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Fish play fundamental role in reproducing mussels

A cache of clubshell and Northern riffleshell mussels are prepared for release into Big Darby Creek.
 
Sunday, September 1, 2013
 
NATURE
Jim McCormac
 
At a glance, mussels seem uninteresting. Freshwater mussels — clams — look like rocks, and they lie partly buried in streambeds, out of sight and out of mind.

Yet these aquatic paperweights have one of the wildest reproductive strategies of any animal.
Luck, and helpful fish, must come together to make mussels. The male jettisons sperm into the water, which drifts downstream. Hopefully, a female mussel will filter the male’s sperm from the water. If so, she’ll produce larval clams known as glochidia.

And this is where things get downright bizarre.

Most mussels require fish hosts. To lure the fish into range, many species use incredible deceptive tactics. The mussel opens its shell and extends a flange of tissue called the mantle. The mantle’s edge resembles a small baitfish or other tasty-looking object. When an inquisitive fish investigates, the mussel blasts it with a barrage of glochidia, which attach to the fish’s gills.

The larval glochidia remain on the fish until partly grown, then drop off and embed in the stream bottom. There, they grow to maturity and might live a long life — sometimes more than a century.

Adult mussels filter-feed: They siphon water into their bodies and extract diatoms, algae and other tiny fare. In pre-settlement Ohio, when streams abounded with mussels, their collective masses probably played a big role in cleansing water.

European colonization soon brought tough times for mussels. In 1857, a pearl was found in a mussel in New Jersey; it was worth a princely sum. This sparked the Pearl Rush. Millions of mussels were yanked from streams, shucked and discarded by people lusting for pearls. In 1887, German immigrant Johann Boepple saw a new way to exploit mussels: He spawned a massive button trade in which mussel shells were hole-punched, and the round chads became shirt fasteners.

Pearling and button-making ran their course, but the degradation of streams from large-scale land-use changes has not. Bottom-dwelling filter-feeders such as mussels have been severely affected, and many mussels are now imperiled. Of the 80 species found in Ohio, 28 are listed as endangered or threatened, 11 are extirpated (gone from Ohio) and six are extinct.

Stream conservation efforts have brought hope for mussels, and perhaps the best story involves Big Darby Creek. Land protection along the stream, most notably by Franklin County’s Metro Parks, has safeguarded water quality in the Darby and allowed restoration opportunities for rare mussels.

Mussels have their advocates, and the Ohio Division of Wildlife, Columbus Zoo and Aquarium, Ohio State University, U.S. Fish & Wildlife Service and other partners have collaborated to help. Experts from these organizations recently released 4,000 specimens of two endangered species: Northern riffleshell and clubshell. Once common in Big Darby’s drainage, they had almost vanished. Thanks to these efforts, healthy mussel populations should be purifying the Darby — and engaging in weird reproductive rituals.

Naturalist Jim McCormac writes a column for The Dispatch on the first and third Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.


Learning more

The Freshwater Mussels of Ohio (Ohio State University, $78.80) belongs on the shelf of anyone interested in Ohio’s natural history. Published in 2009 and written by G. Thomas Watters, Michael A. Hoggarth and David H. Stansbery, the 421-page book is loaded with fascinating information.
 

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