USGS scientist Thierry Work takes a sample from diseased coral at Tunnels Reef on the north shore of Kauai, Hawaii

A coral disease epidemic is killing unusually large numbers of coral on the north shore of the Hawaiian island, Kauai, and USGS scientists, in collaboration with researchers from the University of Hawaii Institute of Marine Biology, are investigating the cause.

Coral reefs cover less than 0.5 percent of the earth’s surface, but provide habitat for an estimated 25 percent of all marine species. Second only to tropical rainforests in size and complexity, more than one million species of plants and animals may be interlinked with coral reefs.

“Coral reefs are important to Hawaii’s underwater environments and the financial well-being of its tourism industry,” said USGS scientist Thierry Work. “Like it or not, ecosystem health is closely intertwined with human and animal health.”

What is Causing the Disease?

Scientists have collected coral samples from the diseased areas, which are referred to as lesions, and examined them in the laboratory. The lesions are closely associated with a mysterious cyanobacterial infection. Cyanobacteria, a type of blue-green algae, often cause visible blooms in freshwater lakes; however, many cyanobacteria are also present in the ocean. Some species of cyanobacteria produce toxins that can sicken wildlife, domestic animals, and humans. The effects of this current outbreak appear limited to corals.

This coral disease outbreak is the first instance where a cyanobacterial disease has been documented in Hawaii on such a large scale. Scientists are trying to figure out what is promoting the outbreak. An unusually large amount of sediment is present on two affected reefs, and this is known to adversely affect corals in other areas.  However, what role sediment or other land based pollution has in driving this disease remains unclear.

Cyanobacteria-affected coral taken at Makua, Kauai on August 5, 2012. The green dots indicate macroalgae; the red dots indicate cyanobacteria-associated tissue loss; and the blue dots indicate live coral.

Why Study this Outbreak? You Can’t Manage What You Don’t Measure and You Cannot Measure What You Don’t Know

Wildlife disease outbreaks are indicators that something is awry in the environment. Understanding causes of disease and what drives those causes is important because this information helps management agencies make informed decisions to prevent further spread of the disease or minimize impact of disease.  Like many other places, coral reefs in Hawaii are adversely impacted by global climate change, land-based pollution, overfishing, and disease. Understanding the role and causes of disease in corals and their prevention may contribute to prevention of additional outbreaks and aid in their recovery.

Coral Reefs are Important

Coral reefs are not only essential for other marine species, they are also economically important. Reefs shelter and provide nursery grounds for many commercially and culturally important species of fish and invertebrates, they protect the islands’ harbors, beaches, and shorelines from erosion and wave damage by storms, and they are vital to the Pacific’s marine tourism industry. Globally, these diverse ecosystems may provide valuable goods and services worth about $375 billion each year to communities around the world.

Coral reefs are sensitive indicators of the health of marine environments. Yet coral reefs are in decline in many parts of the world. It is estimated that 30 percent will be destroyed or seriously degraded in the next 10 years. Disease has played a major role in the decline of coral reef cover in certain parts of the globe such as the Caribbean. In many cases, the causes of mortalities of marine invertebrates are unknown. USGS is collaborating with state, territorial, and other federal agencies to develop tools to assess health of corals and other marine organisms and to determine causes of coral mortality to preserve this unique and valuable natural resource.

For more information on coral disease, see this publication:

Dr. Greta Aeby (left), a coral expert with the Hawai‘i Institute of Marine Biology at the University of Hawai‘i, and Dr. Thierry Work, wildlife disease specialist for the USGS National Wildlife Health Center exit the water at ‘Anini after more than six hours of documenting and photographing diseased rice corals.

Work, T.M., Russell, Robin, & Aeby, G.S. (2012). Tissue loss (white syndrome) in the coral
Montipora capitata is a dynamic disease with multiple host responses and potential causes. Proceedings of the Royal Society B-Biological Sciences, 279(1746), 4334-4341.

http://rspb.royalsocietypublishing.org/content/279/1746/4334.long

A comparison of normal coral with some dead skeletal material covered by typical secondary colonization (right) and a wilting, dying coral covered with oil plume debris (left). Also affected were brittlestars, seen climbing in the healthy coral. Image courtesy of, Lophelia II 2010, NOAA OER and BOEM

Nearly two years after the Deepwater Horizon oil spill, the meticulous, long-term efforts of scientists finally yielded the official results: namely, that the brown, wilted, dying corals found at the Mississippi Canyon lease block 294 were indeed damaged by a plume of oil from the spill.

