Marine Oases

Charles Darwin wrote about much more than evolution. Among other things, after his ’round-the-world trip in the 1830s, he wrote a book about coral reefs—an attempt to explain the origins of different types of reefs. A century and a half after the book was published, people got the idea that Darwin described reefs as “oases in marine deserts.” He didn’t—and they’re not.

A recent study showed that, while reefs are some of the most vibrant ecosystems on the planet, the waters around most of them are busy as well.

Researchers studied satellite observations of reefs and their surrounding waters from around the world. They also studied direct measurements of many of those environments. They looked at two key markers. One was chlorophyll—a pigment that tiny organisms use to produce energy. It colors the water green, so green water means a lot of life. The other marker was a set of compounds that serve as nutrients.            

They found that about 80 percent of all the reef systems were surrounded by plentiful conditions—waters that were teeming with both chlorophyll and nutrients. Currents, tides, and fish and other organisms carry those life-giving ingredients onto the reefs. That makes the reefs oases in a land of plenty. But the easy way that these materials infiltrate the reefs also means that reefs can be more easily influenced by pollution, global warming, and the results of other human activity—damaging these vibrant ecosystems.