No more a many splendoured thing

By Tharuka Dissanaike

Have you taken a glass-bottomed boat ride in Hikkaduwa recently? If so, the disappointment would have been acute. For those who have seen the corals in their splendid colour, teeming with life, the contrast of the bleached, dying coral would be depressing.

Those who are seeing corals for the first time would not be able to compare, but wonder what is so wonderful about this patch of lifeless white-brown underwater shapes.

Yes, corals in most parts of Sri Lanka's coast have been bleached by the rise in sea surface temperatures last year. The global phenome-non affected various ocean countries at different times and in different levels of intensity. But overall, there has never been a time in recent history when coral bleaching was so widespread and severe. Coral bleaching was recorded in 32 countries during the 1997-1998 period. Widespread bleaching was reported from sites in the Pacific, Indian Ocean, Red Sea, Persian Gulf, Mediterranean and Caribbean.

In Sri Lanka, coral bleaching has occurred from Kalpitiya and the Bar Reef area, right down the western and southern coasts, Hikkaduwa, Rumassala, Weligama to Kalmunai on the eastern coast. But strangely enough, Trincomalee appears to have been unaffected. Some researchers believe that the warm water currents have travelled towards the Andaman Islands from the south east of Sri Lanka, sparing the corals further north of the Batticaloa area.

The El Nino effect on global climate has been touted as the main reason for this unprecedented bleaching of corals. The rise in sea surface temperature in many oceans due to the strongest El Nino of this century correlates to the pattern of coral bleaching.

The National Aquatic Resources Agency (NARA), monitoring sea surface temperatures in Galle recorded an increase of over five degrees Celsius during the month of April 1998. Temperature rose from a normal of 28-30 C to 35 C.

Corals are sensitive to temperature changes. The bleaching occurs quickly- a matter of a few weeks. Shallow corals (upto five metres) are the worst affected. But in Kalmunai even corals at a depth of 42 metres were bleached. Deeper corals have a better rate of recovery than those in the shallow areas, which are more exposed to UV radiation.

"Bleaching is most severe in branching and table-like forms of corals," said Arjan Rajasuriya, Research Officer heading the Coral Reef Research Programme at NARA. "These are the most proliferate reef building corals and most of these have been completely wiped out after the bleaching."

Certain coral species, especially the non-reef building variety have not been affected by the temperature change last year.

Gradually, due to dying corals, the reef breaks up. This could lead to coastal erosion. If ocean warming and climatic changes occur frequently, reef-building corals will not survive and the entire reef eco-system could change.

"A very obvious example is the coral dwelling butterfly fish. In the Bar Reef there used to be huge numbers of butterfly fish but recently we recorded only a couple. The fish is fast becoming rare due to the loss of habitat," Mr. Rajasuriya said. He added though, that harvesting of butterfly fish for the ornamental fish trade is still on. "It would be unwise to pluck the few remaining fish out, until their populations have recovered."

Coral bleaching would also affect fisheries -again due to loss of habitat. "When corals die, many fish lose their environment and food source. It's like cutting down a forest. The animals that lived within will perish, some faster than others."

Conversely other species, like the algae blooms on dead coral and algae-eating fish will thrive in the new environment.

Since bleaching to this magnitude, has not occurred before, locally or internationally, very few studies and research have been done on its impact.

"There is no way to say how long it could take to establish new coral reefs either. Corals are more than 250 million years old. Humans have probably not seen coral reefs coming up from scratch," he said.

Very little can be done to hasten coral recovery. A NARA team has tried transplanting live corals washed ashore at Weligama into bleaching, dying colonies in Hikkaduwa to increase their chances of survival. But glass-bottomed boats are already damaging these colonies.

"What is important at this stage is to reduce the man-made impact on corals, affording them a better chance for recovery and survival," said Mr. Rajasuriya.

In areas with high human impact the rate of recovery has been very slow. Hikkaduwa is a prime example.

Regulating the glass-bottomed boat operation is a must. By banging on the corals they are hastening the breaking up of the reef.

Fish harvesting, ornamental or otherwise has to be done in a more responsible manner. Dynamite fishing is still practised in many parts of the country.

"Even in Trincomalee, a high security zone, we have heard dynamite explosions in the shallow sea."

Pollution has to be controlled. Effluent from hotels and garbage from coastal towns are chief pollutants of coral habitat. This generally encourages algae blooms.

But the sad fact is there is no one to take responsibility. Although the Bar Reef and Hikkaduwa are designated as Marine Sanctuaries and protected by the Wildlife Department, their status affords very little protection. Even as 80 percent of the country's coral reefs lie dying or dead, no agency will take on the task of controlling man-made impacts, to hasten their recovery.

What is bleaching?

The starkly white, bleached coral is not dead. Far from it. The 'bleached' coral has just lost its outer covering of single-celled algae called Zooxanthallae, which give corals their green, brown and yellow colour. Zooxanthellae have a symbiotic relationship with reef-building corals. When, due to stress factors, the corals lose these organisms; they also lose a major food source and their protection from ultra-violet radiation. Corals cannot survive for long without the Zooxanthellae. Without the colourful organisms, the coral's translucent tissues make it look stark white or light coloured.

If the stress factors continue and corals are unable to attract the organisms back, the coral animals will begin to perish and other forms of algae will grow on the dead portions. Often the algae proliferate and cover the entire coral colony.

"In places like the Bar Reef, the shallow areas are completely covered with filamentous algae, which have grown over the dead coral," Rajasuriya said. "It looks like a bed of grass than a coral reef."

Seaweed and other marine forms like sea anemone also thrive on the dead coral.

Some corals do recover though. Even after initial algae invasion certain corals have been able to recover and attract Zooxanthellae back into their tissues. But recovery rates have been extremely slow, especially in places like Hikkaduwa, where pollution, glass bottomed boats and fluctuating salinity have made things worse for the dying corals.

"Only 7% of Hikkaduwa's corals are alive now and recovery as compared with other places in the country is very slow."

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