Acropora recruits were visible several years before the
appearance of Isopora, following the 1998 bleaching
event (L. DeVantier, personal communications).
Genetics and phylogeny
Acropora has a large and complex genome and this has
been studied in detail for certain species and species
groups as well as in the context of genus-level phylogenies. Molecular (genetic) studies show corals to have
two main evolutionary lines, known currently as the
“Robust” and “Complex” clades. Acropora and other
members of the family Acroporidae fall within the Complex clade (Romano and Cairns, 2000; le Goff-Vitry
et al., 2004; Chen et al., 2002). Evolution of the mitochondrial genome of all Anthozoa is typically slower than that
of other animals, making it difficult, for example, to use
cytochrome b to study population genetics in these animals, but it is faster in Acropora than in confamilial genera
(Van Oppen et al., 1999). The tempo of evolutionary
change is faster in the nuclear and slower in the mitochondrial genomes for Acropora (and other corals studied),
making them more similar to plants than other animal
groups in this respect (Hellberg, 2006; Chen et al.,
2009). Genetic studies and laboratory cross-fertilization
experiments on Acropora from within species groups
(especially the A. aspera, A. cervicornis, and A. humilis
groups) have indicated that hybridization and introgression may play a significant role in maintaining variety
within populations and associations of Acropora species,
perhaps contributing to resilience in the face of adverse
conditions (Van Oppen et al., 2000; Wolstenholme et al.,
2003). These and many other genetic findings for
Acropora and other corals are contributing to a major revision of the characteristics and relationships within the
order Scleractinia. Because corals have a hard skeleton
and this remains after death, there is a superb fossil record
and long-known paleontological information is currently
being integrated with the molecular results to develop
a new overview of relationships and evolution.
Biogeography and evolution
The greatest living diversity of Acropora is seen in Indonesia, where 91 species have been recorded (Wallace,
2001) and similar numbers are present in the Philippines
and Papua New Guinea. The Indonesian diversity is
greatest within the region known as “Wallacea,” that is,
the region of islands between the Asian and Australian
continental shelves (Wallace, 2001). The Indonesian
Acropora diversity includes species with very extensive
Indo-Pacific ranges, others restricted to the central IndoPacific, and yet others which have either predominantly
Pacific Ocean or Indian Ocean distribution, with some
overlaps in Indonesia. (Wallace, 2001; Wallace et al.,
2001). In the Caribbean, only three living species occur.
Through post-Cretaceous time, Acropora has been present
in all the major reef-bearing parts of the world, including
the fossil deposits of the Middle East and Europe, fossil
and modern reefs of the Caribbean and the Indo-Pacific,
where the majority of the living species occur. It is known
in the fossil record from the Paleocene of Somalia
(approx. 60 million years ago) and was possibly present
before the end of the Cretaceous (Baron-Szarbo, 2006).
Nine of the twenty species groups are represented in the
mid-Eocene fossil record of England and France and this
is taken to indicate that the diversification of this genus
began well ahead of its later Indo-Pacific diversification
(Wallace, 2008). Several species of Acropora also await
description from the Oligocene to early Miocene of
Europe and Miocene-Pliocene of the Caribbean. The first
case of Acropora being abundant and dominant on a coral
reef is seen in the Oligocene of Greece (Schuster, 2003).
Summary
Acropora, the staghorn coral genus, has persisted for some
60 million years and now remains in living form in the
Caribbean and the Indo-Pacific, the two main reef-bearing
regions of the world. It is regarded as extremely successful
because it contains the greatest number of species of any
coral genus, and its species typically occur in great abundance. While it plays a major role in many aspects of reef
ecology, Acropora has been shown to be extremely vulnerable to major disturbances on reefs, and thus there is
concern about its persistence into the future, in the face
of changes due to bleaching, disease, and other factors
resulting from global climate change. The fossil record
tells us that this genus has persisted and diversified
through time, and genetic research is indicating that rare
species may have a resilience to local extinction because
of the potential for hybridization with other species.
Recent decadal changes in both the Caribbean and the
Pacific, however, show that Acropora can undergo local
extinction in certain circumstances. It is clear that the
future of this coral genus is intimately linked with the
future of the world’s coral reefs.
Acknowledgments
Dr. P.R. Muir of Museum of Tropical Queensland for preparing figures and reviewing text.
Bibliography
Aronson, R. B., and Precht, W. F., 1997. Stasis, biological disturbance, and community structure of a Holocene coral reef. Paleobiology, 23, 326–346.
Babcock, R. C., Bull, G. D., Harrison, P. L., Heyward, A. J., Oliver,
J. K., Wallace, C. C., and Willis, B. L., 1986. Synchronous
spawnings of 105 scleractinian coral species on the Great Barrier
Reef. Marine Biology, 90, 379–394.
Barnes, D. J., 1972. The structure and formation of growth-ridges in
scleractinian coral skeletons. Proceedings of the Royal Society of
London B, 182, 331–350.
Baron-Szarbo, R. C., 2006. Corals of the K/T- boundary:
scleractinian corals of the suborders Astrocoeniina, Faviina,
Rhipiogyrina and Amphiastraeina. Journal of Systematic
Palaeontology, 4, 1–108.
