Predicting Coral Health By Identifying Nearby Microscopic Algae
ScienceDaily (July 23, 2008) — A new indicator of coral health has been discovered in a community of microscopic single-celled algae called dinoflagellates. The study reveals that a particular type of these algae renders corals more susceptible to disease.
"Corals are fascinating organisms whose survival is dependent on dinoflagellates that live inside the coral's tissue," says lead author Michael Stat, an assistant researcher at the Hawaii Institute for Marine Biology (HIMB) at the University of Hawaii at Manoa. "The relationship between these dinoflagellates and corals has long been considered mutually beneficial, with the dinoflagellates supplying the coral with food via photosynthesis in return for recycled nutrients and shelter. Over the last 20 years it has been made clear that there are many different types of dinoflagellates in corals and that the unions or symbiosis between a given coral and their dinoflagellates can be very specific."
It had previously been considered that all dinoflagellates found in coral are equally beneficial to their coral host, but in this study Stat, along with HIMB researchers Ruth Gates and Emily Morris, present evidence that a particular type of dinoflagellate can be found in corals that are diseased or show evidence of having had a disease.
"We show that this same symbiont, called "clade A", does not produce as much food that can be used by the coral as other types of coral dinoflagellates," says Stat. "We suggest that because these coral are not receiving enough food they become more prone to disease."
The researchers sampled corals that appeared healthy and corals that appeared diseased from French Frigate Shoals in the Papahanaumokuakea Marine National Monument in the Northwestern Hawaiian Islands (NWHI). By using genetic analyses, they were able to identify the type of dinoflagellate that was present in each of these corals. They found that the healthy coral contained one type of dinoflagellate and the diseased coral contained a different type of symbiont.
"We have discovered that a group of diseased corals in the NWHI associate with a type of endosymbiotic algae that has never been found in Hawaiian corals before," says co-author Ruth Gates, an Associate Researcher at HIMB. "Our analyses suggest that these endosymbiotic algae are not providing the coral with nutrition and that the corals may be starving, making them more susceptible to disease."
To mimic the inside of coral tissue, they performed lab-controlled experiments looking at the amount of carbon produced and released by different coral dinoflagellates in an artificial environment. They found that the dinoflagellate found in healthy coral produced large amounts of carbon that it released into the outside environment, making it available to a coral as a source of food. In contrast, the dinoflagellate found in diseased coral produced a very small amount of carbon and did not release any to the outside environment to make available to a coral host as a source of food.
"Just as we have tests for human diseases such as cancer and tuberculosis, we now have the ability to screen corals for disease susceptibility," says Gates. "This discovery is a key finding that will contribute to the conservation and protection of ecologically important corals in Hawaii and elsewhere."
"This work shows for the first time that different types of coral dinoflagellates are not equally beneficial, and that there is a link between the type of dinoflagellate and coral disease," says Stat. "We also suggest that some dinoflagellates living inside coral may be acting more as a parasite than a mutualisticsymbiont. The next stage in our research is to further understand the range of interactions between coral and dinoflagellates and to determine whether some types are directly harming the coral and acting as parasites."
This research was funded by the National Marine Sanctuary Program, the Hawaii Institute of Marine Biology Reserve Partnership and the National Science Foundation.
Hot Southern Summer Threatens Coral With Massive Bleaching Event
ScienceDaily (Jan. 3, 2009) — A widespread and severe coral bleaching episode is predicted to cause immense damage to some of the world’s most important marine environments over the next few months.
A report from the US Government’s National Oceanic and Atmospheric Administration (NOAA) predicts severe bleaching for parts of the Coral Sea, which lies adjacent to Australia’s Great Barrier Reef, and the Coral Triangle, a 5.4 million square kilometre expanse of ocean in the Indo-Pacific which is considered the centre of the world’s marine life.
“This forecast bleaching episode will be caused by increased water temperatures and is the kind of event we can expect on a regular basis if average global temperatures rise above 2 degrees,” said Richard Leck, Climate Change Strategy Leader for WWF’s Coral Triangle Program.
The bleaching, predicted to occur between now and February, could have a devastating impact on coral reef ecosystems, killing coral and destroying food chains. There would be severe impacts for communities in Australia and the region, who depend on the oceans for their livelihoods.
The Coral Triangle, stretching from the Philippines to Malaysia and Papua New Guinea, is home to 75 per cent of all known coral species. More than 120 million people rely on its marine resources.
“Regular bleaching episodes in this part of the world will have a massive impact on the region’s ability to sustain local communities,” said Leck. “In the Pacific many of the Small Island Developing States, such as the Solomon Islands, rely largely on the coast and coastal environments such as coral reefs for food supply. This is a region where alternative sources of income and food are limited.
