Catching a Coral Killer

First ever case of human-caused marine disease

Coral reefs play an important role in marine ecosystems, so it's concerning to scientists, as well as ocean conservationists, that many coral reefs around the world are in distress or dying off. "The corals themselves provide three-dimensional structure for the reef, and then the fish and invertebrates inhabit the reef," says Kathryn Sutherland, a Rollins College biology professor who studies the bright orange Elkhorn coral. "These coral reefs provide protection and food for these other organisms."

With support from the National Science Foundation (NSF), Sutherland has identified the first marine disease caused by humans, and it's proving fatal for Elkhorn coral in Florida. The disease is White pox, which causes a slowing of growth, followed by white patches of tissue loss that occurs all over the coral colony.

Many diseases, such as swine flu, avian flu and HIV are known as zoonotic, moving from animals to humans. Sutherland has identified a marine disease that is a "reverse zoonosis." "This is the first example of a human pathogen infecting a marine organism," she says. In 2002, she determined that the pathogen of White pox is Serratia marcescens, which is a bacterium. She knew that Serratia marcescens was a pathogen found in human waste. "But at the time, I could only speculate that humans were the source of the pathogen to the marine environment and so I began a widespread study to determine where the pathogen was coming from and how it was getting to the marine environment," says Sutherland.

Her study is a collaborative research project between Rollins College and the University of Georgia.

Sutherland discovered the bacteria was found in the raw sewage influent going into wastewater treatment plants, but it was not found in the treated effluent coming out. "So, this wastewater treatment does work. The problem is that the majority of the Florida Keys have historically been on septic tanks, and septic tanks are not designed for areas like the Florida Keys. They're designed for areas with low population density, and for areas where you have a soil drain field," she says.

Even though it has been expensive, officials and residents of the Florida Keys have supported advanced wastewater treatment, to kill the bacteria. And they are working to get residents to switch from septic tanks to city sewage systems.

"The people in the Florida Keys recognize that the coral reefs are their livelihood. It's actually a $3 billion a year industry for tourism in that region, and so in order to protect the economics of the Florida Keys, they need to maintain good water quality, and treating the sewage is a huge step in that direction," says Sutherland.

On research dives, the scientists use needle-less syringes to collect surface mucus on the Elkhorn coral. It does not harm the animal. Just like in humans, the mucus layer is the first line of defense against pathogens.

Then in the lab, in addition to studying Serratia marcescens, Sutherland's team looks for other microbes that might actually help coral resist disease.

"We're doing analyses of the whole microbial community in the mucus, so we can see what else is there in addition to the pathogen. So we can see how that microbe community changes from a healthy coral to a diseased coral," she says.

Rollins College marine biology student Hunter Noren has been working with Sutherland on the White pox project, including research dives in the Keys. He learned how to scuba dive in the icy waters of Scandinavia.

"I don't understand how it hooked me but it was in a quarry in Sweden and it was about 4 degrees Celsius outside. I loved it and I've been diving ever since," he says. "The state of Elkhorn in the Keys right now is ... it's sobering."

He has explored the waters of the Arctic Circle, the Red Sea, Cypress, and Malta, as well as more popular diving destinations.

"If we continue to harm the oceans and the reefs, we're harming ourselves in the long run. If we harm the reefs, those food webs that are dependent or interlocking with the reefs will be disrupted and they're so complex it's hard to say what will happen, but it definitely won't be good," says Noren.

Sutherland says the best case scenario for the Elkhorn coral in the near future would be advanced wastewater treatment throughout the Florida Keys to eliminate the source of the White pox pathogen and give these important ocean creatures a chance at recovery.

"We do now see that sometimes the disease signs stop, and stop progressing, so the lesions stop growing and, in some cases, during the cooler times of the year, you can see coral tissue growing back over a lesion. So, there is hope for some coral. Some may be more resistant. They may still be infected, but they're more able to fight the infection and recover from the infection," says Sutherland.

Sutherland says climate change may also be playing a role in White pox and other marine diseases. "Pathogens proliferate more when it's warmer and we see White pox disease only when temperatures are warm. It tends to disappear during the cooler times of the year and the lesions increase in size faster when the temperature is warmer. Also, climate change stresses corals," she explains.

Stressed corals often bleach, meaning they expel the algae that they depend on and appear bright white. While corals can survive a bleaching event, they are under more stress and can die. White pox is not the only threat to corals around the world. Other stressors include elevated seawater temperatures and poor water quality, pollution, growing human populations, and development on coastlines.

