El Nino - Coral Bleaching in the Maldives
Posted By Sara-Lise Haith on 21 October 2002
In 1912, Captain Edward J. Smith spoke some ill-fated words, just a few years before Titanic set sail on its maiden voyage across the Atlantic.
"I cannot imagine any condition which would cause a ship to founder. I cannot conceive of any vital disaster happening to this vessel".
This gentleman believed that modern shipbuilding had achieved mastery of the elements. However, there was a very important factor, which he had omitted from his voyage plan to carry all those passengers across the ocean. Like most sea captains of his time, he knew nothing about El Niņo. Only the fishermen of Peru knew the term applied to this phenomenon, which has recorded occurrences since 1525. Unpredictable weather phenomenon...
Due to the unforgiving nature of El Niņo, unforeseen occurrences happened during the Titanic voyage. Actually, each year between 10 to 15.000 icebergs detach from the glaciers of west Greenland and drift down the Labrador Current towards Grand Banks of Newfoundland, approximately 2500 kilometres away. In most instances the bergs would melt off in the Streams warm waters, but due to the disturbing actions of El Niņo, this occurrence changed completely in 1912. As the northerly winds that blow the icebergs down the east coast of Canada strengthen, El Niņo makes sure that more icebergs are driven much further south than normal. Apparently the annual average numbers that cross the 48ēN line are less than 500. However, by April 1912, there were more than 1000.
Unbeknown to the crew and passengers of the ship, the world had already been influenced by El Niņo activity for several months, and the world's weather systems were all haywire.
The previous September during the same year, there were more than a handful of weather related incidents worldwide. The Yangtze River flooded, and deluged Shanghai. Crops failed in Australia due to droughts, following in India and Russia. In southern Africa hundreds of people died due to East Coast fever (cattle disease), coinciding with a drought so many people were forced to migrate in search of work. The Mississippi flood reached record water heights. Countless disasters occurred related to the constant variations in weather systems.
The Peruvian fisherman started noticing warm counter currents, overriding the normal cool waters of the Humboldt Current. By the 19th century, this recurring current became known as the Corriente del Niņo, or just el Niņo. In Spanish this means the Current of the Christ Child, referring to its appearance around Christmas. However, just to confuse matters, it is not the same Niņo as we know today. Over the years harsh weather conditions coincided with the warm current movements, by abundance of rain and floods. In Peru, the term El Niņo then referred to this exceptional period of rain. In global terms, the name has emerged from total obscurity to be synonymous with complete disaster.
So what does all this have to do with coral bleaching? Temperature plays a large part. The onset of El Niņo has been attributed, according to scientific theories, to various activities. Seismic activity, changes in the Indian Ocean, Antarctic pack ice. Whatever the cause of the Niņo, one of the outcomes is unusual sea surface temperatures, resulting in drastic effects on the temperature-sensitive corals and sponges. In Part 2 the realities of these effects come to life in the Maldives where coral bleaching has been dramatic.
Coral reefs live idyllically in water temperatures between 24-27ēC. During 1998, when the last Niņo occurred, surface temperatures in the Indo-Pacific region reached up to 33ēC. To give a general background to the reader, reef-building corals (Scleractinia), which have limestone skeletons, build massive coral reefs. To do this they require sunlight, warm temperature and full marine salinity, and a stable hard bottom. Corals however, live in a symbiotic relationship with algaes, with give them their beautiful colours. These algae, known as zooxanthellae, live within the tissue of the corals. They supply nutrients enabling the corals to grow and reproduce quickly enough to build reefs. In turn, the coral provides protection and access to light for the algae. Divers and freedivers who spend time close to corals can see the movement of the 100s of polyps on the stems of the corals - a gem for macro photographers.
In 1998, the water temperatures of the Maldives, Seychelles and other Indian Ocean regions reached a high of 35ēC in some areas. These temperatures stressed the algae (zooxanthellae) enormously and they left the coral in search of cooler areas or die (perhaps a reason why in Maldives, you can see healthy corals at 30m/100ft in protected overhangs in channels with strong currents). The coral is left with just its limestone structure, which is white. This gives the bleaching effect. However, the coral does not stay bleached for long. They are then moved in upon by a green/brown algae, which is a heavenly diet for many reef fishes. This is one of the reasons why the amount of reef fish in the Maldives increased in numbers, especially marked by large populations of convict and powder-blue tangs which thrive on this food.
In addition to increases in temperature, UV, and vibrios (bacteria) bleaching of reef corals has also been associated with (citing only a few studies):
Cold water; low temperature evokes rapid exocytosis of symbiotic algae by a sea anemone, Turbidity and sedimentation; the effect of shading on coral reef structure and function. Reduced salinity may also affect reef-building corals. There was also a mass expulsion of zooxanthellae from Jamaican reef communities after Hurricane Flora, and also protozoan infections may cause bleaching.
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