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Biologists Re-introduce Mussel Species To Big Darby Creek.
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1700 former Pennsylvania ‘residents’ are settling into their new homes in the bed of the Big Darby Creek. In a partnership with Battelle Darby Metroparks and the U-S Fish and Wildlife Service, Ohio State University researchers waded into the Big Darby Creek Wednesday to transplant 1700 Northern Riffleshell Mussels. It’s the largest single release of an endangered species in Ohio history. WOSU’s Jonathan Hickman has the story.
After putting up with two weeks of sloshing around in buckets and igloo coolers and a layover in a mussel rearing facility, these Northern Riffleshells are starting new lives in the Big Darby Creek. OSU Museum of Biological Diversity’s Curator of Molluscs Tom Watters thinks they’ve handled the trip quite well for a species that’s struggling to avoid extinction.
“We’ve lost, I think, six out of the original 1750, which is really extraordinary considering, I mean, they started out in Pennsylvania, and they’ve been bouncing around every place.” Says Watters.
Like a number of other freshwater mussels, just 30 or 40 years ago the Northern Riffleshell was common in the streams of the Ohio River basin and parts of Lake Eerie. But changes to rivers throughout the Midwest have Watters worried about the future of these native sons of Ohio.
“My kids will be going, oh come on, come on now granddad, there never were any freshwater mussels, you’re making all that up.” Says Watters.
Now limited to just a few rivers in the United States, the riffleshell is extinct everywhere in Ohio except a short section of the Big Darby Creek. Though other mussels are still plentiful there, it’s been 15 years since Watters has found a living Riffleshell in the Big Darby.
“They seem to require really high water quality; other species of mussels can put up with a lot more than these riffleshells. This riffleshell belongs to a group of freshwater mussels that are the most endangered of all the frshw mussels, and in fact probably half of them are actually extinct. The rest of them are on the federally endangered list except for one, and that one’s going to be.” Says Watters.
Researchers are still uncertain exactly what was responsible for the widespread decline of the Riffleshell, but an unusual aspect of its reproductive cycle may provide an important clue. Like all freshwater mussels, juvenile Riffleshells go through a larval stage, where they live as parasites on the surface of fish. But where other mussels simply release larvae into the water to find a passing fish, the Riffleshell goes a step further.
“They actually require the fish to be caught by the mussel. The fish sticks its nose inside the mussel’s shell, the mussel closes on it like a bear trap, and then starts pumping its larvae onto the fish. Which is very unique; no other mussels do that.
Unfortunately for the riffleshell, they’ve also evolved to use host fish that can be just as rare as they are. And if the stream is regularly disturbed-say, by suburban development or streambank erosion–where the mussels once easily caught fish in a bear-trap kiss, now they might pass like two ships in the night.
“The fish have to see the mussels in order to get lured in this. But what we’re seeing is, well you see it out there now, the turbidity of the water. The mussels may be there, the fish may be there, but they never see each other anymore because the water’s so turbid.”
And that’s not the only reproductive challenge freshwater mussels face. Since these little guys don’t have legs, males and females can’t reach one another to physically mate; instead, the male releases sperm into the water and hopes it finds its way to a female. OSU graduate student Kody Kuehnl, who has been working on the riffleshell transplant, says the males employ a special strategy to help increase their chances of success.
“So if a male releases sperm into the water, it might go everywhere, you know, it might take a lot of individual sperm that a female would have to siphon in order to fertilize all her eggs. So the way they’ve compensated for this is they make this structure that consists of millions of sperm in one ball or Frisbee type shape. The males actually release hundreds of these, maybe even thousands. You know, when they release them, they can actually turn a small aquarium white.” Says Kuehnl.
Now scientists think the Northern Riffleshell is ready to set up camp in Ohio again, at least in the Darby Creek, which hasn’t suffered from pollution and erosion the way many other Midwestern rivers have.
“It should, if everything works as planned, it should spread out from these points and go back to its original range, which was most of the lower half of the Darby Creek system. And who knows, maybe go back into the Scioto. It used to be there as well. The Scioto has had obviously major problems being downstream of Columbus, but it’s cleaned up a lot, so who knows.” Says Watters.
For now, researchers will focus on the 1700 mussels they plopped into five secluded areas in the Big Darby Creek on Wednesday. Each mussel is tagged with a special transponder that will help researchers like Kuehnl check up on them year after year; he’s already had some practice
“We put out a pilot study with a different species and also 50 Northern Riffleshells last year, and these guys don’t move a whole lot, once they get into the substrate they might move a couple feet a year, but they don’t move hundreds of yards or anything like that, so they’re pretty easy to find again.” Says Kuehnl.
Starting next year, they’ll also be keeping an eye out for baby Riffleshells-those will be the ones without the transponders. But the baby showers will have to wait; for now, Watters is giving the Riffleshells a chance to settle in to their new home in the Darby.
“I think they’re happy now. They’ve been sitting in facilities and bouncing around in trucks for two weeks now. So I’ll finally give them a rest.”
Jonathan Hickman, WOSU News.