The freshwater mussels of Maine
March 11, 2008 - TRC
In Maine we have thousands of lakes and ponds, as well as tens of thousands of miles of rivers and streams. These serve as essential habitat elements for all of Maine’s wildlife, but there’s a class of animals that live under these waters that usually escapes notice. Freshwater mussels in Maine are often the dominant animals in terms of biomass (total weight of all animals in an area) in waters throughout the state. Their shy, inconspicuous lifestyle keeps them from commanding much attention, but they have a highly unusual lifestyle when it comes to reproducing.
For the vast majority of their long lives, freshwater mussels simply sit partially buried and filtering water to feed on algae. When they reproduce, however, almost all freshwater mussels require a period of parasitism on fish “hosts.” As parasites go, mussel larvae (called “glochidia”) are fairly innocuous to the fish. The mussels are simply hitching a ride on their host by clamping on to either gills or fins and dropping off after a certain period of transformation. This habit allows them to colonize widely separated areas, as well as traveling upstream.
To further complicate matters, generally each mussel species (there are 10 in Maine) requires specific fish species to successfully transform into juveniles. To attract a desirable species, female mussels of some species have evolved a “mantle lure.” This is an outgrowth of the soft part of the body that resembles some food item of the targeted fish. When a fish attacks the “minnow” or other lure, the female releases a cloud of glochidia into its mouth to parasitize the gills. One species of mussel in Maine is known to use a lure resembling a minnow, but species in other states have lures that look like crayfish or leeches. Other mussels package the glochidia in a structure that looks like food and release it into the water. These often appear to be worms or insect larvae, and once attacked by a fish they disintegrate, allowing the glochidia to latch onto the gills.
Given their unusual way of overcoming mobility difficulties and the fact that mussels are a long lived and extremely important organism in aquatic habitats, I recommend learning more about these interesting organisms. The Freshwater Mussels of Maine is a book that was released by IF&W several years ago, and it does an excellent job teaching identification and life histories of Maine species. Another resource on the Web is the Unio Gallery on Missouri State University’s Web site, http://unionid.missouristate.edu/. There are some amazing pictures of mantle lures on this site.
-- By Philip Wick, Fishery Biology Specialist, Fisheries Research Section, Bangor
Submitted by : Deborah Turcotte, Acting Public Relations Representative
Maine Department of Inland Fisheries and Wildlife
284 State St.
Augusta, ME 04333
W: (207) 287-6008, C: (207) 592-1164
NOTE - This article reflects the views of the author and not necessarily those of the TRC Alliance Team.