They are one of the most biodiverse habitats, if not the most diverse, home to a vast array of often spectacular species. And unlike other highly biodiverse habitats, much of this spectacle is densely represented and constantly on show.

In a tropical rainforest, you can ramble uncomfortably through dense undergrowth for hours, hearing many animals but glimpsing few, usually from a limited range of phyla, and seeing mostly plants. On a healthy reef, drift but a few minutes through the clear, warm seawater, and the sheer abundance and variety of algae, corals, anenomes, molluscs, echinoderms, sponges and many other invertebrate phyla, as well as algae and of course fish, will be immediately apparent.