Reef Architecture
The International Year of the Reef 2008 is a worldwide campaign to raise awareness of the value and importance of coral reefs and threats to their sustainability, and to motivate people to take action to protect them. To that end, over the next year, articles about coral reefs will be written as a regular feature in this magazine.
From the beautiful to the bizarre, corals form the architecture of reef cities found around the world’s oceans. These underwater wonders are built by millions of architects called polyps that secrete calcium carbonate to create the hard structure that not only hosts the coral, but also provides food and shelter for hundreds of types of inhabitants such as fish, molluscs, sponges, crustaceans and reptiles.
As with the above-ground architecture found around the world, coral reefs have their own type and style of architecture. Charles Darwin was the first to explain this architecture by describing patterns of development that he observed during his five-year Pacific Ocean voyage on the HMS Beagle during the 1830s. He found three distinct types of reefs: the fringing, the barrier and the atoll.
The fringing reef begins to grow in shallow water, close to and along coastal shores. It may also form in the mouth of a harbour where, over tens to hundreds of years, it may eventually close off the bay and become a salt pond. Many of the reefs in the BVI are fringing reefs.
The second type of reef Darwin observed was the barrier reef. It typically grows along the outer edges of continental shelves and is separated from the mainland by open water. Barrier reef corals often grow on top of one or more ancient reef structures that had grown during previous “interglacial” periods but then dried out during following glacial periods. The Australian Great Barrier Reef is the most famous of barrier reefs. Although the Horseshoe Reef in Anegada does not quite fit Darwin’s definition, it is considered a barrier reef by definitions today.
The third type of reef is the atoll. Atolls begin by colonizing around a seamount or volcano as a fringing reef, and then grow upward as the seamount sinks or as sea level rises. Eventually, the seamount sinks below the sea surface, while the coral reef continues to grow upward resulting in the characteristic donut-shaped reef enclosing a central lagoon. Many people think that Anegada is an atoll because it is called a “drowned island,” but Anegada is not a true atoll. While this basic reef classification scheme still exists today, there are many other types of reefs identified and found around the world. They include bank-barrier reefs, channel reefs, deep-sea reefs and the patch reef, with the latter being commonly found throughout the BVI.
As for the style of architecture on a reef, corals around the world come in similar shapes, although not similar species for each geographical location. Of course this makes it difficult to learn every species of coral found in the world, but learning the similar styles is fairly easy. Corals may be branching or pillar (such as elkhorn or finger corals), plated or leafy (such as the lettuce corals), fleshy (such as the cactus corals), brain corals, cup and flower (such as the rose coral) or encrusting, mound or boulder corals (such as the great star corals, the most common coral in the Caribbean).
So the next time you are out diving and snorkelling, don’t just think of the reef as something pretty to look at, remember it is its own city, full of unique and beautiful architecture.
