Coral reefs — the rainforests of the ocean

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Coral reefs support 25 per cent of marine species in a complex ecosystem.

THE old adage, ‘out of sight, out of mind’, can be applied to coral reefs. We often shout loudly about the damage done to our terrestrial environments by deforestation, urbanisation and pollution, but we seldom appreciate that these factors ultimately affect the quality of marine life.

Increased run-off from the land leads to acceleration and accumulation of sediments on the seabed, while oceans are also absorbers of man-made atmospheric gases caused by pollution. All of these affect the potential for coral growth.

Vital to ocean ecosystems

Whilst coral reefs make up less than 0.2 per cent of the ocean environment, they support 25 per cent of marine species in a complex ecosystem living in tropical waters of between 23 and 25 degrees Celsius.

Although corals can be found in deep water, most are located up to a depth of 25 metres, thriving on sunlight and are located between 40 degrees north and south of the Equator. Some species grow in temperate waters.

Understanding corals

Corals belong to a group of animals, the Cnidarians. With a free-swimming larval stage, they have a central mouth which receives and emits material and a ring of tentacles with stinging cells to trap their prey, usually zooplankton.

Coral polyps tend to grow in colonies, secreting limestone (calcium carbonate) skeletons beneath their living outer tissues. The calcium carbonate, in its dissolved form, is obtained from the seawater.

As a coral polyp expands at night to feed, it alights very slightly from its skeleton and releases its bodily fluid in the form of minute needle-like crystals beneath it to form ridges of limestone.

During the day the coral polyp retracts and lies on the previous night’s newly-laid structure, filling the gaps between the ridges with yet more calcium carbonate.

There are over 2,500 species of coral, each taking a different shape in the form of boulders, fans, branches, trees and tables, often according to their positions on the reef and the amount of sunlight each species needs for growth. Their shapes are also affected by ocean currents and waves.

Corals live a symbiotic existence with Zooxanthellae. The latter are single-celled algae surviving within the coral tissues. These plant forms carry out the process of photosynthesis, producing both food and oxygen, whilst the coral polyps emit carbon dioxide and other nutrients. These algae provide the coral polyp’s colouring and indeed the colour of the coral’s skeleton.

Significant reefs

I have witnessed the sheer beauty of various types, shapes and colours of corals when snorkelling in the Indian Ocean off Madagascar, Mauritius, the Seychelles and Kenya and locally in the South China Sea off Sabah.

These memories of the undersea world and its wonders will always live with me. I hasten to add, I tend to forget close encounters with lion fish, moray eels and jellyfish. As I write, I am staring at a paperweight, a chunk of corallian limestone, which I collected 33 years ago from Winnat’s Pass, a deep limestone gorge, in the United Kingdom’s first national park in the Peak District.

Locally, it is known as Reef Knoll limestone denoting that, in past geological times, Britain once experienced a tropical climate with offshore coral reefs. Subsequent plate tectonic movements pushed these marine deposits up out of the sea to create mountain ranges.

In 2001, the United Nations Environmental Programme World Monitoring Centre (UNEP-WCMC) published the World Atlas of Coral Reefs. It revealed that 25 per cent of the largest areas of the world’s coral reefs are owned by Australia, France, the UK and the United States, allowing for their overseas territories.

Actually the largest reef nations are Indonesia (18 per cent), Australia (17 per cent) and the Philippines (9 per cent). The greatest density of coral reefs worldwide, covering 33 per cent of the total reef areas is, in what marine biologists refer to as ‘The Coral Triangle,’ comprised of Indonesia, Malaysia, the Philippines and Papua New Guinea, with 600 coral species found in each of these countries.

Coral bleaching

Last February, the US National Oceanic and Atmospheric Administration (NOAA) released a report warning that severe levels of coral bleaching, as observed last year, are likely to worsen this year. You may well ask, “what is coral bleaching?” Simply put it is the result of an increase in ocean temperatures. As the sea temperature rises the algae are expelled from the coral polyps leaving their skeletons to appear as a ghostly white shade.

The El Nino event in 1997 to 1998 and again in 2010 caused severe bleaching and the death of many coral species in the Tunku Abdul Raman Marine National Park in Sabah. This progressive and gradual rise in the temperatures of the Indian and Pacific Oceans creates what is known as thermal stress on coral growth.

NOAA has established a weekly Coral Reef Watch, open online to all, which forecasts the potential for coral bleaching up to four months in advance. This is a truly remarkable website with explicit maps and locations worldwide to indicate the perceived degree of coral bleaching at any one location.

The Coral Reef Watch grades areas of the world’s reefs into potential thermal stress levels from very low to the highest levels and in descriptive terms, starting at No stress and progressing in values to Watch, Warning, Alert Level 1, onto the highest level, Alert 2.

Currently the Sabahan coral reefs are observed as: No stress, but those in East Kalimantan, North West Sumatra, Java and Bali are at grade Watch. The Coral Triangle is being especially scrutinised in the middle of this year by NOAA.

As far as Malaysia is concerned, its reefs account for 1.27 per cent of the coral area worldwide. Climate change is, indisputably, affecting sea temperatures and thus coral growth.

Coral reefs in danger

Biological influences also affect coral. Crown of thorn starfish, upon reaching maturity, feast on live coral and infestations of these creatures leave coral reefs with little time to recover. Human beings come into focus again, on reef grief, through over-fishing, dynamiting, and the use of sodium cyanide spraying as a preferred method of live fish capture.

Sewage outlets, coastal dredging and soil erosion run off from agriculture, logging and construction add to the devastation. The bacteria in sewage and fertiliser, washed into the sea by rivers, provide a boost to algae growth but, combined with extra inputs of sediments, water clarity is reduced. This makes photosynthesis exceedingly difficult for Zooxanthellae.

Oil spills, dredging for building materials, anchor damage, and the over collection of red and black corals to feed the jewellery industry all add to the list of threats that coral reefs face. Tropical cyclones and tsunamis play their part too in destroying sections of coral reefs. Nine years ago the UNEP-WCMC, in its report, estimated that coral reefs were worth between US$500,000 and US$600,000 per square km. What are they worth now in 2015?

Coral reefs provide a lifeline to millions of people in terms of fish protein in their diets, to the local community’s income and social benefits in areas where scuba diving is well managed, together with national marine park entrance fees and responsible coastal tourist development.

Bioprospectors – scientists believe that coral reefs and their plants and fish can provide remedies through antiviral drugs to combat HIV and herpes, non-addictive painkillers, sunblock lotions and cancer treatments. Currently 50 per cent of all new cancer-related drug research focuses on marine organisms. Our challenge lies in finding ways of exploiting the amazing ecosystems of each and every coral reef to avoid their destruction.

To learn more go to www.noaa.gov, www.coralreefwatch.noaa.gov or www.tracc-borneo.org. Also read ‘The Blue Planet – a natural history of the oceans’ by A Byatt, A Fothergill and M Holmes (BBC Worldwide Limited) London 2001.