Native freshwater mussels play a variety of important roles in any ecosystem, but perhaps the most important is water filtration. Mussels are filter feeders, that is, they get all of their food and oxygen from the flow over water over their internal gills, much like a fish. And they are REALLY REALLY GOOD AT IT - they can filter, on average, a gallon of water every hour. Observe a simple demonstration set up streamside:
Two small tanks filled with water from the stream in the background. Sediment has been stirred up, as would occur with stormwater flow or someone walking or driving across a stream. The tank on the right has about a dozen native mussels, the one on the left has nothing but water and substrate.
Elapsed time: 10 minutes
20 minutes
30 minutes
35 minutes
The difference is pretty dramatic. These animals are helping to keep your water clean by feeding on algae and bacteria that I'd prefer NOT to be in my glass of water! How effective are they in a large body of water? Take Chesapeake Bay for example: before we buggered it up, that particular gigantic estuary was FULL of oysters, a mussel relative, also a filter feeder. Those oysters kept that water crystal clear, filtering every single drop about every 2 days. In the whole estuary. Just to give you an idea, that's about 19 trillion gallons of water in that particular bay. 19,000,000,000,000 gallons. More than we can comprehend. In two days.
However, there is limit to their "mad filtering skillz." If the water has any toxic chemicals in it (for example, mussels are VERY sensitive to chlorine and ammonia, both commonly found in wastewater outfalls draining into streams and rivers), they cannot survive and typically, fatal levels of these chemicals are far lower than water quality standards set by states. Also, sediment can quickly smother a mussel if the source is ongoing. Think of it this way: if you make a cup of coffee and it has a few grounds in it, you will probably still drink it. However, if it's chockablock full of grounds, you will clam up (haha) and abstain. Same thing for mussels: they can filter out small amounts of sediment but if there is too much, they will be unable to breathe and they will die. Yet another reason to control sediment input into water, which I discussed here.
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