Freshwater Mussel Biology
Little is known about the life history and the reproductive biology of the majority of freshwater mussel species. Most freshwater mussels use larval parasitism to begin their life cycle. Freshwater mussels have a complex life cycle and depend on a specific fish-host along with river currents to reproduce. Males release sperm into the water column where it is taken up by an incurrent aperture in the females. Fertilized eggs develop into larvae known as glochidia which are released into the water column using a number of methods. The method of fish host attraction varies among species. Several described methods include producing glochidia in bundles that resemble food items (conglutinates), producing superconglutinates of glochidia that are attached to the mussel by a long mucus string to mimic prey fish, discharging glochidia in a mucus web, modification of mantle flaps in the females to mimic small fish, and releasing glochidia into the water column. After the glochidia have infested the fish, they will transform into juveniles and they will excyst from the gills or fins and drop off onto the substrate. Where they will grow and become adults.
The Apalachicola-Chattahoochee-Flint (ACF) River Basin
The Apalachicola-Chattahoochee-Flint (ACF) River Basin is located in the southeastern United States. The ACF River Basin drains approximately 51,282 km2 in western Georgia, eastern Alabama, and the Florida panhandle. The Chattahoochee and Flint Rivers merge together at Lake Seminole to create the Apalachicola River. The Apalachicola River flows south through Florida into the Apalachicola Bay, where it meets the Gulf of Mexico. The basin is currently home to 29 species of mussels.
The Apalachicola-Chattahoochee-Flint River Basin (ACF) supports one of the most diverse freshwater mollusk assemblages in the Southeast United States. Historically, the ACF had at least 14 genera and 33 species with six species being unique to the basin. Over the past decade, numerous surveys were conducted in the ACF and concluded that only 29 native mussels currently exist within the ACF. Of which, four species (Amblema neislerii, Hamiota subangulata, Medionidus penicillatus, and Pleurobema pyriforme) are listed as endangered and two species (Elliptio chipolaensis and Elliptoideus sloatianus) are listed as threatened under the Endangered Species Act of 1973, as amended (Act).
Due to both natural and human factors, the mussel fauna in the ACF are declining. The majority of native mussels cannot tolerate impoundments and backwater, though two or three species thrive in these conditions. For the most part the sixteen dams on the Chattahoochee and Flint rivers have long-term negative impacts. Engineering changes in the ACF prevent immigration and emigration (recruitment), many of these species will require population management and manipulation to prevent extinction, to maintain genetic flow between isolated populations, and to reintroduce species to restored habitats. These efforts are consistent with recovery of federally listed species under the 1973 Endangered Species Act by U.S. Fish and Wildlife Service (USFWS) and with goals of a National Strategy for Conservation of Freshwater Mussels.
Warm Springs NFH's Role in Freshwater Mussel Recovery
Back in the late 1990’s, South Georgia was experiencing one of the longest droughts in recorded history, many streams became completely dry and several rivers were at lowest levels in years. The WSNFH was asked to assist in savage operations in the summer of 2000 in Spring Creek, a tributary of the Flint River, there mussels became isolated to specific reaches within the stream. Approximately 1,375 live mussels were transported to WSNFH to be held in refugia until conditions in the stream improved. A total of 1050 mussels were returned to their original habitat in Spring Creek on June 5, 2001 (71% survival for 1-year in captivity). All mussels returned to the creek were tagged for future survival studies. WSNFH held back several species (approximately 25 mussels), as of January 2008, 12 were is alive and doing well (48% survival after 7 years in refugia). While the mussels were held at WSNFH, propagation techniques were developed, glochidia were collected from several species and transformed juveniles were collected and kept alive for six months and studied.
The Warm Springs NFH relies on two freshwater springs to provide water required for hatchery and pond production operations. Two ponds, each with a surface area of 1,012 m2, supply soft water to the mussel facility at a rate of up to 190 liters/minute. Spring water from Cold Springs Creek is supplied to the ponds and re-circulated while being treated to obtain water quality similar to mussel’snative habitat.
