To study rare, mysterious animals, some biologists climb into submersibles and plunge two miles down to the bottom of the sea. Michael Hoggarth has only to leave his office at Otterbein College in Westerville, Ohio, and climb into a pair of waders. He slides his feet into rubber boots welded to waterproof canvas overalls that come up to his armpits, and steps slowly into Killbuck Creek, a soupy green river that winds through rolling cropland in north central Ohio. Under a low lid of clouds the countryside can remind him of his native Washington State, although when the sky clears there are no snowy mountains in the distance. But what the Pacific Northwest has in mountains, the Mississippi River watershed has in freshwater mussels, and they are what Hoggarth is looking for. The entire West Coast has only eight native freshwater mussel species. The Mississippi valley has virtually all the nearly 300 other North American species--the richest collection of freshwater mussels on Earth--including Hoggarth’s quarry today: the elusive purple catspaw.
A few years ago Hoggarth would have considered this a fool’s errand. Only two populations of the purple catspaw were known, one in Tennessee and one in Kentucky. The species hadn’t been seen in Ohio since the Civil War. But in 1991, Hoggarth turned over a recently dead shell in the Walhonding River (of which the Killbuck is a tributary) and was startled by a distinctive flash of purple. For two years Hoggarth and his students scoured the Walhonding for the endangered purple catspaw without luck. A year later, while looking for rare fish in Killbuck Creek, Hoggarth stumbled onto a live population of the mussels. Now he visits the Killbuck regularly in the hopes of finding more.
In the telling, Hoggarth’s mission might be mistaken for a pleasant little episode in malacology. It is not. The remarkable diversity of mussels like the purple catspaw in this region and their equally remarkable elusiveness are significant ingredients of the most important ecological questions of the day: Is the diversity of life diminishing at a catastrophic rate? And if it is, just how fast is it disappearing?
When asked to think of the biodiversity crisis, people tend to envision distant locales like the Amazon or the forests of Sumatra. In fact the crisis is just as real here in Ohio. The purple catspaw belongs to a vast tribe of freshwater mussels known as the unionoids, which once flourished in the great North American inland rivers. Pioneers might have preferred the word infested; they named one species heelsplitters for the menace they posed to livestock and barefoot humans. The unionoids were so numerous that they accounted for more than half the world’s species of freshwater mussel. But they were also remarkable in that they were all endemic species--that is, they were localized species that adapted to a particular ecosystem and thus were limited to one range. The purple catspaw, for example, was a big river mussel, a lover of strong currents and hard river bottoms.
