Archive for the 'Indian Ocean' Category

Extensive coral bleaching is destroying reefs

According to the National Oceanic and Atmospheric Administration (NOAA) of the U.S., the longest coral bleaching ever is occurring in the tropical seas. The on-going, especially strong El Niño is prolonging the event, which started in 2014 and which is likely to lead to a wide-spread die-off of reef corals around the world. The scientists of NOAA expect the bleaching to continue in 2016 and 2017. So far, the Caribbean, Indian Ocean and Pacific Ocean have been affected.

The current bleaching is a serious environmental accident not only for all of us fascinated by the oceans, but especially for those 500 million people whose survival depends on the reefs. Fish species important for human consumption live in the coral communities. In addition to provision of food, the reefs also protect the islands and coastal areas from erosion and other damage caused by powerful waves.

Partly bleached coral colony in Saint Lucia. Copyright (c) 2016 Erkki Siirila.

Partly bleached coral colony in Saint Lucia. Copyright (c) 2016 Erkki Siirila.

Coral reefs are also key habitats for marine biodiversity and, related to that, increasingly important for underwater tourism. NOAA estimates the positive annual contribution of coral reefs to world economies to be about 30,000 million US dollars.

When corals get stressed by elevated seawater temperatures, they expel their zooxanthellae, the microscopic algae living in their tissues. As the pigment is in the algae, the corals lose their typical color. Bleaching is a serious occurrence, because without their symbiotic zooxanthellae the corals are starving as the microscopic algae are a significant food source. The bleached corals also become attacked by diseases more easily than before.

In case the average water temperature continues at levels higher than normal for several days, the corals can not recover their symbiotic algae and may die. When the colonies die, erosion starts eating reef structures away. A high percentage of the coral area may be lost for ever if a new bleaching hits the reef within a few years, i.e. when there has been too little time for recovery. As in many cases there are also other environmental stress factors (overfishing, sediment runoff, etc.) present, in today’s world, complete recovery is often impossible.

The first serious global bleaching in history occurred in 1998. The second one occurred in 2010. Like in the current third one, the El Niño / La Niña phenomenon is seen as the main underlying course (via elevated mean sea water temperatures). Global climate change is considered as a significative contributing factor behind the exceptionally strong El Niño and La Niña weather changes.

Thai challenge: warming seas bleach the coral

Several popular dive sites at seven marine parks have been closed to diving in Thailand. The ban covers coral reefs suffering from serious coral bleaching which started in 2010. The reefs which will be off-limits to diving are located in the Andaman Sea on Thailand’s west coast.

The purpose is to let the reefs rest under circumstances in which as few environmental pressures as possible affect the coral. “We will give the reefs time to recover naturally,” Sunan Arunnopparat, director general of the National Parks, Wildlife and Plant Conservation Department, said in an interview. The comments were published by the Thai newspaper The Nation on 20 January, 2011.

The director general added that more than 80% of the coral in the areas was affected by bleaching.  Overall the situation is serious: more than 50% of all the reefs in southern Thailand show signs of whitening and loss of colour. Divers visiting Thailand tell that it is not question of bleaching only. They say that at least in some places a high percentage of the bleached coral has actually died.

Widespread bleaching and death of corals could be one of the first concrete signs of climate change in the ocean. Photo (c) 2010 Erkki Siirila.

While announcing the ban, Sunan Arunnopparat also told that the restrictions were introduced in consultation with academics. As regards the duration of the emergency measures, Sunan Arunnopparat said: “The recovery of the coral will be monitored before the ban is lifted.”

In addition to the reef closure, the Department will apply other habitat protection measures. Limiting admissions to national parks and educating the tourists in environmentally sound practices were mentioned as examples.

The new restrictions are likely to hurt Thailand’s tourism industry and especially the dive business in the short term. In the long term the dive business may benefit. In case the new conservation measures lower enough the combined environmental stress factors on the reefs they could prove helpful – globally coral reefs are mainly threatened by the warming of seawater. The root cause is climate change.  Not only tourism is at stake, reef health is crucial to maintenance of local fisheries and prevention of coastal erosion.

