Oval pigtoe

Appearance

The oval pigtoe is a small freshwater mussel that can reach a length of 2.4 inches (six centimeters). This species has a flattened oval-shaped shell that is a yellowish-brown on the outer section with a white or salmon (yellowish-pink) inner section. It also has two large teeth in the left and right valve (Florida Natural Areas Inventory 2001, University of Georgia 2008).

Behavior

The oval pigtoe is a filter feeder (filters food out of water) that feeds on plankton and detritus (dead organic matter).

Little is known about the life history of the oval pigtoe. Reproductive females have been found between the months of March and July when water temperatures are 55.4-77.0°F (13-25°C) (NatureServe 2010). It is believed that males release sperm into the water and females receive the sperm through a siphon. Eggs are fertilized in the female’s shell and the glochidia (larvae) release into the water. The larvae attach to the gills or fins of a host fish to develop. The sailfin shiner (Pteronotropis hypselopterus) and eastern mosquitofish (Gambusia holbrooki) are the primary host fish for the oval pigtoe. The time of development depends on water temperature and the species of host fish (University of Georgia 2008). When the larvae metamorphose into juvenile mussels, they release from the fish and settle in their primary habitat.

Habitat

The oval pigtoe inhabits mid-sized rivers and small creeks with a slow to moderate current and a sandy silt to gravel floor. In Florida, this species can be found in the Chipola, Ochlockonee, and Suwannee river systems and Ecofina Creek; while found in the Ochlockonee, Flint, and Chattahoochee river systems in Georgia (Florida Natural Areas Inventory 2001).

Threats

Freshwater mussels face a host of threats due to an increased human population and development. The main threat to fresh water mussels is the impoundment of waterways. Waterways are impounded for fresh water supply, flood control, and hydropower. Impounding waterways causes the water current’s velocity to decrease, causing sediment to build up in the river and cover the mussels. Impoundments also cause habitat fragmentation, separating mussel populations and individual mussels from algae and host fish (U.S. Fish & Wildlife Service 2006). River dredging also threatens to destroy freshwater mussel populations on the river floors. The Asian clam (Corbicula fluminea), an invasive species, can out-compete the oval pigtoe for resources in its habitat (Florida Natural Areas Inventory 2001). Pesticide and chemical pollution poses a significant threat to mussels, since they are filter feeders and may ingest chemicals directly from their habitat.

Conservation and Management

The oval pigtoe is protected as an Endangered species by the Federal Endangered Species Act and as a Federally-designated Endangered species by Florida’s Endangered and Threatened Species Rule. It is one of the target species in a 7-species Federal Recovery Plan.  Specific actions needed to recover the species include (USFWS 2003):

• Secure extant subpopulations and currently occupied habitats and ensure subpopulation viability.
• Search for additional subpopulations of the species and suitable habitat.
• Determine through research and propagation technology the feasibility of augmenting extant subpopulations and reintroducing or reestablishing the species into historical habitat.
• Develop and implement a program to evaluate efforts and monitor subpopulation levels and habitat conditions of existing subpopulations, as well as newly discovered, reintroduced, or expanding subpopulations.
• Develop and utilize a public outreach and environmental education program.
• Assess the overall success of the recovery program and recommend actions.

Other Informative Links

Florida Natural Areas Inventory

References

Florida Natural Areas Inventory. 2001. Field guide to the rare animals of Florida. https://www.fnai.org/PDFs/FieldGuides/Pleurobema_pyriforme.pdf

NatureServe. 2010. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/ (Accessed: July 12, 2011).

University of Georgia. (2008). Oval Pigtoe Pleurobema pyriforme. Retrieved July 12, 2011, from Museum of Natural History: http://naturalhistory.uga.edu

U.S. Fish and Wildlife Service. 2003. Recovery Plan for Endangered Fat Three ridge (Amblema neislerii), Shinyrayed Pocketbook (Lampsilis subangulata), Gulf Moccasinshell (Medionidus penicillatus), Ochlockonee Moccasinshell (Medionidus simpsonianus), and Oval Pigtoe (Pleurobema pyriforme): and Threatened Chipola Slabshell (Elliptio chipolaensis), and Purple Bankclimber (Elliptoideus sloatianus). Atlanta, Georgia. 142 pp.

U.S. Fish & Wildlife Service. (2006, June 8). Current Threats. Retrieved July 9, 2011, from Freshwater Mussels.