Most worldwide coral reefs are located in the Indian & Pacific and a small portion of Atlantic oceans
Coral reefs today represent a development episode of only some thousand years ago when sea level remained relatively stable, because 15,000 years ago seas were as much as 150m below the present level. As explained by Charles Darwin’s theory for Coral Reefs development they are closely related to volcano island subsidence and sea level fluctuations.
Environmental conditions exert a great influence on determining how an individual coral polyp copes with its basic needs. Optimum coral reefs are strongly correlated with very clean and relatively shallow waters (<70m depth) to obtain maximum sunlight at a warm temperature (optimum 23°-24°C).
But during periods of million years, succeeding generations of coral species became gradually modified in a manner allowing them to utilize most efficiently their environment. The end result is communities of organism that are finely tuned to their environment.
Why should we care about coral reefs in Asia Pacific?
Southeast Asia contains the largest area of coral reefs in the world known as the Coral Triangle shared between Indonesia, Malaysia, Philippines, Timor-Leste, Papua New Guinea and the Solomon Islands, .
The biodiversity of coral reefs in Southeast Asia is unparalleled in the world according to the Global Coral Reef Monitoring Network in their 2008 report on the status of coral reefs.
More than 138 million people in Southeast Asia live on the coast within 30 km of a coral reef, which is more than in all of the other coral reef regions combined. Fish, including reef fish, form a major part of the diet even in urban populations; across the region, fish and seafood provide an average of 36% of dietary animal protein.
Contribution of observation satellites to coral reef mapping and monitoring
Since the late 1990s, the contribution of satellites for remote sensing of coral reefs has been fundamental to improving their mapping and monitoring.
The observation satellites – such as Landsat (USA), Spot (EU) or IRS (India) - with optical sensor resolutions ranging from 10 to 50 m and capable of recording the radiation emitted in the visible and IR by the benthic environment, make it possible to obtain after treatment very accurate mapping of coral reefs, while monitoring their health and surveying the quality of their environment (bleaching thermal stress).
Specific treatments can eliminate noise as sun glint factors of the marine environment. The study of spectral signatures help to differentiate the various components of the benthic coral habitat: type of coral, living or dead, type of coral rubble, type of green algae or red by the absorption due to the presence of specific pigments, discrimination of coral sand or silt sediments by their reflectance, correction of the light signal attenuation in the water column by bathymetric treatment etc.
The University of South Florida (USF) had provided an exhaustive worldwide inventory of coral reefs using high-resolution satellite imagery. By using a consistent dataset of high-resolution multispectral Landsat 7 images acquired between 1999 and 2002, USF characterized, mapped and estimated the extent of shallow coral reef ecosystems in the main coral reef provinces (Caribbean-Atlantic, Pacific, Indo-Pacific, Red Sea).
Similar studies were conducted in Europe (IRD) , Australia and Indonesia from the data supplied by Landsat, SPOT, satellites or IRS.
Distribution of worldwide coral reefs habitat by region
Under the project called the Millennium Coral Reef Mapping a team of international researchers compiled an updated inventory of all "marine protected areas" containing coral reefs and compared it with the most detailed and comprehensive satellite inventory of coral reefs.
The World Reef Initiative (WRI) was founded in 1994 by eight governments: Australia, France, Japan, Jamaica, the Philippines, Sweden, UK, and the USA. It was announced at the First Conference of the Parties of the Convention on Biological Diversity in December 1994, and at the high level segment of the Intersessional Meeting of the U.N. Commission on Sustainable Development in April 1995.
The main result concerning the distribution of worldwide coral reefs by region is summarize in the following Figures 1 & 2 (see RWI 2011 Coral Reefs revisited ).
The world’s coral reefs are covering an area of approximately 250,000 sq km which the richest concentration being in Southeast Asia (30% of all coral reef areas in the planet), then Pacific (28%) and Australia (17%), followed by Indian Ocean (13%), Atlantic (10%) and the Middle East (6%) (see Figure 1 & 2).
Figure 1: Distribution of Coral Reefs by regions (From WRI 2011)
|Figure 2 : Distribution of Coral Reefs and the associated population by regions (From WRI 2011)|
Coral Reefs associated human population
As reported in WRI “Reefs at risk revisited -2011” , the coral’s reefs associated worldwide population could be featured by two values:
- Close population within 10 km of coast and 30 km from the reef : 275 Mil
- Larger area population within 100 km of the reef : 850 Mil
Figure 3 : Population associated with coral reefs by regions
There is a great variation of the population close to the reefs:
- Highly populated reef areas are: Indian Ocean 2065.5 people /km2; Southeast Asia 1,983.9, Atlantic 1,645.8 and Middle Eas 1,322.4
- Low populated reef areas are: Pacific 113.5, Australia 82.9
The ratio between larger and close area populations for reefs region is more or less stable between 2.5 (for low population countries) to 3.5 (highly populated).
Are coral reefs doomed to shrink progressively?
We must never forget that when we are seeing the coral reefs distribution around the world such as the one presented here, it is a snapshot in a development episode of some 5000 years of coral reefs life.
Coral have disappeared or have been greatly reduced in every part of the world.
Over the past 50 years for example, the Great Barrier Reef in Australia has decreased by 50% due to agricultural and industrial development of the western side of Australia!
Most of this coral reef reduction is due to the extraordinary development of people living on Earth which increased by a factor of 2.3 in average over the past 50 years, due to the correlative increase or human population direct or indirect pressure on coral reefs which are particularly heavy in the Asian Pacific region.
So our ocean and coral reefs are changing a lot and what we see today- if we don’t take the greatest care - maybe is doomed to shrink progressively! There in the contemplation of the beauty of corals a fragile and transient aspect and perhaps we must keep the memory of what will perhaps one day disappear.
Such is the aim of the Catlin Seaview Survey study which is a unique global study, working with some of the world's leading scientific institutions, dedicated to monitoring our oceans change and communicating on it to the world.
The aim of the survey is to document a baseline record by video and pictures of the world’s coral reefs seaview, in high-resolution panoramic vision.
Our oceans are changing and coral reefs are a clear visual indicator of this change – with a 40% loss of corals around the globe in the last 30 years alone.
The painstaking work that scientists realize could well be a kind of archive that will be quickly out of date due to ocean acidification, bleaching of the reefs, death of species and habitat.
In addition to their aesthetic appeal, coral reefs are also natural defenses against waves and coastal erosion. Their disappearance is a double punishment face of rising sea levels, expected over the next century.