Tropical islands are an obvious magnet for life.
But things are just as busy underwater.
Deep currents collide with these islands,
forcing small but vital amounts of nutrients up from the depths.
At 50 metres deep, sea fans are amongst the first to benefit.
Closer to the surface, corals have sunlight to help them grow.
And thanks to the smallest trickle of nutrients,
a barren desert can bloom into an underwater oasis,
supporting a greater variety of life than any other ocean habitat.
These coral reefs are a magnet for green turtles,
offering a service not available in the open ocean -
a good clean-up by a shoal of tangs.
This work-over is far from cosmetic.
As well as removing parasites,
the cleaning stops the build-up of algae,
so the turtle can swim freely.
But it's also got to feel good.