There's one fish species that is so good at defending its particular patch of reef. But it's responsible for more attacks on divers than any others. And that's this species here. This is a white damsel, and it's a constant gardener, nurturing and caring for a patch of algae. 

 

Much of the algae growing on the sandy sea bed is edible. So the damsel farms it in green patches, encouraging some species nipping down others and gently transforming the landscape around her. After all this hard work, she doesn't look kindly on trespassers. Anything that swims too close is chased away. But is she brave enough to try to see me off.