New research reveals how the algae behind red tide thoroughly disables – but doesn’t kill – other species of algae. The study shows how chemical signaling between algae can trigger big changes in the marine ecosystem.
Marine algae fight other species of algae for nutrients and light, and, ultimately, survival. The algae that cause red tides, the algal blooms that color blue ocean waters red, carry an arsenal of molecules that disable some other algae. The incapacitated algae don’t necessarily die, but their growth grinds to a halt. This could explain part of why blooms can be maintained despite the presence of competitors.
In the new study, scientists used cutting-edge tools in an attempt to solve an old ecological mystery: Why do some algae boom and some algae bust? The research team used cultured strains of the algae that cause red tide, exposed competitor algae to its exuded chemicals, and then took a molecular inventory of the competitor algae’s growth and metabolism pathways. Red tide exposure significantly slowed the competitor algae’s growth and compromised its ability to maintain healthy cell membranes.
“Our study describes the physiological responses of competitors exposed to red tide compounds, and indicates why certain competitor species may be sensitive to these compounds while other species remain relatively resistant,” said Kelsey Poulson-Ellestad, a former graduate student at the Georgia Institute of Technology, now at Woods Hole Oceanographic Institution, and the study’s co-first author, along with Christina Jones, a Georgia Tech graduate student. “This can help us determine mechanisms that influence species composition in planktonic communities exposed to red tides, and suggests that these chemical cues could alter large-scale ecosystem phenomena, such as the funneling of material and energy through marine food webs.”
The study was sponsored by the National Science Foundation and was published June 2 in the Online Early Edition of the journal Proceedings of the National Academy of Sciences (PNAS). The work was a collaboration between Georgia Tech, the University of Washington, and the University of Birmingham in the United Kingdom.
The algae that form red tide in the Gulf of Mexico are dinoflagellates called Karenia brevis, or just Karenia by scientists. Karenia makes neurotoxins that are toxic to humans and fish. Karenia also makes small molecules that are toxic to other marine algae, which is what the new study analyzed.
“In this study we employed a global look at the metabolism of these competitors to take an unbiased approach to ask how are they being affected by these non-lethal, subtle chemicals that are released by Karenia,” said Julia Kubanek, Poulson-Ellestad’s graduate mentor and a professor in the School of Biology and the School of Chemistry and Biochemistry at Georgia Tech. “By studying both the proteins and metabolites, which interact to form metabolic pathways, we put together a picture of what’s happening inside the competitor algal cells when they’re extremely stressed.”
The research team used a combination of mass spectrometry and nuclear magnetic resonance spectroscopy to form a holistic picture of what’s happening inside the competitor algae. The study is the first time that metabolites and proteins were measured simultaneously to study ecological competition.
"A key aspect of this study was the use of high-resolution metabolomic tools based on mass spectrometry," said Facundo M. Fernández, a professor in the School of Chemistry and Biochemistry, whose lab ran the mass spectrometry analysis. "This allowed us to detect and identify metabolites affected by exposure to red tide microorganisms.”
Mass spectrometry was also used for analysis of proteins, an approach called proteomics, led by Brook Nunn at the University of Washington.
The research team discovered that red tide disrupts multiple physiological pathways in the competitor diatom Thalassiosira pseudonana. Red tide disrupted the energy metabolism and cellular protection mechanisms, inhibited their ability to regulate fluids and increased oxidative stress. T. pseudonana exposed to red tide toxins grew 85 percent slower than unexposed algae.
“This competitor that’s being affected by red tide is suffering a globally upset state,” Kubanek said. “It’s nothing like what it would be in a healthy, normal cell.”
The work shows that chemical cues in the plankton have the potential to alter large-scale ecosystem processes including primary production and nutrient cycling in the ocean.
The research team found that another competitor diatom, Asterionellopsis glacialis, which frequently co-occurs with Karenia red tides, was partially resistant to red tide, suggesting that co-occurring species may have evolved partial resistance to red tide via robust metabolic pathways.
Other work in Kubanek’s lab is examining red tide and its competition in the field to see how these interactions unfold in the wild.
“Karenia is a big mystery. It has these periodic blooms that happen most years now, but what’s shaping that cycle is unclear,” Kubanek said. “The role of competitive chemical cues in these interactions is also not well understood.”
