Coral bleaching

SRI LANKA — Have you taken a shower in the middle of the day these past few months and winced at the heat of the water gushing through in the first few minutes? The intense heat is not just affecting us, it is affecting corals – the delicate organisms in the sea that are exposed to the sun all day long.

“We have seen early signs of coral bleaching in the East Coast recently,” says Prasanna Weerakkodi, a marine environmentalist and regular diver who showed us a series of photos taken during a dive two weeks ago near Coral Island and Pigeon Island. The corals are pale in colour or have turned completely white. Some corals are deep purple and that too is an early sign of bleaching, he says, warning that about 50% – 60% of the corals in Pigeon Island and nearby Coral Island are partially bleached while about 5% are completely dead.

Coral reefs are known as rainforests of the ocean considering their rich biodiversity and are the breeding grounds of many fish. Corals in Trincomalee, Batticaloa, Galle, Unawatuna and Hikkaduwa are reportedly being affected according to other divers.

Coral bleaching occurs when coral polyps, the organisms that build corals, shed the algae (zooxanthellae) that gives them their colour. These tiny algae live in harmony with the corals and provide food for the host through the process of photosynthesis. Without this algae, the coral looks pale white and the coral polyps can be exposed to ultraviolet radiation. Without food, oxygen or cover from dangerous rays, the coral polyps in the reef will die a few weeks after they start getting paler. Our corals show signs of entering into the first stage of such a bleaching explains Mr. Weerakkodi.

Coral scientists believe warming waters are the most likely cause of these bleaching events. The Indian Ocean experienced its worst coral bleaching in 1998 due to a warm oceanic current. The Sea Surface Temperature (SST) of some parts of the Indian Ocean had gone up due to the La Nina climatic phenomenon at that time and resulted in warm oceanic currents killing pristine coral reefs in many parts of Sri Lanka, including the Hikkaduwa coral reef that is still to recover. However, the corals in the East Coast escaped the 1998 coral bleaching.

According to recent Sea Surface Temperature data, it is now around 32 C where the normal average temperature should be around 28 C. This increase could have triggered the bleaching. A regional warning of a possible coral bleaching has been issued. Sri Lankan marine biologists are also in touch with their Maldivian colleagues.

If the sea’s temperature goes down, or cool upswells come to the rescue, healthy corals also have the ability to recover. “It is too early to say whether this will develop into a full-scale coral bleaching event as happened in 1998. But it is important to monitor the phenomenon,” Mr. Weerakkodi pointed out.

Marine biologist for the National Aquatic Resources Research & Development Agency (NARA) Arjan Rajasuriya, recently reported some dying corals in reefs near Galle. After the severe bleaching of 1998, corals in many areas in Sri Lanka showed temporary bleaching during the months of April/May/June when temperatures are high. Some corals die, but others recover after the conditions return to normalcy. However, if the warm conditions prevail for long, it could be deadly. Arjan recalls the coral bleaching in 1998 had occurred during April/May and within a few weeks it sealed the fate of many coral reefs like those in Hikkaduwa.

Nishan Perera, another marine specialist, who was diving at Trincomalee a few weeks ago, verified the bleaching of corals and reported severe bleaching in the Dutch Bay area. This year the early part of the monsoon was a bit slack which might have contributed to this situation, he feels. “If conditions become normal soon it should not be a problem, but otherwise there can be some coral mortality,” he says.

Can anything be done? “Keeping the corals healthy is the only way to fight this global phenomenon,” says the NARA officer. Corals that are not healthy lose the ability to adapt to changes in their environment. Frequent fishing, pollution from land-based sources, dynamiting reefs, and sedimentation are other threats to the reef ecosystem which reduce their ability to withstand a catastrophe like bleaching.

Ocean Acidification is the latest threat added to this list. Acidification is a phenomenon linked to increased atmospheric carbon dioxide. Carbon dioxide dissolved in the ocean reacts with the water to form carbonic acid. Many oceanic ecosystems such as coral reefs are adapted to a narrow range of pH levels and increases in these levels can be catastrophic.

Marine experts also say it is important to pay more attention to the corals in the East coast. “The West coast is experiencing the monsoon these days which will cool the seas a little, while regular cloud cover will also reduce the heat,” Arjan says. But the East coast is not so fortunate and is also experiencing new threats. Pollution and over-fishing were not problems earlier as the Eastern and Northern seas were restricted due to security reasons, but this is changing after the war and over-visitation is already causing problems to fragile marine national parks like Pigeon Island.

Save the wrecks

On May 2, the Sunday Times reported a racket involving the removal of scrap from ship wrecks off the Eastern seas. NARA’s Arjan Rajasuriya points out the wrecks are now jungles of coral and have become a spawning ground for fish.

Destroying them will destroy budding corals as well as harm the fisheries industry. “This is like killing the hen that lays the golden eggs,” said Arjan highlighting the value of these wrecks. They could even be a tourist attraction, so keep them intact, appeals the marine biologist.

Corals heading towards rapid extinction

The Global Biodiversity Outlook report backed by IUCN’s (International Union for Conservation of Nature) data shows coral species are heading most rapidly towards extinction, while Amphibians are on average the group most threatened.

According to the Red List Index shown in the graph, a value of 1.0 indicates that all species in a group would be considered as being of Least Concern (not expected to become extinct in the near future) and a value of 0 would indicate that all species in a group have become extinct.

by Malaka Rodrigo