The Atlantic and Eastern Pacific
93
Caribbean and Brazilian sub-regions, suggesting
immigration from both areas.
In many areas of the Caribbean, including remote
localities, there have been wide declines in coral cover
together with dramatic increases in algal cover While
these can sometimes be directly related to human
impacts in specific localities, there also appears to
have been a regional decline. Much can be linked to the
widespread die-off of the long-spined sea urchin
Diadema antillarum, which occurred in 1983-8'i Isee
page 611. This species was a major algal grazer on
the reefs and, in places where overfishing was
particularly high, it was often the major herbivore on
reefs. The die-off appears to have been pathogenic -
caused by a bacterial infection - and may have been
natural or may have been carried to the region in
ballast water from ships. At the same time wide areas
have been afflicted by coral diseases. White band
disease has infected and l
Acropora palmata, which were once among the main
structural components of reefs. Dead corals are rapidly overgrown with algae, especially because of the
loss of grazing Diadema, and large areas of reef have
now become algae-dominated and are showing little
sign of a return to previous conditions.
The degree to which these problems are the result
of entirely natural processes remains unclear, but this
region is also widely affected by many direct human
impacts, including sedimentation, nutrient pollution
and overfishing. Tourism is probably the most
important industry across the wider Caribbean, with
most tourists seeking beach-based holidays. In many
places, coastal development associated with the
growing tourism industry has greatly exacerbated the
problems facing the reefs of the region. In the 1998
Reefs at Risk analysis, 71 percent of the reefs in the
Wider Caribbean were described as threatened by
human activities. In areas where these problems are
most extreme, the rates of recovery of reef systems are
certainly being slowed. Efforts to improve reef status
and recovery through the implementation of marine
protected areas and other coastal management
regimes are varied, but include important success
stories. At the same time, the indirect nature of many
threats means that, even with legal protection, many
reefs are still in decline.
The Eastern Pacific
The western shores of the Americas are completely
separated from the Caribbean Sea and have very
different coral reef communities. Although part of the
Pacific, this region is quite distinct from the rest of this
ocean in terms of its reefs. Much of the continental
coastline plunges into relatively deep water as the
oceanic plates are subducted under the continental
plates of North and South America. There are only a
few offshore islands lying beyond the continental shelf.
Water conditions on the continental shelf fluctuate
considerably, with cool water upwellings in most
years, occasionally reversed to warm water upwellings
during El Nirio Southern Oscillation (ENSOl events.
The isthmus of Panama closed between 3 and
3.5 million years ago and. apart from possible very
minor breaches of this gap. there has been no marine
connection between the coral reefs on either side of
this land bridge since that time. Dramatic changes
have been wi nught on the marine communities since
the closure of lie isthmus. Initially the two separated
communities wei e probably very diverse. However, the
Pliocene/Pleistocene glaciations wiped out large numbers of species, and almost completely removed coral
species from the Pacific shores of the Americas. There
has been some recolonization of these shores by corals,
but they have come from the Pacific. Recolonization
has been slow and sporadic due to the great physical
distance between these shores and the nearest reefs
around the Central Pacific islands. This "East Pacific
Barrier" is enhanced by unfavorable patterns of ocean
currents, further reducing the chances of larval transport across the Pacific.
The coral reefs of the Eastern Pacific are thus
highly distinctive communities. Their closest affinities
are with the reefs of the Pacific, but they have a much
lower diversity of species and many are endemic. The
reefs themselves are rarely well developed as physical
structures - most are simply coral communities. The
few structural reefs are mostly small in overall extent,
and consist of only a few meters depth of carbonate
deposits. The one exception to this generalization is
Clipperton Atoll, a true atoll administered by French
Polynesia (and described in Chapter 141.
Fluctuating oceanographic conditions have a
considerable impact on coral reefs. The first regionwide mass mortalities associated with coral bleaching
were linked to a major ENSO event in 1983. The 199798 ENSO event also caused high levels of bleaching,
although mortality appears to have been lower
Localized centers of upwelling appeared to suffer least
and may be important refuges for the East Pacific
fauna during such events.
Human impacts on this region are generally low.
Most of the reefs are associated with offshore islands
and therefore not heavily impacted by terrigenous
influences. Overfishing is certainly a problem in some
areas. There is virtually no tourism, with the exception
of the highly controlled visits to the Galapagos.
