WORLD ATLAS OF CORAL REEFS
sediments, particularly in the shallowest waters. In some
places, including many reefs in the western Indo-Pacific.
these are the dominant benthic organisms in the shallower
parts of coral reefs and may play a more important role in
reef building than the corals themselves.
Brown algae (Phyaeophyta)
These are more familiar in temperate rocky shore areas,
where they often form the major plant communities. There
are no unicellular species and many form quite complex
"plants". Although not dominant on reefs, a number of
species are widespread, including Lobophora, Padina.
and Sargassum in the Indo-Pacific and Dictyola in the
Caribbean.
Green algae (Chlorophyta)
This is a large and diverse group, including unicellular
and complex forms. As with the red algae, some produce
secondary calcification. Among these, Halimeda is widespread and the calcified remains of its disc-shaped
segments are often a major component of reef sand.
Caulerpa is another common genus in both Caribbean and
Indo-Pacific reefs, formmg complex and mtricate plant
structures. There are some 75 species, the majority of
which are found in coral reef areas.
In addition to these main groups, there are several other
algal groups, such as the diatoms (Bacillariophyta) which,
although not important components of the benthos, form
a dominant part of the marine phytoplankton. Another
group, the dinoflagellates (Dinophyceae) are sometimes
considered alongside the algae, but here are considered
separately, below.
Higher plants
Two groups of higher plant are often discussed in
association with coral reefs, although in reality they
form distinctive habitat types which may, or may not.
be found in close proximity to reefs. In contrast to coral
reefs, the habitats associated with these species have low
species diversity.
Seagrasses
Seagrasses are actually a polyphyletic group of marine
angiosperms (flowering plants) which are broadly distributed from the tropics to the Arctic, although there is a
peak in their diversity in the tropics. All species belong
to the monocotyledon families Potomogetonaceae and
Hydrocharitaceae. Only one genus. Thatassodendron, is
able to grow on rocky substrates and is found in very
close association with corals, although many species are
frequently associated with the soft sediments of reef flat
and lagoon areas.
Mangroves
Mangroves are a similarly varied group, and are typically
defined as trees or shrubs which normally grow in, or
adjacent to, the intertidal zone and which have developed
special adaptations in order to survive in this environment.
Interpretations of this definition vary, and hence there
IS no fully agreed list of what does and does not constitute a mangrove. The association between mangroves
and coral reefs is somewhat opportunistic: although
they are sometimes observed growing on coral rock,
mangroves usually require soft sediments and sheltered
environments. In many areas the calm waters behind
fringing and barrier reef systems provide such areas. The
ability of mangrove communities to bind silts and muds
may reduce levels of siltation in offshore areas and enable
reefs to flourish. There is also a considerable movement of
fish species between the two habitats, but again this would
appear to be opportunistic rather than essential. Globally
the distribution of mangroves and reefs is quite distinct.
While both are largely restricted to the tropics and neartropics (with the exception of mangroves in southern
Australia and New Zealand], mangroves flourish in many
Left: Encrusting red algae can be a major structural component of tfie reef crest. Right: Seagrasses are a common
component of deeper reef flat and lagoon areas.
sediments, particularly in the shallowest waters. In some
places, including many reefs in the western Indo-Pacific.
these are the dominant benthic organisms in the shallower
parts of coral reefs and may play a more important role in
reef building than the corals themselves.
Brown algae (Phyaeophyta)
These are more familiar in temperate rocky shore areas,
where they often form the major plant communities. There
are no unicellular species and many form quite complex
"plants". Although not dominant on reefs, a number of
species are widespread, including Lobophora, Padina.
and Sargassum in the Indo-Pacific and Dictyola in the
Caribbean.
Green algae (Chlorophyta)
This is a large and diverse group, including unicellular
and complex forms. As with the red algae, some produce
secondary calcification. Among these, Halimeda is widespread and the calcified remains of its disc-shaped
segments are often a major component of reef sand.
Caulerpa is another common genus in both Caribbean and
Indo-Pacific reefs, formmg complex and mtricate plant
structures. There are some 75 species, the majority of
which are found in coral reef areas.
In addition to these main groups, there are several other
algal groups, such as the diatoms (Bacillariophyta) which,
although not important components of the benthos, form
a dominant part of the marine phytoplankton. Another
group, the dinoflagellates (Dinophyceae) are sometimes
considered alongside the algae, but here are considered
separately, below.
Higher plants
Two groups of higher plant are often discussed in
association with coral reefs, although in reality they
form distinctive habitat types which may, or may not.
be found in close proximity to reefs. In contrast to coral
reefs, the habitats associated with these species have low
species diversity.
Seagrasses
Seagrasses are actually a polyphyletic group of marine
angiosperms (flowering plants) which are broadly distributed from the tropics to the Arctic, although there is a
peak in their diversity in the tropics. All species belong
to the monocotyledon families Potomogetonaceae and
Hydrocharitaceae. Only one genus. Thatassodendron, is
able to grow on rocky substrates and is found in very
close association with corals, although many species are
frequently associated with the soft sediments of reef flat
and lagoon areas.
Mangroves
Mangroves are a similarly varied group, and are typically
defined as trees or shrubs which normally grow in, or
adjacent to, the intertidal zone and which have developed
special adaptations in order to survive in this environment.
Interpretations of this definition vary, and hence there
IS no fully agreed list of what does and does not constitute a mangrove. The association between mangroves
and coral reefs is somewhat opportunistic: although
they are sometimes observed growing on coral rock,
mangroves usually require soft sediments and sheltered
environments. In many areas the calm waters behind
fringing and barrier reef systems provide such areas. The
ability of mangrove communities to bind silts and muds
may reduce levels of siltation in offshore areas and enable
reefs to flourish. There is also a considerable movement of
fish species between the two habitats, but again this would
appear to be opportunistic rather than essential. Globally
the distribution of mangroves and reefs is quite distinct.
While both are largely restricted to the tropics and neartropics (with the exception of mangroves in southern
Australia and New Zealand], mangroves flourish in many
Left: Encrusting red algae can be a major structural component of tfie reef crest. Right: Seagrasses are a common
component of deeper reef flat and lagoon areas.