Bivalves: Nature’s Water Filters

Small but mighty

On ocean floors and riverbeds, colonies of organisms clad in armor plating filter minute organisms out of the water around them.  These creatures remain in the same spots for years at a time and can siphon huge amounts of water throughout the course of their lifetimes.  Tiny fortresses nestled among the rocks and sand, they are essential recyclers and filters for aquatic environments. These interesting creatures, collectively called bivalves, can be of use to us in the monitoring and restoration of damaged aquatic ecosystems.

What kind of creatures are bivalves?

Mussels, oysters, and clams are the most commonly recognized bivalves however it is an ancient and varied class of animals.  The vast majority excel at pumping water through their gills in order to grab whatever small morsels float their way.  Oysters, for example, are estimated to be able to filter up to 30 gallons a day.  To put this in perspective, a human-sized oyster would go through over 13,000 gallons of water a day.  Mussels can’t match the individual pumping power of an oyster but they are able to pack themselves much tighter together.  This gives them the ability to pick through a huge amount of H2O- according to the USGS it takes resident invasive zebra mussels less than a month to filter through Lake Erie’s 115 cubic miles of water.

It’s all about the gills

The gills in these bivalves are extremely delicate and fine-tuned filters that are able to gather very small organisms and other nutrients from the water around them.  They are not picky eaters;  some fish farming operations are actually using certain types of mussels to consume fish waste that could otherwise pollute local waterways.    

Because of the intricate nature of bivalve gills, they also gather many pollutants that are in the environment.  Bivalves collect and store pesticides, heavy metals, and other pollutants and are able to store large amounts without ill effects.  This makes them effective at combating levels of these pollutants in rivers and oceans around the world.  Scientists in recent years have been using bivalves such as mussels as toxin sensors, observing the buildup of pollutants in their bodies and using it to gauge the level of pollutants in the immediate environment.  These mussels are placed in areas of concern and left for a pre-established amount of time in order to collect pollutants.  It’s a testament to our current age of technology that I am able to write the following sentence:  these mussels are then subjected to processes such as neutron activation analysis and atomic absorption spectrophotometry to gauge their levels of impurities.  Using bivalves as pollutant sensors allows scientists to more accurately judge the levels of certain dangerous pollutants and helps give an early warning sign for potential contaminations.

Native bivalves

There are many different species native to North America. For example, North Carolina is home to some unique native bivalves.  In fact the Tuckasegee River is one of the last bastions of the Appalachian elktoe mussel, which beats out all other mussels in my opinion on name alone.  Unfortunately the vast majority of native bivalves including the Appalachian elktoe are imperiled.  Studies as recent as 2004 showed that almost 75% of native North American mussel populations were in decline largely due to silt buildup from construction, agriculture, and other human interactions.  Sediment from runoff is usually larger than the microscopic particles bivalves are used to dealing with and can clog the delicate filters they depend on.  Even a relatively small amount of sediment can degrade water quality, affect bivalve reproduction, and cover rocks that are usually preferred housing sites.  Luckily there are many local activists working tirelessly to preserve our native bivalves such as the Appalachian elktoe.  Do your part by not contributing to sediment runoff into local waterways.


This article was originally published in The Sylva Herald. 


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