Tag Archives: Great Barrier Reef

Study: Coral reefs like ‘junk food’

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United Press International, 28th March 2008

Townsville, Australia — Australian scientists have discovered coral reefs have an addiction to “junk food” and order symbiotic algae to produce it. James Cook University researchers said the symbiosis between coral, a primitive animal, and zooxanthellae — tiny one-celled plants — has not only built the largest living organism on the planet, the Great Barrier Reef, but also underpins the economies of many tropical nations.

The issue of whether the partnership is robust enough to withstand climate change is driving a worldwide scientific effort to decipher how corals and their symbiotic algae communicate, said JCU Professor David Yellowlees.

“It’s an incredibly intricate relationship in which the corals feed the algae and try to control their diet, and the algae in turn use sunlight to produce ‘junk food’ — carbohydrates and fats — for the corals to consume,” said Yellowlees. “Where it all breaks down is when heated water lingers over the reef and the corals expel the algae and then begin to slowly starve to death.

“This is the bleaching phenomenon Australians are by now so familiar with, and which is such a feature of global warming.”

Coral reef fish act as “lawnmowers” in the fight against climate change

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BBC News, 20th March

A healthy fish population could be the key to ensuring coral reefs survive the impacts of climate change, pollution, overfishing and other threats. Australian scientists found that some fish act as “lawnmowers”, keeping coral free of kelp and unwanted algae. At a briefing to parliamentarians in Canberra, they said protected areas were rebuilding fish populations in some parts of the Great Barrier Reef.

Warming seas are likely to affect the reef severely within a few decades. Pollution is also a growing problem, particularly fertilisers that wash from agricultural land into water around the reef, stimulating the growth of plants that stifle the coral. The assembled experts told parliamentarians that fish able to graze on invading plants played a vital role in the health of reef ecosystems.
“The Great Barrier Reef is still a resilient system… and herbivorous fish play a critical role in that regenerative capacity, by keeping the dead coral space free of algae, so that new juvenile coral can re-establish themselves,” said Professor Terry Hughes from James Cook University in Townsville. His research group has conducted experiments which involved building cages to keep fish away from sections of reef. They found that three times as much new coral developed in areas where the fish were present as in the caged portions.

Parrotfish in particular use their serrated jaws to scrape off incipient algae and plants. More recently, his team has also identified the rabbit fish – a brown, bland-looking species – as a potentially important harvester of seaweed. “So managing fisheries can help to maintain the reef’s resilience to future climate change,” he said. In recent years, Marine Protected Areas have been set up along the Great Barrier Reef in order to provide sanctuaries where fish and other marine creatures can grow and develop.

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“Corals kick out housemates that can’t stand the heat”

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New Scientist, 19th March 2008

When the going gets hot, corals can kick out heat-sensitive strains of symbiotic algae and take on a type that can withstand higher temperatures. This could mean certain reefs will be less susceptible to global warming than had been thought.

Like most other hard coral species, Acropora millepora, which is common in the Indo-Pacific region, relies primarily on microscopic algae for its nutrient supply. During sustained periods of high temperatures, heat stress causes the algae – which live within the coral – to pump out oxygen free radicals, which damage coral tissue. The coral is then forced to eject the algae – a phenomenon known as bleaching. It’s a lose-lose situation: the algae loses its home, and the coral its food supply. In some cases, it can lead to the coral starving to death.

Alison Jones of the Australian Institute of Marine Science, Townsville, and colleagues studied A. millepora living off Miall Island, part of the Keppel Island group in the southern inshore Great Barrier Reef, before and after a mass bleaching event in early 2006.

Heatwave effect

During this event, sea temperatures around Miall reef hit 30.2 °C for 30 days. This compares with an average for the season of 27.1 °C. Corals in this region start to show signs of heat stress when sea temperatures stay above 28.5 °C for more than 25 days, or above 29.5 deg C for longer than five days.

