Some coastal cities have begun replacing concrete seawalls with oyster reefs. The oysters are better at the job. Concrete seawalls begin to degrade the minute they're installed. Waves chew them up, storms crack them, and they have to be repaired, replaced, and rebuilt forever. An oyster reef doesn't break down. It actually grows. The oysters stack, reproduce, and fuse into something akin to living rock that gets stronger every year. A mature reef can cut incoming wave height by up to 83%. It traps sediment, rebuilds the shoreline behind it, and shelters fish, crabs, and shrimp in the process. One hectare of oyster reef provides up to $85,000 a year in shoreline protection. Concrete costs over a million dollars a hectare to build and only gets weaker.