Reflection 2

"Invasive species"

Gawande's discussion of the fight against Polio in "The Mop-Up" describes a concerted effort to vaccinate millions of children in India following the appearance of a single outbreak of the disease. Thousands of volunteers went house to house in the region of the outbreak, carrying the refrigerated vaccine, attempting to vaccinate every child. Sometimes children weren't home. Sometimes parents refused the vaccination for their children, due to mistrust (rumors had circulated that the vaccine was causing infertility or other problems.) The vast majority of children were vaccinated, however. After a successful vaccination, a mark was made on the child's fingernail to record that the vaccination had taken place. Similar attempts had been made in the past in an effort to eradicate Polio from the planet, but the disease has kept cropping up. In theory, if every single child were vaccinated, the disease would simply vanish for lack of hosts. Despite the diligence of the vaccination effort, it has proven very difficult to vaccinate every child. Compounding the problem is the resilience of the disease: it can remain latent and contagious for long periods. In short, the effort to stop Polio can only be successful when the virus is eradicated entirely, and efforts thus far, despite massive investments of money and manpower, have only been able to quench the majority of the disease.

Invasive species are species that are not native to an ecosystem, but whose introduction causes economic or environmental harm. Invasive species are difficult to control, often occupying the niches of natural fauna. Foreign to an ecosystem, they often grow unchecked, wreaking havoc. The only way to control the most insidious invasive species is to remove them from the ecosystem, just as we attempt to remove polio from the world: eradication.

Zebra mussels are an invasive species in the Great Lakes region. Introduced sometime around 1990, the zebra mussel has colonized vast areas of the Great Lakes and surrounding water basins. The mussels are so prolific that they clog water intakes of power plants, factories, and other enterprises. The mussels interfere with almost any endeavor that deals with the lakes, growing on any smooth, hard surface. The mussels crowd out native species by eating all the algae and nutrients in the water. In some cases, the mussels actually kill other species by growing on them: native clams populations have plummeted due to zebra mussels.

Any effort to control the mussels has failed. The mussels are seemingly too prolific. A single mussel can release millions of offspring every year. They exist in a microscopic larval stage until they find a suitable substrate to grow on; these larva are nearly impossible to detect, let alone control. Efforts have instead turned to creating surfaces that the mussels cannot attach to, as well as preventing the spread of the species to other waterways. In one sense, the use of surfaces that the mussels cannot attach to has largely alleviated the problem as far as industrial usage of the water resources is concerned; however, the ecological ramifications of the mussels have been unaffected. The mussels continue to spread, being carried on boats, for example, despite public education efforts to curb the species' range. Any effort at eradication in existing affected ecosystems is neutralized by the shear scope of the problem. Introduction of predators of the mussel cannot hope to overcome the shear number of mussels that exist.

Metzger Marsh in western Lake Erie is one such area that has been inundated with zebra mussels, but is unique in that native clam populations have been able to survive. In 1994, a large-scale project was undertaken to restore the wetlands of Metzger Marsh, which had been in decline since the 1940's due to human overuse. This plan was not intended to curb the zebra mussel population (because zebra mussels are so difficult to control) but rather to restore the natural wetland habitat. The plan to restore the marsh included a three-year transition period in which the water of the marsh would be drained and restored, with native species being relocated and then reintroduced after the water level had been returned (most fauna would not survive the low water levels).

A survey of the wildlife in the marsh indicated extensive zebra mussel infestation and patchy areas of native clams (among other animals); however, the population of native clams was found to be much more extensive than initially estimated during the relocation phase beginning in 1996. This indicated that perhaps the mussel problem either was not as terrible as believed, or perhaps had a solution; in any case, over 7000 individual specimens of native clams were removed from the marsh to a facility for the duration of the water-level fluctuations. Reintroduction of the clams in 1999 proved successful, although zebra mussels continue to colonize the area. What was unexpected was the persistence of the native clams despite the mussels' presence. In this instance, the invasive species was not eradicated, but it still did not seem to be as detrimental as could be expected.

Much research revealed the reasons why: The waters of Metzger Marsh were slightly warmer than other waters of the area. This caused the clams to burrow down into the mud, effectively scrubbing off any zebra mussel larvae that had attached to their shells. Additionally, the silt where the unaffected clams lived had smaller-sized particles that the silt of other areas; evidently the zebra mussels were unable to grow on such a substrate. This offers little hope of a solution to the zebra mussel problem: all that has allowed these clams to survive is a lucky coincidence of climate and geology. If zebra mussels are to be eradicated from the Great Lakes and surrounding watersheds, an effective way of removing them must be found.

Lessons from the efforts to stop Polio can be directly applied to the zebra mussel problem. Some families refuse the Polio vaccine, meaning that a pool of potential hosts for the virus exists. To stop the spread of the zebra mussel, all aquatic vessels must have all mussels removed if they travel between various waterways. The transmission of the mussels does not seem like it will be stopped, however: the problem is simply too unimportant for the vast amount of effort it would take to inspect every boat or motivate every boat owner to take the initiative in preventing the spread of the mussel. The zebra mussel is incredibly resilient, just as the Polio virus is. To eradicate it would take a relentless (diligent) effort using an as of yet undiscovered method of killing the mussel.