Environment: Algae-Harboring Hydrilla Causing Bald Eagle Deaths in the Southeast

The aquatic invasive plant hydrilla harbors a blue-green algae which is potentially toxic to birds. Birds--namely waterfowl--eat the algae-harboring hydrilla, become poisoned and eventually die. Eagles that prey on infected waterfowl contract the disease and perish as well.

The aquatic invasive plant hydrilla (Hydrilla verticillata) not only is a costly nuisance impeding waterways and recreational lakes, it also may have deadly impacts on eagles and waterfowl. Its invasive nature earned it a spot on the Federal Noxious Weed list in 1979 and it is the topic of this Invasive Plant Spotlight from the Weed Science Society of America.

Hydrilla is a quick growing, invasive plant that forms a dense mat in lakes, ponds and reservoirs. It is a safe haven for the fast-growing epiphytic cyanobacterial algae, a blue-green algae, which grows on top of the hydrilla and is potentially toxic to birds. It is suspected that when waterfowl, namely coots, eat the algae-harboring hydrilla, they become poisoned by the algae's neurotoxins and subsequently suffer from a neurological disease known as avian vacuolar myelinopathy. The eagles, in turn, eat the infected coots and succumb to the disease as well.

"According to the research, avian vacuolar myelinopathy was first documented in 1994 at DeGray Lake in Arkansas," says Susan B. Wilde, Ph.D., research professor at the University of South Carolina and member of the Weed Science Society of America. "Since then, more than one hundred bald eagle deaths are believed to be associated with the disease. And it is estimated that the numbers of deaths are much higher, but because of scavenging animals, it often is difficult to recover the carcasses of dead eagles soon enough to test for the disease. But in places where dead eagles are found, invasive aquatic vegetation---primarily hydrilla---and the blue-green algae are always present," says Wilde.

Hydrilla is an invasive plant that originated in India and Asia. It was first introduced into the United States as an aquarium plant back in the 1950s. Improper disposal of hydrilla from aquariums, distribution through animal contact and the plant's ability to "hitchhike" on boats that have been in multiple bodies of water and not cleaned underneath after each use, has lead to its voracious spread over the years. "Hydrilla is most prevalent in the southeast but can be found in fresh water lakes and rivers in most coastal states," says Wilde.

Hydrilla is just one example of a problematic invasive plant. The overall effects of invasive plants on the nation's agriculture, water quality, wildlife and recreation have been estimated to cost the U.S. $34.7 billion annually, according to a recent Cornell University report.

The Weed Science Society of America educates the public on the issues surrounding invasive plants. The information and awareness the Society provides about the destructive effects of invasive plants, assists researchers, scientists, land management professionals and the general public in limiting their spread.

For more information about invasive plants visit www.wssa.net.

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