Considered by some to be under-studied and under-appreciated organisms, freshwater mussels play a vital role in preserving the water quality of lakes, rivers, and streams. Projects that take place underwater often require a review of sensitive aquatic species—including mussels.
Senior Ecologist Shaughn Barnett discusses how these extraordinary bivalves contribute to their environment, when they might be encountered during project work, and the process for surveying and relocating mussels.
Q: What are freshwater mussels and why are they important?
Freshwater mussels are a group of bivalve mollusks belonging to a family called Unionidae. North America has the world’s largest variety of these organisms, with approximately 300 species in the United States. In a sense, mussels act as the kidneys of aquatic environments. They filter-feed large amounts of small organic particles (e.g., bacteria, algae, and detritus) from the water column, improving water quality in the process. One mussel can filter up to 8 gallons of water a day. And through their excrement, they deposit organic matter and nutrients, which provide food for aquatic plants and other species.
Q: What types of projects might need a mussel survey or relocation?
Projects that could potentially impact water quality or the benthic zone (the lowest level of the water column, including the sediment surface) of rivers, lakes, or streams might trigger a mussel survey or a relocation, though they are usually only needed in areas with known or suspected threatened or endangered mussels. Common projects where these services might be called for typically involve mining, channelization, dredging, pipeline maintenance, bridge replacement, or dam projects.
For example, Barr recently assisted with a large-scale freshwater mussel survey and relocation on the Kankakee River in Illinois. Pipeline maintenance aimed at restoring the depth of cover over the line that crossed the river meant there was a need to survey and, eventually, relocate the mussels. We processed and relocated over 20,000 individuals–approximately 25 species. Some of these species included the federally endangered sheepnose mussel and the state-listed monkeyface, spike, and purple wartyback mussels.
Freshwater mussels are an under-studied organism, and a lot of discoveries about them are still being made. Mussel surveys can sometimes turn up species not known to occur within a specific waterbody or even identify a species once thought to be extirpated from that area. To me, mussel surveys are all about discovery.
Q: What happens during a mussel survey and why might the mussels need to be relocated?
Freshwater mussel surveys are like a treasure hunt. They generally include snorkel and SCUBA surveys that involve hand-digging through the substrate to locate mussels. Some states have specific protocols for conducting surveys and relocations, which can become more complex when threatened or endangered mussels or other species are found. Qualitative surveys (or timed searches) are done to determine mussel presence and species richness, while quantitative surveys (or quadrant samples) are done to estimate mussel density.
If a project requires the mussels to be relocated, the process typically starts with a reconnaissance survey to identify areas with suitable habitat and a similar species assemblage. We also use substrate characterization and water-quality parameters to establish a baseline for the habitat. Mussels are usually relocated upstream of a project footprint to a nearby area with a similar habitat and mussel community.
Freshwater mussels are regarded as one of the most imperiled groups of animals in North America, with an estimated extinction rate of approximately 1 percent per decade. Approximately two-thirds of freshwater mussels species are of conservation concern. As a result, regulatory agencies have put a high emphasis on preventing and minimizing impacts to these organisms. Often, freshwater mussel surveys and relocations may be a condition of a required environmental permit before beginning work on a project.
Q: What is something you find interesting about mussels?
I’m intrigued by their lifecycle. Most freshwater mussels in the family Unionidae are dependent on fish to complete their lifecycle. As glochidia (the microscopic larval stage of mussels), they are parasitic and attach to the gills, scales, and fins of fish until they metamorphose into juvenile mussels and drop off the fish, living the rest of their lives at the bottom of a river or lake. Freshwater mussels have evolved interesting strategies to attract a host fish. Some species have sophisticated lures, which females display and actively move to resemble bait fish. Other species release conglutinates, which look like insects a fish may eat. Both lures and conglutinates are filled with mussel glochidia and when a fish strikes either, they burst open and the glochidia are flushed onto the fish.
Interested in learning more about how Barr can help permit projects in water bodies? Contact our team.
About Shaughn Barnett
Shaughn has over four years of experience with freshwater mussel surveys, protected species reviews, environmental permitting, environmental assessments, securement of grants, and water quality monitoring. His work includes conducting environmental reviews; performing natural resource surveys; conducting wetland and waterbody delineations (WOTUS), inventories and functional assessments; participating in field studies; and performing desktop and threatened and endangered species reviews.