The Great Barrier Reef
218
(3) Family Poritidae (‘golf ball’ corals, ‘bommie’
corals) (Fig. 20.6A–C)
Colonies in this family are massive, encrusting, plating
or branching. In all cases, corallite walls are formed by
upward growth of fine trabecular elements. This family
contains one of the most remarkable zooxanthellate
genera, Porites. Although species of Porites can exist in
branching and plating forms, it is the massive species
that provide examples of the longest-lived and largest
solid coral forms. Growth in these massive colonies is
in usually in increments of 1–2 centimetres per year,
with two growth seasons being recorded by a ‘dark’
and a ‘light’ (dense and less dense) band. By counting
and measuring these bands, it is possible to calculate
the age of the colony and witness the history of environmental conditions that the colony has encountered.
Colonies of over 700 years old have been identified and
these sometimes form the basis of the huge ‘bommies’
found within lagoons and just outside the reef slope on
reefs of the GBR. Not surprisingly, species of Porites
form the subject of numerous studies of coral growth,
vulnerability to environmental conditions, effects of
coastal runoff and many other research topics.
Some situations favour the development of Poritesdominated coral assemblages, for example, calm, shallow offshore shoals or fringing reefs. Goniopora may
also be present in these habitats. This genus is most
notable for its long-columned polyps that are extended
during the day. It is a popular aquarium subject and is
apparently tolerant of high turbidity and low-light situations. Another genus, Alveopora, looks superficially
like Goniastrea because its polyps are also extended
during the day, but genetic studies indicate it may
belong in the Acroporidae.
(4) Family Pocilloporidae (‘brown stem corals’)
(Fig. 20.6D–G)
This is a family of genera with relatively small colonies, a branching mode of growth, simple, small corallites with reduced walls, only two septal cycles and
always separated by coenosteum. All genera are
brooders, and in some species of Pocillopora, planulae
can be produced asexually by budding. Pocillopora is
regarded as a ‘weedy’ genus, its species recruiting
soon after catastrophic events and living short lives,
with relatively regular monthly release of larvae
throughout the year. Early observations of the breeding patterns of genera in this family led to the misconception that all corals release brooded larvae
throughout the year, making larvae available for settlement on the reef at all times. This misconception
influenced ecological thinking about reef corals until
the 1980s, when mass broadcast spawning in corals
was discovered (see Box 20.1). The best-known species
are Stylophora pistillata and Pocillopora damicornis,
which have been used for much published experimentation on the effects of water chemistry, light, temperature and other factors on corals.
(5) Family Fungiidae (‘mushroom corals’)
(Fig. 20.6H–K)
Most species in this family occur as individual polyps
that grow very large instead of multiplying, and that
remain free living (unattached to the reef) during adult
life. These corals contain zooxanthellae, are mostly
regarded as non reef-building, or ‘ahermatypic’,
because they generally do not contribute much to the
reef structure (though there are notable exceptions
when they and their dead predecessors occur in large
mounds of thousands of individuals). Sexual reproduction often involves gonochoric gamete development
(individuals of separate sexes), followed by simultaneous release of eggs or sperm by many individuals of
the same species. Polyps settle on the reef to form an
attached juvenile coral that may bud to form a ‘stack’ of
cloned individuals: as these grow, they break off the
stack and lie free on the reef floor. Generally found in
the subtidal parts of reefs, fungiids may occur in great
abundance and diversity.
(6) Family Mussidae (‘spiky brain corals’)
(Fig. 20.7A–C)
Genera in this family have massive or encrusting colonies, with pronounced teeth on the septa and corallite
walls formed by complex trabecular growth, which
leads to very sturdy corallites, including some of the
largest corallites to be seen in colonial corals. Polyp tissues are very fleshy and sometimes very colourful.
These corals contribute great bulk to the reef structure.
218
(3) Family Poritidae (‘golf ball’ corals, ‘bommie’
corals) (Fig. 20.6A–C)
Colonies in this family are massive, encrusting, plating
or branching. In all cases, corallite walls are formed by
upward growth of fine trabecular elements. This family
contains one of the most remarkable zooxanthellate
genera, Porites. Although species of Porites can exist in
branching and plating forms, it is the massive species
that provide examples of the longest-lived and largest
solid coral forms. Growth in these massive colonies is
in usually in increments of 1–2 centimetres per year,
with two growth seasons being recorded by a ‘dark’
and a ‘light’ (dense and less dense) band. By counting
and measuring these bands, it is possible to calculate
the age of the colony and witness the history of environmental conditions that the colony has encountered.
Colonies of over 700 years old have been identified and
these sometimes form the basis of the huge ‘bommies’
found within lagoons and just outside the reef slope on
reefs of the GBR. Not surprisingly, species of Porites
form the subject of numerous studies of coral growth,
vulnerability to environmental conditions, effects of
coastal runoff and many other research topics.
Some situations favour the development of Poritesdominated coral assemblages, for example, calm, shallow offshore shoals or fringing reefs. Goniopora may
also be present in these habitats. This genus is most
notable for its long-columned polyps that are extended
during the day. It is a popular aquarium subject and is
apparently tolerant of high turbidity and low-light situations. Another genus, Alveopora, looks superficially
like Goniastrea because its polyps are also extended
during the day, but genetic studies indicate it may
belong in the Acroporidae.
(4) Family Pocilloporidae (‘brown stem corals’)
(Fig. 20.6D–G)
This is a family of genera with relatively small colonies, a branching mode of growth, simple, small corallites with reduced walls, only two septal cycles and
always separated by coenosteum. All genera are
brooders, and in some species of Pocillopora, planulae
can be produced asexually by budding. Pocillopora is
regarded as a ‘weedy’ genus, its species recruiting
soon after catastrophic events and living short lives,
with relatively regular monthly release of larvae
throughout the year. Early observations of the breeding patterns of genera in this family led to the misconception that all corals release brooded larvae
throughout the year, making larvae available for settlement on the reef at all times. This misconception
influenced ecological thinking about reef corals until
the 1980s, when mass broadcast spawning in corals
was discovered (see Box 20.1). The best-known species
are Stylophora pistillata and Pocillopora damicornis,
which have been used for much published experimentation on the effects of water chemistry, light, temperature and other factors on corals.
(5) Family Fungiidae (‘mushroom corals’)
(Fig. 20.6H–K)
Most species in this family occur as individual polyps
that grow very large instead of multiplying, and that
remain free living (unattached to the reef) during adult
life. These corals contain zooxanthellae, are mostly
regarded as non reef-building, or ‘ahermatypic’,
because they generally do not contribute much to the
reef structure (though there are notable exceptions
when they and their dead predecessors occur in large
mounds of thousands of individuals). Sexual reproduction often involves gonochoric gamete development
(individuals of separate sexes), followed by simultaneous release of eggs or sperm by many individuals of
the same species. Polyps settle on the reef to form an
attached juvenile coral that may bud to form a ‘stack’ of
cloned individuals: as these grow, they break off the
stack and lie free on the reef floor. Generally found in
the subtidal parts of reefs, fungiids may occur in great
abundance and diversity.
(6) Family Mussidae (‘spiky brain corals’)
(Fig. 20.7A–C)
Genera in this family have massive or encrusting colonies, with pronounced teeth on the septa and corallite
walls formed by complex trabecular growth, which
leads to very sturdy corallites, including some of the
largest corallites to be seen in colonial corals. Polyp tissues are very fleshy and sometimes very colourful.
These corals contribute great bulk to the reef structure.