Elliptio spinosa, the Altamaha spinymussel, is an endangered species of freshwater mussel in the family Unionidae. They live in southeastern Georgia in the Altamaha river and its tributaries. It is one of three species of North American spinymussels which are recognizable by their prominent spines. The Altamaha spinymussel genetically diverged from the other spinymussels 3.76 million years ago. This suggests that their spines evolved separately from the spines of other North American spinymussels. The Altamaha spinymussel is on the Endangered Species Act because of many threats with the most prominent threats being habitat loss, decrease in water quality, shrinking range, small population size, and vulnerability to disturbances.
The Altamaha spinymussel grows up to 11 cm (4.3 in) in length and their shells are smooth and shiny. In young mussels, the outside of the shell is greenish yellow with green rays that darken over time to brown while the inside of the shell is pink or purple. The overall shape of the shell is triangular or diamond-shape and has moderate inflation. Each mussel has 1-5 spines that vary from 1-2.5 cm (0.4-1 in) in length and these spines can be either crooked or straight and are in a parallel line from the shell’s hinge to the wide outer edge of the mussel.
Altamaha spinymussels are generally found in a range of coarse to fine sediments in sandbars, sloughs, and mid-channel islands. These habitats provide the spinymussel with cover and sites for breeding and reproduction. Altamaha spinymussels are restricted to areas of swift flowing water and will bury 5-10 cm into the sediment (1.96-3.94 inches). They need swift flowing water because it transports food, removes waste, and provides oxygen. Their habitat is the coastal plains region of the Altamaha river and its tributaries. The tributaries include the Ohoopee, Ocmulgee, and Oconee rivers. The water quality that Altamaha spinymussels need has not been studied but mussels in general need to tolerate a wide range of conditions because they are sedentary. The Altamaha spinymussel survives in an area as long as the sandbar, slough, or mid-channel island habitat is maintained and water quality is high enough year-round.
The historic range of the Altamaha spinymussel restricts to the state of Georgia, specifically the coastal plains area of the Altamaha River in the southeast region of the state. The Altamaha River is fed by three tributaries, the Ocmulgee, Ohoopee, and Oconee rivers. There have been historic sightings of the Altamaha spinymussels in all 4 rivers (see Species Status Assessment for range map).
The Altamaha spinymussel uses the spines on their backs to help anchor themselves in the shifting environments of sandy river bottoms. They usually anchor themselves 5-10 cm (1.96-3.94 inches) below the surface. There is currently no information on mating and territorial behavior.
Juvenile Altamaha spinymussels feed with their foot by pulling bacteria, algae, and decomposing organisms from the sediment on the river floor. Adult spinymussels are filter feeders which are capable of filtering up to 40 gallons of water per day. As water passes through their gills they are able to capture their food and can filter out the undesirable parts and intake small pieces of prey all at once. This prey comes in the forms of phytoplankton, diatoms, and other microorganisms.
The Altamaha spinymussel is facing many distinct threats. The most common threat is destruction and modification of its habitat. Sedimentation has become an increasing disturbance as forest management in the area has increased unpaved roads. There has also been increased ATV activity in the area that has increased sedimentation. This leads to greater surface runoff which causes more particles and debris to enter the water. Increased sediments in the water decreases breathing and feeding efficiency, making it more difficult for the mussels to survive, especially in the juvenile stages. Other contaminants may enter the water through community wastewater, and agriculture. These contaminants decrease the amount of oxygen in the water through eutrophication and increase the water acidity which is lethal to mussels. The Edward I. Hatch Nuclear Power Plant is also located near the Altamaha River. This power plant could leak dangerous toxins into the waters which would hurt the mussel populations.
Overcollection may have also caused population declines. This is especially present in the Ohoopee river where localized declines have been seen.
Invasive species such as the Asian Clam have been introduced to the Altamaha River. This increases the competition for space and nutrients with the Altamaha spinymussel and makes survival more difficult.
The final major threat to the Altamaha spinymussel is risk of inbreeding and low genetic diversity. This is caused by the decreased population sizes and physical separation of the populations. Low genetic diversity could lead to decreased resilience to disturbance because all individuals would be equally able to survive.
There is currently no recovery plan for the Altamaha spinymussel, but the 5-year review established future goals for species conservation. The first goal was to create an adequate recovery plan. Second, a range wide survey in the Altamaha spinymussel native habitat should be conducted to inform future conservation. Additionally, the temperature and flow of the water and substrates in the water should be monitored. Third, there should be strong efforts in identifying host fish populations to help in captive breeding efforts. Finally, the 5-year review believes that a genetic analysis should be conducted on the Altamaha spinymussel. This will inform researchers of species that are similar and can then be used to inform management and conservation decisions.
