The Great Barrier Reef
24
the modern GBR benefits from a wider whole-ofsystem approach, grappling with the GBR in time and
space requires a broader conception of coral communities than just the clear water platform reefs where we
might prefer to go diving.
N WHAT CAN WE LEARN FROM
PALAEOECOLOGICAL RESPONSES IN
ANCIENT REEFS?
Like tropical marine communities throughout the
world, the corals, coral communities and coral reefs of
the GBR are fundamentally influenced by their response to climate change and associated environmental parameters, including magnitude and rates of sea
level change, CO 2 , temperature, and turbidity. There is
a growing recognition that the integration of palaeoecological and climate data on the GBR provides
essential insight into how natural communities are assembled and structured in the face of environmental
variability over extended periods of time. Given our
ability to discriminate among the various kinds of coral
and reef development on the GBR, we next consider
some examples of the ecological dynamics of coral reef
communities over long time frames.
Although less true for the GBR, many reef organisms
are sufficiently preserved in fossil sequences around the
world as to provide generic or even species level information on community structure, including corals, molluscs, echinoderms, coralline algae, and foraminifera.
We will discuss these examples to help illustrate what
the long term ecology of GBR reefs might have been.
In the Indo-Pacific, recent evolution of corals has
been rather slow, with less than 20% of new taxa
appearing in the past 2–3 My. In the Caribbean, only
two species have gone extinct in the past 125 ky As
such, palaeoecological patterns from Quaternary reefs
(past 1.8 to 2.6 My) can be investigated from what are
essentially modern faunas. For example, during the
last interglacial (128–118 ka), sea level was two to six
metres higher than present levels. This has left a fossilised remnant reef in a large number of locations
through the tropics (Fig. 3.2D), giving global insight
into the ecological nature of reefs in the recent geological past.
One of the best archives for understanding the ecological effects of sea level fluctuations on coral reefs is
contained in Pleistocene reef sequences from several tectonically active sites around the world, the most famous
of which is the Huon Peninsula in PNG, where nine such
reefs were developed between 125 ka and 30 ka (Fig. 3.2B).
This series of coral reef terraces, formed by the interaction between Quaternary sea level fluctuations and local
tectonic uplift, allows investigation of the assembly of
coral reefs during successive sea level rises. Here, ecological trends over millennial time scales point to high
levels of persistence in community structure, regardless
of the magnitudes of change in environmental variables.
In the Caribbean, similar coral community structure
was noted among four reef-building episodes ranging in
age from 104 ka to 220 ka on Barbados. Remarkably, the
high similarity in community composition derived from
surveys of common species was also characteristic of
separate surveys targeting rare taxa. These studies point
to persistence in coral community structure over successive high sea level stand reefs that grew optimally during
rising sea level, and are consistent with the rare glimpses
we have of the GBR that also show that recurrent associations of coral reef communities are the norm (Fig. 3.4A).
Current concern over the deteriorating condition of
coral reefs worldwide has focussed intense attention
upon the relationship between past ‘natural’ levels of
disturbance and community change versus modern
human-induced agents of decline. To understand the
impact of humans our only recourse is to study the fossil
record. The uplifted Holocene reef at the Huon Peninsula,
PNG, age-equivalent to the GBR, has been studied to
determine the frequency of disturbance in fossil sequences with little or no human impacts. Rates of mass
coral mortality were far lower (averaging one in 500
years) than are presently being experienced in living
reefs (multiple events per decade) (Fig. 3.4B). Recovery
from disturbance was swift and complete, and the history of communities provides predictive power for the
nature of their recovery. The stark contrast between living and fossil reefs provides novel insight to the abnormally high disturbance frequencies now occurring.
But what happens when sea level falls or stands still,
and how do reefs respond to habitat reduction caused
by lowered or lowering sea level? Some spectacular
24
the modern GBR benefits from a wider whole-ofsystem approach, grappling with the GBR in time and
space requires a broader conception of coral communities than just the clear water platform reefs where we
might prefer to go diving.
N WHAT CAN WE LEARN FROM
PALAEOECOLOGICAL RESPONSES IN
ANCIENT REEFS?
Like tropical marine communities throughout the
world, the corals, coral communities and coral reefs of
the GBR are fundamentally influenced by their response to climate change and associated environmental parameters, including magnitude and rates of sea
level change, CO 2 , temperature, and turbidity. There is
a growing recognition that the integration of palaeoecological and climate data on the GBR provides
essential insight into how natural communities are assembled and structured in the face of environmental
variability over extended periods of time. Given our
ability to discriminate among the various kinds of coral
and reef development on the GBR, we next consider
some examples of the ecological dynamics of coral reef
communities over long time frames.
Although less true for the GBR, many reef organisms
are sufficiently preserved in fossil sequences around the
world as to provide generic or even species level information on community structure, including corals, molluscs, echinoderms, coralline algae, and foraminifera.
We will discuss these examples to help illustrate what
the long term ecology of GBR reefs might have been.
In the Indo-Pacific, recent evolution of corals has
been rather slow, with less than 20% of new taxa
appearing in the past 2–3 My. In the Caribbean, only
two species have gone extinct in the past 125 ky As
such, palaeoecological patterns from Quaternary reefs
(past 1.8 to 2.6 My) can be investigated from what are
essentially modern faunas. For example, during the
last interglacial (128–118 ka), sea level was two to six
metres higher than present levels. This has left a fossilised remnant reef in a large number of locations
through the tropics (Fig. 3.2D), giving global insight
into the ecological nature of reefs in the recent geological past.
One of the best archives for understanding the ecological effects of sea level fluctuations on coral reefs is
contained in Pleistocene reef sequences from several tectonically active sites around the world, the most famous
of which is the Huon Peninsula in PNG, where nine such
reefs were developed between 125 ka and 30 ka (Fig. 3.2B).
This series of coral reef terraces, formed by the interaction between Quaternary sea level fluctuations and local
tectonic uplift, allows investigation of the assembly of
coral reefs during successive sea level rises. Here, ecological trends over millennial time scales point to high
levels of persistence in community structure, regardless
of the magnitudes of change in environmental variables.
In the Caribbean, similar coral community structure
was noted among four reef-building episodes ranging in
age from 104 ka to 220 ka on Barbados. Remarkably, the
high similarity in community composition derived from
surveys of common species was also characteristic of
separate surveys targeting rare taxa. These studies point
to persistence in coral community structure over successive high sea level stand reefs that grew optimally during
rising sea level, and are consistent with the rare glimpses
we have of the GBR that also show that recurrent associations of coral reef communities are the norm (Fig. 3.4A).
Current concern over the deteriorating condition of
coral reefs worldwide has focussed intense attention
upon the relationship between past ‘natural’ levels of
disturbance and community change versus modern
human-induced agents of decline. To understand the
impact of humans our only recourse is to study the fossil
record. The uplifted Holocene reef at the Huon Peninsula,
PNG, age-equivalent to the GBR, has been studied to
determine the frequency of disturbance in fossil sequences with little or no human impacts. Rates of mass
coral mortality were far lower (averaging one in 500
years) than are presently being experienced in living
reefs (multiple events per decade) (Fig. 3.4B). Recovery
from disturbance was swift and complete, and the history of communities provides predictive power for the
nature of their recovery. The stark contrast between living and fossil reefs provides novel insight to the abnormally high disturbance frequencies now occurring.
But what happens when sea level falls or stands still,
and how do reefs respond to habitat reduction caused
by lowered or lowering sea level? Some spectacular