Mussels filter food out of the water with their gills. That makes them a great tool for testing water quality. By studying what mussels ingest, researchers can get a good idea of what contaminants might be present in the surrounding environment.
Scientists have even created artificial mussels that can measure trace metals in aquatic environments. When trace metals build up in water, they can harm both wildlife and humans.
Did you know? A single mussel can filter 38 litres of water a day!
The problem of bioaccumulation
If water is contaminated with trace metals, creatures like mussels ingest those metals. Over time, they accumulate in the mussels’ tissue. This process is called bioaccumulation.
Bioaccumulation is especially dangerous in animals like mussels because they’re low on the food chain. In other words, many different animals eat mussels. And any animal that eats a mussel will also ingest the trace metals in its tissue.
Illustration of how contaminants bioaccumulate upward through the food chain, affecting the health of humans and animals that consume fish (US Geological Survey)
- Contaminants are washed into water and build up in the sediment
- Bottom-dwelling organisms such as zebra mussels concentrate contaminants and are then eaten by gobly and other small fish
- Predator species like small mouth bass continue to concentrate toxins by eating the goby. Bass are then consumed by humans
This is an example of how contaminants like trace metals move up the food chain. First, they build up in the mussels that filter the water. Then, they accumulate in the tissue of animals that eat the mussels.
This process is called biomagnification. It’s especially worrisome for predators near the top of the food chain, like humans. Top predators not only consume all the metals in their prey. They also consume all the metals in their prey’s prey.
Did you know? Mussels attach themselves to the ground, rocks or artificial surfaces using a bundle of threads called a byssus.
How mussels help with biomonitoring
As you can imagine, it’s important to keep an eye on contaminants in food webs, like trace metals in aquatic ecosystems. Scientists call this biomonitoring. They look for biological responses that signal the presence of contaminants.
This is where mussels come in. Live mussels have often been used as biomonitors. Scientists collect mussels from the water, then measure contaminant levels in their tissue. These levels help scientists determine the levels of contaminants in the surrounding environment.
In 2007, researchers at Hong Kong’s Centre for Coastal Pollution and Conservation created the Artificial Mussel (AM). Since then, scientists have been able to use AMs as biomonitors, instead of the real thing.
AMs are small tubes containing a gel. Researchers place them in baskets, which are then lowered into the water. When water enters through openings at the end of the tube, the gel traps trace metals. The metals accumulate in the gel similarly to how they would accumulate in a living organism.
AMs were tested in Australia in 10 locations that scientists considered at risk for metal accumulation. After spending four weeks in a river system, the gel in the AMs contained many contaminants. These included cadmium, copper, lead, mercury and zinc. Tests like these help identify contaminant-heavy, high-risk regions for wildlife and humans.
Did you know? Mussels feed on plankton and other small organisms, which they filter from the water.
Do you think AMs have advantages over real mussels for biomonitoring? Can you think of other technologies that are based on processes observed in nature? And how do you think researchers use the environmental information they gather from real mussels and AMs?
About mussels and other bivalves:
About biomagnification and biomonitoring:
About artificial mussels: