Tuesday, November 27, 2007

Mollusc madness

A story of fresh water mussels: Will we lose the "snot-line fishing mussel"?

Ohio's diverse native fresh water mussel fauna has suffered extinctions, extirpations, and severe population declines while introduced species like Asian clams and zebra mussels have enjoyed population explosions in rapidly expanding ranges. And; more invasive species wait in the wings ready to invade. It's only a matter of time.

This sad story is not unique to Ohio. From Ohio's purple cat's paw mussel to Alabama's "snot-line fishing mussel", most species are in decline and many have already been lost in time like the fleeting brilliant glimmer of a raindrop splashing stream water above a sandbar mussel bed.

It's a mess!

Dr. Tom Watters, mollusc expert with The Ohio State University (GO BUCKS) brought his talk, "Freshwater Mussels: From Living Rocks to Mean Mothers" to Hopewell National Historical Park near Chillicothe, Ohio for presentation to the Scioto Valley Bird and Nature Club Monday night November 26.

G. Thomas Watters, PhD
Curator of Molluscs
Department of Evolution, Ecology, and Organismal Biology
The Ohio State University

It's a story of silent disappearance:

Freshwater mussels originated in North America long long ago in a place not very far away (right here in the Mississippi watershed) sometime during the Triassic Period when the biggest things disturbing them were dinosaurs. These dinosaurs were far less effective mussel killers than today's human poachers collecting for the cultured pearl trade--a continuing modern threat to rare mussels.

The Mississippi watershed is ancient, and throughout the undisturbed native river system there were riffles, rapids, sandbars, emergent vegetation like water willow, snags and sawyers, stream side shade trees, low silt loads, no industrial chemical pollution, and most importantly, seasonal rise and fall in river system water levels; the slow heart-beat of the continent.

The undisturbed heart-land offered habitat heterogeneity throughout ancient natural continental arteries, the streams and rivers of unspoiled North America. The Mississippi watershed supported the diversification of our mussels in diverse streams and rivers rising in diverse geology and physiography. North America once supported more than 300 species. The vast Mississippi river system, heart of our continent, supported great fish diversity too, and mussels rely on fish to complete their life cycle, and they rely on fish migration to disperse them.

North America is the center of diversity holding most of the world's species. The Mississippi River watershed is the heart of this diversity.

The life cycle of mussels may span decades yet aged individuals may never leave a particular sandbar. They are ingenious creatures--well, they have evolved ingenious reproductive strategies to ensure their propagation and dispersal--under natural conditions.

Pictured above is a fish mimic structure used by the mussel to bring host fish close enough to inhale larvae (original presentation photo by G. Thomas Watters, PhD)

My favorite species, introduced to me through video by Dr. Watters at our meeting, has an impossible Latin name so I'll toy with Dr. Watters' description and call it the "snot-line fishing mussel". It occurs only in Alabama, but we won't hold that against the creature.

Picture this:

The female snot-line fishing mussel, a fist-size denizen of river sand, spends most of her life softly filtering stream water for nutrients--just about anything biological that she can filter. At maturity, she is compelled to reproduce. When she has received semen, randomly released into the water by her local male mussel, she is soon ready to go fishing for her host, the Suwanee bass. She is particular about her host selection and no other fish species will do!

She grows a zillion little fertilized larvae called glochidia. She is expert at the small egg gambit wherein she plays the nickel slots rather than high stakes poker! She does this by making a zillion tiny glochidia for release--a zillion nickel bets. The slots need pay only once. Any given individual has a very very low chance of survival but by releasing so many she hedges; success through overwhelming numbers--small inexpensive (energy-wise) larvae.

She packs these zillion glochidia into a fish lure, that's right, a small fish-looking glochidia container, another hedge. Now she produces a long thin strand of mucus (snot-like) fishing line that is nearly invisible in the water and a good 18 feet long! Guess what's at the end of the line? Yeah, the fishing lure. It even wiggles in the current!

Well, the unwitting Suwanee bass can't resist the lure and when it bites into it the lure explodes in its mouth releasing the zillion glochidia. Some of these land among the gills where they clamp on like tiny bear traps and hitch a ride with the bass while they develop into small adult mussels. Eventually they will drop off and make a home in the sand for the next few decades, softly filtering stream water--and playing the nickel slots.

The story of loss of freshwater mussel species is dismal. Surely, we would have acted sooner and more effectively if these creatures were showy flights of fancy like many of our birds, for example (though we have lost wonderful birds like the Passenger Pigeon and the Carolina Parakeet).

The numbers tell the dismal story:

Of the nearly 300 North American species about two dozen are already extinct and about 20% of remaining species are federally endangered. Fresh water mussels are the most imperiled animals in North America by percentage. Only about one-third of North American species have stable populations.

Ohio has a large share of mussel diversity but of our 80+ native species we've already lost six species to extinction and several others are in precipitous decline. Another 13 species have been extirpated from our state.

Mussels suffer numerous threats. Among these the most profound has been the damming of rivers and streams into series of lakes that drown habitat heterogeneity. These dams are like clots in the heartland's arteries. They are good for boats and commerce but they attack the heart of our natural waterway system. Further, siltation of streams weakens and suffocates many species. Industrial and agricultural pollutions take their tolls, too. And, urbanization channelizes and homogenizes our once diverse headland streams.

Perhaps the most disturbing and surprising loses are due to commercial mussel harvest still legal in several southern states. Even more surprising is the commercial mussel poaching in Ohio and other states responding to the need to protect fresh water mussels. Teams of night-operators illegally collect tons of mussels to sell in the cultured pearl manufacturing trade--most of which go overseas. Our freshwater mussels are the magic secret to success of cultured pearl manufacture. Our mussels are collected for the fleshy lining of their shells that seeds the oysters making the pearls.

The harvest of native mussels should have ceased when the invention of plastic buttons replaced mussel shell buttons at the turn of the last century but vanity rules worldwide demand for pearls today just as vanity ruled the hat-making trade in days gone by when fancy-plumed hats were in such demand that plume hunters nearly wiped out showy bird species. Late in the Nineteenth Century the worldwide market for plumes lured commercial punt-gun and net hunters into all corners of the globe--but mostly in our United States. The trade stopped only after loud protest and a shift in ladies' fashions.

Unfortunately for our native mussels they are not showy charismatic creatures like North America's Snowy Egret or Indonesia's Birds of Paradise. Mussels don't demand our attention (until you see Dr. Watters' videos of mussel fish lures).

Who protests for fresh water mussels? How many women examine the origin of their cultured pearls?

Native mussels continue their silent decline. We may lose the rare snot-line fishing mussel unless we protect and restore the ancient rhythm, the rise and fall of continental waters, the natural heart-beat of North America. And, we may never restore the rare mussels until we reevaluate our fascination with cultured pearls.

The content above is based on my memory of Dr. Watters' presentation so if there are errors they are mine. Use these websites for additional authoritative information:

Visit the OSU Division of Molluscs at:

Join the Freshwater Mollusk Conservation Society at:

Educators, this pdf is the place to start:

Additional agency resources:





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