A Natural History of the Republic of Maldives
By Guy Stevens, Manta Trust Director
Like ripples radiating from a giant stone skimmed hundreds of kilometres across the tropical waters of the Indian Ocean, the 26 coral atolls which form the Maldives Archipelago stretch out in a long line from 7° North straight down 870 kilometres (540 miles) to just south of the equator. Lying 475 kilometres (300 miles) from the southern shores of India the Maldives is no more than 128 kilometres (80 miles) across at its widest; tiny specks of land, naturally reaching no more than 2.5 metres above sea level at any point, rise 2,000 metres straight up from the depths of the Indian Ocean to create a thriving marine oasis amidst the barren wilderness of the open sea. The Maldivian coral reefs are some of the most abundant and diverse anywhere in the world, with a myriad of countless invertebrates, including 200 species of stony corals and nearly 1000 different species of fish; from the smallest gobies the size of your fingernail to the largest of all, the manta rays and whale shark…
Directly beneath the Maldives Archipelago lie two of the earth’s tectonic plates, which 65 million years ago planetary forces were causing to shift, creating a fault line which today stretches almost 3,000 kilometres (1,750 miles) in a long line from the Laccadive, Minicoy and Amindivi Islands (known collectively as the Lakshadweep) off the West Coast of Southern India, 320 kilometres (200 miles) south to the Maldives Archipelago and on again another 500 kilometres (300 miles) ending all the way down in the remote Chagos Archipelago. All along this fault line in the depths of the Indian Ocean fissures in the earth’s crust gave rise to massive volcanoes which created the Laccadive-Chagos Ridge, upon which the Maldives, Lakshadweep and Chagos islands stand today. While these ancient volcanoes formed the foundations for these islands, to fully understand what makes a coral atoll we must first delve more closely into the lives of the corals themselves.
Corals are animals, most closely related to Jellyfish and Anemones; collectively they form the Phylum of the Animal Kingdom known as the Cnidarians. The Cnidarians name is derived from this group’s ability to catch prey and defend themselves with the aid of stinging tentacles that fire venom tipped harpoons into the flesh of their prey or would-be attacker. Across the oceans of the world there are a wide variety of coral types; from the soft, to the whip, fan and stony corals which in total comprise several thousand species, each perfectly adapted to survival in their own habitat. However it is this last group of Stony or “Reef Building” Corals which are the key to the formation of the Maldives, and indeed all tropical coral reefs, as we know them today.
These reef builders thrive in the shallow waters throughout the world’s tropical oceans, forming distinctive rock-like structures which are characteristic for each species, but which is also subject to environmental influences. Each of these structures is actually a colony comprised of thousands of individuals known as polyps. Each coral polyp is cable of existing independently, but most species clone themselves, replicating and dividing to form ever-expanding colonies over countless generations. Packed tightly against their neighbours, each polyp secretes an external skeleton of calcium carbonate within which to retreat should danger threaten and it’s this calcium skeleton which gives the coral their rock-like appearance.
Like miniature sea anemones, each polyp is equipped with a ring of stinging tentacles around a central mouth. Extending these tentacles out from the safety of the colony mainly at night, when fewer predators are active, the corals impale and engulf plankton as it drifts past on the current. While this ability to catch their own prey is important, the reef building corals also rely on a special relationship with flagellate protozoa known as Zooxanthellae. These autotrophs actually live within the safety of the coral’s body, harnessing the sun’s energy to produce sugars and amino acids through photosynthesis. In return for this safe haven, the Zooxanthellae pass on some of their food to the coral hosts, thus forming a mutually beneficial symbiotic relationship which has enabled corals to flourish in the shallow tropical waters of our planet for millions of years.
In order for these reef building corals to colonise new areas, they must first find solid foundations upon which to build within reach of the sun’s life giving energy. 50 million years ago the Maldives provided just such a place, as newly created rock was thrust upwards from the depths of the Indian Ocean by the volcanic action of the shifting tectonic plates. Over millennia tectonic activity ceased and the once active volcanoes which created towering granitic islands in the Maldives, much like many of the French Polynesian Islands today, became inactive and slowly began to sink back into the depths of the ocean as subsistence and erosion by wind, wave and rain all took their toll.
