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The Silent Apocalypse: The Mysterious Disappearance of America’s Freshwater Mussels

We recently posted a mussel dissection video (which you can check out here), where we explored the anatomy and physiology of this often overlooked, fascinating bivalves. To many, mussels may not seem as exciting as many other animals we have covered on the channel before, because mussels can be seen everywhere–in the fish tank of supermarkets, attached to rocks near the beach, or even at your dinner table yesterday. However, there is an important distinction to make. All of the mussels you see commercially sold, or during your beach vacations are marine mussels. There is an equally fascinating group of mussels that inhabit freshwater habitats–referred to as ‘freshwater mussels’– that are known for incredible diversity, longevity, and ecological importance. Unfortunately, unlike their marine counterparts, freshwater mussels are the most endangered animal group in the world.


Statistics demonstrating the threat freshwater mussels face in North America
Statistics demonstrating the threat freshwater mussels face in North America

The threat facing freshwater mussels is greatest in North America, as scientists estimate that a staggering 70% of all freshwater mussel species in North America are either extinct, or on the verge of extinction. So what is happening to our freshwater mussels, why do we care, and what can we do to prevent freshwater mussels from being wiped off the face of Earth?


A dead freshwater mussel along the Clinch River, Tennessee
A dead freshwater mussel along the Clinch River, Tennessee

Although countless species of animals around the world face extinction, freshwater mussels are unique in that they are one of the few species scientists have not been able to identify the cause of the decline in population. There are two main reasons as to why we are unaware of the specific threats freshwater mussels face. One reason is that the freshwater mussels are facing the harmful effects of countless human actions, so much so that it is very difficult to identify the factors that are primary contributors to the population decline. The second, less obvious reason for our ignorance on the plight of the freshwater mussels, is the lack of societal attention, and the subsequent lack of research conducted on freshwater mussels.


Lock and Dam No.19–A dam located on the Upper Mississippi River near Keokuk, Iowa
Lock and Dam No.19–A dam located on the Upper Mississippi River near Keokuk, Iowa

There are dozens of human-caused environmental factors that scientists attribute to the staggering decrease of freshwater mussel populations, but I’ve narrowed it down to three most prominent candidates. First, dams. Humans are building more and more dams on rivers for reasons varying from recreation to generating hydropower. A freshwater mussel’s life includes the young mussel attaching to the gills of a few select species of fish, wandering around with the fish until it finds a suitable habitat it can detach itself in. As sedentary animals, this is the only way young mussels can seek out the best places they can live in, but dams have unfortunately been preventing the fishes from traveling to the mussels. A prime example is the population decline of the elephant ear mussel and the ebony shell mussel, both freshwater mussels that live in the upper Mississippi River, and solely depend on the skipjack herring to transport them upstream/downstream for reproduction purposes. Because of these mussels' dependence on a particular species of fish, once a dam was erected Mississippi River at Keokuk, Iowa, in 1913 preventing the skipjack herring from reaching mussels to the north of the dam, reproduction for elephant ear mussels and ebony shell mussels have ceased completely. Although some individuals of these two species still exist due to their extraordinarily long lifespan, scientists predict that both species will soon go extinct due to their inability to reproduce. Second, another possible cause of massive mussel death is sedimentation and pollution. Both agricultural production and man-built bridges have caused much erosion and have led to large amounts of sediment entering rivers and streams. Freshwater mussels can only live on hard surfaces (gravel, rock, firm sand), and the muddy, sandy underwater surface caused by erosion and sedimentation has buried or washed away many freshwater mussels. In addition, the pesticides often found in the sediment from runoff, in addition to the toxic contaminants in industrial discharge (mercury, PCBs, lead) have also led to decimating mussel populations–mussels are very sensitive to water quality.

Freshwater mussel infested with zebra mussels
Freshwater mussel infested with zebra mussels

Finally, the introduction of invasive species has also taken a heavy toll on freshwater mussels. Although there are many examples of invasive species that harm freshwater mussels, zebra mussels are the most abundant and do the most damage. First introduced to the great lakes from Europe by humans, zebra mussels have since spread around freshwater habitats across the U.S., out-competing native freshwater mussels with their fast reproduction. Zebra mussels also often attach to native freshwater mussels, stifling the native mussel’s feeding and reproduction.


