One of the world's most unusual and delicate life forms, coral comprises millions of minute simple soft-bodied animals called polyps. Hard corals are so called because the polyps extrude an outer skeleton of calcium carbonate that links with the skeletons of other hard coral polyps and over time creates what we know as a coral reef, made up of many millions of individuals.
Coral polyps get nutrition in two ways. They catch their food by means of stinging tentacles that paralyze suitable prey—microscopic zooplankton—but they also engage in a symbiotic relationship with zooxanthellae, a microscopic algae that live within their own structure. The corals provide zooxanthellae with protection, and the zooxanthellae provide enough nutrition to allow the polyps to form reefs. Zooxanthellae need the sun's energy to produce their own food, so coral can only grow in clear, shallow waters less than 1,000 feet deep, where the sun's rays can still penetrate.
To form an extensive reef, corals need waters of at least 73°F, but they can't thrive in waters above 82°F. Growth is slow—between two and eight inches per year—and the structure is incredibly fragile, susceptible to physical damage such as boats dropping anchor, or to changes in water quality.
Coral reproduces asexually, by the division of existing individual polyps on the same reef, but also sexually. On a given night, when the moon and tides are exactly right, polyps will extrude millions of free-floating eggs and sperm into the water. When these combine, the result is a polyp that will be carried by ocean currents to found a new colony and a new reef.
Without coral reefs, the Maldives wouldn't have their fabulous beaches. The fine white sand is in fact tiny bits of coral bitten off the reef by parrotfish, then discarded and polished by the action of the water. The reefs protect the beaches, stopping them from being washed away by ocean currents.
Reefs are not only fascinating in their own right; they also form the basis of a whole marine ecosystem. The structure provides protection for myriad small fish—from colorful butterfly and cheeky sergeant majors—to crustaceans, and this abundant life attracts larger pelagic species from marlin and ray to sharks. Over 16 whale species have been spotted around the atolls of the Maldives, along with numerous dolphins; you may even find a family of these playful mammals swimming alongside your tender, one of the most heart warming welcomes you could hope to have.