This research is supported by the National Science Foundation under award number OCE-1060300. Any conclusions or opinions are those of the authors and do not necessarily represent the official views of the sponsoring agency.
CITATION: Kelsey L. Poulson-Ellestad, et al., “Metabolomics and proteomics reveal impacts of chemically mediated competition on marine plankton.” (June, PNAS) www.pnas.org/cgi/doi/10.1073/pnas.1402130111
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Writer: Brett Israel
To test whether the presence of RNA in DNA duplexes could alter the elasticity and structure of DNA, a group of researchers at Georgia Tech and Georgia State University, inspired by Francesca Storici, and including the labs of Elisa Riedo, Angelo Bongiorno and Markus Germann conducted a multidisciplinary study at the interface of physics, chemistry and molecular biology. The group employed atomic force microscopy (AFM)-based single molecule force-measurements of short rNMP(s)-containing oligonucleotides in combination with molecular dynamics (MD) simulations and nuclear magnetic resonance (NMR).
Ribonucleotides (rNMPs), the units of RNA, are the most abundant non-canonical nucleotides found in genomic DNA. rNMPs, either not removed from Okazaki fragments during DNA replication or incorporated and scattered throughout the genome, pose a perturbation to the structure and a threat to the integrity of DNA. The instability of DNA is mainly due to the extra 2’-hydroxyl (OH) group of rNMPs which gives rise to local structural effects that may disturb various molecular interactions in cells. As a result of these structural perturbations by rNMPs, the elastic properties of DNA may also be affected.
DNA has unique mechanical properties that are crucial in many natural biochemical processes and play an important role in DNA-based nanotechnology applications. Despite demonstrations of their abundance and importance, no data exist in literature regarding elastic measurements and sequence-dependent structural distortions of DNA with isolated single rNMP intrusions. With the goal to bring insights on how rNMPs change elastic properties of DNA and its structure, the Georgia Tech team with Hsiang-Chih Chiu and Kyung Duk Koh, a postdoctoral fellow at the time in the lab of Elisa Riedo in the School of Physics, and a PhD candidate in the lab of Francesca Storici from the School of Biology, respectively, together with the graduate student Annie Lesiak from Angelo Bongiorno lab in the School of Physics and School of Chemistry and Biochemistry, and in collaboration with Markus Germann and his graduate student Marina Evich from the Department of Chemistry at Georgia State University, conducted an innovative, experimental and theoretical study utilizing two short DNA molecules containing isolated rNMP intrusions. Storici said: <<We examined and identified how the elasticity and structure of DNA are altered by the rNMP intrusions in the studied DNA sequences>>. AFM-based single molecule force spectroscopy demonstrated that rNMP intrusions in short DNA duplexes can decrease – by 32% – or slightly increase the stretch modulus of DNA depending on specific sequence contexts next to the rNMPs. In addition, MD simulations and NMR experiments indicated that rNMP inclusions locally change the torsional distortion of the sugar-phosphate backbone in DNA only when the rNMPs are in specific locations in the DNA sequence. Riedo concluded: <<Our work opens up the route to use AFM single molecules measurements to understand how defects and the base sequence can affect the elasticity of short DNA molecules>>.
The demonstrated ability of rNMPs to locally change DNA mechanical properties and structure may find applications in structural DNA nanotechnology and help understanding how such intrusions impact DNA biological functions. Overall, these findings open a new route for understanding how rNMPs may influence DNA structure, chemistry, and biology.
The study is just published as an article in the journal Nanoscale (accepted, 2014):
Chiu HC*, Koh KD*, Evich M, Lesiak AL, Germann MW, Bongiorno A, Riedo E, Storici F (2014)
RNA intrusions change DNA elastic properties and structure. Nanoscale, DOI: 10.1039/C4NR01794C; *equal contribution.
http://pubs.rsc.org/en/content/articlepdf/2014/nr/c4nr01794c
This project was supported by the Office of Basic Energy Sciences of the US Department of Energy (DE-FG02-06ER46293), the National Science Foundation (NSF)(CMMI-1100290 and DMR-0820382), the Samsung Advanced Institute of Technology and the NSF grant CHE-0946869, the Integrative Biosystems Institute grant IBSI-4, the Georgia Research Alliance grant R9028 and the NSF grant MCB-1021763.
