The Rivanna Rambler

October 30, 2008

 

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This show originally aired on October 30, 2008 on “The Rivanna Rambler,” a weekly public affairs show airing every Thursday at 11:55 a.m. on WTJU 91.1 FM or wtju.net.

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. Those who row on the reservoir say its been a recent addition, only first noticed a couple of years ago, but dramatically increasing during this last growing season.

Hydrilla came to the US through the nursery trade in the 1950’s and has infested waters in coastal areas since the 1970’s – producing thick mats of vegetation on still and slow moving waters in Florida, Washington state, and now in the mid-Atlantic. Nearby in Louisa County, hydrilla management has been in effect for almost a decade to keep water intakes to the power plant unobstructed – and simultaneously clearing the surface of the water for recreational boating.

True to its invasive nature, hydrilla has multiple means of reproduction – tubers at its roots, seeds from flowers, and turions – those small seed-like growths at the axil of the plant stem.  These can survive ice, ingestion, and burial in bottom sediments for several years.  Mowing or chopping down plants only results in more aggressive growth.

Other biological characteristics contribute to hydrilla’s success.  Because it absorbs carbon from the water more efficiently than other plants and can store its own phosphorous, it thrives during summer months when these nutrients can be limited.  Because of this, some say that hydrilla improves water quality – and though fisherman will say that it’s presence improves fishing for large mouth bass and channel catfish, biologists warn that inevitably an ecosystem that is imbalanced by over-crowding of a dominant species suffers.

The real question is, how do we suffer?  Next week, we’ll look more closely at the aquatic conditions of the South Fork Rivanna Reservoir.  Please tune in again at 11:55 a.m. on Thursday for the next installment of the Rivanna Rambler on WTJU, 91.1 FM or wtju.net, the sound choice in central Virginia – for podcasts of this show, visit www.rivannarambler.org.  If you’ve enjoyed this – and any of the shows you hear on WTJU, please vote your support by giving generously to this station.