The death of 2 million fish in Chesapeake Bay isn't a sign of apocalypse, historical or otherwise, but it does offer a chance to consider what could happen if colder winters become routine in the eastern United States.
Some climatologists have proposed that, paradoxically, a warming Arctic will actually push cold air south, producing patterns like the one believed to have caused the Chesapeake fish kill.
If cold snaps grow deeper even as year-round temperatures rise, Chesapeake Bay's ecosystems would adapt -- but perhaps not, as is usually forecast, through the northward migration of warm-loving species, but by favoring species that can handle extremes.
"The long-term makeup of ecological communities is more driven by extremes than average conditions," said Boris Worm, a marine biologist at Nova Scotia's Dalhousie University. "Whatever can survive the extreme makes it in the long-term."
The Chesapeake Bay fish kill was the latest in a series of animal die-offs to gain attention -- and more than a little hysteria -- after the dramatic New Year's Eve death of 5,000 red-winged blackbirds over Beebe, Arkansas, and the subsequent report of 100,000 drum fish dying in the Arkansas River.
Those die-offs were not exceptional in the history of single-event die-offs, and paled in comparison to what's ongoing among North American bats and bees, and in amphibians around the world. But the timing, proximity and general eeriness of the deaths captured the public's imagination, and suddenly people started paying attention to die-offs that would normally have gone unremarked.
Bird deaths were reported in Sweden, Kentucky and Louisiana, and dead crabs off the English coast. The "aflockalypse" went viral, and the internet filled with (mostly) tongue-in-cheek chatter about the End Times. When the Maryland Department of the Environment released a statement Jan. 5 about 2 million spot and croakers dying in Chesapeake Bay, the public was primed to perceive catastrophe.
Unlike the other die-offs, though, the Chesapeake fish kill occurred in a region where ecological monitoring is intensive, thanks to the importance of the estuary's historic fisheries, and ongoing efforts to fix the damages of pollution and overfishing. Oxygen, temperature and toxin readings are taken constantly throughout the estuary. History is also a guide: 20 million fish died in similar circumstances in 1976 and again in 1980. Researchers quickly identified unusually cold water as the prime suspect.
Chesapeake Bay waters were colder on average in December than they'd been in 25 years. In terms of temperature anomaly, they were actually the most unusually cold waters in the world. Extreme cold can alter the function of gill membranes, resulting in salt dysregulation and ultimately dehydration. And while fish can often swim away from environmental stress, they can be vulnerable to sudden temperature drops, or end up trapped by currents or other ocean conditions. That's what appears to have happened this time.
Biologists say that, from a long-term ecological perspective, the deaths will cause barely a ripple. They are interesting, though, in that the Chesapeake Bay has gradually warmed over the last several decades, particularly in the spring and summer, and even in winter. If, mid-Atlantic winters become severe or highly variable, "that's a very interesting dynamic," said David Secor, a population ecologist at the University of Maryland's Chesapeake Biological Laboratory. "We're shifting the range of warm-adapted fish like spot and croaker -- but then we lure them into an ecological trap."