As the Flint River winds its way through west-central Georgia, its waters teem with one of the most diverse collection of fish anywhere in the country.
But look a little more closely and you’ll see an important role some of these fish play. Not only are they an indicator of the water’s health, but they also serve as incubators to microscopic mussels that also help keep this ecosystem healthy. To the naked eye they might look like grains of sand stuck to fish fins and gills, but they’re actually glochidia, small mussel larvae that cling to fish while they develop into juvenile mussels.
They’re an integral part of freshwater systems like the Flint River, but there’s still much we don’t know about them. Now, a project launched by University of Georgia faculty in conjunction with Albany State University and the Flint Riverquarium aims to learn more about these bivalves.
“The Flint is one of the most diverse river basins in Georgia, for both fishes and mussels. So, it’s really important for conservation reasons,” said Peter Hazelton, an assistant professor at the UGA Warnell School of Forestry and Natural Resources. Out of the 28 mussel species in the river basin, nearly a dozen are listed as endangered at either the federal or state level.
Hazelton teamed up with John Wares, a professor in the Odum School of Ecology specializing in genomics, to launch the first phase of an ongoing project to learn more about the relationships between mussels and the fish who serve as hosts early in the mussels’ lives. The two are part of a team of researchers including biology professor Shayla Williams and Gail Cowie of the Water Planning and Policy Center, both at Albany State University.
They started about a month ago by taking students at Albany State University out into the river to catch samples of four fish known for hosting glochidia. From there, the fish were taken to a lab at the Flint Riverquarium, where students worked behind large windows in view of visitors. There, the mussel larvae grew, naturally fell off and were collected by students for the next phase in the study: DNA testing.
This phase is critical, said Wares, in order to identify which mussel species had attached to which fish. “In this case, DNA is super useful because mussels are very difficult to tell apart even when they’re adults, never mind when they’re less than 1 millimeter in length,” he added.
Wares, who specializes in DNA research, took the students through the process of preparing the mussels for DNA sequencing. Students follow a process to preserve samples and amplify the targeted “barcode” gene, then send them to an external lab that identifies DNA markers. These markers, said Wares, are similar to an identification barcode on a box of cereal and are useful in identifying any species, not just mussels.
Using a catalog of barcode sequence data from all the freshwater mussels found in Georgia compiled by former UGA doctoral student Katherine Bockrath, the students and faculty can trace what they find to understand more about which mussels prefer which fish—or, which fish serve as hosts to a variety of mussels.
This first phase of the project took place over a few weeks this summer, but Hazelton said the project will continue into additional seasons.
“We currently have at least four different fish species and probably three different mussel species that were active on some of those fish species. We’ll repeat that in the fall and in the spring because different mussels will be active at different parts of the year,” said Hazelton. “Because some mussels are generalists and some are specialists, some fishes may be really important. We only know host relationships for about 60% of mussels in the river.”
As Hazelton and Wares begin to go through the initial DNA results with the students, it’s clear their work is already showing results—and also bringing up more questions. For example, said Wares, some of the glochidia failed to transition into juvenile mussels. Rather than showing mussel DNA, tests revealed the presence of additional protozoans—organisms that might tell us more about the fate of larvae that don’t transform.
Faculty from both universities are now working with students to determine their next steps, which will include a presentation about their findings.
“So, we can start to see, for example, if there’s any truth that if the glochidia doesn’t transform, it’s not a viable organism. The students really enjoyed that, too,” said Wares. “They all got experience catching fish, they all got experience at the Riverquarium watching the juveniles drop off and talking with people. Now we need to make sure we convey the most effective way of looking at the data.”