Coral bleaching - A report from Axel Horn

All divers and snorklers who visited the Maldives during April/May 1998 noticed an increase in the water temperature. In some places the temperature on the surface rose up to 34° C and even in a depth of 30 meters up to 32°C was measured. Color variations were noticed among stony-, fire-, and soft coral and also among the sea anemones. Those who were ignorant of the facts were enthused about the new colors of the reefs. Among the divers and snorklers who were familiar with the facts, alarm bells went off. What had happened?

During the first 6 months of 1998 there was an extended period of high water temperatures in all of the Indian Ocean which caused coral bleaching. Actually, this was nothing extraordinary since phases of higher water temperature occur about every 10-15 years, for instance in 1987/88. During this time I managed the diving base at Embudu in the south atoll.

I informed the Maldevian government about the extent of the damage. They acted immediately and called scientist from England for a conference at Male. There was quite a difference between the 2 occurrences. While in 1987/88 only the coral reefs north of the equator were affected, which meant the Maldives also, in 1998 the northern and southern hemisphere were affected. This included: Seychelles, Kenya, Reunion, Mauritius, Somalia, Madagascar, Maldives, Indonesia, Sri Lanka, Golf of Thailand, Andamans, Malaysia, Oman, India and Cambodia. Never before had the extend of bleaching in the entire Indian Ocean been this great. It was linked to El Nino at the end of 1997 and the beginning of 1998. At that time coral bleaching was reported in the Mexico/Pacific, Panama/Pacific, Galapagos, Great Barriere Reef in Australia, Papua New Guinea and Samoa. While on the Maldives the surface water temperature began to slowly drop to normal again in June 1998, the temperature in the Philippines and in the Florida Keys rose higher still causing more coral bleaching. Coral reefs are the rainforests of the oceans with an unbelievably rich diversity of species. They are important for the eco-system.

Corals are very sensitive creatures and react vehemently to even slight interferences like higher temperatures for instance. They get into a stressful situation and discharge their zooxanthelles. Some species react very quickly, others take a longer time to react. Especially in the upper regions to about 10-15 meters under the surface of the water, here the temperatures are the highest, this effect is most noticeable. Of course, other factors play a part also, like intensity of currents etc. When the higher temperatures remains constant for a longer period, the coral can\\\'t recuperate, they die but at the same, they form the base for new growth! The first to settle on the dead coral are algae. We were able to make some interesting observations regarding the fish population. Especially those species that feed mostly on algae, like the redtooth triggerfish, increased more than the average. This again attracts predators, so we saw an increase here too. From all of this we can deduct that nature replaces on one end of the spectrum while she takes it away from the other end. This of course only works when humans do not interfere and no other environmental influences occur.

What does it look like on the Maldives now? Many coral did recuperate or have started to grow new coral, mostly the fast growing kinds. And I\\\'m not saying that just because I work here. Really! Total regeneration will take some more time. So, why did the press report dramatically about dead reefs on the Maldives this year and not already in 87/88? The explanation is relatively simple. In 87/88 the diving tourism did not have the significance it does today. I am talking about the incredible increase in divers especially on the Maldives during the last few years. The Maldavian government is doing a lot to safeguard the underwater flora and fauna. They have employed their own marine biologists who work together with interested diving bases to protocol changes and discuss and create programs of protection.. Years ago they had already prohibited the catching of turtles. In September 1998 a ban on fishing sharks was announced. This is in effect for the atolls that cater to tourists, certainly an exceptional occurrence. It is the recurring natural phenomena like elevated water temperatures caused by El Nino, that no government can fight.

Axel Horn - 2001