Why are oysters a keystone species?

Without oysters many coastal ecosystems would collapse. Each oyster can filter up to 50 gallons of water per day. A healthy oyster bed can  dramatically improve water quality, in addition to cycling water between the water column and bottom-dwelling species. In Louisiana and other Gulf states, they are considered crucial to coastal restoration.

Here's how some smart folks in Mobile are utilizing oyster shells to help restore the health of Mobile Bay: Alabama oyster bed restoration among first since Gulf oil spill