The Indian Ocean and Southeast Asia
179
structures occur in isolated oceanic locations. There
are numerous atolls and platfornn structures in the
west and central regions of the oceans, and the
Maldives and Chagos Archipelago include the largest
atoll structures in the world. The continental coastlines of India and Sri Lanl development as there are various adverse conditions,
including high turbidity, fluctuating salinity and high
wave energy. There are important though little known
reefs around the Andaman and Nicobar Islands and
to the north of Sumatra. Australia also has significant
reef communities, including extensive fringing reefs,
offshore platform and barrier structures and high
latitude communities (these are considered further in
Chapter 111.
Species diversity is high across the region,
following a narrow band of high diversity in the Central
Indian Ocean and forming two distinctive sub-centers
of diversity in the Western Indian Ocean and the Red
Sea. Elsewhere there is greatly reduced diversity,
notably in the Arabian Gulf and along the shores of
mainland India. Despite their high latitude there is
relatively little diminution of diversity in the reefs of
the northern Red Sea. By contrast there are latitudinal
declines in species numbers, and as a consequence in
the development of reefs themselves, in both southern
Africa and Western Australia.
Wide areas of this region were affected by the
1997-98 El Nino Southern Oscillation event, and in
1998 warm waters swept across wide areas of the
Indian Ocean, leading to bleaching and massive levels
of coral mortality on reefs from Western Australia to
the shores of East Africa. In the Maldives. Chagos and
Seychelles (which together make up over 5 percent of
the world's coral reefsl. more than 60 percent of corals
died in all areas, and up to 100 percent of corals were
lost in some places. Recovery has now begun in most
areas, but the overall scale of this event was so large
that full recovery may take years or decades, while
there are concerns that such events may be repeated
with global climate change.
Direct human pressures on coral reefs in the
Indian Ocean are highly varied. The Arabian Gulf contains the largest concentrations of oil reserves in the
world, and there is chronic oil pollution in this sea.
exacerbated by occasional massive oil spills. Tanker
traffic also carries the threat of oil pollution to other
areas, notably the narrow straits at the mouth of the
Arabian Gulf, and at the northern and southern ends
of the Red Sea. Coastal development is sporadic -
there are vast areas of the Arabian coastline with
little development, but in others, such as around the
major ports and some of the tourist areas of East
Africa, coastal development is having a direct impact
on reefs. Tourism too is sporadic, but is critical to the
economies of Egypt, Kenya. Tanzania and the islands
of the Indian Ocean.
Southeast Asia
Southeast Asia is one of the most important areas in
the world for coral reefs. Over 30 percent of the world's
reefs are found in this complex region which straddles
the waters between the Indian and Pacific Oceans. The
region includes the continental coastlines of Myanmar
and Thailand. Malaysia. Cambodia. Vietnam and China.
The most extensive coastlines, however, follow the
great complex of islands which are dominated by the
Philippines and Indonesia. Indonesia alone has over
50 000 square kilometers of coral reefs, nearly 18
percent of the world total. Japan lies on the edges of
this region, and also has a considerable area of reefs
surrounding island chains which follow natural dines
of diminishing species diversity. The coastlines define
a large number of partially enclosed seas. While the
waters around the continental shores are generally
shallow, deep oceanic waters come in close contact
with offshore islands in many areas.
Fringing reefs predominate, although there are
also extensive barrier reef systems, and a number of
atolls and near-atolls. This region is the great center
of coral reef biodiversity, and there are more species
here, in almost all animal groups, than anywhere else.
To some degree this diversity is encouraged or maintained by the complexity of coastline and the great
range of habitats found in the region, but its ultimate
origins can be traced back over geological timescales.
While extinctions were occurring in other regions it
would appear that species were able to survive in this
region, and even to diversify as sea levels fluctuated
and areas became isolated and then reconnected with
one another.
Unfortunately this region is also the most
threatened and disturbed by human activities. Some
82 percent of the region's reefs were considered to
be threatened by human activities in the 1998 Reefs
at Risk study Most of these threats are linked to the
rapidly growing economies and populations in this
region. These are driving massive changes in the
landscape, with forest clearance and agricultural
intensification leading to increased sedimentation
and pollution from agricultural chemicals. Massive
urban expansion has also led to enormous pollution
problems close to urban centers. Fishing pressures
are ubiquitous, from chronic overfishing for local
consumption and the highest rates of blast fishing in
the world, to target species overfishing even in many of
the remotest parts of the region.