A collaborative ad by Coca Cola & WWF, raising awareness of the threats faced by polar bears.
A collaborative ad by Coca Cola & WWF, raising awareness of the threats faced by polar bears.

As evidenced by just a few of the threats listed above, you may be wondering what society is doing to curve the mass extinction of freshwater mussels. The answer is–not much. Freshwater mussels, despite being the most endangered group of animals in the world, garner nowhere near a proportionally significant amount of society’s attention nor research funding. Why? As biologist Jordan Richards states: “freshwater mussel apocalypse has been a challenge, particularly because the mollusks lack the cultural cachet and fuzzy faces of pandas and tigers.” Scientists and environmental activists can’t run a campaign with a picture of a sad mussel and raise millions of dollars to fund research and conservation efforts, although this endeavor is possible with animals like tigers, pandas, and polar bears. For example, the image above shows a collaborative ad by Coca Cola & the World Wildlife Fund aiming to raise awareness about threats facing polar bear populations. Such ad works because polar bears are an animal considered cute and lovable by the general public–a similar ad with freshwater mussels would be ineffective and inconceivable. Society does not view freshwater mussels as significant nor interesting enough to pay attention to , and the lack of funding and research that ensues from this neglect has prevented scientists from identifying, studying, and trying to resolve the biggest threats freshwater mussels face. However, what many fail to realize is that freshwater mussels play a crucial role in many ecosystems, acting as natural filters purifying the water, serving as a food source for many animals, and holding value as a potential source of groundbreaking research (freshwater mussels don’t get cancer, and scientists want to find out why to help cure human cancer–such endeavor would be impossible if more and more freshwater mussel species went extinct). In a sense, the decimation of the freshwater mussel is truly a silent apocalypse: an event that is not focused on or prioritized, but an event that could lead to grave consequences.


Minnesota Zoo's Freshwater Mussel Conservation program rears multiple freshwater mussel species for eventual release into Minnesota rivers.
Minnesota Zoo's Freshwater Mussel Conservation program rears young mussels for eventual release into rivers.

Despite the seeming hopelessness of the situation, all is not lost. The passing of the Endangered Species Act and the Clean Water Act have each contributed to the recovery of many freshwater mussel species to a certain extent, and many are still fighting for bold legislations that could curve the extinction rate of freshwater mussels. Luckily, you can help make a change at the individual level as well! By conserving energy you would contribute to limiting the number of new hydroelectric power plants being built, and by sharing this article and spreading awareness, you would help draw light on the crisis that freshwater mussels face. In addition, you could also donate to the Minnesota Zoo foundation’s Freshwater Mussel Conservation project here, or get involved with the FMCS’s (Freshwater Mollusk Conservation Society) work here.






Sources:

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

http://passengerpigeon.org/SpeciesAtRisk_doc-foto/mussels.html

https://knowablemagazine.org/article/living-world/2019/hidden-strengths-freshwater-mussels

https://www.npr.org/2019/12/06/784422726/natures-brita-filter-is-dying-and-nobody-knows-why

https://www.smithsonianmag.com/smart-news/scientists-dont-know-why-freshwater-mussels-are-dying-across-north-america-180973802/

https://www.nationalgeographic.com/animals/2019/12/freshwater-mussels-die-off-united-states/


Photo Credits:

https://knowablemagazine.org/article/living-world/2019/hidden-strengths-freshwater-mussels

https://undark.org/2020/04/13/freshwater-mussel-death/

https://www.tripadvisor.com/Attraction_Review-g38040-d12989013-Reviews-Lock_and_Dam_No_19-Keokuk_Iowa.html

https://www.stcroix360.com/2017/03/workshop-will-share-information-about-controlling-zebra-mussels/

https://www.campaignlive.co.uk/article/coca-cola-ties-wwf-polar-bear-csr-campaign/1166646

https://mnzoo.org/conservation/minnesota/freshwater-mussels/


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