“Time is crucial and Australia needs to step up to the plate. Following the government’s lack of resolve to seriously reduce future domestic carbon emissions, Australia has a huge role to play in assisting Coral Triangle countries and people to adapt to the changes in their climate.“
The Australian government this week announced a 2020 target for reducing its greenhouse gas pollution by 5 per cent, which WWF criticised as completely inadequate. Reductions of at least 25 per cent by 2020 are needed to set the world on a pathway to meaningful cuts in greenhouse pollution.
Australia’s Coral Sea, which will also be affected by coral bleaching and climate change, is a pristine marine wilderness covering almost 1,000,000 square kilometres and is extraordinarily rich in marine life, including sharks and turtles, with a series of spectacular reefs rising thousands of metres from the sea floor.
WWF is urging the Australian government to declare the Coral Sea a marine protected area, as well as working to establish a network of marine protected areas that will assist ocean environments to adapt to the changes caused by rising temperatures, and to absorb the impacts from human activity.
What's Killing The Coral Reefs?
ScienceDaily (Feb. 4, 2009) — The answer to what’s killing the world’s coral reefs may be found in a tiny chip that fits in the palm of your hand.
Scientists at Lawrence Berkeley National Laboratory and the University of California, Merced are using an innovative DNA array developed at Berkeley Lab to catalog the microbes that live among coral in the tropical waters off the coast of Puerto Rico. They found that as coral becomes diseased, the microbial population it supports grows much more diverse.
It’s unclear whether this surge in microbial diversity causes the disease, or is a result of it. What is clear is that coral disease is accompanied by a microbial bloom, and the DNA array, called the PhyloChip, offers a powerful way to both track this change and shed light on the pathogens that plague one of the ocean’s most important denizens.
“The PhyloChip can help us distinguish different coral diseases based on the microbial community present,” says Shinichi Sunagawa, a graduate student in UC Merced’s School of Natural Sciences who helped to conduct the research. “This is important because we need to learn more about what’s killing coral reefs, which support the most diverse ecosystem in the oceans. Losing them is much more than losing a reef, it means losing fish and marine mammals, even tourism.”
Worldwide, coral is threatened by rising sea temperatures associated with global warming, pollution from coastal soil runoff and sewage, and a number of diseases. The organism’s acute susceptibility to environmental change has given it a reputation as a canary in the coalmine: if it suffers, other species will soon follow.
Fortunately, there are ways to give coral a health checkup. Scientists have recently learned that healthy coral supports certain microbial populations, while coral inflicted with diseases such as White Plague Disease support different populations.
Understanding these microbial shifts could illuminate the magnitude and causes of coral disease, and possibly how to stop it, which is where the PhyloChip comes in. The credit card-sized chip can quickly detect the presence of up to 9,000 species of microbes in specially prepared samples of air, water, soil, blood, and tissue. The chip is carpeted with thousands of probes that scour a sample for the unique DNA signatures of most known species in the phyla bacteria and archaea. Specifically, the probes bind with a gene, called 16S rRNA, which is present in all life.
Developed by Gary Andersen, Todd DeSantis, EoinBrodie, and Yvette Piceno of Berkeley Lab’s Earth Sciences Division, the PhyloChip offers a quick and low-cost way to canvas environmental samples for the presence of microorganisms.
“It’s a fast and inexpensive way to conduct a complete microbial community assessment of healthy and diseased corals,” says DeSantis.
In this study, the PhyloChip was used in conjunction with a more common technique, clone library sequencing, to analyze healthy and diseased samples of the coral Montastraeafaveolata, which were plucked from reefs in the waters off Puerto Rico. The PhyloChip analyses, which were conducted at Berkeley Lab, found more species than the slower and more expensive clone sequencing technique.
But neither technique yielded what the scientists anticipated. The diseased coral was expected to contain the pathogen Aurantimonascorallicida because the coral exhibited symptoms identical to another coral species stricken by the pathogen. In this case, however, A. corallicida was not found.
“This means there are possibly other pathogens out there that we don’t know about,“ says Sunagawa. “There are only a handful of known coral pathogens, and we didn’t find the pathogen that causes a similar display in a different species of coral.“
In addition, the scientists have yet to determine whether the microbial bloom that accompanies coral disease causes the disease, or is caused by it.
“We need to determine what comes first: the disease or the microbial population change,” says DeSantis. “We don’t know if the disease-associated microbial population kills the coral, or if the microbes are simply feeding on dead coral tissue.”
Adds Sunagawa, “We have only recently realized how microbes, and microbial diversity, play an important role in the health of coral reefs. And the PhyloChip offers a great way to catalog the microbiota associated with coral reefs around the world.”