Monthly Archives: March 2008

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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Has the Great Barrier Reef got a future?

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Once I would have thought that a ridiculous question. Yet today, if we assemble all the best science we have, the answer can at best be “maybe”.

It may seem preposterous that the greatest coral reef in the world – the biggest structure made by life on Earth – could be seriously (I mean genuinely seriously) threatened by climate change. The question itself is probably already relegated in your mind to a ‘here-we-go-again’ catch-bag of greenie diatribe about the state of our planet. This view is understandable given that even a decade ago, there were many scientists who had not yet come to grips with the full implications of climate change.

Very likely you have a feeling that dire predictions about anything almost always turn out to be exaggerations. What you really think is: OK, where there’s smoke there’s fire, so there’s probably something in this to be worried about, somewhere. But, it won’t be as bad as those doom-sayers are predicting. When I started writing “A Reef in Time”, I knew that climate change was likely to have serious consequences for coral reefs, but even I was shocked to the core by what all the best science that existed was saying. In a long phase of personal anguish I turned to specialists in many different fields of science to find anything that might suggest a fault in my own conclusions. No luck. The bottom line remains: the GBR can indeed be utterly trashed in the lifetime of today’s children. That certainty is what motivates me to broadcast this message as clearly, as accurately and, yes, as loudly, as I can.

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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.

“Extinct seal tells of once-teeming Caribbean reefs”

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Paris (AFP), 19th March 2008

Several hundred years ago, the coral reefs of the Caribbean had up to six times more fish than they have today, according to a study published Wednesday.

The estimate is made by US scientists poring over the fate of the Caribbean monk seal, a fish-loving mammal driven to extinction in 1952.

Historical records from the 17th and 18th century show there were huge numbers of monk seals, distributed among 13 colonies across the Caribbean.

They were so plentiful that some ships’ maps of the West Indies even noted particularly dense locations of seals.

Alas for Monachus tropicalis, colonisation of the West Indies unleashed unbridled hunting, the bounty being seal oil that was used to grease machinery in sugar plantations.

Towards the end of the 19th century, the seals were reduced to a final redoubt of a few atolls — and their worst enemy became natural history museums and private collectors keen for monk seal skeletons.

In one disastrous episode, a 1911 expedition to Mexico by natural-history enthusiasts killed 200 seals, leaving just a handful alive, and driving the depleted population further towards extinction.

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“Humanity’s extra CO2 could brew a new kind of sea”

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a9391_1148.jpgTerrie Klinger is starting to wonder about the future of kelp sex. It’s a delicate business in the best of times, and the 21st century is putting marine life to the acid test.

Klinger, of the University of Washington in Seattle, studies the winged and bull kelps that stretch rubbery garlands up from the seafloor off the nearby Pacific coast. These kelp fronds do no luring, touching, fusing of cells or other sexy stuff. Fronds just break out in chocolate-colored patches.

The patches release spores that swim off to settle on a surface and start the next generation. The new little kelps don’t look as if they belong to the same species, or even the same family, as their parents. The little ones just grow into strings of cells, but these are about sex.

“Those of us who have spent far too long looking at this can tell the males from the females,” says Klinger. The subtly female-shaped filaments form eggs and release kelp pheromones to call in the male filaments’ sperm.

Sex filaments have kept kelp species going for millennia, but Klinger says she wants to know what’s happening now that carbon emissions are changing seawater chemistry. The intricate reproductive cycle of kelp is an example of a delicate system that can experience big effects from seemingly small changes in ocean chemistry.

This chemistry is already shifting, powered by the increased concentration of carbon dioxide in the atmosphere from human activity. Not all the carbon dioxide from burning fossil fuels stays in the air. The oceans have absorbed about half of the CO2 released from burning fossil fuels since the beginning of the industrial age, says Richard Feely of the National Oceanic and Atmospheric Administration in Seattle. The ocean takes in about 22 million tons of CO2 a day, he says.

The influx causes what scientists call ocean acidification. It’s a term of convenience. The ocean isn’t acid now, nor do Feely and other ocean chemists expect that seawater will become acid in the foreseeable future. However, the extra CO2 is driving the oceans closer to the acidic side of the pH scale. By the end of this century, Feely says, the upper 100 meters or so of ocean water will be more acidic than at any time during the past 20 million years.

