Sandy Sheehy

The best way to understand and appreciate the natural world that surrounds us may be to explore beneath its surface – not by digging, which destroys the very natural systems we seek to examine, but by looking under water, which we can do with little or no disruption of whatever is going on. Birth and death, growth and decline, the interaction of plants, animals and minerals, of predators and prey – in short, everything that happens in our own, familiar environment above ground happens below the waves. And natural phenomena are easier to scrutinize down there, partly because, unlike soil or rock, water is transparent and partly because the underwater world is unfamiliar, so whatever goes on in it is more likely to grab our attention. Venturing there is the closest almost any of us will come to visiting another planet.

Life on earth began in the sea four billion years ago. The world’s oceans combined contain 300 million trillion gallons. Each drop of seawater holds between 2,500 and 300,000 single-celled organisms – bacteria, viruses – a hundred million times more than the estimated number of stars in the universe.

In terms of having a lot going on, even in the ocean, nothing beats a tropical coral reef. Situated between a foot or two below the surface and about 200 feet down, coral reefs benefit from plenty of the filtered sunlight that algae and other aquatic plants require for photosynthesis, which in turn fuels the ever-looping chain of life for sponges, crustaceans, eels, marine mammals and fishes large, small and tiny. Although they occupy only 0.1 per cent of the oceans’ surface, reefs of hard coral sustain 25 per cent of marine life. A third of all the species in the ocean (somewhere between two million and ten million) live on coral reefs. Coral reefs dot the earth’s shallow oceans, extending generally to 30 degrees latitude on either side of the equator. In some areas where waters farther north or south are unusually warm -- such as Bermuda, located at 32.3 degrees north but bathed by the temperate Gulf Stream -- patch reefs of hard corals survive.

Coral reefs come in three major varieties: fringe, which surround islands; atoll, which started as fringe reefs but became more or less circular free-standing structures when their central islands subsided; and barrier, which can form along continental shelves, often linking islands that lie close to each other. For the purposes of this book, I decided to focus on one particular reef, the Mesoamerican Barrier Reef, also known as the Great Mayan Barrier Reef, in the Western Caribbean. I made this choice for several reasons. First, although coral reefs occupy only that 0.1 per cent of the surface area of the world’s oceans, as mentioned above, that was still too much territory for me to cover in my remaining lifetime. Second, I already had at least a passing acquaintance with this particular stretch of coral; I’d been diving parts of it for decades. And third, all the beauty and drama of the coral ecosystem, and all the forces and follies that imperil coral reefs everywhere, are clearly evident along that 620-mile formation.

Stretching from Isla Contoy, just north of Cozumel, Mexico’s largest Caribbean resort island, to the Bay Islands of Honduras – Roatán, Útila and Guanaja – the Mesoamerican Barrier Reef is the second-longest continental coral structure on earth. As its official name reflects, this underwater paradise is a multinational asset, skirting the coasts of Mexico, Belize, Guatemala and Honduras, lying between a few hundred yards and 22 miles offshore. Four of the North Atlantic’s nine atolls, rings of islets rising barely above the surface – Chinchorro Banks, Turneffe Atoll, Lighthouse Reef and Glover’s Reef – are part of the barrier reef system. (Arrecife Alacránes, or Scorpion Reef, consisting of five mini-atolls, sits more than 200 miles to the west of its northern tip, in the southern crescent of the Gulf of Mexico.) Resting on a foundation of limestone and hard corals, the Mesoamerican Barrier Reef measures less than half the length of Australia’s Great Barrier Reef; yet in variety and richness of species, it rivals its more famous cousin.

A person needn’t be a scuba diver or a snorkeler to explore the fascinating complexity of life beneath the surface. In fact, you don’t even have to be able to swim. Personally, I prefer to visit this engagingly alien world in person, listening to the gentle bubbles of my exhalations as I glide lazily along, enveloped in warm liquid about the same salinity as amniotic fluid and only about 15 degrees cooler. (As a diver, I’m something of a wuss. I never was one for cold-water diving and have a decided preference for the tropics.) But I have become increasingly amazed at the quality and detail captured by the world’s great underwater cinematographers and even by some marine biology graduate students; the latter’s camera work may waver, but their enthusiasm, including the exclamations of “Awesome grouper!” and the like that they and their colleagues contribute to their voice-overs, make up for the home-movie visual quality.

Much has been made about coral reefs in recent years, especially about the perils they face due to global warming. The hard corals that form the foundation for the reef ecosystem are very particular about temperature. If the warmth of the water they inhabit falls below 64° Fahrenheit for more than a few hours, they die; if it rises above 90° F, most species expel the algae with which healthy corals live symbiotically -- and which lend them their vivid colors. Called “bleaching,” this visually striking symptom indicates a patch of coral under extreme stress and vulnerable to lethal damage from storms and disease.

The book that follows does address bleaching and the other threats to the Mesoamerican Barrier Reef and its cousins worldwide. Changing acidity of the ocean, nutrient-laden runoff from fertilizer, sediment kicked up by storms, debris and sewage from coastal development, introduction of invasive species, over-fishing, inept divers and plain old trash, such as plastic soda bottles – all these and more endanger this fragile ecosystem, as well as the other 99.9 per cent of the earth’s oceans. Most of these threats result from human activity. Some can be halted or at least curbed relatively easily, given broader awareness, targeted economic incentives and international cooperation. The concluding chapters of this book describe specific examples of successful programs and specific ways in which we can act, collectively and individually, to limit and even reverse the damage.

But people don’t protect what they don’t value. The purpose of this book is to raise understanding and appreciation of one particular, fascinating and fragile ecosystem and thus, by extension, of coral reefs throughout the tropical oceans and of the rest of the earth’s environment everywhere.