[The Rainbow Warrior's marine biologist, Kat, explains everything you ever wanted to know about coral but were too confused to ask - Dave]
If you mention the word 'coral' to most people, it conjures up a mental image of the white branching skeletons you see in seaside tourist shops, or brightly coloured reefs with darting fish and dancing shrimp, and maybe Nemo and his father Marlin swimming by. But what is coral? It looks like a plant, but seems to have a stone skeleton, and didn't I hear somewhere that corals were actually animals?
Yes. Corals belong to a phylum of marine animals called Cnidaria (Ny-dare-ee-ah), which also includes jellyfish, anemones and sea-pens. Some corals are solitary (with individuals living by themselves, not forming colonies), but the best-known kinds form reefs. These may be broad and flat, like shelf mushrooms, or tall and branching, like trees. New Zealand has over 105 species of coral in its waters, and 70 of these form reefs, either in the sunny shallows, or, more importantly to us on this trip, in the deep sea. In fact, more than 50% of the world's coral lives in the deep sea, as far down as 5 km!
Hard coral reefs generally begin when a single free-swimming larva (planula) settles on a hard surface and begins to divide itself into many identical polyps, each one smaller than your little fingernail. A polyp is much like an upside-down jellyfish, with the bell replaced or protected by the hard limestone skeleton it produces, and the stinging tentacles stretching upward to catch particles and small prey in the water above. As individual polyps are eaten or die off, their hard skeletons are overgrown by new polyps. In this way, over tens to hundreds of years, coral reefs form.
Reefs harbour an amazing range of sea life. Fish, crustaceans, worms, molluscs, sponges, and many other animals congregate on and around coral structures to feed on them and each other, and to seek shelter in, around, or beneath them. Corals are at least as important in the deep sea as in the shallows; there they also provide a hard surface to which other sessile (stationary) animals may attach, as well as providing shelter in an otherwise largely exposed habitat.
When a deep-sea coral colony is knocked over, most of the polyps usually die, either from starvation (from being oriented the wrong way), or by suffocating in the sea floor. Sometimes a few can survive and begin to form a new colony on the dying old one, but most often a broken coral dies entirely, especially if it is taken from the water and thrown back, or broken into many pieces. It is quickly covered over with encrusting animals like bryozoans, and much of the other sea life that fed or sought shelter there moves elsewhere. What was once a thriving community becomes a ghost town.
Many of the deep-sea corals around New Zealand grow into large, beautiful forms, some of which sell for high prices overseas and are already under threat without the help of bottom-trawling. A few of these have never been found anywhere else. Since most of them grow very slowly, if we are not careful we may lose the chance to learn anything about them for several hundred years - if they recover at all.
