Scientific American has a report on Hawaii's use of sea urchins as a way to combat invasive seaweed in their coral reefs. By breeding sea urchins to boost numbers, they can act like goats on hillsides, keeping the weeds mowed.
"To combat the smothering seaweed, scientists from Anuenue Fisheries Research Center have now started breeding native collector urchins (Tripneustes gratilla), which can eat the invaders without damaging the local coral."
The idea was tested out in 2009 and is now being rolled out. Get the full story on Scientific American.