Ochre sea star

Understand the significance of a keystone creature.

Purple sea stars on the California coast were the key to finding out the answer to ecologist Fred Smith's question, what keeps the world green? Or more directly, why don't plant eaters eat all of the green things? Using some small but diverse tide pools on the coast, Ecologist Robert Payne removed green eaters one by one from the pool.

He found only the removal of one of the predators from a pool caused the ecosystem of the tide pool environment to collapse, the purple sea star.

A diverse biological culture stays in balance when a top predator holds a population in check.

In the case of the tide pools, purple sea stars feeding on mussels kept the total system in balance.

Without its keystone predator, over time, a community becomes a diminished, distressed, and dead system.

Understand purple sea stars, key to finding out what keeps world green.

Ecologists remove green eaters from the tide pool.