Friday, Apr 20, 2018
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Tom Henry

Decline of mayflies befuddles scientists

They're called mayflies, junebugs, Canadian soldiers, and shadflies by us mortals. Many of those who spent the 1970s with slide rules in their shirt pockets call them by their real name, Hexagenia, even at cocktail parties.

Entomologists might disagree, but I doubt if any insect draws as much affection - especially one that splatters itself on windshields, blankets street lamps, and can, with a locust-like swarm, make Port Clinton's roads slicker in June than in January.

Mayflies, which typically emerge in early June - go figure - have captured our hearts because of what they have come to symbolize over the past decade: Lake Erie's recovery.

Unfortunately, a new report suggests we've been lulled into premature back-patting.

The recovery is not nearly as widespread as a team of scientists headed by Ohio's top Mayfly Guy, Heidelberg College's Ken Krieger, had expected it would be by now.

The burrowing bug is an indicator of Lake Erie's health because it spends its first two years beneath sediment as a worm-like nymph. In short, it needs clean sediment to survive.

It dies hours after it reaches adulthood and sprouts wings. That part isn't dictated by pollution per se. Nature didn't give it a mouth.

Mr. Krieger headed a team that included Michael Bur and Don Schloesser of the U.S. Geological Survey, plus Jan Ciborowski and David Barton of the University of Windsor and the University of Waterloo, respectively. They studied mayfly distribution and abundance from 1997 through 2005. Results were announced Tuesday by the International Association for Great Lakes Research.

The team concluded that densities varied from year to year, especially near the Lake Erie islands.

That's not a surprise. Nothing is automatic. But the research team expected mayflies to be colonizing sediment as far east as Buffalo by now.

"Instead, after increasing in numbers in some areas off the Ohio shore through 2000, they virtually disappeared in 2001 and have not returned [to the numbers they were]," Mr. Krieger said.

So what gives? Is the sediment from Cleveland east that much more polluted?

Not necessarily. It's deeper. So it's colder. But it was deeper and colder when mayflies swarmed out to Buffalo during the first half of the 1900s.

The central basin's infamous "dead zone" - a shifting pocket of water that doesn't have enough oxygen to support life - is one possible factor.

So is the round goby, a pesky little fish that invaded the Great Lakes after its main source of food, the zebra mussel, started showing up in 1986.

Both came from eastern Europe in the ballast water of oceanic vessels, as have other exotics. Each represents failures of the U.S. and Canadian governments to keep the Great Lakes free of intruders, something which the U.S. Environmental Protection Agency identified five years ago as the lake system's No. 1 issue.

Round gobies feed on mayfly nymphs, as well as the mussels.

But that's nothing new: Fish have snacked on mayflies since Day One. Birds too: Many of the mayflies lucky enough to sprout wings get gobbled by avian creatures. Yet even as tasty morsels, mayflies outproduced their predators by the billions.

What other explanations are out there? Who knows? The team is befuddled why, in its 2004 lakewide survey, mayflies were found at 63 of 89 western basin stations, but only seven of 112 in the central basin and none in the eastern part of the lake.

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