90
WORLD ATLAS OF CORAL REEFS
material prepared at finer resolutions for specific areas.
Although it is theoretically possible to prepare a more
standardized global map using remote sensing, the
realization of this goal remains some way off
The approach adopted by UNEP-WCMC in this work
has been hierarchical. As a starting point, a commercially
available global base map of digital coral reef data was
used plotting the world's reefs at a scale of 1:1 000 000.
based on the US Defense Mapping Agency Operational
Navigational Chart series. Although broadly accurate, this
information was at too low a resolution to show many
reefs. Further data were then added from the Coral Reefs
of rhe World volumes, focussing on those countries
where the 1:1 000 000 source was deemed particularly
inadequate, notably the Caribbean and parts of the
Western Indo-Pacific. In parallel with this work a datagathering phase was initiated. Funds were insufficient for
a systematic outreach, but improvement of national data
has continued on an opportunistic basis, with particular
focus directed towards those countries where existing data
were considered particularly poor.
The result of this mapping work, by 2001, was a
comprehensive and detailed GIS dataset, outputs from
which are presented in the maps contained in this volume.
These maps represent a summary of the best global
map of coral reefs available. A list of the source materials
is presented for each map. In all. around 70 percent
of countries include source material from new sources
at scales finer than 1 : 1 000 000. Many of these were at
scales of 1 :250 000 or finer, including navigational charts,
topographic map series, processed satellite images and,
more occasionally, specialist coral reef or shallow
substrate maps.
With a world map derived from multiple sources there
will be variation in the definition of coral reefs which is
used although remarkably few maps, other than detailed
habitat surveys, provide these definitions in their keys or
in accompanying documentation. Despite this weakness, it
is usually possible to determine what has been mapped
from an understanding of reef geomorphology, combined
with some independent knowledge of the reefs of each
region. Coral reefs portrayed on navigational maps and
charts typically include shallow reef flat and reef crest
areas only. High resolution resource inventories may give
less attention to areas of reef flat where bottom cover is
primarily bare rock or sand, but typically extend beyond
the reef crest. The outer limits of coral reef areas as shown
on maps may be set by the depth limitations of the survey
techniques rather than by any clear ecological boundary.
With this information it is possible to distil out a
more generalized definition common to all sources. Such
a definition, in fact, conforms quite closely to the broad
definition provided in Chapter 1. As they are mapped in
this volume, coral reefs are shallow structures built by
corals and other hermatypic organisms, and in every case
they are associated with an important living component,
including hermatypic corals.
These shallow reef areas are among the most
important areas in terms of reef growth, productivity,
coastal protection and diversity, but it is important to
realize that there are considerable additional areas,
including sub-surface structures and coral communities
which lack clear physical structures and are not shown in
these maps. Other authors, using broader definitions of
reef, have calculated significantly higher reef areas than
those presented in Chapter 1, although the lack of available data means that such calculations are inclined to
be more predictive, and are of little value at regional or
national resolutions.
Work on coral reef mapping at UNEP-WCMC is
an ongoing activity. The contribution of remotely sensed
data is likely to expand in coming years, with increasing
collaboration with partners around the world. It will be
equally important to try to capture some of the sub-surface
reefs, particularly in those parts of the world where these
are more common, and may harbor important reservoirs of
biodiversity. New priorities include the improved mapping
of biodiversity patterns to overlay the coral reef distribution
information, and the mapping of related habitats, notably
seagrasses. It will also be important to develop a better
understanding of human interactions with coral reefs,
through continued mapping of the threats to reefs, and also
improving the available information on marine protected
area boundaries. This latter information will enable a more
complete assessment of the global distribution and coverage of marine protected areas with coral reefs and will help
to highlight the gaps in this network.
Corinna Ravitious incorporating coral reef data into UNEP-WCMC's global GIS.
WORLD ATLAS OF CORAL REEFS
material prepared at finer resolutions for specific areas.
Although it is theoretically possible to prepare a more
standardized global map using remote sensing, the
realization of this goal remains some way off
The approach adopted by UNEP-WCMC in this work
has been hierarchical. As a starting point, a commercially
available global base map of digital coral reef data was
used plotting the world's reefs at a scale of 1:1 000 000.
based on the US Defense Mapping Agency Operational
Navigational Chart series. Although broadly accurate, this
information was at too low a resolution to show many
reefs. Further data were then added from the Coral Reefs
of rhe World volumes, focussing on those countries
where the 1:1 000 000 source was deemed particularly
inadequate, notably the Caribbean and parts of the
Western Indo-Pacific. In parallel with this work a datagathering phase was initiated. Funds were insufficient for
a systematic outreach, but improvement of national data
has continued on an opportunistic basis, with particular
focus directed towards those countries where existing data
were considered particularly poor.
The result of this mapping work, by 2001, was a
comprehensive and detailed GIS dataset, outputs from
which are presented in the maps contained in this volume.
These maps represent a summary of the best global
map of coral reefs available. A list of the source materials
is presented for each map. In all. around 70 percent
of countries include source material from new sources
at scales finer than 1 : 1 000 000. Many of these were at
scales of 1 :250 000 or finer, including navigational charts,
topographic map series, processed satellite images and,
more occasionally, specialist coral reef or shallow
substrate maps.
With a world map derived from multiple sources there
will be variation in the definition of coral reefs which is
used although remarkably few maps, other than detailed
habitat surveys, provide these definitions in their keys or
in accompanying documentation. Despite this weakness, it
is usually possible to determine what has been mapped
from an understanding of reef geomorphology, combined
with some independent knowledge of the reefs of each
region. Coral reefs portrayed on navigational maps and
charts typically include shallow reef flat and reef crest
areas only. High resolution resource inventories may give
less attention to areas of reef flat where bottom cover is
primarily bare rock or sand, but typically extend beyond
the reef crest. The outer limits of coral reef areas as shown
on maps may be set by the depth limitations of the survey
techniques rather than by any clear ecological boundary.
With this information it is possible to distil out a
more generalized definition common to all sources. Such
a definition, in fact, conforms quite closely to the broad
definition provided in Chapter 1. As they are mapped in
this volume, coral reefs are shallow structures built by
corals and other hermatypic organisms, and in every case
they are associated with an important living component,
including hermatypic corals.
These shallow reef areas are among the most
important areas in terms of reef growth, productivity,
coastal protection and diversity, but it is important to
realize that there are considerable additional areas,
including sub-surface structures and coral communities
which lack clear physical structures and are not shown in
these maps. Other authors, using broader definitions of
reef, have calculated significantly higher reef areas than
those presented in Chapter 1, although the lack of available data means that such calculations are inclined to
be more predictive, and are of little value at regional or
national resolutions.
Work on coral reef mapping at UNEP-WCMC is
an ongoing activity. The contribution of remotely sensed
data is likely to expand in coming years, with increasing
collaboration with partners around the world. It will be
equally important to try to capture some of the sub-surface
reefs, particularly in those parts of the world where these
are more common, and may harbor important reservoirs of
biodiversity. New priorities include the improved mapping
of biodiversity patterns to overlay the coral reef distribution
information, and the mapping of related habitats, notably
seagrasses. It will also be important to develop a better
understanding of human interactions with coral reefs,
through continued mapping of the threats to reefs, and also
improving the available information on marine protected
area boundaries. This latter information will enable a more
complete assessment of the global distribution and coverage of marine protected areas with coral reefs and will help
to highlight the gaps in this network.
Corinna Ravitious incorporating coral reef data into UNEP-WCMC's global GIS.