Coral reefs are all about symbiosis - the art of living together. When we look at an underwater scene like this one, we tend to focus on the brilliant blue fish Chromis viridis, or the blue Acropora coral, or perhaps the Dasyatis stingray in the sand. We see them all as separate, individual creatures. But they are, even as we watch, a collective being, and owe their very existence to mutually beneficial actions.

The blue demoiselle fish and the blue coral are excellent examples of this.

The blue coral thicket is the crystalized history of the behavior of millions of tiny anemone like creatures that extract calcium carbonate from the sea and secrete intricate skeletal homes - the small nodes you see on the coral branches.

Each branch grows upwards into the sea as the coral polyps bud new examples of themselves and convert the clear sea water into the calcium carbonate skeletal shelters that protect their soft tisues. The branch elongates at about 40 to 70-mm per year depending on the depth and availability of nutrients.

The coral tissue is filled with tiny algae symbionts, called zooxanthellae. These creatures convert sunlight into sugars and oxygen for the corals and facilitate the rapid extraction of calcium carbonate to build the skeleton of the coral branch. In turn, the zooxanthellae are protected by the coral skeleton and supplied with carbon dioxide and nutrients - like phosphates and nitrates (fertilizers) from the corals. Since the carbon dioxide and nitrates and phosphates are waste products for the corals this is an excellent partnership.

Nitrates and phosphates are rare compounds in the clear tropical waters of the Pacific and although the corals could get sufficient energy to survive from the photosynthetic activity of the zooxanthellae, they both would perish without phosphates. So the coral branches extend up into the sea water, allowing the tiny tentacles of the coral polyps to comb the sea for microscopic plants and animals that will supply the needed fertilizers.

These branches also protect swarms of fish. Some of these, like the blue Chromis demoiselle fish, swim up into the sea above the coral thickets and feed on plankton from the sea water. The fish drop their waste products back into the coral thicket in little pellets, rich in phosphates and nitrates. The coral polyps catch these fish droppings and ingest them, providing fertilizers that enhance the growth of the whole coral colony.

Just as the coral branches are a symbiosis of zooxanthellae and coral cells reaching up into the sea, the schools of tiny plankton feeding fish are an extension of this, reaching even further into the sea and bringing the nutrients back to help the entire assembly of creatures to grow larger. Over hundreds of years the coral thickets grow into coral reefs, forming lagoons and passes and islets that together act as one vast living system with myriad symbiotic systems of a wonderful, brilliant, exhilarating complexity.