Throughout this process of subsistence and erosion, the coral reefs continued to flourish, encircling the volcanoes base as they continued to grow, one generation on top of another, for countless millennia. Each generation of reef building coral deposited its calcium skeleton on top of the remains of their predecessors, inexorably inching their way towards the surface of the ocean as the mass beneath them slowly descended. Over time, all that remains visible from above is a ring of coral reef, formed around the base of the now completely submerged volcano. This coral ring is the atoll itself; some of which are tiny like Thoddhoo Atoll, just 2.5 kilometres in diameter and containing just one island along its atoll rim. While others like Huvadhoo Atoll in the South of the Maldives are vast; one of the largest atolls in the world, it contains over 244 islands and stretches 66 kilometres (41 miles) from one side of the atoll to the other.
It was Charles Darwin who first theorised that atolls were formed in this way, and like some of his other revolutionary thoughts at the time, his theory’s where dismissed by many of his peers as preposterous. It was not until the 1950’s that Darwin’s theory was irrefutably validated, when American scientists testing nuclear weapons at Eniwetok Atoll in the South Pacific drilled 1,220 metres (4,000 feet) down through solid coral rock until they found the fossilised remains of shallow water species, sure evidence that the rock had indeed changed position. While the Maldives greatly helped to shape Darwin’s theories on atoll evolution, he never actually visited the country. And while his overall theory is still correct, we now know that the evolution of the Maldivian Atolls was not quite as simplistic as it is with the majority of other atolls around the world today. With periods of dramatic sea level rises and falls from one ice age to another, the Maldivian reefs were at times left exposed hundreds of metres above sea level and then alternately, as sea levels rose again, plunged deep below the sea at rates too fast for even the fastest growing corals to keep up with. All of these events have shaped the Maldives as we know it today and none more so than the reef building corals themselves, without whom today the Maldives would be nothing more than open blue seas.
Coral reefs all over the world are shaped by the forces of nature, evolving over millennia into the myriad of formations we find throughout the shallow tropical waters of our planet today. It’s this constant state of change which drives the evolution of the reefs, never allowing one group or species to dominate. The huge variety of different reef species, including the corals, each prosper under differing environmental and competitive pressures; some coral species preferring the more sheltered leeward reefs that protect their colonies fragile but faster growing forms, while other species growing on the outer reef crest where waves and storms restrict growth, allowing only the more robust slow growing corals to thrive. Competition for real estate within these niches can be fierce, with colonies resorting to stinging and devouring their rivals in a battle of slow motion waged along colonial boundaries at night.
The rhythm of change is everywhere; hungry parrotfish scrape off chunks of the reef with powerful beak-like jaws, crushing the coral rock to fine sand with yet more teeth in their throats. They digest the coral animals and their algae inhabitants, excreting the remnants of the coral skeleton in a constant stream of cloudy sand which settles on the atoll’s lagoon, or is swept by currents to form the sandy beaches of the 1,200 Maldivian coral islands and countless sandbanks. It is thought that a large parrotfish will produce up to a ton of coral sand each year, which, as one of the Maldivian reefs most numerous fish families, amounts to a lot of picture perfect islands!
Strong monsoonal and lunar currents drive channels through the atolls outer rim, breaking up the outline of the atolls into a series of elongated islands while these same currents deposit sediments in the atoll’s shallow lagoonal centre which drives the formation of the more circular reefs and islands within. Each of these processes is constantly in a state of flux, with sandbanks and islands dramatically shifting in size and shape from one season to the next, or even disappearing completely, while others emerge. These processes can happen surprisingly quickly at times, yet most, from our perspective take place at a snail’s pace, allowing the slow growing corals to adjust and flourish.