Sir Isaac Newton probably wasn’t thinking about how animals urinate when he was developing his laws of gravity. But they are connected – by the urethra, to be specific.
A new Georgia Institute of Technology study investigated how quickly 32 animals urinate. It turns out that it’s all about the same. Even though an elephant’s bladder is 3,600 times larger than a cat’s (18 liters vs. 5 milliliters), both animals relieve themselves in about 20 seconds. In fact, all animals that weigh more than 3 kilograms (6.6 pounds) urinate in that same time span.
“It’s possible because larger animals have longer urethras,” said David Hu, the Georgia Tech assistant professor who led the study. “The weight of the fluid in the urethra is pushing the fluid out. And because the urethra is long, flow rate is increased.”
For example, an elephant’s urethra is one meter in length. The pressure of fluid in it is the same at the bottom of a swimming pool three feet deep. An elephant urinates four meters per second, or the same volume per second as five showerheads.
“If its urethra were shorter, the elephant would urinate for a longer time and be more susceptible to predators,” Hu explained.
The findings conflict with studies that indicate urinary flow is controlled on bladder pressure generated by muscular contraction. The study has just been published in the Proceedings of the National Academy of Sciences (PNAS).
Hu (George Woodruff School of Mechanical Engineering and School of Biology) and graduate student Patricia Yang noticed that gravity allows larger animals to empty their bladders in jets or sheets of urine. Gravity’s effect on small animals is minimal.
“They urinate in small drops because of high viscous and capillary forces. It’s like peeing in space,” said Yang, who is pursuing her doctoral degree in the School of Mechanical Engineering. “Mice and rats go in less than two seconds. Bats are done in a fraction of a second.”
The research team went to a zoo to watch 16 animals relieve themselves, then watched 28 YouTube videos. They saw cows, horses, dogs and more.
The more they watched, the more they realized their findings could help engineers.
“It turns out that you don’t need external pressure to get rid of fluids quickly,” said Hu. “Nature has designed a way to use gravity instead of wasting the animal’s energy.”
Hu envisions systems for water tanks, backpacks and fire hoses that can be built for more efficiency. As an example, he and his students have created a demonstration that empties a teacup, quart and gallon of water in the same duration using varying lengths of connected tubes. In a second experiment, the team fills three cups with the same amount of water, then watches them empty at differing rates. The longer the tube, the faster it empties.
“Nature has shown us that no matter how big the fire truck, water can still come out in the same time as a tiny truck,” Hu added.
The trick is gravity. Newton would be proud.
It’s 3:15 p.m. and the sun is setting at Anvers Island. Just off the Antarctic Peninsula, surrounded by 300-foot cliffs of ice, Jeannette Yen pauses outside Palmer Station to watch. The sun spills over the ice cliffs. The frozen landscape melts in a golden glow.
This is one of nature’s great laboratories. Yen and her team of scientists are conducting experiments here that are possible nowhere else. Outfitted in red parkas, they are not here to drill into frozen lakes or fly over thinning ice sheets. They spend what little daylight they have searching for tiny organisms in the frigid waters.
The scientists climb aboard the R/V Lawrence M Gould, a massive research vessel operated by the National Science Foundation (NSF). They cruise past giant icebergs and through rafts of loose ice to Palmer Deep, a location where the water is 2,000 feet (600 meters) deep. From the huge stern A-frame of the ship, they lower plankton nets into the zero-degree Celsius water and haul live animals aboard. In Antarctica, zero degrees Celsius is a pleasant day, but the recent bout of 80-knot wind gusts tells them the austral winter is on its way.
“The weather has been good,” Yen said. “We’ve gone out and have been collecting plankton all around.”
Yen, a professor of biology at the Georgia Institute of Technology in Atlanta, is on her second polar plunge. She’s an ecologist with an engineer’s eye. Her team of biologists and engineers haul each day’s catch back to the lab at Palmer Station, which provides no escape from the cold. There, the scientists study plankton swimming motion with video cameras in a room kept at zero degrees Celsius, to mimic the animals’ natural environment.
Plankton are the base of the food chain, but their environment is changing. Around the southern continent, the water temperature is stable at around zero degrees Celsius because of the Antarctic Circumpolar Current. Carbon dioxide, a potent greenhouse gas, easily dissolves in the cold water, acidifying the ocean. The acidifying oceans might be triggering a destructive chain of events underwater that could harm the food web around the world.
