October 30, 2008
While the Virginia Film Festival showcases movies about aliens from other countries, other lives, and other worlds, we need look no further than out own watershed for invasives of the biological variety. The South Fork Rivanna Reservoir is now infested with Hydrilla verticillata, an aquatic weed that has caused problems in lakes, rivers, and sounds in other parts of the country.
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I was reading in the paper how Richard Herkowitz, director of the Virginia Film Festival, decided that the subject of aliens could have social, political, as well as entertainment value – and now we are in the midst of the movies about topics that range from immigration to space invasions. We use the word alien to describe something that is “not from here” and usually with the connotation that it has no business being here. Many times, we ascribe to aliens the notion that they are “invading,” and thus underscore the menacing potential.
Well, these terms are also used in the biological world. While an alien species is simply “one not native to an area,” it may become invasive if it is able to out-compete similar but native species. If it is able to overcome – or even thrive – within the ecological limits provided by other native organisms, the plants, insects, and animals that have evolved together in a healthy balance.
While alien space invaders may be thrilling or scary to contemplate, it is usually much harder for any of us to have a similar reaction about an invasive plant species – like the common reed, Phragmites, that is overwhelming wetlands across the eastern seaboard and changing the visual and ecological character of marshy areas. Or the Zebra mussel, whose capacity for feeding and filtering has rendered waters from the Great Lakes to the St. Lawrence Seaway stunningly clear, but biologically barren. Usually, we first become aware of such invasions when they have an economic impact – such as the need to keep water intakes from fowling with Zebra Mussels.
But thanks to the focused attention of the South Rivanna Reservoir Task Force, we now know that we have an aquatic invasion in our watershed. Hydrilla verticillata, commonly known as hydrilla, is forming dense mats of growth along the margins of the reservoir, reducing access to rowing lanes, snagging fishermen’s lures and stopping the strokes of boater’s paddles.
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