Putting Mussels on Your Mind

While marine life and pollinators are the focus of a lot of media and conservation attention, and deservedly so, freshwater mussels in the U.S. are also in trouble – in fact, they are amongst the most at-risk animals in the U.S. More than seventy percent of all species of North American freshwater mussels are considered endangered, threatened, or of special concern.

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Endangered freshwater mussels in the Clinch and Powell River Watersheds in Virginia (Bottom diagonal row, left to right: Cumberlandian combshell, Oyster mussel. Middle Row: Shiny pigtoe, Birdwing pearlymussel, Cumberland monkeyface. Top row: Rough rabitsfoot) Photo: USFWS

Like pollinators, freshwater mussels provide vital services that underpin an entire ecosystem – one that’s already in serious trouble – but capturing the public’s imagination when it comes to freshwater mussels is hard. They aren’t especially cuddly. They don’t exhibit human-like qualities we can easily connect with. While they were used as a food source by native peoples when other options were scarce, they’re far from the delicacy that certain marine mussels are famous for. They go largely unseen – living at the bottom of streams, looking like rocks, and remaining pretty much stationary their whole lives.

But freshwater mussels are the things you never knew you couldn’t live without. Given their crucial role in preserving water quality and supporting a broad range of wildlife, mussels should be very much on your mind.

Mussels De-Mystified

Mussels are bivalve mollusks, with hard shells and gooey bodies. They have no head, eyes, ears, or appendages with the exception of a single foot, which they use to burrow down into the mud or sand. What they do possess is a mouth, one that sucks in water and along with it small pieces of dead leaves, sediment, and other organic matter, as well as very small microorganisms like algae, bacteria, and viruses. Additionally, freshwater mussels filter and sequester dangerous chemicals and heavy metals. As filter-feeders, water exits mussels significantly cleaner than when it went in. But wait, there’s more – so much more.

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Both aquariums were filled with water from the nearby stream. A small collection of western pearlshell (Margaritifera falcata) was added to the aquarium at left. After three hours, the difference in water quality with and without the mussels is clear. Photo, Teal Waterstrat / USFWS.

Mussel beds also create habitat for other aquatic invertebrates, which in turn are eaten by fish. Empty mussel shells are a refuge for crayfish, snails, and fish. Decaying shells are a slow-release source of calcium, phosphorous, and nitrogen. Mussels are energy-rich prey for birds, otters, muskrats, raccoons, and other wildlife. Incredibly, some species can live for up to 100 years and are relatively stationary. We can look at tree rings to measure the age of a tree and learn about the climate and conditions of a forest over many years. It’s the same with mussel-biologists who can determine the age of freshwater mussels by counting the rings on their shells and make observations about long-term stream health. And if all of that isn’t enough, common names such as pearlshell and pistolgrip should elucidate you as to their long history of use by humans.

Why would mussels do this seemingly thankless work? Because their livelihood depends on it. As mussels filter water, they breathe and collect food. To reproduce, male mussels must also disperse sperm directly into the water where is carried through the current and taken in by female mussels. Impregnated females then produce larvae (known as glochidia) which need to catch a ride on a host fish, where they’ll hang out and mature into “baby mussels” before being deposited elsewhere in the stream – thus spreading the colony. Poor water quality could interfere with this process in a number of ways, and cleaner water certainly benefits and increases the availability of host fish.

Riches Squandered

Long before plastics proliferated, freshwater mussels were harvested en masse and used for buttons, decorations on gunstock, and for other commercial purposes. Photo: Wikimedia

Long before plastics proliferated, freshwater mussels were harvested en masse and used for buttons, decorations on gunstock, and for other commercial purposes. Photo: Wikimedia

Recognized for their physical properties, our human history with native freshwater mussels is one of discovery and exploitation. Archeological records show that Native Americans have harvested mussels for at least ten thousand years, using their bodies as a subsistence food and the shells for all manner of tools, utensils, and “home goods.” In the mid-nineteenth century, the discovery, in New Jersey, of a freshwater pearl which sold for $2,500 ($50,000 today) led to a bit of a craze and entire streams were soon stripped of their mussels. In 1891, before the advent and widespread use of plastics, a factory in Muscatine, Iowa realized the potential of thick-shelled species such as the yellow sandshell (Lampsilis teres) and pistolgrip (Tritogonia verrucosa) as a material for creating “pearl” buttons. At the time, there seemed to be an endless supply of the shiny, durable shells, but soon others across the country followed suit, and at its peak nearly 200 factories were in the business of harvesting and processing freshwater mussel shells for a variety of uses. Today, freshwater mussels are still exploited for their shells. The hard, thick shells of freshwater mussels are broken into pieces and placed inside marine oysters to stimulate the production of pearls.

North America is rich in freshwater mussel diversity, boasting approximately 300 species. To put that in perspective, Europe has around a dozen species while China has some 60 species. A single creek in Ohio is known to contain 44 different species of freshwater mussel, almost half the mussel diversity of the entire continent of Africa, which can claim about 100 species. And yet, according to the U.S. Fish and Wildlife Service, 78 species in the Midwest are classified as federally endangered, threatened, or of special concern. The Xerces Society has concentrated our conservation efforts and research into western populations, conducting an IUCN Red List assessment, in partnership with the Confederated Tribes of the Umatilla Indian Reservation, of the four most imperiled species and groups west of the Rockies which found significant declines. In other parts of the country where populations haven’t been as carefully studied the picture is less clear, but likely to be equally as grim.

Global threats to freshwater mussels are unique and specific to each environment in which they occur. In the western U.S., for example, freshwater mussels are likely to be impacted by new dams or other alterations to watercourses, which can kill existing populations, deteriorate water quality, and create barriers for the host fish mussels depend on. In the Midwest and eastern states, water pollution and agricultural runoff are big threats. In other areas, drought fueled by climate change may cause already impacted streams to run dry. Mussels are also more sensitive than fish to some water conditions. In a cruel twist of fate, degraded water quality throughout the U.S. may be destroying the very organisms that could be critical to keeping the streams clean.

As with other threatened animals, non-native invasive species also play an outsized role. The introduction of non-native species can cause competition for resources. Non-native fish entering streams can outcompete native fish, but they can’t serve the vital role as hosts for our native mussels.

Freshwater Mussels in the West

A handful of western freshwater mussels. Photo by Celeste Mazzacano.

Freshwater mussels in the Pacific Northwest have a special significance, one that can be appreciated by anyone who likes lox on their bagel. Salmon is the native host fish for several species of freshwater mussels found in streams throughout the Pacific Northwest. In return, freshwater mussels improve the river habitat that salmon rely on for their eggs and fry to grow. Yet reduced water quality, habitat loss, dams, dewatering, pollution, and the introduction of invasive species have had impacts on both freshwater mussels and their native salmon hosts.

Some western mussels are already absent from portions of rivers and entire watersheds where they were once plentiful. Despite these declines, no western freshwater mussel species have yet to be awarded federal protection. There is still much to be learned about their distribution, biology, and habitat requirements – before it’s too late.

While it may feel as though we’re swimming upstream when it comes to preserving populations of freshwater mussels, we hope that by engaging with government agencies, researchers, citizen scientists, and the public we can change the course for freshwater mussels.

by Justin Wheeler, Web and Communications Specialist


For more information:

http://www.xerces.org/western-freshwater-mussels/

http://www.xerces.org/wp-content/uploads/2015/08/Mussel_Outreach_July_20_2015_Final_low_res.pdf

http://www.xerces.org/wp-content/uploads/2009/01/mussel_article.pdf

https://www.fws.gov/midwest/endangered/clams/mussels.html

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