That’s why Yen and her team have come here, in search of a tiny organism that could be a canary in the coal mine of climate change.
Written by Argonne National Laboratory
A study published in Scienceby researchers from the U.S. Department of Energy’s Argonne National Laboratory and co-authored by Georgia Tech may dramatically shift our understanding of the complex dance of microbes and minerals that takes place in aquifers deep underground. This dance affects groundwater quality, the fate of contaminants in the ground and the emerging science of carbon sequestration.
Deep underground, microbes don’t have much access to oxygen. So they have evolved ways to breathe other elements, including solid minerals like iron and sulfur.
The part that interests scientists is that when the microbes breathe solid iron and sulfur, they transform them into highly reactive dissolved ions that are then much more likely to interact with other minerals and dissolved materials in the aquifer. This process can slowly but steadily make dramatic changes to the makeup of the rock, soil and water.
“That means that how these microbes breathe affects what happens to pollutants — whether they travel or stay put — as well as groundwater quality,” said Ted Flynn, a scientist from Argonne and the Computation Institute at the University of Chicago and the lead author of the study.
About a fifth of the world’s population relies on groundwater from aquifers for their drinking water supply, and many more depend on the crops watered by aquifers.
For decades, scientists thought that when iron was present in these types of deep aquifers, microbes who can breathe it would out-compete those who cannot. There’s an accepted hierarchy of what microbes prefer to breathe, according to how much energy each reaction can theoretically yield. (Oxygen is considered the best overall, but it is rarely found deep below the surface.)
According to these calculations, of the elements that do show up in these aquifers, breathing iron theoretically provides the most energy to microbes. And iron is frequently among the most abundant minerals in many aquifers, while solid sulfur is almost always absent.
But something didn’t add up right. A lot of the microorganisms had equipment to breathe both iron and sulfur. This requires two completely different enzymatic mechanisms, and it’s evolutionarily expensive for microbes to keep the genes necessary to carry out both processes. Why would they bother, if sulfur was so rarely involved?
The team decided to redo the energy calculations assuming an alkaline environment — “Older and deeper aquifers tend to be more alkaline than pH-neutral surface waters,” said Argonne coauthor Ken Kemner — and found that in alkaline environments, it gets harder and harder to get energy out of iron.
“Breathing sulfur, on the other hand, becomes even more favorable in alkaline conditions,” Flynn said.
The team reinforced this hypothesis in the lab with bacteria under simulated aquifer conditions. The bacteria, Shewanella oneidensis, can normally breathe both iron and sulfur. When the pH got as high as 9, however, it could breathe sulfur, but not iron.
There was still the question of where microorganisms like Shewanella could find sulfur in their native habitat, where it appeared to be scarce.
The answer came from another group of microorganisms that breathe a different, soluble form of sulfur called sulfate, which is commonly found in groundwater alongside iron minerals. These microbes exhale sulfide, which reacts with iron minerals to form solid sulfur and reactive iron. The team believes this sulfur is used up almost immediately by Shewanella and its relatives.
“This explains why we don’t see much sulfur at any fixed point in time, but the amount of energy cycling through it could be huge,” Kemner said.
Indeed, when the team put iron-breathing bacteria in a highly alkaline lab environment without any sulfur, the bacteria did not produce any reduced iron.
“This hypothesis runs counter to the prevailing theory, in which microorganisms compete, survival-of-the-fittest style, and one type of organism comes out dominant,” Flynn said. Rather, the iron-breathing and the sulfate-breathing microbes depend on each other to survive.
Understanding this complex interplay is particularly important for sequestering carbon. The idea is that in order to keep harmful carbon dioxide out of the atmosphere, we would compress and inject it into deep underground aquifers. In theory, the carbon would react with iron and other compounds, locking it into solid minerals that wouldn’t seep to the surface.
Iron is one of the major players in this scenario, and it must be in its reactive state for carbon to interact with it to form a solid mineral. Microorganisms are essential in making all that reactive iron. Therefore, understanding that sulfur—and the microbe junkies who depend on it—plays a role in this process is a significant chunk of the puzzle that has been missing until now.
