Coral—In Danger and Dying
NOWHERE is the ocean clearer than in the Tropics. Crystal clear. Blue crystal. The white sandy bottom 50 feet [15 m] below seems so close you could touch it! Put on swim fins and a face mask. Adjust your snorkel as you slip into the warm water, bubbles clouding the view for a moment. Then look below. There! See the large red and blue parrot fish biting on coral and spitting out bits, which become part of the sandy bottom. Suddenly, a silvery rainbow of tropical fish—red, yellow, blue, orange, purple—flashes by. Life is in motion everywhere. It overwhelms your senses.
This is the coral jungle. It rises from the sandy bottom below, reaching out with thousands of living arms. Just ahead is a magnificent stand of elkhorn coral, over 20 feet [6 m] tall and about as wide. Some 75 feet [23 m] away are staghorn coral, smaller than the elkhorn, their slimmer branches filling the area like a forest. How aptly these corals are named—looking, for all practical purposes, like animal horns! Fish and other marine life find food and shelter in their branches.
Once thought to be made up of plants, coral is now known to be a limestone formation made by communities of animals called polyps. Most polyps are small, less than one inch [2.5 cm] in diameter. The soft-bodied coral polyp links itself to its neighbor with mucus-covered tissue. The coral looks like stone in the daytime, since the polyps withdraw into their skeletons. But it is transformed at night as their extended tentacles wave gently, giving the reef a soft, fuzzy appearance. The stony “tree” the polyps share is their combined skeleton, cemented together by the extraction of calcium carbonate from the seawater.
Each type of coral community constructs its own unique skeletal shape. Throughout the world, there are over 350 different types of coral, with astounding shapes, sizes, and colors. Their common names remind you of objects on land—tree, pillar, table, or umbrella coral—or of plants—carnation, lettuce, strawberry, or mushroom coral. See that large brain coral? It’s easy to see how it got its name!
This underwater jungle teems with life, from microscopic plants and animals to rays, sharks, large moray eels, and turtles. And here are some fish you may never have heard of—bright yellow clown fish, purple Beau Gregories, black-and-white Moorish idols, orange trumpet fish, dark blue surgeonfish, indigo hamlets, or brown and tan lion-fish. And how about barbershop shrimp, painted lobsters, or scarlet hawk fish? All colors, all sizes, all shapes. Some beautiful, some bizarre—but all interesting. See, there’s an octopus hiding behind that pillar coral! It’s dining on a clam it has opened. As in jungles on land, a tremendous variety of life is interwoven in the fabric of this marine world, all dependent on its diversity. Coral’s reproductive cycle and its ability to travel on ocean currents to build new reef communities was detailed in the June 8, 1991, issue of Awake!
Coral reefs form the largest biological structures on earth. One of these, the Great Barrier Reef, off the northeast coast of Australia, extends 1,250 miles [2,010 km] and encompasses an area the size of England and Scotland combined. A coral can weigh several tons and rise more than 30 feet [9 m] from the ocean floor. Coral reefs grow in all shallow tropical waters at a depth of as much as 200 feet [60 m]. They have characteristics that differ from area to area, so by examining a piece of coral, experts can tell the ocean and even the locale in which it grew. The environment needed for the growth of coral reefs is one with limited nutrients in the water, which explains why the ocean is unusually clear in their vicinity. Nutrition for the coral is supplied by algae (scientifically called zooxanthellae), which live in the polyp’s transparent body, and also by microscopic animals that are captured in the coral’s tentacles. The end result is a coral reef that is home to thousands of marine species in otherwise shelterless oceans.
Coral reefs are also the most biologically productive of all marine ecosystems. U.S.News & World Report described it this way: “Reefs are the marine equivalent of tropical rain forests, teeming with a profusion of living forms: undulating sea fans and sea whips, feathery crinoids, neon-hued fish and sponges, shrimp, lobster and starfish, as well as fearsome sharks and giant moray eels. All depend on the continuing industry of coral for habitat.” Coral reefs also support life on land by providing a barrier between crashing waves and shorelines and by laying the foundation for thousands of tropical islands.
Healthy coral is brown, green, red, blue, or yellow, depending on the type of algae residing in the transparent coral-polyp host. The algal microscopic plants use the sunlight shining through their animal symbionts and absorb the polyp’s waste products, including carbon dioxide, for their nutrition. In turn, through photosynthesis the algae provide oxygen, food, and energy for the coral tissues. This partnership with algae allows coral to grow faster and survive in the nutrient-poor tropical waters. Both have the best of plant and animal worlds. What a masterly and wise design!
Bleached Skeletons Devoid of Life
No wonder there’s so much activity below! But what’s that? Bleached skeletons devoid of life. Branches are broken off and crumbling. Some have already disintegrated. This part of the coral forest is dead or dying. No fish. No shrimp. No lobster. Nothing. It’s an underwater desert. You stare in disbelief. What a shock! Your idyllic experience is ruined. Even when you are back on the boat, troubling questions remain. What could have caused this devastation? An accident? Disease? Natural causes? You want answers.
Although stony coral looks tough, it is extremely fragile. A human touch can cause damage, so wise divers avoid handling it, and careful boaters avoid anchoring on it. Other dangers to coral are chemical pollution, oil spills, sewage, logging, farm runoff, dredging, sedimentation, and freshwater intrusion. Direct impact by boat keels wreaks havoc. And temperature extremes can damage and kill coral. When stress occurs, coral expels its algae in thick clouds, and fish quickly eat it. If stressful conditions persist for weeks or months, bleaching occurs and the coral dies. And when the coral dies, the reef environment dies. The fabric of life unravels and disappears.
Bleaching has become widespread in all tropical oceans. As a result, there is alarm in the marine science community worldwide. When large-scale bleaching occurs, the damage is irreversible. The extent of coral bleaching and its subsequent death has been brought painfully to world attention by what has occurred throughout the world’s tropical seas in recent years. While there has been periodic and localized bleaching of corals for many years, the current outbreaks are unprecedented in severity and are global in scope. Something has been attacking the living corals of most species earth wide, causing the collapse of reef environments.