Most threatened coral reefs in the world are located in Southeast Asia

Thermal stress can cause coral reefs to bleach from losing their symbiotic algae giving them colour  (from imgarcade)

Coral reefs are not only a critical habitat for numerous species, they provide also essential ecosystem services such as:

• For food and livelihood a healthy, well-managed reef can yield between 5 and 15 tons of fish and seafood per square kilometer each year;

• Reefs are vital in many tropical countries for developing eco-tourism new revenues:  attracting divers, snorkelers, and recreational fishers, not to mention providing much of the white sand for beaches;

• Many reef-dwelling species have developed complex chemical compounds- such as venoms and chemical defenses- aiding their survival in highly competitive habitats which might offer the basis of life-saving new pharmaceuticals including treatments for cancer, HIV, malaria, and other diseases;

• Beyond their biological value, reefs dissipate wave energy, reducing erosion and lessening damage during storms with an estimated 150,000 km of reef bordered shoreline in more than 100 countries and territories; this function protects human settlements, infrastructure, and valuable coastal ecosystems such as sea grass meadows and mangrove forests.

Despite their importance, coral reefs face unprecedented threats throughout most of their range and many reefs are already degraded and unable to provide the vital services on which so many people depend.

Some threats are highly visible and occur directly on reefs. Levels of fishing are currently unsustainable on a large proportion of the world’s reefs, and have led to localized extinctions of certain fish species.

Many threats are also the result of human activities occuring far away from reefs, such as forest clearing, crop cultivation, intensive farming, polluted sewage runoff and poorly planned coastal development. Pollution and waste from ships and from oil and gas exploitation further exacerbate the situation.

Furthermore beyond these extensive and damaging local-scale impacts, reefs are increasingly at risk from the global threats associated with rising concentrations of greenhouse gases in the atmosphere.

Even in areas where local stress on reefs are relatively minimal, warming seas have caused mass coral bleaching occurring when corals become thermally stressed and are massively losing  the “zooxanthellae” symbiotic algae that live within their tissues and normally provide their specific colors.

It is rare for any reef to suffer only a single threat. More often the threats are compounded. For instance, overfishing eliminates a key herbivore such as “Parrot fish”, while runoff from agriculture supplies nutrients that cause a bloom in macro algae, impairing the growth of coral and ultimately reducing the competitive ability of coral communities.

Despite widespread recognition that reefs are severely threatened, information regarding threat assessment  to specific reefs are limited. Only a fraction of reefs have been studied or monitored consistently over time- such as Jamaica, Florida, and Australia’s Great Barrier- where changes in coral condition are well-documented. 

In most places, however, the availability of detailed information is limited, inhibiting effective management.

More than 15 years after the foundation of the World Reef Initiative (WRI), reef maps are showing clearly that the growth in threats has largely outpaced efforts to address those threats. 

In the mid-1990s, climate change was still perceived as a somewhat distant threat. However, in 1998, a powerful El Niño event further increased sea surface temperatures that were already rising due to climate change, triggering the most severe and expansive coral bleaching event on record.

As a result an update of the global coral reef threats analysis is clearly necessary in order to identify and understand the outcome  and implications of changes to the world’s reefs and to help guide targeted interventions aimed at mitigating existing threats .

Ranking of worldwide human threats to coral reefs

(see “WRI-Coral Reefs at risk revisited-2011”)

There is a difference between threats and damages. A threat analysis is an assessment of the likeliness (within 0-100%) of a specified type of damage.  A threat model measures threat rather than real conditions. 

Concerning coral reefs, harmful damage might result from the following threats:

• Overfishing and destructive fishing : such as destruction of fish habitat and species;
• Watershed land-based pollution : discharge of land base sediment or pollutant ;  
• Coastal development : sewage and pollutions from ports, industry, resorts;  
• Marine-based pollution and damage : discharge of marine waste and marine fuels;
• Thermal stress : damage from sea surface temperature increase.

Figure 1 : Worldwide human local threats to coral reefs  (WRI 2011)

Overfishing and destructive fishing

Threats to coral reefs from overfishing were evaluated based on coastal population density and extent of fishing areas, with adjustments to account for the increased demand due to proximity to large populations and market centers.

Areas where destructive fishing occurs (with explosives or poisons such as cyanide) were also included, based on observations from monitoring and mapping expert analysis.

The threat estimate was reduced inside marine protected areas rated by experts as having “effective” or “partially effective” management (meaning that a level of management is present that helps to guard ecological integrity).

Limitations: 

• Accurate, spatially referenced global data on fishing methods, catches, and number of fishers were not available; therefore, population pressure is used as a proxy for overfishing.

• The model fails to capture the targeting of very high value species, which affects most reefs globally, but has fewer ecosystem impacts than wider scale overfishing.

• Management effectiveness scores were only available for about 83% of the reefs within marine protected areas.

Reef regions ranking for overfishing and destructive fishing (see Figure 2 below): most threatened are Southeast Asia (N°1) & Atlantic (N°2); less threatened are Pacific (N°5) and Australia (N°6).

Watershed land-based pollution

The threat from land-based pollutants was modeled over 300,000 watersheds (catchments area drained by a river and its tributaries) discharging to coastal waters. Relative erosion rates were estimated across the landscape based on slope, land cover type, precipitation, and soil type.

