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Corals are such a key part of the tropical marine environment that any loss could have incalculable consequences not just for the survival of countless marine species but also for the economic well-being of many communities that rely on the reefs for fishing and tourism. The problem is that despite their diversity and richness, coral reefs are actually incredibly fragile communities, and can be upset by even small changes.

The threats they face are both global and local. The biggest global threat to corals is global warming. The relationship between corals and their algal partners, zooxanthellae, is incredibly sensitive. Corals depend on the presence of these micro-organisms for energy for growth and their vivid colours. If water temperatures rise even very slightly, the corals expel the algae in a stress response and the corals stop growing and lose their colour in what is called a ‘bleaching event’. The coral turns white and begins to weaken, making it prone to disease. Sometimes, the coral regains some of its algae and survives. Often, however, bleaching is irreversible and the coral dies. When this happens on a large scale, algal turf smothers both the dead coral and living coral, enabling herbivorous fish and sea urchins to flourish and opening the way to the destruction of the whole reef community.

Bleaching events have become increasingly common in the last decade or so as sea temperatures have risen. Very few corals are now entirely free of bleached sections, and in some

places the bleaching is extensive. In April 2009, scientists were relieved to note that sections of the Great Barrier Reef that were ruined by a bleaching event in 2006 had recovered in just a few years. But the worry is that bleaching events will become more frequent as global temperatures increase, and coral’s ability to recover may diminish as ocean acidification robs the water of the carbonates that the corals need to build their skeletons.

If, as feared, global warming brings stormier weather, recovery from bleaching events could be further impaired. Research in the Caribbean showed that after powerful hurricanes, coral ‘recruitment’ (the regrowth of new young corals) drops by two- thirds to three-quarters. Severe storms can damage the skeletal reef itself as it is battered and broken by violent waves.

takiNG fiSh for taNkS

On a local level, reef communities face pressure not just from overfishing for the dining table but also the capture of fish for the aquarium trade. According to the United Nations environmental programme, 20 million colourful reef fish from 1,471 species, ranging from the sapphire devil to the copperhead butterflyfish, are taken each year. Some 12 million stony corals are taken, too. The spectacular Banggai cardinalfish has been brought to the point of extinction in the wild by demand for it for aquariums, and many other species have been severely depleted.

One especially depressing aspect of the aquarium trade is the use of poison. It is not easy to capture darting reef fish, so many people in the Philippines and Indonesia, often desperate for an income, resort to poisoning the water. Sodium cyanide, squirted h Even a slight warming of the ocean can cause corals to turn deathly

white and stop growing. Such ‘bleaching events’, like this one here in the Philippines, are becoming increasingly common.

from a bottle, immobilizes the fish, making them easy to catch. But it also kills any coral it touches. Even the captured fish die of liver failure in a few months. Some accounts say most aquarium fish from the Philippines are caught this way. bloWiNG up the reef

Even more brutal techniques are sometimes used to catch fish for the dining table. The structure of the reef makes desirable reef fish hard to net, but a stick of dynamite lobbed into the water kills the fish and makes them easy to scoop up from the surface. Unfortunately, the explosion destroys the reef, too.

Even the more subtle methods of fishing can be damaging if overdone. The giant triton sea snail, for instance, is highly prized for its beautiful shell and has been severely overfished. Unfortunately, the triton is one of the key organisms that prey on the crown-of-thorns starfish – one of the few carnivores that

can stomach corals. With the tritons diminished, the crown- of-thorns starfish population can explode without check, with devastating effects for the corals.

Some of the threats to coral are simply down to its proximity to human activity in busy ports and holiday developments – and are even linked to the huge popularity of reefs and reef areas for diving and leisure activities.

Although it needs international agreement to slow the global effects of the planetary warming, action is being taken on a local level at least. Well over a fifth of the world’s coral reefs are now within marine reserves and in March 2010, the world’s largest reserve, which is about the size of France, was created by the UK around the Chagos Islands in the Indian Ocean. Some felt the park’s creation took little account of the wishes of local people, but it will provide a valuable buffer against the destruction of the reefs through development and overfishing.

PAcIfIc OcEAN PAcIfIc OcEAN ATLANTIc OcEAN Gulf of Mexico Baltic Sea ArcTIc OcEAN ATLANTIc OcEAN INDIAN OcEAN SOuTHErN OcEAN

Threats to Corals Worldwide

This map shows the variety of dangers threatening corals in different parts of the world.

Tourism Poison fishing Over exploitation Sedimentation coral harvesting Dynamite fishing Pollution

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angroveshavenoneoftheglamour and colour of coral reefs, and much less than the reef ’s staggering array of species. Yet their role in the tropical environment is crucial. They act as a unique bridge between the land and the sea, and provide a safe nursery for many of the species that head out to the reef and the ocean beyond for their adult lives.

Mangroves cover vast areas with an unvarying dense mat of foliage and dark tangled roots, all dipping into murky, muddy stretches of water. Even in their most varied regions in Indonesia, there are just 40 different species of mangroves, and only a few more of the other supporting shrubs that live alongside them. No wonder then that they have been neglected, and even exploited as wildlife refuges. But this is a mistake. the Sea tree

Even the mangrove trees themselves are very special plants. They are the only trees that can tolerate immersion in salt water, and survive the almost completely deoxygenated sodden mud in which they plant their roots. They cope with the lack of oxygen in the mud by propping themselves up on high roots that branch off the trunk, or by extending root tubes up like snorkels to take in air through pores called lenticels when the tide is out. They cope with the salinity by keeping their roots partially sealed, and by excreting excess salt through their trunks and leaves. Mangrove leaves taste very salty!

Interestingly, they increase the chances of their offspring surviving to maturity in this very salty environment by allowing seedlings to develop as ‘propagules’ while still attached to the parent tree, presumably taking care of salt processing and

In document UNIVERSIDAD DE COLIMA FACULTAD DE MEDICINA (página 26-56)