Cross-references
Acanthaster planci
Corals: Environmental Controls on Growth
Earthquakes and Emergence or Submergence of Coral Reefs
Emerged Reefs
El Niño, La Niña, and ENSO
Fringing Reefs
Glacio-Hydro Isostasy
Pacific Coral Reefs: An Introduction
Postglacial Trangression
Volcanic Disturbances and Coral Reefs
MASS EXTINCTIONS, ANOXIC EVENTS AND OCEAN
ACIDIFICATION
John E. N. Veron
Townsville, QLD, Australia
Introduction
The five great mass extinction events that have greatly
influenced paths of evolution of life on Earth have
attracted a wide range of speculation about original causes
and ultimate effects. In this context, reefs are among
the most widely studied of marine communities, partly
because carbonate platforms are so enduring, but also
because the fossil record of corals is relatively well known
in terms of abundance and distribution. The marine tropics
in general and reef taxa have been particularly targeted in
mass extinctions. In each case, they have taken many millions of years to recover, intervals of time known as “reef
gaps.” Many authors have speculated on the causes of
mass extinctions and reef gaps, the outcome being
a wide array of hypotheses involving climatic upheavals
of both terrestrial and extraterrestrial origin. This article
reviews these proposals and examines them in the light
of the biology of extant corals and their Pleistocene
history.
Mass extinctions, corals, and reef gaps
Mass extinction events are characterized by fundamental
changes in plant and animal diversity as many high-level
taxonomic groups go extinct over the same geological
time interval. They are also characterized by very slow
recovery, led by the evolution of new species rather than
recolonization by survivors.
The five great mass extinction events occurred at widely
spaced intervals, each at or near the end of major divisions
in Earth history. Of these, extinctions at the Permian and
Cretaceous were so profound that they respectively mark
the end of the Palaeozoic and Mesozoic eras. However, present interest in mass extinctions is not so much in their geological timing, but in their cause, for they illustrate
outcomes of extreme environmental upheavals and are thus
worst-case scenarios of climate change.
Mass extinctions are usually perceived as dramatic catastrophes inflicted on an otherwise peaceful Earth, but this is
not the case. There were actually many minor or background extinction events at other times that left clear marks
in the fossil record – no fewer than 27, according to
a particularly detailed study (Raup and Sepkoski, 1986;
Sepkowski, 1995). Although not global, some background
extinctions were just as catastrophic as mass extinctions
for particular ecosystems or particular places, and many
had major impacts on coral reefs. Reefs, more than any
other major type of ecosystem, leave a geological record
that tracks such events (e.g., Sepkowski, 1995; Wood,
1999; Stanley, 2001). On an Earth history scale, this record
does not show a process of gradual evolutionary development or improvement, but rather a stop-start response to
a succession of environmental upheavals. Reefs are actually
uncommon throughout the Phanerozoic and appear to have
a “boom or bust” existence (Veron, 2008a and Kiessling,
2009). Environmental conditions that lead to reef proliferation are generally well understood; it is those which lead to
their demise that are addressed below.
The end Ordovician mass extinction
The first great mass extinction “event” took place at the
end of the Ordovician, a time when, according to the fossil
record, 26% of all families and 60% of all genera of both
terrestrial and marine life worldwide were exterminated
(Hallum and Wignall, 1997). This extinction occurred at
the end of a period of high mean global temperatures,
probably caused by global greenhouse stability, a condition that seems to have prevailed since the end of Cambrian 70 million years earlier. The extinction, however,
was not just one “event.” It took place over a very long
time span, perhaps several million years, and appears
to have been the cumulative outcome of a succession
of disasters. Possible causes that have been suggested
include major fluctuations in sea level, multiple shortlived polar glaciations, and changes in ocean temperature,
circulation, and chemistry. The extinction was particularly
disastrous and long lasting for reefs (Webby, 1992;
Copper, 2001). Extreme levels of carbon dioxide have
been recently implicated (Berner, 2006). Although some
individual rugose and tabulate coral taxa survived, living
reefs disappeared from the face of the Earth and did not
reappear for another 4–6 million years, long after the climate had returned to preextinction conditions. This is the
first true “reef gap,” meaning a gap in the geological
record of reefs.
