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CORAL REEF ARE AL E  X TENT

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What

What Is It?

BENCHMARK

Coral reef areal extent is a measure of the area (e.g.,

No decrease in current coral reef

No

hectares or km2) covered by coral reef habitat. (This

extent.

extent.

measure is not the same as the measure of percent

living coral cover on the reef.)

TA R G E T

Any increase in coral reef extent.

Sites of extensive reef development include the

Belize Barrier Reef and atolls, Sian Ka'an and Banco

RED FL AG

Chinchorro Biosphere Reserves in Mexico, and the

Any decrease in current coral reef

Any

Bay Islands in Honduras.

extent.

extent.

Why Do We Measure It?

Why

Measurements of the areal extent of coral reefs tell

How Do We Measure It?

us, first and foremost, just how much sea bottom

Remote sensing (by satellite or aircraft) can be

is covered by coral reef habitat. This measure is a

used to estimate and track coral reef areal extent.

key indicator of habitat extent and can provide an

Conversion of satellite images into habitat maps is a

indication of how much habitat is still available versus

technically complex process often occurring in well-

how much has been lost (when historical data are

established university centers. In order for data to

available).

be fully comparable, the same processing methods

Large-scale disturbances, like hurricanes or massive

and decision rules need to be applied over the entire

coastal developments, can result in the loss of entire

region and during the full time series of the analysis.

coral reefs.

Data are normally entered into a GIS format where

they are readily accessible for a variety of uses.

There has been a significant loss of live, reef-building

corals in the MAR. Dead reefs with intact structure still

Usefulne s s

Usefulness

provide viable habitat, but without net reef accretion

Satellite- or aircraft-derived reef habitat maps are very

they will eventually erode or be washed away by

useful when selecting field monitoring and sampling

storms.

sites, allowing representative sites within each habitat

class to be chosen.

Sergio Hoare / WCS

When data are collected at more than one point in

time, these data can also be used to track changes in

the areal extent of reefs, although large discrepancies

can occur if standardized image processing and

decision rules are not followed.

The Millennium Coral Reef Mapping Project is

producing maps that are based on a standardized

method of classifying and comparing reef types36.

Satellite data are not, however, able to differentiate

live versus dead coral, or coral versus algae. As a

result, a totally dead reef might still be mapped as

reef habitat. The maps will need to be ground-truthed

and, as needed, corrected.

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