The Louisiana pearlshell, ''Margaritifera hembeli'', is a rare species of

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

mollusk in the family

Margaritiferidae Margaritiferidae is a family of medium-sized freshwater mussels, aquatic bivalve molluscs in the order Unionida. Text may have been copied from this source, which is available under Attribution 4.0 International (CC BY 4.0)licence. It is the ...

. This

freshwater mussel Freshwater bivalves are molluscs of the order Bivalvia that inhabit freshwater ecosystems. They are one of the two main groups of freshwater molluscs, along with freshwater snails. The majority of bivalve molluscs are saltwater species that l ...

is native to

Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...

in the United States, and was previously present also in Arkansas. It grows to a length of about and lives on the sand or gravel stream-bed in riffles and fast flowing stretches of small streams. Its life cycle involves a stage where it lives parasitically inside a fish. This mollusk is sensitive to increased sedimentation and cannot tolerate impoundments. Because of its limited range and its population decline, the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

has rated this mollusk as being "

critically endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...

Description

This mussel reaches about long by wide and high. It is dark brown or black in color with a white

nacre Nacre ( , ), also known as mother-of-pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer. It is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is ...

.USFWS
Final endangered status for Louisiana Pearlshell (''Margaritifera hembeli'').
''Federal Register'' February 5, 1988.

Ecology

This mussel lives in small, shallow creeks with sandy or gravel bottoms. They are found more often in

riffle A riffle is a shallow landform in a flowing channel. Colloquially, it is a shallow place in a river where water flows quickly past rocks. However, in geology a riffle has specific characteristics. Topographic, sedimentary and hydraulic indica ...

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 The glochidium (plural glochidia) is a microscopic larval stage of some freshwater mussels, aquatic bivalve mollusks in the families Unionidae and Margaritiferidae, the river mussels and European freshwater pearl mussels. These larvae are t ...

, into the water where they enter the bodies of fish as

parasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

to develop into juvenile mussels. Host fish species for this mussel include striped shiner (''Luxilus chrysocephalus''),

redfin shiner The redfin shiner (''Lythrurus umbratilis'') is a freshwater is a freshwater ray-finned fish belonging to the family Leuciscidae, the shiners, daces and minnows. The redfin shiner is most commonly found in the Ohio and Mississippi River basins, ...

(''Lythrurus umbratilis''),

golden shiner The golden shiner (''Notemigonus crysoleucas'') is a species of freshwater ray-finned fish belonging to the family Leuciscidae. This fish occurs in Eastern North America. It is the sole member of its genus. Commonly used as a bait fish, it is pr ...

(''Notemigonus crysoleucas''), and brown madtom (''Noturus phaeus'').Johnson, P. D. and K. M. Brown. (1998)
Intraspecific life history variation in the threatened Louisiana pearlshell mussel, ''Margaritifera hembeli''.
''Freshwater Biology'' 40(2) 317-29.

Status

When it was first placed on the Endangered Species List in 1988 the mussel was thought to remain only in the

Bayou Boeuf Kraemer is a census-designated place (CDP) in Lafourche Parish, Louisiana, United States. As of the 2010 census, its population was 934. Its ZIP code is 70371. It is also known as Bayou Boeuf. Demographics Education Lafourche Parish Public ...

river system in

Rapides Parish, Louisiana Rapides Parish () () is a parish located in the U.S. state of Louisiana. As of the 2020 census, the population was 130,023. The parish seat and largest city is Alexandria, which developed along the Red River of the South. ''Rapides'' is th ...

. 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 is a parish located in the North Central portion of the U.S. state of Louisiana. As of the 2020 census, the population was 22,169. The parish seat is Colfax. The parish was founded in 1869 during the Reconstruction era. ...

.USFWS
Determination to reclassify the Louisiana Pearlshell (''Margaritifera hembeli'') from endangered to threatened.
''Federal Register'' September 24, 1993. It also once occurred in

Arkansas Arkansas ( ) is a landlocked state in the West South Central region of the Southern United States. It borders Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, Texas to the southwest, and Oklahoma ...

, but it has been

extirpated Local extinction, also extirpation, is the termination of a species (or other taxon) in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions. Local extinctions mark a chan ...

from all the waterways there. It is a federally listed threatened species of the United States. 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 A beaver dam or beaver impoundment is a dam built by beavers; it creates a pond which protects against predators such as coyotes, alligators, cougars, foxes, eagles, wolves and bears, and holds their food during winter. These structures modify th ...

s. Some areas, including streams in the

Kisatchie National Forest Kisatchie National Forest, the only National forest in Louisiana, United States, is located in the forested piney hills and hardwood bottoms of seven central and northern parishes. It is part of the Cenozoic uplands (some of Louisiana's oldest ...

, undergo increased

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

ation from nearby

silviculture Silviculture is the practice of controlling the growth, composition/structure, as well as quality of forests to meet values and needs, specifically timber production. The name comes from the Latin ('forest') and ('growing'). The study of forests ...

, road maintenance, and

livestock Livestock are the Domestication, domesticated animals that are raised in an Agriculture, agricultural setting to provide labour and produce diversified products for consumption such as meat, Egg as food, eggs, milk, fur, leather, and wool. The t ...

grazing. Gravel mining may also cause increased sediment.

Genetic analysis Genetic analysis is the overall process of studying and researching in fields of science that involve genetics and molecular biology. There are a number of applications that are developed from this research, and these are also considered parts ...

reveals the species has low

genetic variability Genetic variability is either the presence of, or the generation of, genetic differences. It is defined as "the formation of individuals differing in genotype, or the presence of genotypically different individuals, in contrast to environmentally ...

, which makes it more vulnerable to changes in its environment. Because it is restricted to only two river drainages in central Louisiana, and declined by over 80% during the last few decades, the

has rated this mollusk as being "

References

{{Taxonbar, from=Q3018832 Natural history of Louisiana hembeli Critically endangered fauna of the United States Bivalves described in 1838 Taxa named by Timothy Abbott Conrad Taxonomy articles created by Polbot ESA threatened species