Coral reefs provide dazzling examples of natural architecture in the world. They are essential to the health of oceans and to the health of humans as well. Scientists have recently issued a warning about the dire state of coral reefs. Can we preserve them yet?
I will be writing a series of articles on coral reefs, their economic and ecological importance, the dangers they face through pollution and global warming, and artificial reefs to revive dwindling reef population.
What are Coral Reefs?
Long long before animals walked on land, coral reefs – the awe-inspiring sea gardens and the earth’s oldest living communities of plants and animals – started forming in the seas. Coral reefs are the oldest complex natural communities or ecosystems existing on Earth, supporting a staggering diversity of marine life.
Image via Wikipedia
Coral reefs constitute less than 1% of vast oceanic space, yet supports 25% of all marine life. Because of this, coral reefs are often called “the rainforests of the sea“.
Corals are marine animals related to jellyfish and anemones that occur in dense colonies in warm shallow waters of oceans. Almost all corals are colonial organisms. This means that they are composed of thousands of individual animals, called polyps. The coral polyps have a mouth in the middle and a ring of tentacles around the mouth with which they catch plankton (microscopic plants and animals) and other suspended food particles. The tentacles possess stinging cells and can be used to sting, paralyze, and catch prey.
Coral polyp via Wikipedia
Most reef-building corals contain photosynthetic algae, called zooxanthellae, that live in their tissues. There is a symbiotic relationship between coral polyps and the photosynthetic algae. The coral provides the algae with a protected environment and nutrients and chemical products such as carbon-dioxide they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, the coral uses the end products of photosynthesis such as glucose, glycerol, and amino acids to make proteins, fats, and carbohydrates, and produce calcium carbonate.
How are coral reefs formed?
Corals secrete a hard skeleton, called a corallite, under their skin. Each polyp secretes a hard, circular corallite made of calcium carbonate. Coral polyps can be solitary or colonial. Solitary forms remain as one polyp and one corallite.
Solitary Corallite showing radiating septa, top view; Credit: Marine Bio;
Coral reefs are formed by the skeleton remains of many generations of corals depositing hard skeletons on top of one another. These hard calcareous exoskeletons form elaborate finger-shaped, branching, or mound-shaped structures that stretch for hundreds of miles.
How do coral polyps reproduce?
Colonial forms can reproduce the polyp asexually (cloning). New clonal polyps bud off from parent polyps to expand or begin new colonies.
Credit: Marine Bio; Pictures: left, Colonial mounding coral; right, Colonial branching coral
Sexual reproduction: Most corals produce male and/or female gametes. They release massive numbers of eggs and sperm that spread over a huge area. The eggs and sperm join to form free-floating, or planktonic, larvae called planulae that are carried by water currents. Click the following link to view a video of coral spawning that shows how corals spawn in mass synchronized events, releasing millions of eggs and sperm into the water at the same time.
Where are coral reefs found?
Reef-building corals are scattered throughout the tropical and subtropical western Atlantic and Indo-Pacific oceans (generally between 30 degrees North and 30 degrees South latitudes) which have warm ocean temperatures (20–28° C), at depths of less than 46 m, where there is sunlight and clear water through which the sunlight penetrates better. The world’s greatest reef is in Australia: the Great Barrier Reef.
Great Barrier Reef, Australia; Credit: mtb4me3000 via Flicker
The major reef formations in India are in Gulf of Mannar, Palk bay, Gulf of Kutch, Andaman and Nicobar Islands and the Lakshadweep islands.
Sea turtle in the gulf of Mannar; Credit: Gulf of Mannar Marine National Park
The Gulf of Mannar in the Indian Ocean is a shallow bay that lies between the southeastern tip of India and the west coast of Sri Lanka.
Some of the corals photographed by Gulf of Mannar Biosphere Reserve Trust
Read Importance of Coral Reefs and How They Are Destroyed: Coral Reefs: Part 2
How Degenerate Coral Reefs Can Be Regenerated: Coral Reefs: Part 3