According to a Washington Post article, Toxic Waters Provide ‘a Snapshot of Evolution,’ from Monday, January 23, New Bedford harbor is now swarming with Killifish. This is remarkable because New Bedford Harbor, designated as a Superfund site, is so polluted by PCBs that almost nothing can live there:

The waters of New Bedford Harbor, Mass., sparkle on sunny days. But beneath the bay’s gleaming surface lies one of the most toxic environments in the nation.

“You’d think nothing, absolutely nothing, would be able to live in New Bedford Harbor,” says Jim Kendall, a fisherman and president of New Bedford Seafood Consulting. “But you’d be dead wrong. Something does live there, and in huge numbers.”

Killifish, three-inch-long saltwater fish common along the Atlantic coast, thrive in these polluted waters…. “Sometimes they’re so thick in the harbor, you could just about walk across on them,” Kendall says….

No one is quite sure how the killifish have managed to adapt to the toxic environment. There are representatives of other species — the article mentions quahogs — living in the harbor, but the killifish are there in great numbers. Why so many killifish?

“That’s the big question,” said toxicologist Mark E. Hahn of the Woods Hole Oceanographic Institution in Woods Hole, Mass. “It’s what can happen when animals are exposed over generations to high levels of contaminants.” The result goes one way or the other, he said. “The population dies out or it adapts through genetic changes to extreme pollution levels.”

In one way, this is a hopeful story: even with all the toxic sludge we’re pumping into the environment, some organisms seem to be able to adapt. In another way, this is a very worrisome story: the killifish are filled with PCBs, they are being eaten by other animals, and so the PCBs have a new entry point into the wider food chain. I’ve seen lots of Mergansers on the harbor this winter; Mergansers eat fish; the Mergansers are likely getting pumped full of PCBs.