ANDROS, Bahamas, Aug. 23 — We know them by the name "coral reefs," but they're much more than coral. Reefs are home, by some estimates, to more than a million species, from the tiniest algae to 10-foot-high coral.

Often called the "rainforest of the oceans," these relatively shallow marine environments are home to most of the world's major groups of organisms. Each species that lives on the reef forms an essential part of the whole sensitive ecosystem: If one part is harmed, it can have a domino effect.

The intense interdependence of the species — marine fauna and flora alike — makes the reef a canary-in-a-coal-mine of sorts for our coastal waters. Reef ecosystems are often the first places to exhibit signs of environmental damage, and the past few years have been filled with news from major studies of coral reefs. Generally, the news is not good.

A slight temperature change in seawater is enough to kill the companion algae that provide living coral with much of its food. And pollution is often much more concentrated and deadly in shallow reefs than in deep-sea ecosystems.

"Coral reefs have evolved to be quite robust," says Dan Brumbaugh, marine program manager at the American Museum of Natural History's Center for Biodiversity and Conservation, and one of the leaders of this expedition. "(But) when symbiotic relationships break down, when the algal organisms that live on coral and give them sustenance start dying, the coral does, too."

Dan, Paula Mikkelsen, curator of malacology at the museum, and an array of other marine biologists have converged on the Bahamian island of Andros, where for the next several weeks they'll conduct a rare interdisciplinary survey of the world's third-largest barrier reef.

Scientists with a passion for algae, moss animals, lobsters, corals, sea urchins, worms, snails and fish will be counting reef creatures — and measuring the light waves they emit — as part of a project to map the reef from space using NASA's Earth-watching satellites.

The biologists want to be able to eventually gauge the health of a reef in an instant — without having to stage such a monthlong, multiscientist survey as this. If, for example, Hurricane Debby hits, satellite images may soon be able to reveal damage not only to a broad area, but even to particular underwater species of plant or animal.

That's part of the long-range goal. But for the next four weeks, join us here in Andros as we collect rarely seen specimens, count critters big and small, and dive on a reef teaming with tropical fish. Among the adventures will be woven — like the beautiful baskets that are created by local artisans — the question: Is this canary healthy?