Oysters are among the hardest working animals in the ocean. As adults, oysters can filter 25-50 gallons of water each day. Back in the day, the entire Chesapeake Bay could be filtered in just five days before oyster populations dropped to just 1% of their historic levels. In fact, oysters are part of the reason the Chesapeake got its name—it’s an Algonquin Native American word that means “Great Shellfish Bay.”

Because oysters filter massive amounts of water, they are vulnerable to what ends up in the ocean. Their numbers can drop if there are increased amounts of runoff or coastal erosion (which is when you would want MORE animals filtering the water). Oysters also can collect toxins in their bodies which can be harmful for the humans who eat them.

Oysters do much more than filter water, though. Oysters latch onto each other to form big reefs that provide shelter for fish and crabs and that stabilize muddy estuary bottoms. Also, filtered water provides better conditions for seagrass, a crucial habitat and breeding ground for animals like rockfish and blue crabs to grow.