The study, “Sulfur-Mediated Electron Shuttling During Bacterial Iron Reduction,” appeared online in the May 1 edition of Science Express and was published in Science earlier this summer. Other authors on the study were Argonne scientists Bhoopesh Mishra (also of the Illinois Institute of Technology) and Edward O’Loughlin and Georgia Tech scientist Thomas DiChristina.
“The exciting findings reported in our study were made possible by combining the microbiology expertise of my laboratory in the School of Biology at Georgia Tech with the geochemical expertise of the Molecular Environmental Sciences group led by Ken Kemner at Argonne National Laboratory,” said Professor DiChristina, “The biogeochemical link between bacterial iron- and sulfur-breathing bacteria is important for survival of microbial communities in modern subsurface environments, and also provides clues to the evolution of ancient metabolic processes on an early Earth that lacked oxygen but contained large amounts of iron and sulfur.”
Funding for the research was provided by the U.S. Department of Energy’s Office of Science. The Advanced Photon Source (APS) is also supported by the DOE’s Office of Science. The team conducted X-ray analysis at the APS GeoSoilEnviroCARS beamline 13-ID-E, which is operated by the University of Chicago and jointly supported by the National Science Foundation and the DOE’s Office of Science. Additional support came from the National Institutes of Health and the National Science Foundation.
The Computation Institute (CI), a joint institute of the University of Chicago and Argonne National Laboratory, is an intellectual nexus for scientists and scholars pursuing multi-disciplinary research, and a resource center for developing and applying innovative computational approaches. Founded in 1999, it is home to over 200 faculty, fellows, and staff researching complex, system-level problems in such areas as biomedicine, energy and climate, astronomy and astrophysics, computational economics, social sciences and molecular engineering. CI is home to diverse projects including theCenter for Robust Decision Making on Climate and Energy Policy, the Center for Multiscale Theory and Simulation, the Urban Center for Computation and Data and Globus.
The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit the user facilities directory.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.
Congratulations to Dr. Greg Gibson for being awarded a T32 training grant from the National Institute of General Medical Science. Titled, "Computational Biology and Predictive Health”, the grant will bridge Biology, Biomedical Engineering, Industrial Systems Engineering and Computer Science through the support of 4 graduate students each year over the five funding period. The Executive Committee for the grant includes Greg Gibson, Melissa Kemp, King Jordan and Nicoleta Serban.
New study, published in Hepatology, shows the regenerative capacity of liver cells
Patients suffering from chronic liver disease often develop liver fibrosis (the accumulation of scar tissue), which frequently results in cirrhosis, which means a loss of liver function, which often comes with a choice between a liver transplant and certain death.
It’s a perfect storm of terrible things as sustained fibrosis dampens the regenerative capacity of hepatocytes, thwarting their ability to make a therapeutic response, resulting in a grim prognosis and high mortality. At its essence, this is a communication problem, based on a study by a team of researchers in the lab of Chong Hyun Shin at the Georgia Institute of Technology.
Their findings explain how signaling pathways and cell-cell communications direct the cellular response to fibrogenic stimuli. But they also identify some novel potential therapeutic strategies for chronic liver disease. Results of the study (funded by the National Institutes of Health, the Emory/Georgia Tech Regenerative Engineering and Medicine Center, and Georgia Tech’s School of Biology) were published recently in the journal Hepatology.
“We aim to understand the molecular and cellular mechanisms that mediate the effects of sustained fibrosis on hepatocyte regeneration, using the zebrafish as a model,” explains Shin, assistant professor in the School of Biology, with a lab in the Parker H. Petit Institute for Bioengineering and Bioscience. Her fellow authors are Frank Anania (Emory), Mianbo Huang, Angela Chang, Minna Choi and David Zhou.
In their fibrotic zebrafish model, they studied the effects that different levels of signaling have on the regeneration of liver cells (hepatocytes). Specifically, they took note of the relationship between ‘Wnt’ and ‘Notch’ (signaling pathways). They discovered that lower level Notch signaling promotes cell regeneration (the proliferation and differentiation of hepatic progenitor cells, or HPCs, into hepatocytes), while high levels suppressed it. And they discovered that antagonistic interaction between Wnt and Notch modulates regenerative capacity: Wnt signals can suppress Notch signals, or, in other words, when Wnt is up, Notch is down, and hepatocyte regeneration can happen.