This article is from Science Nation, a publication of the National Science Foundation, December 19, 2011:

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Photograph by Mark Hay/Douglas Rasher, Georgia Institute of Technology

Chlorodesmis is a green seaweed whose filamentous fronds look like maiden's hair. But this innocuous-appearing seaweed is a killer, scientists have discovered. Field studies have shown for the first time that Chlorodesmis and several common species of seaweeds in both the Pacific and Caribbean Oceans can kill corals upon contact. The seaweeds use chemicals to do the deed. While competition between seaweed and coral is just one of many factors affecting the decline of coral reefs worldwide, this chemical threat may provide a serious setback to efforts aimed at repopulating damaged reefs. Coral reefs are declining worldwide, and scientists studying the problem had suspected that proliferation of seaweed was part of the cause--perhaps by crowding out the coral or by damaging it physically. Find out more in this news release.

Photograph courtesy of NASA

Corals appear to have a genetic complexity that rivals that of humans, have sophisticated systems of biological communication that are being stressed by global change, and are only able to survive based on proper function of an intricate symbiotic relationship with algae that live within their bodies, according to Oregon State University zoologist Virginia Weis and colleagues. The researchers say that disruptions in these biological and communication systems are the underlying cause of the coral bleaching and collapse of coral reef ecosystems around the world. Within their bodies corals harbor highly productive algae--a form of marine plant life--that can "fix" carbon, using the energy of the sun to conduct photosynthesis and produce sugars. "Some of the algae that live within corals are amazingly productive, and in some cases give 95 percent of the sugars they produce to the coral to use for energy," Weis said. "In return, the algae gain nitrogen, a limiting nutrient in the ocean, by feeding off the waste from the coral. It's a finely developed symbiotic relationship." Find out more in this news release.

Photograph courtesy of NASA

A study by Kimberly Selkoe and Benjamin Halpern, both of the National Center for Ecological Analysis and Synthesis (NCEAS) at the University of California at Santa Barbara, sheds light on how threats to the world's endangered coral reef ecosystems can be more effectively managed. The authors studied 14 threats specific to the Northwestern Hawaiian Islands (NWHI) ) - a vast area stretching across more than 1,200 miles of Pacific Ocean--and developed maps of cumulative human impacts as a powerful tool to help natural resource managers make informed decisions about protecting the world's fragile coral reefs. The threats, all generated by humans, included invasive species, bottom fishing, lobster trap fishing, ship-based pollution, ship strike risks, marine debris, research diving, research equipment installation and wildlife sacrifice for research. Human-induced climate change threats were also studied, including increased ultraviolet radiation, ocean acidification, ocean temperature anomalies relevant to disease outbreaks and coral bleaching, and sea level rise. Increased rates of coral disease due to warming ocean temperatures were found to have the highest impact, along with other climate-related threats. Find out more in this news release.

Photograph courtesy of NOAA. Note: The National Oceanic and Atmospheric Administration (NOAA) is a federal agency focused on the condition of the oceans and the atmosphere.

Native to the warm waters of the Pacific and Indian Oceans, the red lionfish is a beautiful creature to behold. Unfortunately, some of these Pterois volitans specimens apparently escaped from aquariums and made it into the Atlantic Ocean. And now, according to research, this lion of the shallow seas is on a deadly rampage. If left unchecked, researchers contend, the lionfish could spell disaster for the coral reef ecosystems that are vital to health of the Atlantic and the rest of the planet. According to Mark Hixon, professor of zoology at Oregon State University, the red lionfish is a voracious and skilled predator. Growing over a foot in length, it can appear to be a drifting clump of seaweed and herd smaller fish into confined space before consuming its prey with a rapid strike. Hixon says the fish species that inhabit Atlantic coastal reefs have never seen such an energetic and effective hunter in their midst. To study the impact of the lionfish on coral reefs, Hixon and his graduate student, Mark Albins, traveled to a coral reef research station at Lee Stocking Island in the Bahamas. Read more in this Discovery.

Related Links

Division of Ocean Sciences (OCE)
The Division of Ocean Sciences (OCE) in NSF's Directorate for Geosciences supports basic research and education to further understanding of all aspects of the global oceans and their interactions with the Earth and the atmosphere.

Human Pathogen Killing Corals in the Florida Keys
A research team from Rollins College in Florida and the University of Georgia has identified human sewage as the source of the coral-killing pathogen that causes White pox disease in Caribbean elkhorn coral.

Study: Severe Low Temperatures Devastate Coral Reefs in Florida Keys
Increased seawater temperatures are known to be a leading cause of the decline of coral reefs all over the world. Earlier this year, researchers at the University of Georgia found that extreme low temperatures affect certain corals in much the same way that high temperatures do.

What's Killing the Coral Reefs?
DNA microarray developed at Berkeley Lab may help scientists learn how to preserve coral. The technology tracks changes in microbial populations that indicate coral disease.