ACROPORA
7
appearance of Isopora, following the 1998 bleaching
event (L. DeVantier, personal communications).
Genetics and phylogeny
Acropora has a large and complex genome and this has
been studied in detail for certain species and species
groups as well as in the context of genus-level phylogenies. Molecular (genetic) studies show corals to have
two main evolutionary lines, known currently as the
“Robust” and “Complex” clades. Acropora and other
members of the family Acroporidae fall within the Complex clade (Romano and Cairns, 2000; le Goff-Vitry
et al., 2004; Chen et al., 2002). Evolution of the mitochondrial genome of all Anthozoa is typically slower than that
of other animals, making it difficult, for example, to use
cytochrome b to study population genetics in these animals, but it is faster in Acropora than in confamilial genera
(Van Oppen et al., 1999). The tempo of evolutionary
change is faster in the nuclear and slower in the mitochondrial genomes for Acropora (and other corals studied),
making them more similar to plants than other animal
groups in this respect (Hellberg, 2006; Chen et al.,
2009). Genetic studies and laboratory cross-fertilization
experiments on Acropora from within species groups
(especially the A. aspera, A. cervicornis, and A. humilis
groups) have indicated that hybridization and introgression may play a significant role in maintaining variety
within populations and associations of Acropora species,
perhaps contributing to resilience in the face of adverse
conditions (Van Oppen et al., 2000; Wolstenholme et al.,
2003). These and many other genetic findings for
Acropora and other corals are contributing to a major revision of the characteristics and relationships within the
order Scleractinia. Because corals have a hard skeleton
and this remains after death, there is a superb fossil record
and long-known paleontological information is currently
being integrated with the molecular results to develop
a new overview of relationships and evolution.
Biogeography and evolution
The greatest living diversity of Acropora is seen in Indonesia, where 91 species have been recorded (Wallace,
2001) and similar numbers are present in the Philippines
and Papua New Guinea. The Indonesian diversity is
greatest within the region known as “Wallacea,” that is,
the region of islands between the Asian and Australian
continental shelves (Wallace, 2001). The Indonesian
Acropora diversity includes species with very extensive
Indo-Pacific ranges, others restricted to the central IndoPacific, and yet others which have either predominantly
Pacific Ocean or Indian Ocean distribution, with some
overlaps in Indonesia. (Wallace, 2001; Wallace et al.,
2001). In the Caribbean, only three living species occur.
Through post-Cretaceous time, Acropora has been present
in all the major reef-bearing parts of the world, including
the fossil deposits of the Middle East and Europe, fossil
and modern reefs of the Caribbean and the Indo-Pacific,
where the majority of the living species occur. It is known
in the fossil record from the Paleocene of Somalia
(approx. 60 million years ago) and was possibly present
before the end of the Cretaceous (Baron-Szarbo, 2006).
Nine of the twenty species groups are represented in the
mid-Eocene fossil record of England and France and this
is taken to indicate that the diversification of this genus
began well ahead of its later Indo-Pacific diversification
(Wallace, 2008). Several species of Acropora also await
description from the Oligocene to early Miocene of
Europe and Miocene-Pliocene of the Caribbean. The first
case of Acropora being abundant and dominant on a coral
reef is seen in the Oligocene of Greece (Schuster, 2003).
Summary
Acropora, the staghorn coral genus, has persisted for some
60 million years and now remains in living form in the
Caribbean and the Indo-Pacific, the two main reef-bearing
regions of the world. It is regarded as extremely successful
because it contains the greatest number of species of any
coral genus, and its species typically occur in great abundance. While it plays a major role in many aspects of reef
ecology, Acropora has been shown to be extremely vulnerable to major disturbances on reefs, and thus there is
concern about its persistence into the future, in the face
of changes due to bleaching, disease, and other factors
resulting from global climate change. The fossil record
tells us that this genus has persisted and diversified
through time, and genetic research is indicating that rare
species may have a resilience to local extinction because
of the potential for hybridization with other species.
Recent decadal changes in both the Caribbean and the
Pacific, however, show that Acropora can undergo local
extinction in certain circumstances. It is clear that the
future of this coral genus is intimately linked with the
future of the world’s coral reefs.
Acknowledgments
Dr. P.R. Muir of Museum of Tropical Queensland for preparing figures and reviewing text.
Bibliography
Aronson, R. B., and Precht, W. F., 1997. Stasis, biological disturbance, and community structure of a Holocene coral reef. Paleobiology, 23, 326–346.
Babcock, R. C., Bull, G. D., Harrison, P. L., Heyward, A. J., Oliver,
J. K., Wallace, C. C., and Willis, B. L., 1986. Synchronous
spawnings of 105 scleractinian coral species on the Great Barrier
Reef. Marine Biology, 90, 379–394.
Barnes, D. J., 1972. The structure and formation of growth-ridges in
scleractinian coral skeletons. Proceedings of the Royal Society of
London B, 182, 331–350.
Baron-Szarbo, R. C., 2006. Corals of the K/T- boundary:
scleractinian corals of the suborders Astrocoeniina, Faviina,
Rhipiogyrina and Amphiastraeina. Journal of Systematic
Palaeontology, 4, 1–108.
ACROPORA
7