussels have been a dominant food consumed in the eastern Great Lakes by greater and lesser scaup and bufflehead ducks. Concentration of trace elements in the mussels kills the birds.

The scaup population fell from an estimated 7.5 million breeding birds in the 1970s to fewer than 4 million in 2005, according to author James H. Thorp. The figures come from his book "Ecology and Classification of North American Freshwater Invertebrates."