Biodiversity
and
ecology
Climate change
Climate history
Climate
monitoring
Coral bleaching
Coral resilience
Marine Blueprint
Ecosystem health
Marine microbes
Monitoring
Sustainable use
Water quality
|
You are at -
Home |
Research |
Climate change and
impact
________________________________________________________________________
Marine Blueprint
Climate change and the fate of the Great Barrier Reef
The Great Barrier Reef (GBR) faces a greater trial of its
resilience and ability to survive in the next 100 years than it
has in the past 10,000, mostly because of global climate change.
This fact has caused some scientists to predict its loss or such
a radical change in its community structure that it will look
nothing like the reef we know today.
The costs to Australias economy and reputation of losing
all or a significant part of one of the Earths greatest
natural wonders make this an issue of pressing national urgency
and a major research effort at the AIMS.
That corals can become extinct we know from fossil evidence of
the Great Death, 250 million years ago, when 96 per
cent of all corals died out.
The truth is we do not know how resilient todays Reef is,
its chances of surviving with its species and ecosystems
relatively intact, or exactly what must be done to give it its
best chance. And while corals are remarkably tough and versatile
organisms, the question of whether they can adapt fast enough to
cope with the speed of climate change is unanswered.
AIMS and its sister scientific institutions are working hard to
find out.
The main issues of global climate change affecting coral reefs
are:
- Heat stress caused by rising sea temperatures which
trigger large-scale bleaching, in which the corals lose
their symbiotic algae. Even if they survive the initial
overheating, they may still experience a lingering death
from starvation or as their tissues are damaged by
chemical changes. In 1998 a severe event killed 16 per
cent of the worlds corals and in 2002 an event in
our region bleached half of the GBR, although most did
recover.
- Ocean acidification caused by CO2 emissions from human
activities dissolving into the oceans. Over time, this
could prevent corals and other organisms from forming
their chalky skeletons. Recent AIMS research has shown
some worrying evidence of a
decline in coral growth on
the GBR and
to a possible effect on
fish ear bone growth.
- An increase in frequency and intensity of extreme weather
events such as tropical cyclones and storm surges,
causing local destruction of reefs
- Food chain effects, in which coral loss leads to loss of
associated fauna including fish, birds, turtles and
mammals (all the many organisms that rely on the reef
structure created by corals for food and habitat) as well
as impacting on fishing catches
- Changes in ocean currents delivering food, larvae and
warm or cool water to reef communities
- Changes in El Niño/La Niña climate patterns affecting
the weather of the Reef.
- Changes in the volume, frequency and timing of floods of
fresh water off the land onto the reef, affecting
salinity, sediment levels and coral health
- Increasing microbial infections of coral, thought to be
due to the stress it is already undergoing from other
causes
- Phase shifts in which damaged reefs fail to
recover quickly and are replaced by weedy growth,
changing the whole ecosystem
- Loss of fish populations which help maintain the health
of the reef
- The interplay of all these effects with declining water
quality and pollution due to human activities, mainly on
land
- An increase in coral destruction by predators such as
Crown of Thorns Starfish, now also thought to be
triggered by nutrients from human activity.
Rising sea levels are unlikely to have a direct impact on corals,
but could cause increased erosion on land leading to poorer water
quality on coasts and loss of habitat for nesting turtles and
seabirds on coral sand cays.
Even if CO2 emissions are reduced now, it is likely to take
several centuries to reverse climate change. The issue is what
can be done in the short term to ensure the reefs survival
and minimise the main impacts. This is a central focus of AIMS
research, not only for the GBR but for all coral systems in
Australias northern tropical waters that make up over a
third of our sovereign territory.
The heat is on
During most summers, corals live in water that is only than 1-2oC
below the temperature at which bleaching occurs. A 2oC increase
kills the coral. Observations indicate that the waters of the GBR
are today 0.4oC warmer, on average, than they were 100 years ago,
but that is only part of the story. It is how long the warm water
lingers over areas of the Reef that decrees how much coral
bleaches or dies. Bleaching also varies with coral species (e.g.
branching corals are more susceptible that massive corals, which
will result in a change in community structure) and in space.