When the team sampled the coral colonies in 2003, they found that 93.5 % harboured mostly type C2 algae, which is relatively heat-sensitive. The remainder was formed of type D algae, which is heat-tolerant. After sweltering in the heat of 2006, 37 % of these colonies had died. By contrast, only 8 % of the colonies that had harboured mostly type D had died.

In follow-up work three months after the bleaching event, the team also found that nearly three-quarters of the colonies that had survived and that had originally harboured mostly C2 had switched to contain mostly type D – making them less susceptible to a bleaching event in future. These surviving colonies had initially had low background levels of D.

“This is great news,” says team member Ken Berkelmans. “It seems coral communities are probably far more adaptable to changing conditions than we’ve previously given them credit for.”

Short-lived adaptation

However, these findings so far relate to only one species in one location. And six months after the mass bleaching, the colonies did show some drift back towards C2, which allows them to grow faster than D.

Ove Hoegh-Guldberg, a leading coral biologist at the University of Queensland, Brisbane, says the findings are very interesting, in that they demonstrate a way in which corals can acclimatise to warmer temperatures – to an extent. However, he is cautious about what the results might mean in the long run, as type D provides the coral with only about an extra 1 to 1.5 °C of heat tolerance.

“After changing to D, corals don’t really have any other options – and the benefits of D will eventually be overwhelmed by climate warming,” he says.

More torrential rainfall in the Great Barrier Reef catchment: La Nina coming to an end?

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After the flooding in late January in the Fitzroy catchment, and the downpour in Mackay causing rising levels in the Pioneer river earlier this month, the turbulent Queensland weather has caused more phenomenal localised rainfall in Rockhampton this morning, with over 200mm of rain falling in less than 2 hours. As residents in Rockhampton begin the cleanup process, the Chief executive officer of the Fitzroy Basin Association (Suzie Christensen) discussed management principals and how to reduce the impact of the recent flooding in the catchment on the inshore reefs of the Great Barrier Reef.

“The Fitzroy Basin is the largest river system draining to the east coast of Australia, with 20,850 kilometres of waterways all leading to the reef lagoon.

“The effect of this flood would have been worse if landholders weren’t already taking steps to reduce impact on the land by retaining ground cover and using best practice farming techniques.”

“In particular where land practices had allowed the ground to be disturbed such as some mining on floodplains and some areas cleared for cropping and grazing.”

Ms Christensen said the flood water plume into the Great Barrier Reef lagoon would have consequences for the reef ecosystem.

“The flood waters are flushing sediment, fertilisers, pesticides, herbicides and other run-off several kilometres out onto the reef.

“The delicate balance of the reef ecosystem is upset by changes in water quality, and the thick cloud of sediment will also block sunlight and prevent coral from photosynthesizing.” (Link)

Further north in Mackay the Mayor of Mackay is quoted as saying that last week’s flooding could be classified as a “one in 200 year event“. Over 625mm of rain fell in 6 hours on February 15th, averaging 132mm per hours (double the total of the classification of a one in 100 year event), peaking at 184mm in a one hour period – quite an event! After such a substantial wet season, the director of meteorology at the Australian Bureau of Meteorology, Dr Geoff Love, stated that the La Nina event identified last November is “probably reaching its peak“. However, according to the World Meteorological Organization, the La Niña period is expected to last until June or July this year, and could last longer.

  • La Niña conditions have become slightly stronger in the last three months
  • Sea surface temperatures are about three to four degrees colder than average over the central and eastern equatorial Pacific Ocean
  • La Niña already has influenced climate patterns in many parts of the globe.
  • La Niña is the meteorological opposite of the better-known El Niño
  • La Niña. Central and eastern Pacific Ocean areas are generally cool, while those in the west remain warmer. This is associated with the frequency of heavy rainfall on the western side of the Pacific Rim.
  • El Niño. The El Niño phenomenon is linked with warmer temperatures in the central and eastern Pacific areas and can lead to drier conditions
  • The El Niño/La Niña cycle historically happens every four to seven years and is strongly linked to major world climate fluctuations:
  • Typically, La Niña will follow an El Niño event and last up to 12 months.
  • Exceptionally, it lasted for two years from early 1998 to 2000. (Link)