For many, it seemed a foregone conclusion. Back in December 2010, when news of the damaged corals first came out, their proximity to the leaking Macondo well seemed to be a “smoking gun” in its own right. What else could brown gunk (flocculent matter, if you are a scientist) covering damaged corals seven miles from the Deepwater Horizon site be, if not oil from the spill?

Yet, to this team of scientists, it was worth taking a closer look at the evidence with two-dimensional gas chromatography, sediment cores, coral samples, and mosaic imagery. Why? Because so much was at stake.

In order to understand the damage in the deep, the scientists had to start by understanding what was down there to begin with.

Amanda Demopoulos sorts and identifies the animals in a sieved sample. Image courtesy of, Lophelia II 2009: Deepwater Coral Expedition: Reefs, Rigs and Wrecks.

To support that mission, enter USGS research benthic ecologist Dr. Amanda Demopoulos, who studies life on the sea floor to piece together what types of organisms typically live together in deep sea communities. Her work involves digging sediment cores from the bottom of the ocean and sorting through the many tiny forms of life found there.

In addition to deep sea coral ecosystems, Demopoulos studies communities in parts of the Gulf where oil naturally seeps up from the seafloor and is in fact a wellspring of life, not a source of damage. Chemosynthetic ecosystems – the ones where food webs are based on chemicals rather than sunlight – tend to have different forms of life, such as tubeworms.

Demopoulos was on the November 2010 research expedition which first discovered the damaged corals. Funded by the National Oceanographic and Atmospheric Administration and the agency now known as the Bureau of Ocean and Energy Management, the goal of that expedition was to gather the basic data needed to construct a scientific understanding of the various undersea ecosystems.  It was part of a decades-long collaborative effort among federal and university scientists to explore deep sea ecosystems in an effort to provide sound baseline information for governance decisions about how to best balance natural resource use with protection. Demopoulos recalled watching the first images from the damaged site come in from remotely-operated vehicle.

An impacted coral with brittlestar climbing through it. Image courtesy of, Lophelia II 2010, NOAA OER and BOEM

“When we were watching the ROV video in the lab, I looked up at the video screen, and it looked starkly different from anything we’d ever seen before,” Demopoulos said. “The corals were all dark grey and lumped over, and it was clear these animals were not healthy. We’d seen dead coral, but this was so different, we immediately knew it was worth investigating further. When we got closer, there didn’t seem to be any secondary colonization, as we’d seen in the past on dead coral.”

The fact that no new animals — such as barnacles or hydroids — had begun to attach to and grow on the dead corals suggested the coral deaths had been recent, noted Demopoulos. This process, known as secondary colonization, is commonly observed on dead corals, but takes time to occur.

After the discovery of the damaged coral, Dr. Charles Fisher from the Pennsylvania State University led a follow-up expedition to more carefully investigate the damage itself, supported by a special National Science Foundation RAPID grant. Fisher worked with Dr. Helen White from Haverford College, Woods Hole Oceanographic Institute, Temple University, USGS and BOEM to assess the damage.

This push core shows discrete layers in a typical sediment sample. The light brown organic layer sits above a dark gray clay sediment. Most of the animals are found in the top layer of sediment. Image courtesy of, Lophelia II 2009: Deepwater Coral Expedition: Reefs, Rigs and Wrecks.

Demopoulos’ part in the overall effort to understand life in the deep ocean has been to understand what lives in the sediments of different types of environments, such as deep-sea corals and chemosynthetic communities. Some species may be generalists found in a variety of environments, while others will be unique to one type of habitat. Demopoulos also pieces together new information about how these tiny organisms are connected through food webs.

Without a baseline for understanding what is typical, Demopoulos would not be able to assess how those sediment dwellers were affected by the oil spill. Based on her expertise with sediment samples, Demopoulos helped design the best approach for assessing the corals at the Mississippi Canyon lease block 294 for the presence of oil and the extent of damage.

“The challenge we faced in this study was piecing together what happened from multiple lines of evidence, because no one was sitting on the sea floor when the plume went by. The corals were the only witness,” said Demopoulos, “We had to consider the proximity to the Deepwater Horizon site and the fact a deep-water plume had recently passed over the site, then closely examine the corals for tissue damage and signs of stress, such as the presence of mucus, and of course, the chemical signature of the oil. It was truly an interdisciplinary effort.”