The diversity and sheer abundance of life supported by coral reefs come second only to tropical rain forests; anyone who has immersed themselves in the underwater world of a coral reef, even if just for a minute or two, will quickly see why. Kaleidoscopes of colours, shapes and patterns dazzle the eye, everywhere movement and life flourishes in a seemingly endless variety of weird and wonderful forms. Yet, life on a coral reef is by no means a paradise for most of its inhabitants; predators and competitors are everywhere in an ecosystem which, while one of the richest on our planet, is paradoxically one of the poorest in terms of nutrient availability. Key to the coral reefs success is the ability to quickly recycle these few essential nutrients through the food chain without losing them from the ecosystem. And it’s the reef building corals themselves, in all their forms and species, shaped by the environment, each other and predators, which results in an ecosystem so rich in design and habitat, that life explodes.
The Maldives’ outer reefs plunge almost vertically down into the ocean depth just a few hundred metres from the breaking waves, falling to 2,000 metres within just 5.5 kilometres from the atoll edge, while the shallow reef crests and island lagoons are usually just a few metres in depth allowing seagrass meadows and mangrove forests to grow around some of the islands. Oceanic and lunar currents squeeze the water through the atoll channels, constantly bathing the more sheltered inner reefs with nutrient rich water. Shoals of fusiliers, unicornfish, red-tooth triggerfish and bannerfish hang in the current, waiting to pick off planktonic morsels which drift past in the current, but never venture too far from the relative safety of their companions or the reef. Closer to the reefs, a plethora of fish and invertebrate species compete for food, mates and space.
Life above water in the Maldives is very different indeed; with fewer than 100 species of naturally occurring plants, a handful of land reptiles, a few common land bird species, and just two native species of mammal, island life is impoverished by comparison. Whilst the Maldives’ official territorial waters extend to over 90,000 square kilometres, the actual total area of land of all its 1,200 islands is a mere 300 square kilometres. Most are just a few 100 metres long and rise only a few metres above sea level at their highest. Nutrient poor soil and a shallow fresh water table means only those plant species adapted to life on the edge can survive and thrive.
Despite this, on these tiny green specks of land in a sea of blue, life did arrive, brought by the whims of the ocean currents or by the wings of ocean travellers. Coconut palms, pandanus, sea lettuce, mangrove trees and others all arrived by sea; their tough and hardy seeds capable of months afloat, drifting across the oceans from distant shores to claim a roothold on solid land. Flotsam also brings with it a few castaways like the Geckos, Agamid Lizard, Skinks and a non-venomous House Snake of the Maldives, but most of the island animal inhabitants flew themselves here. The Flying Foxes or Fruit Bats most likely came from Southern India or Sri Lanka, as did the Indian House Crow and the Asian Koel (a type of Cuckoo) and every year in November the change of the Monsoon brings with it dragonflies, butterflies and other insects from India, swept across the Ocean by changing trade winds.
Most oceanic islands usually support a high number of endemic species; genetic isolation for those few wandering individuals which survive to colonise a new land evolve into new species, adapting over millions of years to their new environments. However, this is not the case for the Maldives, which has virtually no endemic terrestrial species. The exact reason for this endemic poverty is not known, but it may well be due to the relatively recent (when considering things from an evolutionary perspective) episodes of sea level rises and falls which would have wiped out any endemic land species when the Maldives was last fully submerged.
While terrestrial bird species are uncommon, seabirds are plentiful, with a wide variety of terns, herons & waders as well as Tropic Birds, Frigate Birds and Boobies. In all over 120 species of birds have so far been recorded in the Maldives, the majority of which are seabirds or transitory migrants. Some of the most common are the Black-napped and Noddy Terns which are often found feeding on shoals of bait fish close to the reefs and islands, expertly plunging into the ocean to snatch a fish with deadly precision. Along the shoreline migrating waders often stop off to re-fuel before heading on across the Indian Ocean, while resident Grey Herons stalk the shallows, poised with spear-like beak ready to strike at any fish that strays too close.
The Maldives truly is an oasis in the middle of the Indian Ocean; with infinite horizons of kaleidoscopic blues, hundreds of beautiful tropical islands and pristine coral reefs which teem with life, the Maldives is one of the most naturally beautiful locations in the world.