Klinger is just one of the biologists trying to figure out what a shift in seawater chemistry will do to seaweed, corals, fish, and other marine life. The filaments of both bull and winged kelps grow noticeably slower in acidic seawater, she reported last week at the 2008 Ocean Sciences Meeting in Orlando, Fla.

Biologists are discussing what the chemistry change will do to marine creatures: It looks like bad news for calcium users and a new dawn for slimy rocks. It could begin an age of simplification for ocean ecosystems. Either way, there’s a rising consensus that, by changing the oceans’ chemistry and biology, burning fossil fuels is essentially making new oceans.

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“Fast-growing corals key to Caribbean reef”

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Reuters, 14th March 2008

Two dominant coral species have built a good chunk of the Caribbean reef, and their ability to grow quickly may help the region’s coral reefs keep pace with rising sea levels caused by global warming, researchers say.

The endangered staghorn and elkhorn corals grow about 10 times faster than any other in the Caribbean and reproduce in part by breaking into bits for easy ocean spread.

Ken Johnson, who led the study published in the journal Science, said researchers had found that the staghorn and elkhorn coral were not that important until about 1 million years ago, when half the Caribbean coral species went extinct. Today about 60 coral species remain.

Johnson said one reason they quickly became dominant was they may have been able to keep up with rapid sea level rise by growing quickly, Johnson said. And if sea levels rise as predicted in the coming centuries, they may have to reprise this role.

“These are the species that are going to help coral reefs keep up with sea level change,” Johnson, a paleontologist at the Natural History Museum in London, said in a telephone interview.

Coral reefs, delicate undersea structures resembling rocky gardens that are made by animals called coral polyps, are important nurseries and shelters for fish and other sea life. They are also considered valuable protection for coastlines from high seas, a critical source of food, important for tourism and a potential storehouse of medicines for cancer and other diseases.

But researchers say overfishing, climate change and human development are threatening reefs worldwide. Even the dominant staghorn and elkhorn species are considered threatened under the U.S. Endangered Species Act. In the Caribbean, an added concern is that the reefs are especially sensitive because they are dominated by just two species, Johnson said.

“If these two species die out and become extinct, the Caribbean is in trouble,” he said.

The researchers produced their conclusions by using fossils to compare changes in coral diversity and reef development in the Caribbean over the past 28 million years. They showed that the characteristics of a dominant species were more important than the simple number of species, a finding that can better direct conservation efforts, Johnson said.

Climate change affecting fish hearing

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ABC News, 9th March 2007

Marine scientists have found that once fish hatch they use sound to find a home on a coral reef.

But the scientists say warming sea temperatures are affecting the hearing of fish and making them lose their way home.

Dr Steve Simpson from the University of Edinburgh recorded sounds on a reef in Oman and played it to a group recently hatched fish in traps.

He says as coral reef fish move very little after they’ve settled on a reef, finding a good home is crucial to their survival.

“If you’re a centimetre long and you are trying to pick a home, a reef is a pretty dangerous place to arrive at,” Dr Simpson said.

“We’ve described it as having the wall of mouths waiting to receive you. So, you don’t want to get it wrong and have to visit several reefs.

“So, we think that in the same way as say when you are choosing a house, you’d go walking around local areas.

“This gives fish the ability to preview different reefs and make a decision based on those previews. So, they only actually have to take on one wall of mouths.”

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“Alarm bells as evidence of slowed coral growth on the GBR emerges”

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AIMS Media Release, 5th March 2008

Worrying signs that warmer seawater combined with a possible change in the ocean’s acid balance may be curtailing the growth of an important reef-building coral species have been documented by a research team from AIMS in Townsville.

The paper, published in the journal Global Change Biology*, points to a 21 per cent decline in the rate at which Porites corals in two regions of the northern Great Barrier Reef (GBR) have added to their calcium carbonate skeletons over the past 16 years.

The AIMS research team analysed a total of 38 Porites colonies from the two regions. Porites are a common massive coral with a striking spherical appearance. They are long-lived and distributed widely around the Indian and Pacific oceans.

The researchers speculate that their results may be an early signal that the corals, as well as being subjected to warmer water, are being affected by a phenomenon known as ocean acidification. This is a predicted consequence of climate change, in which large quantities of carbon dioxide from the atmosphere dissolve in the oceans, causing their alkaline/acid balance (their “pH”) to shift towards acidic.

AIMS climate change team leader, Dr Janice Lough, a co-author of the paper, said that much more needs to be done to understand all the implications of the increase in carbon dioxide entering the oceans and to put these preliminary coral growth data into context.

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