Photo of Eurasian water milfoil (an exotic species) co-existing with stargrass (a native species) at the mouth of the Susquehanna River. Picture by Jed Kirchbaum of The Sun.

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Exotic species sometimes inspire fear and loathing.  Think kudzu.

But in parts of the Chesapeake Bay watershed, non-native aquatic vegetation appears to be helping a resurgence of underwater plant colonies that are important habitat for fish and crabs.

A report from the Maryland Department of Natural Resources today said that underwater bay grasses increased 10 percent from 2006 to 2007.  Aquatic vegetation last year covered 65,000 acres of the Chesapeake Bay's bottom, up from 59,000 acres in 2006.  That's still only about a third of what a healthy bay would look like -- and down substantially from the 90,000 acres covered with aquatic vegetation in 2002.  But at least it got better last year instead of worse.

Among the areas that saw growth last year was the upper Potomac River, where an exotic Asian aquarium plant -- hydrilla -- is helping to stabilize the river system, clean the water and provide a healthy habitat for other plants.  That's not what was predicted in the 1980's, when hydrilla was denounced as an invasive, river-strangling monster, and the Army Corps of Engineers talked about bombing it with pesticides. 

"Hydrilla is seen as a scourge, but certainly it is providing a habitat," said Bob Orth, a scientist at the Virginia Institute of Marine Science.  "That's where the fishing boats line up for bass, right near the hydrilla." 

Nancy Rybicki, a hydrologist at the U.S. Geological Survey, published a study on hydrilla in the Potomac River last year that came to the same conclusion: that it's not overwhelming native plants, or suffocating the river, as many people expected.

And it's not just on the Potomac River where hydrilla is spreading, apparently with positive results.  The Asian aquarium plant -- first dumped from a fish bowl into a Florida river in the 1980's -- is also growing in the James, Pamunkey and Chickahominy rivers in Virginia, among others.

"Hydrilla is in every single tributary in the bay.  And you can't deny the fact that hydrilla facilitates the growth of a lot of native species, because it provides a filter for water. You have clear plumes of water coming out of the hydrilla beds," said Orth. "If you go back to the newspaper accounts in 1982, they called it the hydrilla gorilla... But now we're seeing healthy populations of both native and nonnative plants together."

An area that experienced even more growth in aquatic vegetation is at the northern end of the Chesapeake Bay, where the Susquehanna River empties into the estuary.  In that area, bay grasses covered 19,000 acres last year, up from 15,500 acres in 2006, according to the DNR report.

Most of the growth in the Susquehanna flats is in wild celery, a native plant.  But another exotic plant, milfoil, is coexisting with the celery and other species.  This peaceful cohabitation isn't what many people expect.  For example, just last June, The New York Times ran a story about milfoil sparking fear among boaters in the Adirondacks.  "A Battle Against an Aggressive Green Invader from the Deep," screamed the headline.

And that was from a newspaper often called the "gray old lady."  How about this for a headline: "Maligned Milfoil Sues for Libel, Battles Purple Prose."