An Aquatic Pandemic Of Its Own Kind: Zebra Mussels
By Deviana Lal
As the most extensive freshwater system in the world, the Great Lakes are an invaluable aquatic ecosystem. Not only do they provide aesthetic and recreational benefits for nearby residents, but they also supply nearly 30 million people across the United States and Canada with drinking water. Additionally, this freshwater system prevents weather calamities like thunderstorms, tornados, and blizzards from being all the more common and disastrous. It’s clear that the health of the Great Lakes is inextricably linked to the health of the people, so let’s examine, dare I say, an aquatic “pandemic” of its own kind: zebra mussels.
What are zebra mussels, and how did they get here?
Dozens of zebra mussels and their shell designs. Source: https://www.texasmonthly.com/travel/zebra-mussels-texas-lakes/
Aesthetically, the zebra mussel is quite a beautiful little creature with its striped patterned shell coming in a gradient of light to dark browns. At only the size of a fingernail, they are deceptively small for the damage these shellfish can do. The zebra mussels are native to the Black, Caspian, and Azov Seas and were first recorded as early as 1769. However, in the 1980s, ballast water from European ships was discharged into Lake St. Clair (north of Lake Erie) from the Black Sea, essentially dumping these invasive species right into the heart of the Great Lakes (LakePro). From there, they quickly spread throughout the entire freshwater system and can now be found in all 5 of the Great Lakes and many other freshwater sources in the United States. Since their occupation, it has been an ongoing battle to grapple with their devious effects.
An image of Lake Saint Claire in context with the Great Lakes. Source: http://www.aquaticnuisance.org/fact-sheets/zebra-mussel
These pesky little mollusks pose significant ecological threats and risks to the water’s health as a whole. The commonly used herbicides and algaecides are not effective at controlling their invasion (LakePro). Thus, they can be easily spread with the downstream current and by attaching themselves to boats, ships, and other mediums.
In a single year, one female zebra mussel can release up to 1 million eggs, which then live for 2-5 years. Hundreds of millions of these filter feeders in our freshwater ecosystems deplete the food source for native species, meaning that zebra mussels consume all the phytoplankton and microscopic algae floating in the water. Despite their size, adult zebra mussels can take in nearly a liter of water a day (Sarnelle). Therefore, in a matter of a week, Lake Erie’s western basin can be completely filtered by the zebra mussels. Additionally, zebra mussels attach to native mussels, which incapacitates them and nearly starves them until they die (Blakely).
Aside from the total consumption of native species’ food sources, zebra mussels’ filter-feeding rids the lakes of their natural “sunscreen.” Without the microscopic algae and phytoplankton, the Great Lakes’ clarity has increased some 600-fold (Blakely). Their lack of “sunscreen” (i.e., microscopic algae and phytoplankton) has increased light penetration to the bottom of the lake, making the vegetation on the bottom grow larger and thicker, offsetting the natural balance of the water.
Zebra Mussels piling up on the banks of the Great Lakes. Source: https://flatheadbeacon.com/2016/12/07/aquatic-invaders/
How do invasive zebra mussels affect humans?
While the ecological effects are disastrous enough to spark resolve for this issue, there are other social and economic effects that these nettlesome critters cause. In lakes with low phosphorus levels, zebra mussels can cause an increase in the levels of microcystis, harmful cyanobacteria that create the green-blue algal-blooms in the Great Lakes. These algal-blooms contaminate the drinking water supply, and there have been several reported cases where farm animals, like cattle, and domestic pets, have died from ingesting this microcystis infested water. It can also create liver problems in humans, sometimes requiring hospitalization (Sarnelle).
Aside from the damaging effects of algal blooms, zebra mussels do something even more dangerous to the freshwater food chain. Since their bodies have a high-fat content and ingest nearly a liter of water every day, they garner about ten times more toxins than other native mussels. These toxins magnify as they move up the food chain, which ultimately reaches humans (Sarnelle). Thus, many species of fish in the Great Lakes have health advisories for human consumption.
Apart from the health issues created by zebra mussels, there are also many economic menaces. Zebra mussels breed quickly and prolifically, sometimes resulting in layers nearly eight inches thick. This is extremely problematic for many obvious reasons, and governments have to dole out funds to remove them. Additionally, zebra mussels often like to be in small spaces, such as intake pipes, requiring more financial assistance to remove and avert further colonization (Blakely).
What can we do about zebra mussels?
The zebra mussel “pandemic,” of sorts, seems like it has gone on for too long and spread too far to do anything, but that is not the case. There are certainly some preventative measures we can take as a society to mitigate the effects described above. The United States Geological Survey, which has conducted comprehensive research on zebra mussels’ behavior and biology, suggests a few different ways. The first of these proposed measures is critical: avoid “catching and transporting zebra mussels for use as bait, food, and aquarium pets.” The other recommendations are more advice-oriented for best boat hygiene practices, including “washing your boat with warm and soapy water” and emptying bait buckets onto land instead of in another body of water (USGS).
As for how to treat the water, there is evidence that hot water is effective, but heating massive bodies of water to the temperature required is not a feasible alternative. At present, chlorine is the best option, but not for the environment, as adding chlorine to the freshwater system prevents it from many of its multitudinous uses. Research has turned to different elements, like bromine, yet no conclusive consensus has been reached (LakePro).
References
Blakely, Natasha. “Zebra Mussels: A Guide to the Good and the Bad of These Great Lakes Invaders.” Great Lakes Now, 27 Feb. 2020, Zebra Mussels: A guide to the good and the bad of these Great Lakes invaders – Great Lakes Now
“How Can the Spread of Zebra Mussels Be Prevented?” USGS, USGS, 2020, How can the spread of zebra mussels be prevented? (usgs.gov)
Sarnelle, Orlando. “Lakes with Zebra Mussels Have Higher Levels of Toxins, MSU Research Finds.” MSUToday, 10 Mar. 2004, Lakes with zebra mussels have higher levels of toxins, MSU research finds | MSUToday | Michigan State University
“Zebra Mussels First Appeared in Lake St. Clair - Do You Know - LakePro Inc.” LakePro, LakePro, 9 Apr. 2014, Zebra mussels first appeared in Lake St. Clair - Do You Know - LakePro Inc.