Mapping the risks

Which risks do corals face?

Coral reefs are put in a very vulnerable position by different threats. Stressed corals are mostly the result of several threats at the same time.

To get a clear view of the level of stress the coral reefs are potentially up to, scientists try to map out the scope of the negative influence of these threats, separately or together in one map, a risk assessment map.

Largely, four categories of direct threats caused by human activities to coral reefs can be distinguished:

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Coastal development
Palm Islands, Dubai.
Source: Helmut Pfau.

Coastal development

  • cities
  • settlements
  • airports
  • military bases
  • mines
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Marine pollution
The Argo Merchant ran aground on December 15, 1976. A silvery oil slick can be seen coming from the center holds.
Source: NOAA.

Marine pollution

  • ports
  • oil tanks
  • wells
  • major shipping routes
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Inland development
Dead fish on the Soummam River, probably because of pesticides.
Source: Zil.

Inland development

  • pollution
  • erosion
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Overfishing
Fishermen in Bangladesh
Source: USAID Bangladesh.

Overexploitation and destructive fishing

  • population density

For each threat, the scope of the negative influence can be determined and used to define a 'low risk', 'medium risk' and 'high risk' zone.

Such a map greatly supports decision-making, especially when scientists are putting up a management plan for the protected areas.

When you have read this page, try the 'Mapping the risks' activity.

Example of the region of Hurghada (Egypt)

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Landsat7 ETM+ TCC
Satellite image of Hurghada (Egypt), Landsat 7 ETM+, 2000. Location of an oil-drilling platform in the NW of the image (red spots).
Source: Vanderstraeten, 2007.

In the NW of the studied area, two oil-drilling platforms are located. The chance that corals are in stress due to an oil leak is biggest close to the platforms. The further you go away from the drilling platforms, the smaller the risk that corals get stressed.

This information can be mapped out in a risk assessment map. This map contains the different zones: a high risk zone (red in the image) close to the platforms passes into a medium risk zone (orange) that is located further away. The risk that corals get stressed due to oil leaks is lowest in the green zone.

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Risk assessment zones
Risk assessment map containing three distinctive risk assessment zones: red = high risk, orange = medium risk, green = low risk.
Source: Vanderstraeten, 2007.

This is the reproduction of the potential level of stress to coral reefs due to the presence of oil-drilling platforms in the vicinity. Of course, this can be extended to other sources of threats.