The data, says Shin, “suggest an essential interplay between Wnt and Notch signaling during hepatocyte regeneration in the fibrotic liver, providing legitimate therapeutic strategies for chronic liver failure in vivo.”
Inducing tissue regeneration via stem or progenitor cells, while delaying fibrosis, has been on the rise as antifibrogenic strategies of great potential, according to Shin, whose studies offer a clue of how to guide the differentiation of HPCs into hepatocytes in patients suffering from chronic liver failure. “Overall,” she explains, “employing the in vivo-based hepatic regeneration strategy may allow us to complement fundamental drawbacks in stem cell therapy, opening up new avenues of endogenous cellular regeneration therapy.”
This research is supported by grant number K01DK081351 from the National Institutes of Health (NIH), the Regenerative Engineering and Medicine Research Center Pilot Award (GTEC 2731336), and the School of Biology, Georgia Institute of Technology.
Read Hepatology journal abstract here
Pacific corals and fish can both smell a bad neighborhood, and use that ability to avoid settling in damaged reefs.
Damaged coral reefs emit chemical cues that repulse young coral and fish, discouraging them from settling in the degraded habitat, according to new research. The study shows for the first time that coral larvae can smell the difference between healthy and damaged reefs when they decide where to settle.
Coral reefs are declining around the world. Overfishing is one cause of coral collapse, depleting the herbivorous fish that remove the seaweed that sprouts in damaged reefs. Once seaweed takes hold of a reef, a tipping point can occur where coral growth is choked and new corals rarely settle.
The new study shows how chemical signals from seaweed repel young coral from settling in a seaweed-dominated area. Young fish were also not attracted to the smell of water from damaged reefs. The findings suggest that designating overfished coral reefs as marine protected areas may not be enough to help these reefs recover because chemical signals continue to drive away new fish and coral long after overfishing has stopped.
“If you’re setting up a marine protected area to seed recruitment into a degraded habitat, that recruitment may not happen if young fish and coral are not recognizing the degraded area as habitat,” said Danielle Dixson, an assistant professor in the School of Biology at the Georgia Institute of Technology in Atlanta, and the study's first author.
The study will be published August 22 in the journal Science. The research was sponsored by the National Science Foundation (NSF), the National Institutes of Health (NIH), and the Teasley Endowment to Georgia Tech.
The new study examined three marine areas in Fiji that had adjacent fished areas. The country has established no-fishing areas to protect its healthy habitats and also to allow damaged reefs to recover over time.
Juveniles of both corals and fishes were repelled by chemical cues from overfished, seaweed-dominated reefs but attracted to cues from coral-dominated areas where fishing is prohibited. Both coral and fish larvae preferred certain chemical cues from species of coral that are indicators of a healthy habitat, and they both avoided certain seaweeds that are indicators of a degraded habitat.
The study for the first time tested coral larvae in a method that has been used previously to test fish, and found that young coral have strong preferences for odors from healthy reefs.
"Not only are coral smelling good areas versus bad areas, but they’re nuanced about it," said Mark Hay, a professor in the School of Biology at Georgia Tech and the study's senior author. "They’re making careful decisions and can say, 'settle or don’t settle.'"
The study showed that young fish have an overwhelming preference for water from healthy reefs. The researchers put water from healthy and degraded habitats into a flume that allowed fish to choose to swim in one stream of water or the other. The researchers tested the preferences of 20 fish each from 15 different species and found that regardless of species, family or trophic group, each of the 15 species showed up to an eight times greater preference for water from healthy areas.
The researchers then tested coral larvae from three different species and found that they preferred water from the healthy habitat five-to-one over water from the degraded habitat.
Chemical cues from corals also swayed the fishes' preferences, the study found. The researchers soaked different corals in water and studied the behavior of fish in that water, which had picked up chemical cues from the corals. Cues of the common coral Acropora nasuta enhanced attraction to water from the degraded habitat by up to three times more for all 15 fishes tested. A similar preference was found among coral larvae.
Acropora corals easily bleach, are strongly affected by algal competition, and are prone to other stresses. The data demonstrate that chemical cues from these corals are attractive to fish and corals because they are found primarily in healthy habitats. Chemical cues from hardy corals, which can grow even in overfished habitats, were less attractive to juvenile fishes or corals.
