FLORIDA MUSSEL BIOLOGY--1999 Article

By Gary Warren

There are three families of bivalves (mussels and/or clams) that are native to North America. These
families are: Sphaeriidae, Magaritiferidae, and Unionidae. The Sphaeriidae, or fingernail clams, are
small in size (usually not larger than 1 inch in length) and are not threatened on the North American
continent. The Margaritiferidae and Unionidae are larger in size and are considered imperiled on a
continent-wide basis. Of the 297 species of these two faimilies occuring in North America, 163 (or 55
percent) are considered imperiled by federal conservation agencies and the Nature Conservancy. Of
the 50 species occurring in Florida, 7 are currently federally listed as threatened or endangered and 5 more are being considered for listing. Federal and state biologists believe that an additional 10 Florida
species should be considered as candidates for listing. This brings the total to 22 (or 44 percent) of
the Florida fauna which is considered to be imperiled.

The continent-wide decline in the mussel fauna has been caused primarily by habitat destruction and
degradation. These detrimental habitat modifications have been caused by construction of water control
structures (mostly dams), siltation associated with runoff from agriculture and silviculture, pesticides,
heavy metals, and organic pollution from both point and non-point sources. Commercial harvest of mussels (for the Japanese cultured pearl industry) has also contributed significantly to the decline of the mussel fauna in several southeastern states.

The Florida mussel rule (39-23.015 Florida Administrative Code) was implemented in 1996 to protect
the state's declining fauna from over harvest by commercial operations associated with the Japanese
pearl industry (Tennessee, Alabama, and Arkansas had already been over harvested), and, also, from
over harvest by individuals collecting mussels in large quantities to sell or use as bait.

It is true that mussels can occur in large numbers in some Florida locations. These locations include the
headwaters of the St. Johns River, some locations on the Ocklawaha River, Lake Monroe, and several panhandle streams. We consider these few areas to be refuges  for the species resident there, and, hence, worthy of the 10 specimen (20 half-shell) limit protection afforded by the Florida mussel rule. Mussels have been extirpated from many areas of the state - mostly upstream from construction of water control structures.

All of the larger (adults longer than 1 inch) native freshwater mussel species currently occurring in Florida
are of the family Unionidae. If a representative species of the Margaritiferidae currently resides in
Florida, it will be limited to the panhandle near the Alabama border. One of these unionid species, Elliptio
buckleyi (the Florida spike), can be abundant in the St. Johns River, and is, in fact, the most abundant
freshwater mussel in peninsular Florida. However, just because a species may be locally abundant doesn't mean that it should not be protected. Results of surveys conducted by both state and federal biologists indicate that the entire Florida fauna is in decline. This decline is most rapid in the panhandle and in
peninsular streams and lakes affected by our recent drought.

There are currently two printed references useful for Florida mussel identification. Both are old and the taxonomy (species names) have changed substantially since their publication (hence, a new manual is being written by Dr. Williams and myself). These two references are: Identification Manual of the
Freshwater Clams of Florida, written in 1979 by Dr. William H. Heard, and Freshwater Unionacean Clams (Mollusca:Pelecypoda) of North America, written by Dr. J.B. Burch in 1973. I believe both of these publications are currently out of print and are fairly technical.

In the photo to the right, the mussel on top is Elliptio buckleyi (protected). It is much wider than high and usually smooth in appearance. The speciman on the bottom, Corbicula fluminea, is an introduced species that is not protected by the rule. You may collect as many of these as you like. This species is about as wide as high and has concentric rings giving it a washboard-like appearance.