Tag Archives: Coral Reefs

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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Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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The “Status of Caribbean coral reefs after bleaching and hurricanes in 2005” is an excellent account of the impact of mass bleaching and hurricanes that hit the Caribbean in 2005. As you will remember, sea temperatures rose sharply in this region in May 2005, intensifying until October by which time hotspots covered most countries in the eastern Caribbean.  This occurred during the hottest year on record for the northern hemisphere at that time, and resulted in a massive die off of corals.

As pointed out by the editors, Clive Wilkinson and David Souter, the 2005 event provided an important opportunity to study the impact of extreme thermal stress on coral reefs.  Via network of hundreds of scientists that were linked by the Internet and backed up by sophisticated monitoring tools, key information and insights would gained into the relationship between thermal stress, bleaching and coral mortality.

Overall, coral reefs in eastern Caribbean were severely damaged by anyone’s estimate in 2005.  What is perhaps most alarming is that the mortality ranged up to 50% in places like the US Virgin Islands and the Greater and Lesser Antilles.  This came on top off a rapid deterioration of reefs that has been occurring over the past few decades.  The coral cover of most (if not all) coral reefs in this region have been sliding rapidly downwards.

This is a useful collection of papers which I recommend that you read (link).  My good friend Billy Causey, who has a long and proud history of fighting for the protection of Florida’s coral reefs, provides a very useful account of the history of bleaching in his region. There is also some useful information as well on the hurricane story, including on what drives their intensity and how they impacted reefs in 2005.

Hammerhead in need of protection

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BBC News, 18th February 2008

Over-fishing and demand for shark fins, an expensive delicacy, have pushed one of the world’s iconic animals towards the brink of extinction, say experts.

The scalloped hammerhead shark is to be added to the official endangered species list this year, under the heading “globally endangered”.

Their plight has been discussed at the American Association for the Advancement of Science annual meeting. It was told that enforcement of marine reserves would aid shark protection.

The observation takes account of new research that shows hammerhead and great white sharks patrol fixed routes in the ocean, gathering at hotspots to mate or feed.

Dr Julia Baum, a marine ecologist at the Scripps Institution of Oceanography, US, and a member of the World Conservation Union (IUCN), said excessive fishing was putting many of the ocean’s “most majestic predators” at risk of extinction.

Speaking at the Boston meeting, she said: “Sharks evolved 400 million years ago, and we could now lose some species in the next few decades – so that would be just a blink of an eye in evolutionary time.”

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First map of threats to marine ecosystems shows all the world’s oceans are affected

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EurekAlert, 14th February 2008

As vast and far-reaching as the world’s oceans are, every square kilometer is affected by human activities, according to a study in the journal Science by researchers at the University of North Carolina at Chapel Hill and others.

The international team of scientists integrated global data from 17 aspects of global change – from overfishing to global warming – that threaten 20 different marine ecosystems, such as coral reefs and continental shelves. Similar to an online satellite map that lets you add layers of highways, retail stores, schools, parks, etc., to find the most congested areas or the highest concentration of fast food restaurants, the global threat map highlights areas in the ocean where threats overlap.

The researchers scored the potential threats – from having very-low to very-high impacts – and found that affects were ubiquitous, and more than 40 percent of the oceans experience medium- to very high-impact threats.

“For the first time we can see where some of the most threatened marine ecosystems are and what might be degrading them,” said Elizabeth Selig, an author on the study and a doctoral student in UNC’s curriculum in ecology in the College of Arts and Sciences.

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Desktop Darwin’s surprise discovery

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The Age, 12th February 2008

One day late last year, Chris Simpson was looking at the waters off the coast of Western Australia on Google Earth when he made an unusual discovery.

Just west of the Kimberleys, a remote area in northern Western Australia, there was an extensive formation of fringing coral reefs – a sight rarely seen anywhere in the world.

“I feel like bloody Charles Darwin up here discovering these new reefs!” Dr Simpson told his boss.

It was a significant find for the coral reef specialist at West Australia’s Department of Environment and Conservation. Most coral reefs occur as isolated reefs and atolls, such as the Great Barrier Reef off the coast of Queensland.

But fringing coral reefs are much rarer. As freshwater kills corals, such reefs can only occur if they are off the coast of an arid location, such as a desert, where no rivers flow out into the waters.

So it was only in locations such as the Red Sea, in south-west Madagascar and at Ningaloo Marine Park off Western Australia where extensive formations were found.

And while the Kimberleys were always a candidate for marine park status, their inaccessibility, turbid waters, massive tides and the presence of crocodiles have deterred would-be explorers from finding out the extent of the reefs.

So when Dr Simpson was exploring the Kimberleys through Google Earth, a practice he has incorporated into his job, he did not expect to spot such a major formation.

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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.