My discoveries in an underwater city — the lively neighbourhoods in coral reefs

Diksha Dikshit

is a marine biologist, dive professional and oceanic educator. Writing for

Times Evoke Inspire

, she discusses how coral reefs form amazing ecosystems — and why these ‘underwater cities’ must be protected:

I come from dry, landlocked Delhi and became acquainted with the oceans a little late in life. Before venturing into marine biology in 2015, whatever I knew of the oceans had been learned through documentaries. To my eyes, coral reefs seemed breathtakingly beautiful but also otherworldly, enigmas I could only imagine from books and videos. I could not have known the huge surprise that awaited me when I began researching coral reefs — and discovered that these were thriving neighbourhoods, indeed, bustling underwater cities.

IT’S THEIR MORNING WALK: A shoal of snappers exercise in a garden of soft corals. Picture courtesy: Vandit Kalia (Photos via D Dikshit)

My journey began when I arrived in the Andaman Islands to pursue my research. I was so unready that on my first swim out, I couldn’t resist tasting the sea water to check that it was truly as salty as the textbooks said (it was). As I fell in love with the ocean’s depths, the sea helped me learn about its awe-inspiring life forms — starting with coral reefs.

Although tropical coral reefs cover only about 0.1% of the sea floor, they support over one quarter of all life in the oceans. Corals are neither plants, nor rocks. They are colonies of thousands of tiny tentacled animals that are cousins to jellyfish. They harbour microscopic algae called zooxanthellae which prepare food for the coral and give them their brilliant colours.

Picture courtesy: Vandit Kalia

Hard coral colonies are the building blocks of a reef, composed of calcium carbonate

exoskeleton

exuded over years. These act as substrates for softer encrusting organisms, like sponges and anemones which, in turn, provide homes for crustaceans like shrimp, crabs and lobsters, small fish like gobies, clown-fish and sea horses and echinoderms like sea stars,

brittle

stars and sea cucumbers. Crevices in the reef also shelter marine life from egg masses to octo-puses. Predators like barracudas and trevallies and graceful visitors like turtles and mantas populate the reefs’ water columns while stonefish and scorpionfish, the ever-elegant lionfish, rays and reef sharks lurk near the bottom, pouncing at prey.

HELLO SUNSHINE! A shy sea horse catches some lunch off a reef weed. Picture courtesy: Vandit Kalia


Together, these reef beings build up a highly productive and balanced ecosystem, with multiple species existing in synchrony. On my dives, I saw intense social activity. For instance, the bubble-tip anemone around a reef corner may look empty — but a clownfish and its family live there, hidden away from predators’ eyes. Right above them was a snapper that tried to evade an eel by entering a narrow cranny — only to land in the mouth of a grouper. On the other side reside cleaner wrasses which consume dead scales weighing down fish — many species swim into their quarters to get a refreshing spa! Somewhere along the reef, you see something move but just can’t locate it — until that master of disguise, an octopus, quietly slides off the rock you’re staring at. But there is no disguising the larger fish — the reef is covered by huge shadows when whale sharks, with over 300 rows of teeth, swim by.

BLUE

ALERT: A whale shark lurks in the waters by the thriving corals. Picture courtesy: Vandit Kalia


When night falls upon the sea, the coral reefs still thrive with life. On a sandy bottom walk a humongous lobster and a little sponge crab, apparently engaged in deep conversation. Below a rock dozes a parrotfish, secure in a mucous bubble which shields it from predators with a sense of smell. Spiny, globular sea urchins parade stylishly in the open ground before the reef, resembling UFOs flying through the skies in a space movie, but far more stunning than anything

Hollywood

can ever make.

BEDTIME: A spotfin lionfish glides sleepily over a coral bed. Picture courtesy: Vandit Kalia

Supporting over 7,000 marine species, coral reefs literally hold up the seas. They also benefit over one billion people worldwide by way of fisheries, tourism, pharmaceutical resources and coastline protection.

Yet, our actions are now destroying the reefs, with emissions heating the seas. Coral reefs are very sensitive to temperature. A rise of less than one degree can cause corals to expel the algae within them, losing the nourishment these give and getting bleached white. The IUCN estimates that such bleaching in

Australia

’s Great Barrier Reef in 2016-17 killed 50% of its corals. I have seen bleaching in the Andaman reefs as well, with entire stretches of broken, destroyed corals, ghost towns where once life thrived. Pollution, boats and nets add to this decay.

Unless we limit our emissions and stop our reckless trespasses now, the end of these wondrous coral cities will soon impact life beyond the seas.