What immediately comes to mind when many of us think of an atoll is a desolate, circular array of coral reefs with white, sandy islands populated by a few lonely, swaying palm trees and perhaps a castaway or two. Were we to consider them more closely, however, we would find that this standard perception just skims the surface. Atolls are, in fact, some of the most complex and vibrant structures on the planet. Built diligently over thousands of years by tiny, sea anenome-like coral polyps, these ring shaped coral structures can be tens of kilometers in diameter with individual reefs large enough to support lush tropical islands and even small cities. As is the case with any living coral structure, countless species of fish and invertebrates can be found inhabiting the waters in and around an atoll. But unlike the fringing reefs along Floridas coast or even the barrier reefs off the shore of Australia, atolls do not border anything. Instead, they sit on a coral base that often rises thousands of meters from the oceans floor in some of the most remote areas of the tropical oceans.
Though scientists have been studying atolls at least since the time
of Charles Darwin in the mid-1800s, many mysteries remain about exactly
how they form and what factors determine their shape. One such question
centers on the degree to which climate conditions affect the growth of
the coral reefs that make up an atoll. Some researchers believe that
the weather acts primarily to erode and diminish the underlying
structure of fully formed reefs. Others believe that given the right
conditions, waves and currents shape the reefs by actually stimulating
growth. Resolving this debate one way or the other hasnt been easy
though, as most atolls are in remote areas of the ocean and are hard to
get to, let alone map or fully analyze.
Two scientists at Dalhousie University in Halifax, Nova Scotia, may now be on their way to solving this riddle of the atolls. Using satellite imagery collected by Landsat 7, marine ecologist Bruce Hatcher and Maldivian doctoral student Abdulla Naseer are mapping out the reefs of the atoll archipelago that make up the Maldives in the Indian Ocean. By comparing the maps to wind and wave data from the region, they are attempting to discern if the monsoons that blow regularly from the east and the west played a role in shaping the Maldives. And they believe such knowledge may have a practical application as well. Understanding how the coral reefs grow could help the Maldives people shield themselves from the rising sea levels that may occur as a result of global warming.
The Maldives are a group of coral islands resting on top of an ancient volcanic mountain range off the coast of India.
For more about using satellites to study coral reefs with satellites, read: Mapping the Decline of Coral Reefs