International marine survey of coral death

11/08/04



A Pachycerus coral in a reef at Palau displays three stages of health and disease: The dark band is the result of a cyanobacterial infection while the white area is dead coral skeleton. Kiho Kim

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ITHACA, N.Y. -- Now that marine scientists know how quickly disease epidemics can spread in the oceans -- up to 10,000 kilometers a year among fish, compared with 1,000 kilometers in diseases carried by flying birds -- they are focusing on dying organisms that can't move: the world's corals.

The researchers are conducting the largest-ever international assessment of ocean disease, called the Coral Reef Targeted Research and Capacity Building project and supported by the Global Environment Fund and the World Bank. With funding of about $28.8 million for the first five years of an anticipated 15-year project, the assessment aims "to fill critically important information gaps in the fundamental understanding of coral reef ecosystems so that management and policy interventions can be strengthened globally," according to C. Drew Harvell, a Cornell University professor of ecology and one leader of the coral reef assessment.

Harvell observes that the World Bank and Global Environmental Fund are focusing on coral reefs because of the organisms' highly threatened condition worldwide and because of their importance to the economy of developing countries. "We hope the new information will guide management policy on marine organisms of all kinds. But first we have to learn what's killing the corals," she says.

Two recently published papers in the journals Frontiers in Ecology and the Environment and Trends in Ecology and Evolution sum up marine science's current understanding of ocean-based diseases. Both papers result from a Working Group on Marine Disease chaired by Harvell and funded by the National Center for Ecological Analysis and Synthesis.



Measuring diseased corals in the Florida Keys are, from left, Cornell students Jessica Ward, Laura Petes and Cornell Professor of Ecology and Evolutionary Biology C. Drew Harvell, a leader of the newly commissioned Coral Reef Targeted Research and Capacity Building project. Kiho Kim

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In the Frontiers paper ("The rising tide of ocean diseases," Vol. 2, No. 7, by Harvell and 16 other researchers at Cornell and affiliated institutions), the researchers say that fast-moving water-borne epidemics can leave the terrestrial kind in the dust. A 1999-2000 herpes epidemic in sardines spread along the Australian coast at approximately 10,000 kilometers a year, while a mid-1980s bacterial infection to long-spined urchins ripped through the Caribbean at 3,000 to 4,8000 kilometers a year. By comparison, birds in North America spread West Nile virus across the continent at about 1,000 kilometers a year. The findings, the Frontiers authors write, "suggest that pathogens may pose a particularly severe problem in the ocean." The Trends paper ("Does terrestrial epidemiology apply to marine systems?" by Hamish McCallum of Australia's University of Queensland, Harvell and four colleagues) explains the difficulties in controlling ocean disease using land-bound methods.

Even where limited inoculation is possible -- by including antibiotics in food for aquaculture fish, for example -- the treatment is problematic. "Spillover of antibiotics from fish pens can lead to low doses of antibiotic being delivered to the wider marine ecosystem, with resulting selection for antibiotic resistance" among disease pathogens, the researchers wrote.

Rather, the marine scientists suggest in the Frontiers article, prevention might be the best medicine. "The most practical immediate remediation for many marine communities is to reduce pathogen inputs (especially from land) and synergistic stressors, such as warm temperatures and eutrophic waters," they write. They add: "Reducing such inputs requires knowing the source of new marine pathogens -- research should focus on identifying sources and reducing inputs while at the same time developing control measures."

That is precisely the prescription marine scientists have written for the their global assessment of coral disease. Preliminary surveys are already underway, with full cooperation of local marine scientists, at the four sites they will target as Centers of Excellence: Australia, the Philippines, Mexico and the western Pacific island nation of Palau. In addition to research, the project also aims at scientific training and capacity-building at the centers.

The ambitious project has a lot of questions to answer. Among them:

  • Does coral disease prevalence correlate globally with warming trends, or regionally with changes in climate and environmental quality?
  • Is disease changing the structure and composition of coral assemblages in all reef regions worldwide? Is disease changing coral reef diversity, perhaps by hampering reproduction of certain coral species?
  • How do pathogens reach the corals? In airborne dust containing spores, for example, of the Aspergillus fungus? Or in the marine worms, snails and fish that frequent coral reefs?
  • What is reducing corals' natural resistance to disease? How do environmental stresses, such as increases in water temperature and nutrients, affect coral immunity?
  • And, ultimately, can new knowledge about coral disease inform science-based policy making?

Project leaders say intensive research during the past decade has produced insights to the role of coral community structure and diversity in maintaining productive fish and invertebrate populations. They have begun to learn how disease affects coral community structure and diversity.

"Ultimately this concerns the human community," says Susan M. Merkel, a Cornell microbiologist and coordinator of the project. "If we find that improvements in waste-water treatment, solid-waste disposal and land-use practices can slow -- or even reverse -- the destruction of coral reefs and protect the fisheries that depend on the reefs, then local communities and governments need to know."

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