179
structures occur in isolated oceanic locations. There
are numerous atolls and platfornn structures in the
west and central regions of the oceans, and the
Maldives and Chagos Archipelago include the largest
atoll structures in the world. The continental coastlines of India and Sri Lanl development as there are various adverse conditions,
including high turbidity, fluctuating salinity and high
wave energy. There are important though little known
reefs around the Andaman and Nicobar Islands and
to the north of Sumatra. Australia also has significant
reef communities, including extensive fringing reefs,
offshore platform and barrier structures and high
latitude communities (these are considered further in
Chapter 111.
Species diversity is high across the region,
following a narrow band of high diversity in the Central
Indian Ocean and forming two distinctive sub-centers
of diversity in the Western Indian Ocean and the Red
Sea. Elsewhere there is greatly reduced diversity,
notably in the Arabian Gulf and along the shores of
mainland India. Despite their high latitude there is
relatively little diminution of diversity in the reefs of
the northern Red Sea. By contrast there are latitudinal
declines in species numbers, and as a consequence in
the development of reefs themselves, in both southern
Africa and Western Australia.
Wide areas of this region were affected by the
1997-98 El Nino Southern Oscillation event, and in
1998 warm waters swept across wide areas of the
Indian Ocean, leading to bleaching and massive levels
of coral mortality on reefs from Western Australia to
the shores of East Africa. In the Maldives. Chagos and
Seychelles (which together make up over 5 percent of
the world's coral reefsl. more than 60 percent of corals
died in all areas, and up to 100 percent of corals were
lost in some places. Recovery has now begun in most
areas, but the overall scale of this event was so large
that full recovery may take years or decades, while
there are concerns that such events may be repeated
with global climate change.
Direct human pressures on coral reefs in the
Indian Ocean are highly varied. The Arabian Gulf contains the largest concentrations of oil reserves in the
world, and there is chronic oil pollution in this sea.
exacerbated by occasional massive oil spills. Tanker
traffic also carries the threat of oil pollution to other
areas, notably the narrow straits at the mouth of the
Arabian Gulf, and at the northern and southern ends
of the Red Sea. Coastal development is sporadic -
there are vast areas of the Arabian coastline with
little development, but in others, such as around the
major ports and some of the tourist areas of East
Africa, coastal development is having a direct impact
on reefs. Tourism too is sporadic, but is critical to the
economies of Egypt, Kenya. Tanzania and the islands
of the Indian Ocean.
Southeast Asia
Southeast Asia is one of the most important areas in
the world for coral reefs. Over 30 percent of the world's
reefs are found in this complex region which straddles
the waters between the Indian and Pacific Oceans. The
region includes the continental coastlines of Myanmar
and Thailand. Malaysia. Cambodia. Vietnam and China.
The most extensive coastlines, however, follow the
great complex of islands which are dominated by the
Philippines and Indonesia. Indonesia alone has over
50 000 square kilometers of coral reefs, nearly 18
percent of the world total. Japan lies on the edges of
this region, and also has a considerable area of reefs
surrounding island chains which follow natural dines
of diminishing species diversity. The coastlines define
a large number of partially enclosed seas. While the
waters around the continental shores are generally
shallow, deep oceanic waters come in close contact
with offshore islands in many areas.
Fringing reefs predominate, although there are
also extensive barrier reef systems, and a number of
atolls and near-atolls. This region is the great center
of coral reef biodiversity, and there are more species
here, in almost all animal groups, than anywhere else.
To some degree this diversity is encouraged or maintained by the complexity of coastline and the great
range of habitats found in the region, but its ultimate
origins can be traced back over geological timescales.
While extinctions were occurring in other regions it
would appear that species were able to survive in this
region, and even to diversify as sea levels fluctuated
and areas became isolated and then reconnected with
one another.
Unfortunately this region is also the most
threatened and disturbed by human activities. Some
82 percent of the region's reefs were considered to
be threatened by human activities in the 1998 Reefs
at Risk study Most of these threats are linked to the
rapidly growing economies and populations in this
region. These are driving massive changes in the
landscape, with forest clearance and agricultural
intensification leading to increased sedimentation
and pollution from agricultural chemicals. Massive
urban expansion has also led to enormous pollution
problems close to urban centers. Fishing pressures
are ubiquitous, from chronic overfishing for local
consumption and the highest rates of blast fishing in
the world, to target species overfishing even in many of
the remotest parts of the region.