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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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Butterfly fish ‘may face extinction’

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Wildlife Extra, 29th February 2008

Scientists have warned that a beautiful black, white and yellow butterflyfish, much admired by eco-tourists, divers and aquarium keepers alike, may be at risk of extinction.

The case of the Chevroned Butterflyfish is a stark example of how human pressure on the world’s coral reefs is confronting certain species with ‘blind alleys’ from which they may be unable to escape, says Dr Morgan Pratchett of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.

 

Highly Specialized Feeding Habit
In a study published in the journal Behavioural Ecology and Sociobiology Dr Pratchett and Dr Michael Berumen of Woods Hole Oceanographic Institution (USA) warn that the highly specialized nature of the feeding habits of this particular butterflyfish – the distinctively patterned Chaetodon trifascialis – make it an extinction risk as the world’s coral reefs continue to degrade due to human over-exploitation, pollution and climate change.

‘The irony is that these butterflyfish are widespread around the world, and you’d have thought their chances of survival were pretty good,’ Dr Pratchett said today. But they only eat one sort of coral – Acropora hyacinthus – and when that runs out, the fish just disappear from the reef.’

Rather Starve Than Change Diet
The team found it hard to believe a fish would starve rather than eat a mixed diet, so they tested C. trifascialis in tank trials on a range of different corals. The fish grew well when its favourite coral was available – but when this was removed and other sorts of corals offered, it grew thin, failed to thrive and some died.

‘We call these kinds of fish obligate specialists. It means they have a very strong dietary preference for one sort of food, and when that is no longer available, they go into decline. We still don’t have a satisfactory scientific explanation for this, as it seems like rather a risky tactic in evolutionary terms – but it must confer some advantage provided enough of its preferred food is available,’ Dr Pratchett says.

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Shifting Baselines, Local Impacts, and Global Change on Coral Reefs – a note from Nancy Knowlton & Jeremy B. C. Jackson

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Healthy Reefs, Dying Reefs, and Corals in Bocas del Toro, Panama:(A) Example of a healthy reef with abundant living coral. (B) Example of a reef in which most coral has died and been replaced by macroalgae. (C) Bleached and healthy coral colonies; both are alive but the bleached colony has lost its symbiotic algae. (D) Coral suffering from disease and with encroaching macroalgae.

PLoS ONE, February 26th 2008

Nancy Knowlton & Jeremy B. C. Jackson

Imagine trying to understand the ecology of tropical rainforests by studying environmental changes and interactions among the surviving plants and animals on a vast cattle ranch in the center of a deforested Amazon, without any basic data on how the forest worked before it was cleared and burned. The soil would be baked dry or eroded away and the amount of rainfall would be greatly decreased. Most of the fantastic biodiversity would be gone. The trees would be replaced by grasses or soybeans, the major grazers would be leaf-cutter ants and cattle, and the major predators would be insects, rodents, and hawks. Ecologists could do experiments on the importance of cattle for the maintenance of plant species diversity, but the results would be meaningless for understanding the rainforest that used to be or how to restore it in the future.

Fortunately, ecologists began to carefully describe tropical forests more than a century ago, and vast areas of largely intact forests have persisted until today, so there are meaningful baselines for comparison. Networks of 50-hectare plots are monitored around the world [1], and decades of experiments have helped to elucidate ecological mechanisms in these relatively pristine forests [2]. But the situation is very different for the oceans, because degradation of entire ecosystems has been more pervasive than on land [3] and underwater observations began much more recently. Monitoring of benthic ecosystems is commonly limited to small intertidal quadrats, and there is nothing like the high-resolution global monitoring network for tropical forests for any ocean ecosystem.

This lack of a baseline for pristine marine ecosystems is particularly acute for coral reefs, the so-called rainforests of the sea, which are the most diverse marine ecosystems and among the most threatened [4–8]. Most of the world’s tropical coastal oceans are so heavily degraded locally that “pristine” reefs are essentially gone, even if one ignores changes associated with already rising temperatures and acidity [3]. Most modern (post-SCUBA) ecological studies have focused on reef ecosystems that are moderately to severely degraded, and we have a much better understanding of transitions between human-dominated and collapsed reefs than between human-dominated and quasi-pristine reefs. Even the classic studies of Caribbean reefs that began in the 1950s were based on reefs that had very high coral cover but were severely overfished, and the first systematic surveys of subtidal Australian reefs in the late 1960s began after a severe outbreak of the crown-of-thorns starfish Acanthaster planci had devastated coral populations along much of the Great Barrier Reef. We are thus left without a clear understanding of how reefs functioned in the absence of major human impacts.

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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)