Tag Archives: Coral Disease

Disease-hunting scientist: Dr Laurie Richardson and black band disease in coral

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bbd1

Just finished reading a great excerpt from a book called ‘Disease-hunting scientist’ by a Canadian author called Edward Willett. The scientist in question is Dr Laurie Richardson from Florida International University, who is well known for her work on ‘black band disease’ (see image above) on Caribbean coral reefs. I’ve never read Willett’s work before (and can’t vouch for the book itself), but I’ve long respected Dr Richardson’s research into black band microbial communities, and the ‘interview’ offered a few intriguing insights. More below:

At 287,231 square kilometers, coral reefs are less than a tenth of a percent of the total ocean floor. But they support more than a million species of marine life. They are also dying, from pollution, overfishing—and black-band disease, among others.

Dr. Richardson started her career researching “microbial mats,” communities of microbes that live in the sulfur-rich water of hot springs. She then worked in Wisconsin on a NASA project that used satellite data in the study of aquatic ecosystems. That led to three years at NASA’s Ames Research Centre in California learning remote sensing and image processing, which in turn landed her in Florida with a NASA-funded grant to work on algal pigments and remote sensing.

One day, while she was diving for fun on a coral reef, somebody showed her an example of black-band disease-and she immediately recognized it as similar to the microbial communities she’d studied in hot-spring outflows.

She looked in the scientific literature, and no one else had made that connection. And that was how the research she’s now been doing for more than 15 years began. (Read more)

Black band disease hits Great Barrier Reef

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A recent article in the ABC news tells of the seasonal dynamics of ‘black band disease’ affecting plating corals on the inshore great barrier reef.  Yui Sato, the lead author of the journal article painstakingly documented 485 coral colonies across an almost 3 year time period. Interestingly, the results seem to point as light as a driving factor of black band disease progression in infected corals – click here to read the full article from the Proceedings of the Royal Society.

bbdABC News, 6th May 2009

An epizootic – the wildlife equivalent of a human epidemic – of black band disease has appeared in the Great Barrier Reef, say Australian researchers.

Scientists, who have been monitoring the progress of the disease, say this is the first time an epizootic of this type has been documented in Australian waters.

Black band disease has decimated coral populations in the Caribbean and researchers are concerned it could spread here.

Marine biologist Yui Sato of James Cook University in Townsville and colleagues report their findings in the latest issue of Proceedings of the Royal Society of Biology.

Sato, who is a research student with the ARC Centre of Excellence for Coral Reef Studies, says the black band disease flourishes in warm seawater, killing coral as it eats through tissue, exposing the fragile skeleton.

He is concerned that predicted warmer ocean conditions caused by global warming will lead to longer outbreaks and faster tissue loss. (Read more)

Death of corals is oceanographer’s murder mystery

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There is a nice story in today’s News and Observer, the local paper for the Research Triangle,  in North Carolina.  Wade Rawlins is an environmental writer who covers a range of issues.  He did an excellent job describing coral reefs, their value and threats to them, for a lay audience.  I wish we could get more basic stories like this across to the public.

“Marine scientist John Bruno became interested in coral reefs as a boy snorkeling in the turquoise waters off the Florida Keys above reefs of golden corals the size of football fields.

“It just went on for acres and acres,” recalls Bruno, 43, an associate professor at UNC-Chapel Hill. “They were just full of fish. We’d see hammerhead sharks on the reef and big critters. That is all gone. The corals are gone and the big fish are gone,” he says. “That’s happened in my lifetime.”

“It’s a wonderful murder mystery for ecologists,” says Bruno, who has been the studying the effects of disease and warming sea water on coral reefs. “It’s not obvious what the cause is. There are lots of potential culprits.”

Among the suspects are pollution, destructive fishing practices, predators that feed on corals, disease and warmer ocean waters.

In the ocean, reef-building corals, which are marine polyps, a class of animals, typically exist in colonies of many identical individuals. They fill the role of trees in a forest, Bruno says. The skeletons of corals create the hardened framework of a reef and, over time, build up and provide habitat for thousands of other animals and plants. Corals require warm, clear water and are sensitive to temperatures.