Are the impacts of climate change on coral reefs exaggerated? Questions and Answers (Part 1)

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For a long time the New Scientist has waged an ongoing battle with the climate change “skeptics”, and have produced some thorough articles such as “Climate change: a guide for the perplexed“, a round-up of the 26 most common climate myths and misconceptions. Time and time again I see people use similar myths and misconceptions regarding corals and coral reefs that are used as an argument as to why global warming is clearly a hoax, how warm water is good for corals (and the list goes on). In response to recent debates, below is the first part of a series called “Are the impacts of climate change on coral reefs exaggerated? Questions and Answers” in which I hope to address these misconceptions following the scientific evidence. Over the coming weeks I will aim to add more in the series: please feel free to add or ask any further questions in the comments below or email me at climateshifts @ gmail.com


1. “Warm water is good for corals”

Corals are locally adapted to the water temperature that they live in. This has taken many hundreds if not thousands of years to occur. It does not happen over decades, which would be the requirement if corals were to tolerate and survive the very rapid changes in sea temperature that we are currently facing.

The statements that “corals calcify faster in warmer waters” and “hotspots of coral diversity are found in warm waters close to the equator” are indeed true, but these conditions are only good for those corals that have adapted to these warmer conditions. For example, if you take corals from the southern end of the Great Barrier Reef and put them at the northern end of the Great Barrier Reef, these corals will suffer from being exposed to warmer than normal conditions and will die.

Although corals thrive within the upper limits of their thermal tolerance (within 1-2ºC), coral bleaching occurs when this tolerance is exceeded, resulting in loss of photosynthetic function, expulsion of symbiotic algae, and ultimately death of the coral. Clearly warm water is beneficial to those corals that are adapted to these warmer temperatures, although exceeding these thresholds results in mortality – a precarious balance.

With respect to the statement “corals in Moreton Bay are regularly stressed as the water is too cold” – it is well-known that corals in Moreton Bay (and other high latitude regions) where conditions that drop below 18°C in the winter lead to coral death. Just like they are sensitive to being too hot, they are also sensitive to becoming too cold. This is called the physiological range or tolerance of species. Conditions at places like Moreton Bay are marginal and therefore an outlier in global coral reefs and are restricted by their latitudes by cold winters.

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Flood waters on the Great Barrier Reef – a report from the Keppels

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On the topic of Great Barrier Reef flood waters posted last week, a rapid response team from my lab, headed by Dr Guillermo Diaz-Pullido and backed by the remote sensing capabilities of Dr Scarla Weeks was busy conducting coral and algal surveys in the Keppels region to determine baselines of coral health before the flood waters hit the reef. Dr Diaz-Pullido and two volunteers (Pim Bongaerts and Norbert Englebert) joined researchers from JCU to determine levels of coral and algae at reefs across the region. Flying out from Rockhampton over the ever rising flood waters confirmed the MODIS satellite images (see bottom left), and shows the level of water damage to the region (see centre): the waters were clearly heading outwards of the reef forming a freshwater lens (see bottom right picture).

Satellite image showing the Fitzroy river (Jan 21st 2008) View of the Fitzroy River in full flood (22nd Jan 2008) Flood plume extending out to the inshore reefs (22nd Jan 2008)

 

As a bit of background to this region: the Fitzroy catchment at nearly 150,000km2 is the largest of the Great Barier Reef, and is dominated by agriculture (grazing, irrigated cotton and horticulture) and by mining (coal production of 100 million tonnes/year, magnesite and nickel), and significant flooding events have been recorded in 1918, 1954, 1978, 1983, 1988 and 1991 (see below from the Bureau of Meterology). The ABC News site has some astounding images from the 2008 flood here.

 

Following the high levels of rainfall in January this year, many have predicted significant flooding and impacts to the inshore coral reefs of the Keppel region. Such disturbances are far from unusual in the Keppels – in 1991, over 85% of coral in shallow reefs died following severe flood events, and again on November 2006, significant mortality occured within 8 hours on the reef flats in the Keppels due to a lethal combination of high rainfall and low tides.