The late Devonian mass extinction
The Late Silurian to Late Devonian period – 75 million
years or so of more or less global greenhouse conditions
with high temperatures set between ice ages – probably
included all-time peaks of Palaeozoic reef development
(Copper, 2002). Sea levels were mostly high, so that seas
flooded extensive areas of continents, forming epicontinental seas. However, despite the apparent proliferation
of reefs, their development was intermittent, with major
periods of worldwide expansion, especially during the
MASS EXTINCTIONS, ANOXIC EVENTS AND OCEAN ACIDIFICATION
671
Acanthaster planci
Corals: Environmental Controls on Growth
Earthquakes and Emergence or Submergence of Coral Reefs
Emerged Reefs
El Niño, La Niña, and ENSO
Fringing Reefs
Glacio-Hydro Isostasy
Pacific Coral Reefs: An Introduction
Postglacial Trangression
Volcanic Disturbances and Coral Reefs
MASS EXTINCTIONS, ANOXIC EVENTS AND OCEAN
ACIDIFICATION
John E. N. Veron
Townsville, QLD, Australia
Introduction
The five great mass extinction events that have greatly
influenced paths of evolution of life on Earth have
attracted a wide range of speculation about original causes
and ultimate effects. In this context, reefs are among
the most widely studied of marine communities, partly
because carbonate platforms are so enduring, but also
because the fossil record of corals is relatively well known
in terms of abundance and distribution. The marine tropics
in general and reef taxa have been particularly targeted in
mass extinctions. In each case, they have taken many millions of years to recover, intervals of time known as “reef
gaps.” Many authors have speculated on the causes of
mass extinctions and reef gaps, the outcome being
a wide array of hypotheses involving climatic upheavals
of both terrestrial and extraterrestrial origin. This article
reviews these proposals and examines them in the light
of the biology of extant corals and their Pleistocene
history.
Mass extinctions, corals, and reef gaps
Mass extinction events are characterized by fundamental
changes in plant and animal diversity as many high-level
taxonomic groups go extinct over the same geological
time interval. They are also characterized by very slow
recovery, led by the evolution of new species rather than
recolonization by survivors.
The five great mass extinction events occurred at widely
spaced intervals, each at or near the end of major divisions
in Earth history. Of these, extinctions at the Permian and
Cretaceous were so profound that they respectively mark
the end of the Palaeozoic and Mesozoic eras. However, present interest in mass extinctions is not so much in their geological timing, but in their cause, for they illustrate
outcomes of extreme environmental upheavals and are thus
worst-case scenarios of climate change.
Mass extinctions are usually perceived as dramatic catastrophes inflicted on an otherwise peaceful Earth, but this is
not the case. There were actually many minor or background extinction events at other times that left clear marks
in the fossil record – no fewer than 27, according to
a particularly detailed study (Raup and Sepkoski, 1986;
Sepkowski, 1995). Although not global, some background
extinctions were just as catastrophic as mass extinctions
for particular ecosystems or particular places, and many
had major impacts on coral reefs. Reefs, more than any
other major type of ecosystem, leave a geological record
that tracks such events (e.g., Sepkowski, 1995; Wood,
1999; Stanley, 2001). On an Earth history scale, this record
does not show a process of gradual evolutionary development or improvement, but rather a stop-start response to
a succession of environmental upheavals. Reefs are actually
uncommon throughout the Phanerozoic and appear to have
a “boom or bust” existence (Veron, 2008a and Kiessling,
2009). Environmental conditions that lead to reef proliferation are generally well understood; it is those which lead to
their demise that are addressed below.
The end Ordovician mass extinction
The first great mass extinction “event” took place at the
end of the Ordovician, a time when, according to the fossil
record, 26% of all families and 60% of all genera of both
terrestrial and marine life worldwide were exterminated
(Hallum and Wignall, 1997). This extinction occurred at
the end of a period of high mean global temperatures,
probably caused by global greenhouse stability, a condition that seems to have prevailed since the end of Cambrian 70 million years earlier. The extinction, however,
was not just one “event.” It took place over a very long
time span, perhaps several million years, and appears
to have been the cumulative outcome of a succession
of disasters. Possible causes that have been suggested
include major fluctuations in sea level, multiple shortlived polar glaciations, and changes in ocean temperature,
circulation, and chemistry. The extinction was particularly
disastrous and long lasting for reefs (Webby, 1992;
Copper, 2001). Extreme levels of carbon dioxide have
been recently implicated (Berner, 2006). Although some
individual rugose and tabulate coral taxa survived, living
reefs disappeared from the face of the Earth and did not
reappear for another 4–6 million years, long after the climate had returned to preextinction conditions. This is the
first true “reef gap,” meaning a gap in the geological
record of reefs.
The late Devonian mass extinction
The Late Silurian to Late Devonian period – 75 million
years or so of more or less global greenhouse conditions
with high temperatures set between ice ages – probably
included all-time peaks of Palaeozoic reef development
(Copper, 2002). Sea levels were mostly high, so that seas
flooded extensive areas of continents, forming epicontinental seas. However, despite the apparent proliferation
of reefs, their development was intermittent, with major
periods of worldwide expansion, especially during the
MASS EXTINCTIONS, ANOXIC EVENTS AND OCEAN ACIDIFICATION
671