The coral bleaching – whitening due to the loss of the symbiotic zooxanthella microalgae from coral tissues – was first observed across the Andaman Sea in May 2010 after a surge in seawater temperatures. Serious bleaching was reported also from other parts of the Indian Ocean in 2010. Furthermore, similar news came from some reef areas in the western Pacific Ocean and the Caribbean Sea.

Bleached coral often dies. As coral grows slowly, the recovery of a reef will usually take years. As coral reefs often suffer from several environmental stress factors, there is no guarantee that a damaged reef will recover.

Healthy reefs are important for the success of dive tourism in many developing countries. Photo (c) 2010 Erkki Siirila.

Alarming coral death on South-East Asian reefs

“It is certainly the worst coral die-off we have seen since 1998. It may prove to be the worst such event known to science,” says Dr. Andrew Baird, an Australian coral reef specialist in an interview by published on 18 October, 2010.

Dr. Baird estimates that approximately 80% of Acropora coral colonies and 50% of colonies by other species have died during the past six months on the bleached coral reefs in the Indian and Pacific Oceans.

Healthy-looking and bleached coral side by side. Photo (c) 2010 Erkki Siirila.

The reefs are numerous: the mass bleaching affects an area which extends from the Seychelles to Sulawesi and the Philippines. Included are reefs in Sri Lanka, Burma, Thailand, Malaysia, Singapore, and Indonesia.  The most diverse reefs of the world are found in the so-called “Coral Triangle” which is within the affected area.

In the Underwatertimes article Dr Baird comments the seriousness of the situation by stating that the live percentage coral cover on the reefs could drop from 50% to about 10% (these are average values).  The recovery, if it ever occurs, will take years.  Fisheries and tourism in the affected coastal and island nations will suffer: the livelihoods of millions of people are likely to be hampered.

The bleaching is being caused by elevated mean seawater temperatures which result in the loss of symbiotic microalgae from the coral tissues. As the pigments are in the algae, the coral colony turns white. When the seawater temperature stays higher than normal for weeks, the bleached coral colonies often die – for nutrition the coral depends on the algae.

The warming of seawater to levels which are higher than normal is related to the planet-wide effects of the periodic El Niño and La Niña weather disturbances, which in turn seem to be getting more extreme with global climate change.

In non-scientific terms the recent events in South-East Asia could perhaps be summarised by stating that “the rainforests of the sea are dying”.  People who have seen a healthy coral reef might also use the expression “a very sad and serious ecological disaster is taking place”.

Coral builds impressive living structures in the tropical oceans. Climate change, seawater warming and coral bleaching may kill these underwater cities. Photo from Hurghada,Egypt, copyright (c) 2010 Erkki Siirila.

Coral reef calcification: hope and controversy

In a controversial article in the journal Geophysical Research Letters Australian scientists state that coral reefs could expand in size by more than 30% in response to ocean warming related to climate change.

The research results published five years ago suggest that coral reef calcification rates would not be in decline.  In fact, they are said to be equivalent to those observed more than 200 years ago.

The observations were done at major reef-building colonies around the globe in the Indo-Pacific coral region and in massive Porites (a genus of finger-like stony coral) reef colonies in Australia, Hawaii, Thailand, the Persian Gulf and New Ireland.

The scientists say that the increase in reef calcification is probably due to enhanced coral metabolism and/or increases in photosynthetic rates of the symbiotic algae. The researchers expect the increases in calcification associated with ocean warming outweigh the decreases associated with higher CO2 levels.   “While initially showing a decrease in calcification up to 1964, ocean warming outweighs the CO2 effect and stimulates recovery of coral reef calcification”, says Richard Matear, one of the researchers, at Scienceagogo: 20041112235853data_trunc_sys.shtml

Enjoying a healthy reef of Roatan Island in Honduras. Photo (c) 2009 Erkki Siirila.