A warming of the ocean by just a degree or two for a few weeks in summer can disrupt the life cycle of corals, Bruno says. Reef-building corals contain tiny plant-like algae that live within their tissue in a mutually beneficial relationship. The algae provide the coral with food and oxygen, as well as the vibrant colors for which corals are known. In return, the organisms receive shelter and nutrients.

Read the full story here

Coral reefs and climate change: Microbes could be the key to coral death

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Coral reefs could be dying out because of changes to the microbes that live in them just as much as from the direct rise in temperature caused by global warming, according to scientists speaking today (Wednesday 2 April 2008) at the Society for General Microbiology’s 162nd meeting being held this week at the Edinburgh International Conference Centre.Tropical ecosystems are currently balanced on a climate change knife edge. Corals in coral reefs, which are made up of animals called polyps that secrete hard external skeletons of calcium carbonate, are living perilously close to their upper temperature limits. This makes them very vulnerable to even small temperature rises of 1-2oC above the normal summer maximum.

“Many of the deaths we see in the coral reefs, which occur following coral bleaching events, when huge areas of reef die off like in 1998 when 17% of the world’s reefs were killed, can be put down to changes in the microbes which live in and around the reefs,” says Dr John Bythell, a biologist from Newcastle University. “These microbes can be thought of as being similar to the bacteria that normally live in our guts and help us digest our food.”

Changes in sea temperature caused by climate change and global warming affect corals, but they also affect the types of bacteria and other microflora that live with them. When the water warms up, some disease-causing bacteria are more successful and can attack the corals. The corals themselves suffer from heat, which reduces their defences. Also, some of the friendly bacteria that normally live in the corals’ guts become weakened, allowing other harmful bacteria to multiply and cause diseases or other problems.

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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 on sunscreen and coral bleaching

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Here is an excerpt from a recent news article (click below for full story):

Sunscreen may be killing corals

Cosmos, Monday 4th October

Some experts are yet to be persuaded by the findings, however.

“Any contaminant can experimentally damage a coral under artificially high concentrations. The amount [in the wild] must be tiny due to dilution,” commented Terry Hughes, director of the Australian Research Council’s Centre of Excellence for Coral Reef Studies at James Cook University in Queensland.

“Imagine how much water a tourist wearing one teaspoon of sunscreen swims through in an hour-long snorkel. Compared to real threats like global warming, runoff and overfishing, any impact of sunscreen is unproven and undoubtedly trivial,” he said.

However, Pusceddu argued that the coral response to sunscreen exposure was not dose dependent, “The mechanism appears to be on-off: thus once the virus has been switched on by [the chemicals in] sunscreen, toxicity is irrelevant.”

Ove Hoegh-Guldberg, director of marine studies at the University of Queensland in Brisbane, said the study is interesting, but notes that many factors are likely to be responsible. “Bleaching is like a runny nose: there are lots of things that could cause it.”

Though sunscreens may contribute to coral death, virus-caused bleaching is only a small part of the big picture, he said: “Climate related bleaching is a direct consequence of heat stress and does not involve viruses or bacteria.”

Coral reefs and climate change

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A colleague of mine, Dr John Bruno forwarded me an excellent article that he wrote for The Encyclopedia of the Earth, titled “Coral Reefs and Climate Change”

“A healthy reef ecosystem literally buzzes with sounds, activity and colors and is populated by incredibly dense aggregations of fish and invertebrates. In this respect, tropical reefs are more reminiscent of the African Serengeti than of the tropical rainforest they are often compared to, where the resident birds and mammals can be secretive and difficult to see. A coral reef can contain tens of thousands of species and some of the world’s most dense and diverse communities of vertebrate animals. Unfortunately, very few remaining coral reefs resemble this pristine condition; on most, corals and fishes are much less abundant than they were only a few decades ago”

John’s expert write-up and summary of threats to coral reefs related to climate change (coral bleaching, disease, ocean acidification) provides an excellent background of the literature and current threats, and is a worthy read for scientists, managers and the general public alike.

Healthy Great Barrier Reef reefscape A recovering Jamaican coral reef Bleached corals off Puerto Rico in 2005