Exosphere Children

Spectacular underwater world

A handout photo received from the ARC Centre of Excellence for Coral Reef Studies at James Cook University shows blue-green chromis on the Great Barrier Reef near Lizard Island in Queensland. Coral reef fish are more likely to make risky decisions, including being unable to identify friend from foe, if they swim in waters contaminated with petroleum-based oil, Australian researchers said on July 19, 2017. / AFP PHOTO / ARC Centre of Excellence for Coral Reef Studies at James Cook University / JODIE RUMMER / ----EDITORS NOTE ----RESTRICTED TO EDITORIAL USE MANDATORY CREDIT " AFP PHOTO / Jodie RUMMER / ARC Centre of Excellence for Coral Reef Studies at James Cook University" NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS - NO ARCHIVES /  

The oceans form a mysterious, watery world. Imagine entering one of them. After swimming by fishes, turtles, jellyfish, you come across the most spectacular of its inmates: the corals.

Spectacular underwater world

In multifarious shades of yellow, red, green and brown, they have been aptly named to match their unusual shapes — Stag Horn Corals, Fan Corals, Brain Corals, even Dead Man’s Fingers Corals….Their shades come from microscopic algae called zooxanthellae that live inside the thousands of polyps that make up the coral colonies.

The zooxanthellae need sunlight for photosynthesis and water between 23° and 25°Celsius. Therefore, corals can survive only upto the depth that sunlight penetrates. In warmer waters, you will only see bleached coral, in which the zooxanthellae have been expelled. Since the polyps can’t live without them, the coral is dead.

Ocean diaries

At night, the coral polyps emerge from their skeleton homes of calcium carbonate and wave their miniscule tentacles to draw food from the water. This gives an illusion of the corals being covered with velvety fur. You are sure to find the coral colonies pulsating with other kinds of marine life that shelter in its folds and labyrinths: giant clams, crabs, sea anemones, sea squirts, lobsters, turtles, sea horses and more.

On the fourth or fifth night after full moon, you may even witness the birth of new corals. The waters transform into a soup of rainbow colours, with thousands of brightly hued specs rising upwards: the coral eggs.

When they hatch, the baby polyps called planulas swim around till they find a suitable surface to attach themselves to — a rock or even a sunken ship — and soon turn into polyps that start drawing calcium carbonate from the sea water, giving rise to a new coral colony.

Often, coral colonies get overcrowded and may wage a silent and merciless war with each other. The polyps shoot out long filaments from their mouths that simply digest their competitors. This is Nature’s way of controlling the excess population. Before you know it, the night has come to an end. At the crack of dawn, you see the polyps withdrawing their filaments. The only signs of them having raged a cold-blooded war are dead coral patches.

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Printable version | Jan 28, 2021 8:00:42 AM | https://www.thehindu.com/children/spectacular-underwater-world/article33200313.ece

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