Coral Reef Diseases

Background

Coral reefs are under increasing pressure from human activities, environmental stressors, global climate change, and a general deterioration of water quality. Throughout the western Atlantic, rapid declines in living coral cover have been observed over the last three decades. Live coral is being replaced by fleshy algae, encrusting and bioeroding sponges and other pest species that monopolize available space thereby preventing recolonization by important reef-building corals.

Since the mid-1990s, scientists have documented an increase in the number of coral diseases, coral species affected, geographic extent, prevalence and incidence, and rates of associated coral mortality. Although coral diseases and bleaching are now recognized as one of the most significant causes of mortality, yet many of the fundamental aspects of these diseases remain poorly understood.

Coral diseases may be caused by:

• Pathogens such as bacteria and fungi (infectious diseases);
• Stresses like elevated sea water temperatures and increased ultraviolet radiation;
• Poor nutrition, genetic mutations (non-infectious diseases); or
• Possibly from a combination of these factors.

Understanding the relationships between coral health and environmental parameters are of key importance in the study of coral disease. Increased sedimentation, nutrients and pollutants may be responsible for a proliferation of pathogens, or they may alter a coral’s defense mechanisms and immune responses, decreasing it’s ability to resist infection. Some disease causing pathogens are thought to have been introduced by man, such as a fungus of terrestrial origin that causes infection and mortality in sea fans and other gorgonians, and is postulated to have entered the marine environment via terrestrial run-off or via clouds of dust from West Africa. White pox, a disease only known to affect Acropora palmata in Florida, is caused by a common fecal entero-bacterium Serratia marcescens, which may have entered the marine environment via sewage discharge. Alarmingly, more and more reefs in unpopulated areas are also being impacted by diseases, despite the absence of most major human impacts in these areas.

Nomenclature

Unfortunately, a great deal of confusion exists over incompletely designated diseases or syndromes, duplicate names, and unsubstantiated causes or agents. Most coral diseases have names that reflect the color of the disease or affected tissue, the appearance of the exposed, recently killed skeleton, or the pattern of tissue loss. There have been over 30 names used by scientists to describe coral diseases. In some cases, different names have been given to the same disease sign, and in other cases what is being described as a disease may, in fact, be caused by a fish, snail, or other predator that feeds on coral. Complicating matters, the appearance of a disease may vary according to depth, season or geographic location, and some corals are affected by more than one disease at a time.

As a first step to rectify this problem, the CDHC organized a workshop in Madison Wisconsin to develop diagnostic criteria and nomenclature for western Atlantic diseases.

Epizootiology

In addition to difficulties in coral disease identification, there are only limited data available on the spatial and temporal distribution and abundance of diseases. Most of the research has been done in areas associated with marine laboratories and universities, including Florida, the U.S. Virgin Islands and Puerto Rico. Although diseases are thought to be more prevalent in areas affected by human threats, very few surveys have been conducted in remoter locations.

NOAA Fisheries is also conducting coral disease monitoring to document the prevalence and impact of coral diseases in the western Atlantic,in Puerto Rico, including reefs off Mona Island, and in Florida, where the main emphasis is on staghorn (Acropora cervicornis) and elkhorn (Acropora palmata) corals.

The goal of the work in Puerto Rico is to determine if remote locations that are removed from direct human impacts are being affected to the same degree by disease. One aspect of this research involves an examination of the spread of yellow-band disease among Montastraea annularis colonies off Mona Island.

Ecosystem Impacts of Diseases

Diseases alter reef community structure and function both directly and indirectly and are considered to be playing an increasingly important role in regulating coral population size, diversity and demographic characteristics. For example, the Caribbean-wide decline of acroporid corals, the two dominant space occupants and most important framework builders in reef crest and fore reef habitats, is the leading cause of the decline in coral cover in the Caribbean reported during the 1980s and 1990s. Coring studies from Belize and other locations revealed that mass mortalities at this scale had not occurred in at least the previous 3000-4000 years. More recently, Montastraea annularis complex populations are experiencing significant declines as a result of multiple diseases including black-band disease, yellow-band disease and white plague.

Coral Disease and Health Consortium

In response to the concerns over emerging coral diseases, the U.S. Coral Reef Task Force recommended formation of the Coral Disease and Health Consortium (CDHC) in March 2000 with the responsibility of organizing and coordinating scientific resources to document the condition of our coral reef ecosystems; determine the causes of decline in coral reef health; and provide technical information and assistance to managers and scientists regarding possible causes of diseases and remedies. The CDHC is being implemented through interagency partnerships of NOAA, the Environmental Protection Agency, and the Department of the Interior's Geological Survey, with involvement by over 50 partner institutions. The vision of the CDHC is to:

• Unify the coral health and disease research community;
• Implement research priorities identified in the National Research Plan;
• Update and maintain the National Research Plan;
• Develop tools and methodologies for diagnosis and assessment;
• Provide an expert knowledge system for use in diagnosis and epizootiology; and
• Provide education and outreach tools to equip a new generation of coral researchers.

NOAA Fisheries Service contributed to the development of the CDHC's National Research Plan which seeks to identify strategies needed to better understand and address the effects of natural and anthropogenic stressors on corals in order to contribute to the preservation and protection of coral reefs. Since the development of the plan, we have begun implementing the recommendations with support from the NOAA Coral Reef Conservation Program. Items in development include:

• Web Tool for Diagnosing Coral Disease to guide researchers through a three tiered diagnostic process to develop a preliminary diagnosis from field observations and recommend the laboratory tests necessary for confirmatory diagnosis;
• Nomenclature Steering Committee to review and evaluate all described coral diseases/syndromes and provide an accepted, standardized list of names;
• CDHC Pacific Workshop: Vision for Action to evaluate the state of knowledge of U.S. Pacific coral diseases and develop a strategy to address diseases; and
• Rapid Response Teams – A team of trained experts geared to providing local response capabilities to coral disease outbreaks.
  

Global Coral Disease Database

To begin gathering more comprehensive data on diseases and associated factors, NOAA Fisheries worked with the United Nations Environmental Program’s World Conservation Monitoring Centre (WCMC) to develop a Global Coral Disease Database, which maps the occurrence of diseases onto coral reef distributional maps, using GIS. This web-accessible database provides information on the type of disease, species affected and global distribution and it includes a reporting form for diseases, as well as more information on disease identification. The database has been recently updated to include reports received through December, 2004.

In partnership with UNEP-WCMC and the Project Aware Foundation we also developed a Field Guide to Western Atlantic Coral Diseases, a CD-ROM for distribution to volunteer divers, dive shops and researchers throughout the western Atlantic.

Management of Coral Diseases

NOAA Fisheries recently published, Priorities for Effective Management of Coral Diseases. This document summarizes much of the available information on coral disease epizootiology, including a compilation of all disease names that have appeared in the literature, information on the distribution and prevalence of the major coral diseases affecting Western Atlantic coral reefs, rates of tissue loss reported for these coral diseases and monitoring approaches that have been used to study disease epizootiology.

Return to NMFS coral reef fisheries management page.

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