Refugium describes the basic biological ability of holding and maintaining individuals in captivity, from isolated populations, of once wide ranging species. This isolation should be considered as only a temporary fix; however, some refugia may be long-standing, thereby having many endemic species, not found elsewhere, that could survive as relict populations, providing the means for broodstock for future population recovery efforts. A handful of the mussels rescued from the drought of 2000 are still housed at the hatchery and are doing well.
FISH HOST TRIALS
Freshwater mussels have a unique lifecycle and may rely on certain fish to complete their metamorphosis. The available information concerning listed mussel species and their relationships with host fish is limited. Therefore, identifying host fish for imperiled freshwater mussel species is critical in conservation efforts. Identification of host fish can be determined through artificial infection in the laboratory using an array of techniques. These techniques are vital for the conservation and propagation of freshwater mussels. The WSNFH has become involved in determining potential fish host species for imperiled mussels. Mussels continue to play an important role in freshwater ecosystems, but basic life history information is lacking in 90% of species found in the Southeast. A number of studies have been performed at WSNFH, to identify the particular host fish for certain mussels (i.e., Elliptoideus sloatianus (Purple bankclimber), Quadrula infucata (Sculptured pigtoe), Hamiota subangulata (Shine-rayed pocketbook), Villosa vibex (Southern rainbow), and Villosa lienosa (Little spectaclecase). This information is important for conservation efforts, since reintroductions and augmentation of mussel populations will only be successful if the mussel’s host fish is present in the same areas as the mussel.
JUVENILE MUSSEL PROPAGATION
Since 2000, WSNFH has been conducting mussel propagation studies. In the early days three species of mussels were used with successful results: Hamiota subangulata (Shine-rayed pocketbook) produced 5,582 mussels, Villosa vibex (Southern rainbow) produced 2,627 mussels, and Villosa lienosa (Little spectaclecase) produced 940 mussels. All juvenile mussels were released in three different locations within Spring Creek after six weeks of growth.
In 2011, a juvenile mussel bucket rearing system was added at the WSNFH. The system consists of ten 5 gallon buckets that house 5 filter cups per bucket. The filter cups can house 1,500 juveniles each, so with the ten buckets we can easily house 75,000 juveniles at a time. The system is based on a design by Dr. Chris Barnhart of Missouri State University. Staff are experimenting with different algae concentrations to develop a nutrition plan to use for juvenile mussel grow out. Past results showed mussels exhibiting a growth rate of about 6 micrometers per day. Once the mussels had reached a length of 3-5 millimeters they would be transferred to the newly developed pond culture system that has been installed in one of the mussel ponds here at the facilities. After one week in the system the juveniles doubled in size, suggesting that our nutritional plan is working adequately. We are currently developing a dietary plan that will allow us to grow the juvenile mussels to a size where they can be moved to separate rearing system that is located in one of our ponds to grow the mussels to a larger size, where they can ultimately be tagged and released into their native habitats. We are currently working with common, un-listed mussel species so that we can refine our methods and incorporate them into protocol and add them to the Warm Springs NFH Mussel Propagation Management Plan for the ACF Basin. This will allow for the propagation of hatchery reared listed mussel species and ultimately to the augmentation of wild populations that are currently in decline and for the re-introduction of listed species to native habitat where they historically occurred in the past.
Hatchery staff assists in the coordination of two mussel workshops held annually in August. The first being, the Apalachicola, Chattahoochee, and Flint River Basin Freshwater Mussel Workshop conducted at the Joseph W. Jones Ecological Research Center in Newton Georgia. This workshop examines the ecology and identification of the 29 native mussel species that are endemic to the ACF Basin. The second workshop is held in Jesup Georgia at the Altamaha Technical College, this workshop examines the 20 native mussel species that are unique and endemic to Altamaha Basin which is comprised of the Ocmulgee, Oconee, and Altamaha Rivers.