The team surveyed shallow and deep reefs of five islands using belt transects, including more than 300 1×1 m photo quadrats. At the time of the surveys, the freshwater plume from the Fitzroy River had already reached the leeward side of some islands, although at the time of surveying Dr Diaz-Pullido reported no visible impacts on the coral reef benthic community. Benthic macroalgae (seaweeds) usually colonise weakened and dead corals, and during the last coral beaching event in 2006, seaweeds experienced an unprecedented macroalgal bloom. Despite the severity of these disturbances and algal blooms, many coral reefs of the area have recovered and currently flourish (see images below)

 

Dr Guillermo Diaz Pullido surveying coral and algal cover prior to the flooding Research assistants Pim Bongaerts and Norbert Englebert collect algal samples Healthy inshore reefs at the Keppels with high coral cover (Acropora sp.

 

The impacts on the reef communities will depend on the residence time of the freshwater plume on the area, the nature and quantity of the sediments and contaminant associated. The team are closely monitoring the oceanographic and meteorological patterns, and depending on the developments of the plume, the research team will head back to the Keppel Islands in the coming weeks. The offshore surface flow in the region is strongly influenced by wind direction, whilst surface flow is primarily offshore (cross-shelf) limited in offshore extent by the frontal boundary created by inflow of oceanic waters due to eddy dynamics further south. Therefore, the Fitzroy outflow will be deflected to the left due to geostrophy (due to rotation of the Earth ) moving along this front.

Coral reefs bursting to go

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Courier Mail, November 22nd

HERE is a chance for you to experience one of the planet’s most spellbinding natural spectacles. Within a few days, in the reefs around the Keppels, off Rockhampton and in the Capricorn Cays of the southern Great Barrier Reef, the annual spawning of coral is expected to take place.

After the bleaching of the corals in January and February in 2006, last summer’s spawning effort was half-hearted. “This year. they’re bursting to go,” said Central Queensland University coral ecologist Alison Jones. “If people can get to a reef and in the water between the 24th (tomorrow) and the 28th, about 7pm-7.30pm, they’ll have a good chance of seeing it happen.”

In a synchronised exercise, corals liberate millions of eggs on still nights, after a full moon, when the tides are not so strong, the water temperature is right, and there’s less chance of the eggs being swept away before fertilisation.

As a prelude to the spawning, reef life, little fish and shrimps become wildly agitated. Then, small pink balls can be seen bulging from the polyp mouths of the corals.

“They glow pink,” Jones explained. “Everything around the reef gets very excited and you know it will happen within half an hour.” (Read More)

UQ Climate Change lab in the news

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One of the students in my lab, Josh Meisel (a Fulbright scholar from Stanford University) was interviewed recently by the Brisbane newspaper The Courier Mail about the recent rebuilding following the devastating fire at Heron Island research station earlier this year (see photographs). Construction is well underway on the new aquaria, research buildings and staff accomodation – read below for more details (good work Josh & Dorothea!)

 

ABC Scienceshow on Cryptochromes – The biggest sex event on earth

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I was interviewed recently by Robyn Williams for ABC’s “Science show” on the moonlight mass spawning of corals on the GBR I posted here earlier this month (“Keylight found to moonlight romance“). Click below to listen to the interview, read the transcript here or download the podcast.

 

[audio:https://climateshifts.org/scienceshow.mp3]

“There are 400 species of corals and hundreds of invertebrates on the Great Barrier Reef. Many spawn in mass over a couple of nights after the full moon in October or November. So how do they all know to do it together? It seems that corals can detect moonlight. Ove Hoegh-Guldberg explains how a class of proteins has been discovered which tune circadian rhythms. They are produced by a particular gene. So despite the faintness of moonlight, organisms can detect it and time their spawning to maximise the chance of reproduction.

When the spawning happens, the sea is clouded with eggs and sperm. Mass spawning is a strategy to lessen the impact of predators. It may be the biggest sex event on earth. Ove Hoegh-Guldberg speculates on the origin of this mechanism.”