Demopoulos pointed out that the cumulative knowledge about deep-sea communities from previous expeditions provided the baseline for scientifically assessing what they saw at the site.  “This is but one site in the Gulf of Mexico,” she said, “but it has shown how important it was for us to have a frame of reference as to what a healthy deep-sea coral ecosystem looks like. We are still trying to understand the extent to which this is occurring elsewhere in the Gulf of Mexico.”

The results of the efforts were recently published in the Proceedings of the National Academy of Sciences of the United States.

Coral reef affected by Montipora White Syndrome. Note the large swath of white skeleton tissue surrounded by normal (brown) corals.

Scientists have discovered an outbreak of coral disease called Montipora White Syndrome in Kāneʿohe Bay, Oʿahu. The affected coral are of the species Montipora capitata, also known as rice coral.

Rice corals provide valuable habitat, shelter, and foraging grounds for a variety of tropical marine fish and invertebrates and provide the fundamental structure of coral reefs. Rice corals are especially important to Hawai‘i’s marine ecosystems because they are one of the more abundant coral reef species in the region.

Thus, loss of corals can have negative effects on many other reef-associated organisms. In fact, losing a coral reef is similar to losing a rainforest, with many species reliant on that ecosystem for survival.

In addition, coral reefs in Hawai‘i are an important source of tourism and other economic income (fisheries).  For example, Kāneʿohe Bay, where this outbreak is concentrated, is a popular spot frequented by snorkelers, bathers, divers, boaters and fishermen.

While this particular disease outbreak seems limited to south Kāneʿohe Bay, coral diseases have the potential to be widespread, affecting large geographic regions. A prime example is the Western Atlantic and Caribbean where large tracts of coral reefs have either declined or disappeared due to diseases.

Science Helping Protect the Reefs

The investigation of this recent outbreak has been led by the University of Hawai‘i’s Hawai‘i Institute of Marine Biology in collaboration with University of Hawai‘i, West Oʿahu, and the USGS National Wildlife Health Center Honolulu Field Station.

Current efforts are focused on determining the extent of the outbreak and collecting samples for laboratory analysis. On a longer term scale, all three partner organizations are trying to devise better methods to detect coral disease and determine their cause.

For the most part, the causes of coral diseases are unknown. Since biologists do not know yet precisely what is killing corals, this has complicated management of coral reef diseases. Scientists are investigating many possible causes, including host immunity, host physiology, potential infectious agents like bacteria or parasites, and environmental variables such as increased seawater temperatures associated with climate change or land-based sources of pollution.

The USGS is one of the few organizations globally that has applied biomedical tools to investigate animal diseases to coral reefs (yes, corals are animals too). The USGS’s focus in this particular outbreak is to characterize the changes seen in sick corals by looking at the whole coral (what we see with the naked eye) as well as at the cellular level (under the microscope). The USGS is also developing other laboratory tools to help enhance our understanding of coral diseases with the eventual goal of pinpointing the causes of such important diseases.

What Is Montipora White Syndrome?

Corals are basically modified anemones, which are a group of predatory — and often strikingly pretty — marine organisms related to jellyfish. Corals secrete a calcium carbonate skeleton covered by a thin layer of tissues that form the foundation of coral reefs. Montipora White Syndrome affects the rice coral and involves loss of tissues from the coral until the underlying white skeleton is revealed/exposed, hence the name “white syndrome.”

History of Outbreak and Future Risks

Coral reef affected by Montipora White Syndrome. Note the large swath of white skeleton tissue surrounded by normal (brown) corals.

Based on surveys done since 2006 by the University of Hawai‘i and USGS, Montipora White Syndrome has historically been documented in coral reefs in Kāneʿohe Bay, albeit at low levels with scattered, isolated colonies affected. Large-scale outbreaks involving multiple coral colonies over a larger geographic area have only been documented since March 2011 and this recent event.

The reasons for this increase in outbreaks are presently unknown. Tissue loss diseases like white syndrome are particularly insidious in that they result in immediate loss of coral cover. Often, dead corals are then overgrown by algae, leading to permanent reduction in corals reefs and a change in the ecosystem from a coral-dominated to an algae-dominated reef.

Whether this will be the case here remains to be seen.

The USGS and partner scientists are actively involved in trying to better understand Montipora White Syndrome and other coral diseases. This will allow managers to also determine the environmental drivers of those causes, leading to better intervention and strategies to protect coral reefs.

For more information on this topic and other wildlife health related issues, visit the USGS Honolulu Field Station website.

Contact: Thierry Work, Jessica Robertson