Sediment delivery at the river mouth was estimated based on total erosion in the watershed, adjusted for the sediment delivery ratio (based on watershed size) and sediment trapping by dams and mangroves.

Sediment plume dispersion was modeled using a linear decay rate and was calibrated against actual sediment plumes observed from satellite data. The model represents a proxy for sediment, nutrient, and pollutant delivery.

Limitations: 

• Nutrient deliveries to coastal waters were probably underestimated due to a lack of spatial data on crop cultivation and fertilizer application. However, agricultural land is treated as a separate category of land cover, weighted for a higher influence.

• The model does not incorporate nutrient and pollutant inputs from industry, or from intensive livestock farming, which might be considerable.

Reef regions ranking for watershed land-based pollution (see Figure 2 below): most threatened are Southeast Asia (N°1) & India (N°2); less threatened are Middle East (N°5) and Australia (N°6)

Coastal development

The threat to coral reefs from coastal development was modeled based on size of cities, ports, and airports; size and density of hotels; and coastal population pressure (a combination of population density, growth, and tourism growth).

Limitations:

• Indicators were likely to miss some new constructions works and tourism locations.

• The model does not directly capture sewage discharge, but relies on population as a proxy for costal development threat.

Reef regions ranking for coastal development (see Figure 2 below): most threatened are Southeast Asia (N°1) & India (N°2); less threatened are Pacific (N°5) and Australia (N°6).

Figure 2 : Comparison of local and past thermal threats by region (WRI 2011) 

Marine-based pollution and damage

Threat from marine-based pollution and damage were based on the size and volume of commercial shipping ports, size and volume of cruise ship ports, intensity of shipping traffic, and the location of oil infrastructure.

Limitations:

• Threat associated with shipping intensity might be underestimated because the data were based on voluntary ship tracking, and does not include fishing vessels.

• The threat model does not account for marine waste (such as plastics), discarded fishing gear, recreational vessels or shipwrecks, due to a lack of global spatial data on these threats.

• The four local threats described above were then  combined to provide an integrated local threat index. Past thermal stress as described below were treated as an additional threat.

Reef regions ranking for marine-based pollution and damage (see Figure 2 above): most threatened are Atlantic (N°1) & Middle East (N°2); less threatened are Indian (N°5) and Southeast Asia (N°6).

Thermal stress

Estimation of thermal stress over the past 10 years (1998 to 2007) combining the following two data layers:

Past intense heating events. These were areas known to have had high temperature anomalies (scores of degree heating weeks > 8), based on satellite sea surface temperature data provided by NOAA Coral Reef Watch; and

Observations of severe bleaching from Reef Base (see ReefBase) .  

How to assess the outcome of threats which are real damage and true habitat condition on reefs?

A unique and important feature of the Reefs at Risk approach is its global coverage—assessing threats to all reefs, even those far from human habitation and scientific outreach. It is, however, a model, and it measures as explained above threat rather than condition. 

The only way to accurately assess condition is through direct measurement of fish, benthic cover (live coral, dead coral, algae, etc.), or other characteristics. Some reefs, including the Great Barrier Reef, have detailed and regular surveys covering numerous areas, but worldwide such observation or monitoring are sparse and irregular. 

Some threatened reefs may still be healthy, but many others might have already suffered some level of degradation.

Where are located the most threatened coral regions?

The Figure 3 & 4 below are showing that Southeast Asia (N°1 ranking) and Atlantic Reefs (N°2) regions are relatively the most threatened reef regions in the world; then slightly better:  Indian Ocean (N°3) and Middle East (N°4); then Pacific (N°5) less than the averaged global risk; Australia's Great barrier reefs being much less threatened (N°6).

Globally, after factoring by the coral reef regions' area, more than 60% of worldwide coral reefs (about 150,000 km2) are threatened by human local activities (see Figue 3 below) and about 75% (about 185,000 km2) are threatened when past thermal stress is included. 

Figure 3 : Integrated local threats consist of the four local threats—overfishing and destructive fishing, marine pollution and damage, coastal development, and watershed-based pollution

Figure 4 : Amount of reef area (in sq km) in each region classified by integrated local threat categorized as low, medium, and high; the four local threats are integrated plus the thermal stress during the past ten years; this figure summarizes current threats: future warming and acidification are not included

On all counts of relatively (see Figure 3 above) or absolute (see Figure 4 ) threats Shouteast Asia is always the most threatened reef regions in the world and Australia is always the best ranking.

This means that the Southeast Asia is definitely the place where the long-term conservation of coral reefs in the world is at stake, including the survival of many biological species that live there.

The largest coral reefs in the world and the most valuable for their biodiversity are located in Southeast Asia

Most worldwide coral reefs are located in the Indian & Pacific and a small portion of Atlantic oceans 

Coral reefs and old growth forests are both nature richest realms. They are deriving their primary energy from plants thriving from solar radiation. As a result their location is within 30°S & 30°N latitudes where sun activity and temperature are at their maximum. Both are extremely complex systems consisting of numerous micro habitats and huge number of species.

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.

Among the coral triangle countries, such as Malaysia and the Solomon Islands, tourism had enabled a rapid diversification of the economy and coral reefs had become one of the most attractive destination.

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.