WORLD ATLAS OF CORAL REEFS
waters, as shown by the statistics in Table 1.2. These and
other patterns are derived from a complex interaction of
historical and contemporary factors. For some groups, the
parallel with coral diversity patterns may reflect direct
ecological associations between them. However, for a
number of others, it may be the same external factors
which have actually driven the change. A number of these
factors are briefly laid out below.
The influence of temperature
To a large extent, both scleractinian corals and the reefs
they build are restricted to a latitudinal band between
30°N and 30°S. This general observation is entirely related
to the decreasing temperatures which generally follow
increasing latitude. Most reef corals cannot survive in
temperatures much below 16-18°C for even a few weeks.
In conditions of extreme cold, corals can die within a
matter of hours or days, while under slightly less extreme
conditions, their growth rates are reduced. There is some
evidence that overgrowth by algae rather than the direct
influence of cold water may restrict coral development m
some high latitude areas.
High temperatures are also inimical to coral growth.
Extreme high temperatures drive the phenomenon known
as "coral bleaching", during which the corals expel their
symbiotic algae (see Chapter 2). Aside from humaninduced climate change, it has been suggested that
occasional high temperatures associated with El Niiio
events may be at least a partial explanation for the highly
limited reef development which is observed, for example,
along the western shores of the Americas.
The role of currents
While temperature influences can be broadly equated with
latitude, ocean currents can disrupt these simple patterns.
In a few areas of the world, major warm currents flow all
year round from the tropics into higher latitudes. These
have allowed the development of reefs quite beyond their
normal limits. Notable are the Leeuwin Current in
Western Australia; the East Australian Current; the
Kuroshio Current in Japan; and the Gulf Stream warming
the isolated oceanic reefs of Bermuda. In a similar way,
cold waters prevent reef growth. Cold water upwellings
along the coastlines of northeastern Somalia and southern
Arabia are perhaps the clearest example, while the
extremely limited development of reefs and coral communities along the western coastlines of the Americas
and West Africa may also be influenced by cold water
upwellings.
Another role of currents is in the transport of larvae
to areas of reef The establishment of corals in new areas
is dependent on the transport of coral larvae in ocean
Left, above: A smalt coral cay on the reef flat of an atoll, Salomon Atoll. Chagos Archipelago. Left, below. The Beqa
Barrier Reef in Fiji. Right: Fringing reefs, near Suva, Fiji.
waters, as shown by the statistics in Table 1.2. These and
other patterns are derived from a complex interaction of
historical and contemporary factors. For some groups, the
parallel with coral diversity patterns may reflect direct
ecological associations between them. However, for a
number of others, it may be the same external factors
which have actually driven the change. A number of these
factors are briefly laid out below.
The influence of temperature
To a large extent, both scleractinian corals and the reefs
they build are restricted to a latitudinal band between
30°N and 30°S. This general observation is entirely related
to the decreasing temperatures which generally follow
increasing latitude. Most reef corals cannot survive in
temperatures much below 16-18°C for even a few weeks.
In conditions of extreme cold, corals can die within a
matter of hours or days, while under slightly less extreme
conditions, their growth rates are reduced. There is some
evidence that overgrowth by algae rather than the direct
influence of cold water may restrict coral development m
some high latitude areas.
High temperatures are also inimical to coral growth.
Extreme high temperatures drive the phenomenon known
as "coral bleaching", during which the corals expel their
symbiotic algae (see Chapter 2). Aside from humaninduced climate change, it has been suggested that
occasional high temperatures associated with El Niiio
events may be at least a partial explanation for the highly
limited reef development which is observed, for example,
along the western shores of the Americas.
The role of currents
While temperature influences can be broadly equated with
latitude, ocean currents can disrupt these simple patterns.
In a few areas of the world, major warm currents flow all
year round from the tropics into higher latitudes. These
have allowed the development of reefs quite beyond their
normal limits. Notable are the Leeuwin Current in
Western Australia; the East Australian Current; the
Kuroshio Current in Japan; and the Gulf Stream warming
the isolated oceanic reefs of Bermuda. In a similar way,
cold waters prevent reef growth. Cold water upwellings
along the coastlines of northeastern Somalia and southern
Arabia are perhaps the clearest example, while the
extremely limited development of reefs and coral communities along the western coastlines of the Americas
and West Africa may also be influenced by cold water
upwellings.
Another role of currents is in the transport of larvae
to areas of reef The establishment of corals in new areas
is dependent on the transport of coral larvae in ocean
Left, above: A smalt coral cay on the reef flat of an atoll, Salomon Atoll. Chagos Archipelago. Left, below. The Beqa
Barrier Reef in Fiji. Right: Fringing reefs, near Suva, Fiji.