Oysters: Nature’s Brita Filter?

I was browsing through the front page of reddit, a popular content gathering site, looking through interesting articles and pictures when suddenly I came upon this picture that was posted:

The title of the post claimed that both tanks had been filled with water from the exact same source and time, the only difference is that the tank on the right has oysters placed in it. Being on the very front page of reddit meant that a lot of people were wondering the same thing that I was: are these oysters actually filtering the water? As it turns out, the answer is yes!

Much to my disbelief, there was no fluke going on with this image. No other process was going on in order to make the water appear clearer. The oysters were actually filtering the tank, and they were doing it for their food source! The mechanism is through the process of “filter feeding,” a task typically performed by bi-valve mollusks. According to In A Half Shell, oysters’ primary diet consists of small plankton and algae that is floating around the water. “Bi-valve” indicates two valves for the animal; one to suck in water, and one to expel water. Once sucked in, the water is filtered through the gills of the oyster. Plant material, plankton, and other particles are trapped along the mucousy portion of the gills and taken to the stomach for digestion. Digested food is excreted as feces, and the remaining undigested particles are then expelled back as pseudofeces, undigested food particles covered in mucous. To add for clarification: the feces and pseudofeces are not expelled out through the second valve, but out of the oyster’s anus. The second valve spits out filtered water after it has been taken in through the first valve and has gone through the filtering process. Through this mechanism oysters get fed and the waters get cleaned up: a real win-win scenario.

The post had a picture of oysters, however I thought to myself, “can other bi-valves do this?” Can clams, mussels, and scallops clean up our waters as well? After some digging online, I found that the answer is a yes. All bi-valve mollusks are capable of filtering water using the same type of digestion system, oysters are no special exception. However, oysters apparently do the best job at it. When fully grown, Eastern oysters are able to filter as much as 50 gallons per day (In A Half Shell). To put that in perspective, that is about as much water as you can fit in a modern bathtub being filtered by an organism the size of your wallet!

Well if the ocean is full of oysters, many of which are capable of filtering large quantities of water, then why is our coastline still full of dirty water? Unfortunately, there may not be as many oysters as we think. Due to overfishing of these mollusks (overclamming?) as well as drastic changes in the water of the East Coast, oyster and other mollusk populations have been whittled down dramatically. In particular, the Chesapeake Bay region near Virginia and Maryland has been hit very hard by this problem. According to an article from baybackpack, the oyster population used to be able to filter the entirety of Chesapeake Bay in less than a week’s time. The oyster population now stands at only 1% of that former glory, and it is estimated that it would take about a year to filter the entirety of the bay. With mollusk populations down, the waters of the Chesapeake do not get the typical filtration that they need, leaving very dirty water with high algae count.

Taken from the Chesapeake Bay Office of the National Oceanic and Atmospheric Administration (http://chesapeakebay.noaa.gov/fish-facts/oysters)

Taken from the Chesapeake Bay Office of the National Oceanic and Atmospheric Administration (http://chesapeakebay.noaa.gov/fish-facts/oysters)

Hope appears to be on the horizon, however. The National Oceanic and Atmospheric Administration (NOAA) has been working hard in attempting to restore oyster populations back to their former glory. Although it will be a very long time to recover from this low, they believe that increasing the oyster populations will be key in increasing the quality of our ecosystems on the East Coast. NOAA’s Chesapeake Bay Office has been working since 1997 in an effort to accomplish this around the Virginia and Maryland area. From then until 2009, NOAA spent over $30,000,000 on this project, and the efforts still continue today. They have created “harvest” areas for which it is okay to clam there, and “sanctuary” areas for the oyster populations to grow and develop. They have also created better environments for the oysters to flourish, so that they can live in homes better than the ones destroyed by overfishing during the 19th and 20th centuries.

They may be oysters, but with progress getting better and better for them, you could say that they’re happy as a clam.



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