marine life. Elsewhere, though, the clarity and warmth of the water is perfect for corals, and corals are the Indian Ocean’s great treasures.
Almost half the continental shorelines in the Indian Ocean are fringed by corals. There are none in the Bay of Bengal and off Pakistan because the massive amounts of freshwater and sediment washing out of the Indus and Ganges rivers prevent corals growing, and the turmoil of the monsoon season hinders their growth in the South of India. But corals are abundant on nearly all the Indian Ocean islands, from the Chagos to the Andaman, and along the coasts of Kenya and Tanzania, Sumatra, and northwestern Australia. The Great Chagos Bank is the world’s biggest atoll. All of these coral reefs are home to a host of marine animals including sponges, worms, crabs, molluscs, sea urchins, brittlestars, and
colourful fish such as snappers, groupers, and triggerfish. Migrating between these hot spots there were once numerous whales, sharks, and sea turtles, but all of them
The Indian Ocean
177 f Named for their strange bulbous foreheads, bumphead parrotfish play a key
part in creating the beautiful coral beaches of the Indian Ocean by grazing on the coral and excreting the skeletal remains as fine grains of sand. However, numbers of bumpheads have been severely reduced by spearfishing.
g Giant groupers appear so docile that they seem harmless, but they are reef predators, and once a victim comes within range, they lunge quickly to make a kill. They are very big fish, growing up to 2.7 m (9 ft) in length.
g Camouflaged almost invisibly among the coral, the reef stonefish (Synanceia verrucosa) is the world’s most deadly fish. The venom in their dorsal spines is enough to cause excruciating pain and kill a human in just a few hours.
In 1998, three months of very warm weather set off by an El Niño event (see page 53) caused the worst coral bleaching episode ever witnessed in the Indian Ocean. As the temperatures stayed warm, 90 percent of all the ocean’s corals were affected – they expelled their symbiotic algae guests, ceased to grow, and turned pale. Only Mauritius’ corals seem to have escaped, because it was cloudy there at the time. It takes a decade or more for coral to recover from such events, and the worry is that as global warming gathers pace, bleaching events may become too frequent in the Indian Ocean for the corals to recover inbetween. There is some encouragement, however. The reefs in the chagos Islands recovered astonishingly quickly. It is thought that this is because the water there is so clear that the corals thrive deeper down and in cooler water. Now half of all the healthy corals in the Indian Ocean are in the chagos Islands, which is why their designation as a Marine Protected Area (MPA) in 2010 was so important. Also encouraging was the discovery in 2010 of a diversity of species of corals housing unusual symbiotic algae that seemed to thrive in warm waters off the Andaman Islands. If new relationships like this develop, the chances of corals surviving mild global warming seem slightly better.
have been the victims of human activity. Whaling had all but wiped out many species of whales by the middle of the last century, and the situation reached a crisis point in the 1970s, when the depletion of whales in Antarctic waters drove Japanese and Soviet whalers north into the Indian Ocean. Populations of some whales such as Oman’s humpbacks were thought to have been entirely destroyed. Then in 1979, at the instigation of the Seychelles, the entire Indian Ocean was made a whale sanctuary. Oman’s humpbacks survived, but only just – and the creation in 1994 of another whale sanctuary in the Southern Ocean, where many Indian Ocean whales commute in summer (see page 193), seems to have given the Indian Ocean’s whales a fighting chance.
All six of the species of sea turtles of the Indian Ocean – green, hawksbill, leatherback, loggerhead, olive Ridley, and flatback – are in some danger. After centuries of
hunting for their meat and shells, most sea turtle populations in the Indian Ocean are at such low levels that all of them are vulnerable to other environmental impacts, such as by-catch. However, decades-long protection plans, particularly at beaches in the Indian Ocean where turtles come ashore
to lay their eggs, have achieved some success with hawksbills and Orissa’s olive Ridleys.
Many of the Indian Ocean’s coastlines are lined with mangrove swamps. Indeed, the Indian Ocean has almost half of all the world’s mangroves. The majority of these are in Indonesia, but the biggest swamp in the world is Bangladesh’s famous Sundarbans, which is the only mangrove swamp in which tigers live. Many of these swamps though are coming under threat from logging, shrimp farming, and pollution.
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t
he red seamayseemlIkejustanarroWInlet. In fact, just as the Indian Ocean was born from a triple junction in the Earth’s crust that pushed away continents, so the Red Sea is on the cusp of a triple junction that will one day – perhaps not for 100 million years – force Africa and Asia apart to form a great ocean. The junction lies where the Red Sea meets the Gulf of Aden.the iNfaNt oceaN