The researchers also soaked seaweed in water and tested fish and coral preferences in that water. Cues from the common seaweed Sargassum polycystum, which can bloom and take over a coral reef, reduced the attractiveness of water to fish by up to 86 percent compared to water without the seaweed chemical cues. Chemical cues from the seaweed decreased coral larval attraction by 81 percent.
"Corals avoided that smell more than even algae that's chemically toxic to coral but doesn't bloom," Dixson said.
Future work will involve removing plots of seaweed from damaged reefs and studying how that impacts reef recovery.
A minimum amount of intervention at the right time and the right place could jump start the recovery of overfished reefs, Hay said. That could bring fish back to the area so they settle and eat the seaweed around the corals. The corals would then get bigger because the seaweed is not overgrown. Bigger corals would then be more attractive to more fish.
"What this means is we probably need to manage these reefs in ways that help remove the most negative seaweeds and then help promote the most positive corals," Hay said.
This research is supported by the National Science Foundation (NSF), under award number OCE-0929119, and the National Institutes of Health, under award number U01-TW007401. Any conclusions or opinions are those of the authors and do not necessarily represent the official views of the sponsoring agency.
CITATION: Dixson et al., "Chemically mediated behavior of recruiting corals and fishes: A tipping
point that may limit reef recovery." (August 2014, Science). http://www.sciencemag.org/content/345/6199/892
Research News
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Media Relations Contacts: Brett Israel (@btiatl) (404-385-1933) (brett.israel@comm.gatech.edu) or John Toon (404-894-6986) (jtoon@gatech.edu)
Scientific Contacts:
Mark Hay
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Fiji phone numbers: 679-833-3300 or 679-979-5991 (cell). 679-653-0093 (landline)
Skype: Markhaygt
Danielle Dixson
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Belize phone: 011-501-532-2392
Skype: Danielle.Dixson
Writer: Brett Israel
Dr. Joel Kostka, a Professor jointly appointed in Biology and Earth & Atmospheric Sciences, was recently awarded $1.0 million in research grants by the U.S. Department of Energy (DOE) to study the microbially-mediated carbon cycle in boreal or northern peatlands. Peatlands sequester one-third of all soil carbon and currently act as major sinks of atmospheric CO2. The ability to predict or to simulate the fate of stored carbon in response to climatic disruption remains hampered by our limited understanding of the controls of C turnover and the composition and functioning of peatland microbial communities. Given their global extent and uncertain fate with climatic change, boreal or northern peatlands are considered a high priority for climate change research. The overall goal of this project is to investigate the rates, pathways, and controls of organic matter decomposition by microbes in response to warming and elevated carbon dioxide in peatlands. The project will be conducted at the Marcell Experimental Forest (MEF) in northern Minnesota where US Department of Energy’s (DOE) Oak Ridge National Laboratory (ORNL) and the USDA Forest Service are developing a climate manipulation field site known as Spruce and Peatland Response Under Climatic and Environmental Change (SPRUCE). In the Minnesota peatland, DOE is building 10 open top enclosures (12 m in diameter and 8 m in height). Inside these enclosures, the peat soil and air will be heated and carbon dioxide concentrations raised to simulate future climate change. Kostka’s project will examine changes to the microbial communities during this large scale climate change experiment. The project team includes collaborators at Florida State University and ORNL.
Dr. Kostka was interviewed last week by BBC radio on microbial hydrocarbon degradation (http://www.thenakedscientists.com/HTML/podcasts/specials/show/20140809/)
It also went out on the 5 Live show on Saturday morning - http://www.bbc.co.uk/programmes/b04cf3q8
GT Biology 2012 PhD graduate Douglas Rasher won the George Mercer Award from the Ecological Society of America this year. This prestigious award recognizes the best paper published in Ecology over the past 2 years by an ecologist younger than 40 years old. Rasher, now a postdoctoral research associate at the University of Maine, provides rich new insights for the management and conservation of coral reefs in his 2013 “Consumer diversity interacts with prey defenses to drive ecosystem function,” in Ecology. The study, which he conducted as a graduate student at the Georgia Institute of Technology, shows that interactions between algal defenses and herbivore tolerances create an essential role for consumer diversity in the functioning and resilience of coral reefs.
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