93
Caribbean and Brazilian sub-regions, suggesting
immigration from both areas.
In many areas of the Caribbean, including remote
localities, there have been wide declines in coral cover
together with dramatic increases in algal cover While
these can sometimes be directly related to human
impacts in specific localities, there also appears to
have been a regional decline. Much can be linked to the
widespread die-off of the long-spined sea urchin
Diadema antillarum, which occurred in 1983-8'i Isee
page 611. This species was a major algal grazer on
the reefs and, in places where overfishing was
particularly high, it was often the major herbivore on
reefs. The die-off appears to have been pathogenic -
caused by a bacterial infection - and may have been
natural or may have been carried to the region in
ballast water from ships. At the same time wide areas
have been afflicted by coral diseases. White band
disease has infected and l
Acropora palmata, which were once among the main
structural components of reefs. Dead corals are rapidly overgrown with algae, especially because of the
loss of grazing Diadema, and large areas of reef have
now become algae-dominated and are showing little
sign of a return to previous conditions.
The degree to which these problems are the result
of entirely natural processes remains unclear, but this
region is also widely affected by many direct human
impacts, including sedimentation, nutrient pollution
and overfishing. Tourism is probably the most
important industry across the wider Caribbean, with
most tourists seeking beach-based holidays. In many
places, coastal development associated with the
growing tourism industry has greatly exacerbated the
problems facing the reefs of the region. In the 1998
Reefs at Risk analysis, 71 percent of the reefs in the
Wider Caribbean were described as threatened by
human activities. In areas where these problems are
most extreme, the rates of recovery of reef systems are
certainly being slowed. Efforts to improve reef status
and recovery through the implementation of marine
protected areas and other coastal management
regimes are varied, but include important success
stories. At the same time, the indirect nature of many
threats means that, even with legal protection, many
reefs are still in decline.
The Eastern Pacific
The western shores of the Americas are completely
separated from the Caribbean Sea and have very
different coral reef communities. Although part of the
Pacific, this region is quite distinct from the rest of this
ocean in terms of its reefs. Much of the continental
coastline plunges into relatively deep water as the
oceanic plates are subducted under the continental
plates of North and South America. There are only a
few offshore islands lying beyond the continental shelf.
Water conditions on the continental shelf fluctuate
considerably, with cool water upwellings in most
years, occasionally reversed to warm water upwellings
during El Nirio Southern Oscillation (ENSOl events.
The isthmus of Panama closed between 3 and
3.5 million years ago and. apart from possible very
minor breaches of this gap. there has been no marine
connection between the coral reefs on either side of
this land bridge since that time. Dramatic changes
have been wi nught on the marine communities since
the closure of lie isthmus. Initially the two separated
communities wei e probably very diverse. However, the
Pliocene/Pleistocene glaciations wiped out large numbers of species, and almost completely removed coral
species from the Pacific shores of the Americas. There
has been some recolonization of these shores by corals,
but they have come from the Pacific. Recolonization
has been slow and sporadic due to the great physical
distance between these shores and the nearest reefs
around the Central Pacific islands. This "East Pacific
Barrier" is enhanced by unfavorable patterns of ocean
currents, further reducing the chances of larval transport across the Pacific.
The coral reefs of the Eastern Pacific are thus
highly distinctive communities. Their closest affinities
are with the reefs of the Pacific, but they have a much
lower diversity of species and many are endemic. The
reefs themselves are rarely well developed as physical
structures - most are simply coral communities. The
few structural reefs are mostly small in overall extent,
and consist of only a few meters depth of carbonate
deposits. The one exception to this generalization is
Clipperton Atoll, a true atoll administered by French
Polynesia (and described in Chapter 141.
Fluctuating oceanographic conditions have a
considerable impact on coral reefs. The first regionwide mass mortalities associated with coral bleaching
were linked to a major ENSO event in 1983. The 199798 ENSO event also caused high levels of bleaching,
although mortality appears to have been lower
Localized centers of upwelling appeared to suffer least
and may be important refuges for the East Pacific
fauna during such events.
Human impacts on this region are generally low.
Most of the reefs are associated with offshore islands
and therefore not heavily impacted by terrigenous
influences. Overfishing is certainly a problem in some
areas. There is virtually no tourism, with the exception
of the highly controlled visits to the Galapagos.