Freshwater mussels serve at the base of the food web and provide a variety of ecosystem services. They filter our water for us, help stabilize the bottom of the river and serve as water quality indictors. Unfortunately, due to many anthropogenic affects, freshwater mussels are one of the most imperiled groups of animals in the world. The heavy pigtoe, Pleurobema taitianum, is endemic to the Mobile Basin in Alabama and Mississippi, and was listed in 1997 as endangered due to population decline with the loss of habitat from the construction of the Tennessee-Tombigbee Waterway.
Location in Taxonomic Tree
Many freshwater mussels spend the majority of their life sedentary and filter feeding on the bottom of rivers and streams. Sometimes they will bury into the sediment, only revealing a small portion of their aperture, which is used for gas exchange and filter feeding.
The heavy pigtoe is a species occurring in rivers that are characterized by gravel and coarse sand substrates, and have a depth of more than 6 meters. This species historically also occurred in large creeks.
A natural body of running water.
Although the diets of freshwater mussels are poorly understood, it is believed to consist of algae, and or, bacteria. Some studies suggest that the diets of freshwater mussels may change throughout their life, with juveniles collecting organic materials from the substrate though pedal feeding and then developing the ability to filter feed during adulthood. Pedal feeding is a form of deposit feeding where the animal uses their muscular foot to bury into the sediment, collecting organic matter. Filter feeding is a process by which mussels feed off suspended organic material by pumping in water through their incurrent aperture and out through their excurrent apertures, capturing the particles and using them as food.
The heavy pigtoe has a thick shell, that is anteriorly inflated and triangular in shape. Its umbo is narrow, inflated, positioned anteriorly and elevated above the hinge line.
MeasurementsLength: Up to 70 mm
Its shell is brown or olive brown to black, and rays are typically absent.
Freshwater mussels live an interesting multi-stage life cycle which depends upon a fish host to complete. Males release sperm into the water column, to be hopefully siphoned in by the incurrent aperture of the females, where the eggs held within her gills are then fertilized. Once the fertilized eggs start to develop, the female becomes inflated, or gravid. The fertilized eggs develop into glochidia, which is the mussels larval stage. This stage requires a fish host for transformation into the juvenile stage, which sometimes requires a little coaxing by females. Glochidia are housed in packets called conglutinates and often mimic a food source of the fishes within that ecosystem to lure the fish to bite. Once the fish bites, the glochidia clamp down onto the fish, becoming encysted, and feed from the fish for several weeks until dropping off as juveniles.
The heavy pigtoe is historically known to occur throughout the Tombigbee and Alabama rivers and some of their larger tributaries of the Mobile Basin. This species disappeared from most of the Tombigbee River due to habitat destruction with the construction of the Tennessee-Tombigbee Waterway. A single extant population of heavy pigtoe is known from the Alabama River, Dallas County, Alabama, as documented by J.T. Garner and M.L. Buntin in 2011. The area of habitat that supports mussels at this site has been quantified to be 6,250 square meters. Based upon quantitative sampling in 2011, J.T. Garner and M.L. Buntin noted that the surviving heavy pigtoe population within this bed was estimated at 81 animals. Our 2015 5-year review confirmed this and also noted that no evidence of recruitment of heavy pigtoe within this bed has been found since its discovery. Propagation attempts with captive adults have been unsuccessful. There have been no surveys or monitoring of this population since 2011, as cited in the 2015 review.
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