This is a guest post from Dr. Stacy Jupiter, Program Director for the Wildlife Conservation Society in Fiji. The photos are by frequent Global Explorers Blog contributor Keith Ellenbogen.

On several occasions, I have been privileged to introduce someone to coral reefs for the first time. In every instance, they have emerged from the water or from viewing through a looking glass with an ear-to-ear smile. Who would have imagined that under the flat blue surface there would be neon cities with Gothic cathedral-like constructions and canopies?



Most coral polyps are smaller than an ant, and like those industrious creatures, their collective labor can yield much more than the sum of its parts. Yet while ants are often preoccupied with dismantling some larger creature to feed their swarm, corals are specialist architects. For reef building species, the jelly-like corals secrete calcium carbonate skeletons outside their bodies. These skeletons are strong, like bone, and have actually been used to make a "bone paste" (developed by Dr. Brent Constantz at Stanford University) which can be injected into human patients with fractures to form an internal cast. I know this because my father, an orthopaedic surgeon at Massachusetts General Hospital, performed some of the first experimental trials.



Coral larvae ("planulae") are free-swimming. After a few weeks of swimming around with the rest of the plankton, they settle down to hard reef substrate where they will spend the rest of their lives, which for some coral giants may be over a thousand years. Each type of reef builder receives direction from its genes on what type of construction to build, however, the overall form may be modified by environmental conditions. For example, a branching Acropora on the reef crest that is chronically bashed by waves may hunker down and thicken its branches, whereas the same species in a sheltered backreef lagoon may extend their arms as they grow quickly towards the light. [Dr. Randi Rotjan and Kathryn Furby posted about these stages of stationary and mobile corals from the 2011 Red Sea Expedition.]



Corals themselves do not need light to grow, but inside their tissues they harbor tiny plant-like algae (called "zooxanthellae") which require the sun's energy for photosynthesis. It's a win-win situation. The corals benefit from the food produced by the algae while the algae stay safe within their coral houses. This energy fuels the fantastic reef building that can create reef structures that stretch for miles. However, the process is slow.




While some corals can extend as long as my index finger during a single year, most deposit only small films of skeleton such that the entire reef platform may only grow less than an inch. It is important to put this into perspective when fishermen use dynamite blasts to catch fish: they are destroying coral platforms that have taken millenia to build and will not quickly come back.



Coral skeletons also provide us important information about changes to the environment. As corals deposit each layer like tree rings, the trace elements that become incorporated into the calcium carbonate scaffolding reflect the conditions in the water at the time the coral was growing.



I have spent many years probing coral skeletons to understand how changes to reef water quality can be related to changes in land use practices in adjacent watersheds. Other trace elements can also tell us how sea surface temperature has changed from the distant past before people began collecting records from thermometers. They thus enable us to have a long-term baseline from which we can assess the effects of global climate change. [Dr. Steve Webster of the Monterey Bay Aquarium described the affects of climate change on corals in the Indo-Pacific in this post from the 2011 Joint Aquarium Fiji Expedition.]



But these thoughts aren't on my mind as I plunge into the coral canyons. As many times as I have been diving, I never tire of their vivid colors and intriguing geometries. And I never forget that these corals form the important foundation for the thousands of other fish and invertebrate species that call the reefs their home.

-Stacy Jupiter, PhD