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No other family of North American organisms are in as much trouble as the freshwater mussels belonging to the family Unionidae . Of the 300 species that exist in North America, 70% have obtained "in need of management" conservation statuses. In one particular genus, historically robust with 15-20 species ( Epioblasma ) depending on who you talk to, all but one species are either extinct or have obtained Federal Status; the remaining species is a Federal Candidate.
The first question most people ask is... "Why should I care?" I mean really, it's just some clams crawling around in the muck, right?
Well, here's some pictures and video that might get your attention!
Plain Pocketbook, Lampsilis cardium 
Wavy-Rayed Lampmussel, Lampsilis fasciola |
Video
(Right Click, Save As to avoid browser lock up)
River Raisin, Sharon Hollow, MI
Duck River, Pottsville, TN
Photos Duck River, Lilard Mill, Tennessee - May 2007 Duck River, Lilard Mill, Tennessee - May 2006 Lake Wilson, Hillsdale, Michigan - July 2006 French Creek, Venago, Pennsylvania - August 2006 Huron River, Zukey, Michigan - September 2006 Lake Erie Seiche Survey Otter Creek Bay - November 2007 (Recruiting with zeebs growing on them?) Severe Lake Seiche Effect on the Maumee River White Street Access & Audubon Island, Maumee, Ohio - November 2005 Delaware Creek City Park, Toledo, Ohio - November 2005
But don't let me stop you there! The story is more amazing than the photos... |
The first answer to the question "Why should I care?" is that these mussels provide a host of beneficial ecosystem services through their habits. One of their feeding strategies is to filter tiny organisms out of the water column such as algae and diatoms. In doing this, water clarity is greatly improved, as they consume the algae and deposit suspended silt particles into the substrate. Additionally, they are a link between the pelagic (open water) and benthic (bottom) food webs, providing food for the larvae of insects that are important food items to fish while in aquatic larval phases, and birds while in terrestrial adult phases. As well, as the mussels move around, they liberate some of the nutrients they've accumulated in the sediment, making those nutrients available again to the pelagic food webs in times where nutrients are limited. Even after death these critters are still working for the ecosystem. Their valves (shells) contribute to stream bed stability, are sediment traps and habitat for a wide variety of organisms such as fish and aquatic invertebrates.
For additional information on mussels as habitat engineers, please check out Dr. Caryn Vaughn's lab website where you can get pdf reprints of her insightful work.
What is most amazing about these critters are their reproductive strategies. When I say amazing, I really mean unbelievable . You see, many mussel species typically live in streams where the flow of water is in a single direction. If you're a benthic critter that crawls around in the mud, maybe over a couple meters in your life time, how do you get your young upstream to other suitable habitats? Mussels have solved this by infecting fish with their young in a semi-parasitic phase known in science as a glochidia . Once infected, the fish move around and disperse the young. However, infecting the fish is the tough part, and in order to infect the fish with the glochidia, mussels have come up with three infection strategies.
The first is to literally grab the fish, and is seen to the left here with this Federally Endangered oystershell mussel (I've highlight the mussel in the inset). Notice the contrasting colors of the valve and tissues (dark and light). A fish investigating the light material as a "free meal of dead mussel" has a little bit of surprise when the dark material, previously appearing as a part of the substrate, suddenly slams shut on a fin or even the fish's nose! To aide in capture, the mussel even has tiny "teeth" called denticles , which are not immediately obvious in this picture, but are almost imposing on the valves of a dead female. A friend referred to one species as the "Venus Fly Mussel" :)
A second strategy is to send off packages of "payload" known as conglutinates . These are basically packets of mucous the female releases that have glochidia ready to slam shut the second they touch a fish. Some of these conglutinates are extremely detailed, looking like larval fish or prey items such as black fly larvae. This increases the rate of infection dramatically, as the fish will strike at the conglutinate, forcing it to explode, and pour glochidia over the mouth and gills, which is the preferred site for infection.
While I don't have any material on conglutinates, Dr. Chris Barnhart made any of my footage obsolete (before I even started) with his Unio Gallery :) You really MUST check this site out, if you find this subject even remotely interesting. The footage he's captured is, as I said, unbelievable.
The third strategy is a modification in the tissue of the female that appears like a fish, a crayfish, a hellgramite... Something a fish would eat. The lures are actively displayed by some species, such as the lure of the plain pocketbook below on the left, or fluttered occasionally, such as the lure of the wavy-rayed lampmussel on the right. Once struck, the mussel dumps her payload right into the fish's mouth.