Some reefs and parts of reef do not warm as much as others due to
strong water movements that prevent the water column warming
under bleaching weather conditions. These sites where
the bleaching risk is lower need to be mapped and given increased
protection as they are likely to provide areas of refuge for
affected species as global warming continues.
A 1-3oC increase in tropical sea temperatures which the
International Panel on Climate Change (IPCC) regards as likely by
the end of this century is estimated to affect 80-100 per
cent of the Reefs corals, depending on where the water
lingers and for how long.
A huge unknown is whether corals can adapt or can employ
defensive strategies that enabling them to withstand this rapidly
changing ocean climate. AIMS research suggests that some corals
have the ability to change the main symbiotic algae inhabiting
their tissues to kinds that tolerate warmer water, and that these
corals will endure ocean temperatures 1-1.5oC higher. However
even this scenario implies loss of corals that lack this ability
and a substantial reduction in biodiversity on the Reef.
Furthermore, the change to more heat tolerant algae comes at a
cost of reduced carbon fixation, growth rate and reduced
reproductive output, possibly affecting their ability to compete
for space and maintain the balance their natural environment.
Whatever the strategy, corals will have to increase their
temperature tolerance by 0.1 to 1oC every decade to keep pace
with global warming, a big ecological ask.
Bleached corals, even if they recover, maybe weaker and more
susceptible to impacts such as tropical cyclones, coral diseases
and nutrients, chemicals or pesticides released by human activity
on land. This, however, is an area where the science gives
confidence that there is much we can do to protect the Reef.
These management actions include developing marine protected
areas, reducing erosion and contaminated runoff from the land to
improve water quality, protecting marine nursery systems like
mangroves and seagrass meadows, reducing fishing pressure to
preserve the balance of life on the Reef, identifying and
protecting coral communities that are naturally resilient to
bleaching (and can act as seed stock to help nearby reefs
recover) and encouraging sensitive coastal development.
AIMS is keeping a keen eye on developments along the Reef through
satellites and one of the worlds most sophisticated
networks of sensor stations which measure information about
weather, water movement, salinity and sea temperatures, most in
real time. This is part of a national and global ocean observing
system and allows scientists to track changes in the physical
environment of the reef and link these to biological responses.
The Acid Bath
The worlds oceans are gradually becoming more acid, as CO2
released into the atmosphere by human activity dissolves into
them. This has profound implications for the marine food chain,
for our food supply from the sea and, indeed, for all life on
Earth.
The oceans are naturally alkaline, and many of the plankton and
corals in them rely on this to form their chalky skeletons. These
make up more than a third of all sea life. The pH of the oceans
has already fallen by 0.1 to 8.2. At the current rate at which
humans are releasing CO2, it will drop to 7.7-7.8 by
the latter part of this century.
Research shows that at pH 7.9, corals and other chalky animals
cease to form their skeletons. Whether they then simply die out,
leaving a huge hole in the planetary food web, evolve to suit the
new circumstances or are replaced with other organisms is not yet
clear, and needs much research to resolve.
Research is the way forward
To prevent the worst-case scenarios we have to drastically and
rapidly reduce greenhouse gas emissions and, at the same time,
respond positively to unavoidable changes. All is not lost: there
are things that can be done and opportunities that will present
themselves with further research. Biologists know that the most
extreme circumstances force living organisms, including humans,
to evolve, innovate and adapt more rapidly.
By being at the forefront in understanding the impact of climate
change on the oceans and their life which underpins all
life on the planet AIMS is helping Australia to position
itself in a strategic leadership role in how humanity meets the
challenge, and what we can do about it.
The expertise, technology and services in how best to manage and
reduce the impact of climate change on marine ecosystems could
become a major 21st century export, just as farming, mining and
medical technology were in the 20th century.
In any crisis there is opportunity, and the opportunity presented
by climate change is to be first in understanding what is going
on in the oceans which make up 70 per cent of our planet and
drive its systems, whether or not it can be managed and how we
can best adapt to changes. AIMS is recognised as a world leader
in this field.
Learning how to safeguard our precious ecosystems, even in the
face of such vast and rapid changes, will give us ways to secure
our own future.
For further information, please contact:
Dr Janice Lough
Team Leader, Climate Change
07-4753 4248
j.lough@aims.gov.au
March 11, 2008
|
|