Two recent news stories from the Chesapeake illustrate well the opposite poles in the debate on invasive species. The first details the appearance of the cuddly-sounding mitten crab in Chesapeake waters, an Asian species that has also hitchhiked in ships to California, Germany and Great Britain. Articles about it use terms like alien and exotic for the little fellas, often pitting them against the beleaguered native blue crabs.
So the news that a foreign species of aquatic vegetation, once considered a major nuisance when it began rapidly colonizing the nearby Potomac River, has instead benefited the watershed’s ecosystem interested me. Hydrilla first appeared in 1983 and created dense vegetation masses and even impeded boat traffic in some areas. It was feared that it would interfere with the native vegetation, itself an important food source for waterfowl and fish.
This 17-year study of hydrilla, though, found that not only did it not crowd out native species, but the natives actually increased. Hydrilla also became an important winter food source for waterfowl communities, which increased over this period. All of which makes me wonder about the hype and hyperbole used to describe each new “invasion.”
Is hydrilla an isolated case? Not if you look at the record. There are other cases where an invasive species came to a new place, caused a stir for awhile, maybe even an outbreak for a year or five, and then faded off into the background and semi-native obscurity. Even the dreaded purple loosestrife, subject of majorly expensive eradication campaigns in the eastern United States, is a source of nectar for native pollinators and its presence has been positively correlated with an increase in bird diversity. Not that North America is having a love affair with kudzu, the zebra mussel, or the eucalyptus tree (though the latter is now the favored West Coast roost of the monarch butterfly), but the exceptions to the rule give me pause.
Immigration is an important natural factor (new islands depend on the phenomena) which humans have merely accelerated with trade and travel. New arrivals on this continent these days often do so well because they’re entering highly disturbed habitats, thanks to us humans, where some trait of theirs is favored. Think excessive, polluting nutrient loads in lakes and rivers, or fragmented forests.
Islands usually are observed to have the worst problems with so-called aliens, where a systemic response to a new life form is seemingly less robust. Then there’s Australia and its cane toad debacle, the rabbit debacle, etc. Yet the degree of human disturbance and ecosystem alteration in these places prior to introduction is seldom noted.
The usual human response to novel critters in the ecosystem is that they’re guilty until proven innocent, and eradication is the rule. The alien invaders are often portrayed as aggressive, greedy, and highly reproductive … all traits and terms commonly ascribed to humans, too, immigrants or not. Prejudice, xenophobia, fear, hatred, projection, and displacement can be found in most anti-alien rhetoric. Having, or creating, an enemy is immensely powerful.
But why be so addicted to ecosystem control, to thinking that we can keep places “pristine,” when the continent has been so heavily altered in the last few hundred years? Human presence in every ecosystem argues against this. A wiser response to a newcomer would counsel patience and observation, to see what negatives and positives result from an organism like hydrilla’s new tenure — and if the critter is deemed to truly threaten balance in an ecosystem, a measured effort at control would be called for. Failing this, too many resources, even toxics, will continue to be leveled in the war against aliens, further illustrating our failure to understand both our home and our sense for what “native” is.