Louisiana pearlshell
Encyclopedia
The Louisiana pearlshell, Margaritifera hembeli, is a rare species of bivalve in the Margaritiferidae
family. This freshwater mussel is native to Louisiana
in the United States. It also once occurred in Arkansas
, but it has been extirpated
from all the waterways there. It is a federally listed threatened species of the United States.
This mussel reaches about 10 centimeters long by 5 wide and 3 high. It is dark brown or black in color with a white nacre
.
When it was first placed on the Endangered Species List in 1988 the mussel was thought to remain only in the Bayou Boeuf river system in Rapides Parish, Louisiana
. It was found in eleven streams with 90% of the total population found in four of the streams. The mussel was downlisted to threatened status in 1993 when more populations were discovered. It was found to inhabit eight streams in the Red River drainage in Grant Parish, Louisiana
.
This mussel lives in small, shallow creeks with sandy or gravel bottoms. They are found more often in riffle
s and areas with faster currents than in stagnant pools. The water is clear and the substrate is stable.
Like other freshwater mussels, this species releases its larvae, termed glochidia
, into the water where they enter the bodies of fish as parasites
to develop into juvenile mussels. Host fish species for this mussel include striped shiner
(Luxilus chrysocephalus), redfin shiner
(Lythrurus umbratilis), golden shiner (Notemigonus crysoleucas), and brown madtom
(Noturus phaeus).
This species is threatened by the loss and degradation of its habitat. These habitat changes are caused by impoundments
of the waterways, including the effects of beaver dam
s. Some areas, including streams in the Kisatchie National Forest
, undergo increased sediment
ation from nearby silviculture
, road maintenance, and livestock
grazing. Gravel mining may also cause increased sediment. Genetic analysis
reveals the species has low genetic variability
, which makes it more vulnerable to changes in its environment.
Margaritiferidae
Margaritiferidae is a family of medium-sized freshwater mussels, aquatic bivalve mollusks in the order Unionoida. They are known as freshwater pearl mussels, because they are capable of producing pearls.-Genera within the family Margaritiferidae:...
family. This freshwater mussel is native to Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
in the United States. It also once occurred in Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...
, but it has been extirpated
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
from all the waterways there. It is a federally listed threatened species of the United States.
This mussel reaches about 10 centimeters long by 5 wide and 3 high. It is dark brown or black in color with a white nacre
Nacre
Nacre , also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent....
.
When it was first placed on the Endangered Species List in 1988 the mussel was thought to remain only in the Bayou Boeuf river system in Rapides Parish, Louisiana
Rapides Parish, Louisiana
-Military Installations:*Camp Beauregard *Esler Airfield *England Air Force Base *Camp Claiborne *Camp Livingston -Demographics:...
. It was found in eleven streams with 90% of the total population found in four of the streams. The mussel was downlisted to threatened status in 1993 when more populations were discovered. It was found to inhabit eight streams in the Red River drainage in Grant Parish, Louisiana
Grant Parish, Louisiana
-Demographics:As of the census of 2000, there were 18,698 people, 7,073 households, and 5,276 families residing in the parish. The population density was 29 people per square mile . There were 8,531 housing units at an average density of 13 per square mile...
.
This mussel lives in small, shallow creeks with sandy or gravel bottoms. They are found more often in riffle
Riffle
A Riffle is a short, relatively shallow and coarse-bedded length of stream over which the stream flows at higher velocity and higher turbulence than it normally does in comparison to a pool....
s and areas with faster currents than in stagnant pools. The water is clear and the substrate is stable.
Like other freshwater mussels, this species releases its larvae, termed glochidia
Glochidium
The glochidium is a special microscopic larval stage of larger freshwater mussels, aquatic bivalve mollusks in the families Unionidae and Margaritiferidae, the river mussels and European freshwater pearl mussels....
, into the water where they enter the bodies of fish as parasites
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
to develop into juvenile mussels. Host fish species for this mussel include striped shiner
Luxilus chrysocephalus
The common name of Luxilus chrysocephalus is the striped shiner. It is one of the 324 fish species found in Tennessee....
(Luxilus chrysocephalus), redfin shiner
Lythrurus umbratilis
The common name of Lythrurus umbratilis is the Redfin shiner. It is one of the 324 fish species found in Tennessee....
(Lythrurus umbratilis), golden shiner (Notemigonus crysoleucas), and brown madtom
Noturus phaeus
The common name of Noturus phaeus is the brown madtom. It is one of the 324 fish species found in Tennessee....
(Noturus phaeus).
This species is threatened by the loss and degradation of its habitat. These habitat changes are caused by impoundments
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
of the waterways, including the effects of beaver dam
Beaver dam
Beaver dams are dams built by beavers as protection against predators such as coyotes, wolves, and bears, and to provide easy access to food during winter. Beavers work at night and are prolific builders, carrying mud and stones with their fore-paws and timber between their teeth...
s. Some areas, including streams in the Kisatchie National Forest
Kisatchie National Forest
Kisatchie National Forest, the only National forest in Louisiana, USA, is located in the state's old growth piney hills and hardwood bottoms of seven central and northern parishes. It totals more than of public lands....
, undergo increased sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
ation from nearby silviculture
Silviculture
Silviculture is the practice of controlling the establishment, growth, composition, health, and quality of forests to meet diverse needs and values. The name comes from the Latin silvi- + culture...
, road maintenance, and livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
grazing. Gravel mining may also cause increased sediment. Genetic analysis
Genetic analysis
Genetic analysis can be used generally to describe methods both used in and resulting from the sciences of genetics and molecular biology, or to applications resulting from this research....
reveals the species has low genetic variability
Genetic variability
Genetic variability is a measure of the tendency of individual genotypes in a population to vary from one another. Variability is different from genetic diversity, which is the amount of variation seen in a particular population. The variability of a trait describes how much that trait tends to...
, which makes it more vulnerable to changes in its environment.
Source
- Bogan, A.E. 1996. Margaritifera hembeli. 2011 IUCN Red List of Threatened Species. Downloaded on 25 September 2011.