From the video it looks like they're pretty amazing.
This is from wikipedia:
"Bivalves, including oysters, are effective filter feeders and can have large effects on the water columns in which they occur.[11] As filter feeders, oysters remove plankton and organic particles from the water column.[12] Multiple studies have shown individual oysters are capable of filtering up to 50 gallons of water per day, and thus oyster reefs can significantly improve water quality and clarity.[13][14][15][16] Oysters consume nitrogen-containing compounds (nitrates and ammonia), phosphates, plankton, detritus, bacteria, and dissolved organic matter, removing them from the water. [17] What is not used for animal growth is then expelled as solid waste pellets, which eventually decompose into the atmosphere as nitrogen"