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The Decline of the Coral Reef--Coral Bleaching and Diseases with Dr. Garriet W. Smith

Presenter: Dr. Garriet Smith
Host: Barbara Kolb
Discussion: SciTalk 6: Coral Reef Destruction

Background Information and Update.


By Garriet W. Smith Department of Biology and Geology, Univ. of South Carolina-Aiken Belle W. Baruch Institute for Marine Biology and Coastal Research Department of Marine Sciences; School of the Environment; Univ. South Carolina-Columbia

Coral reefs and the organisms associated with coral reefs are among the most productive, diverse and beautiful on earth. These ecosystems are not completely safe from danger, however. Although a great deal of attention has been given to a process called coral bleaching in the past few years (the loss or reduction of necessary symbiotic algae), it is becoming apparent that this is not the only threat to the survival of coral ecosystems. Diseases are killing our coral reefs in the tropics all over the world, and have been reported by a variety of marine scientists and divers. Visual evidence of diseases includes white bands, black bands and white and yellow blotches appearing on reef building corals. For the past five years, my research has focused on the causes of many of these diseases. I will begin by summarizing much of what we now know about coral diseases.

Rapid Wasting Disease:

The latest affliction to attack scleractinian or reef-building corals is Rapid Wasting Disease (RWD). RWD leaves the coral skeleton exposed and white with no living tissue on the surface. Massive reef building corals such as Montastraea annularis, and Colpophyllia natans. appear to be stripped of living tissue in the surface on the coral heads. Microscopic examinations conducted by Dr. Ray Hayes of Howard University and myself reveal the presence of a filamentous fungus. In addition, reef fish also appear to attack infected corals. Both parrotfish and damselfish have been observed repeatedly biting apparent infected tissue. Aggressive research is being conducted on this fast acting disease. RWD was first seen in late 1996 by Kalli DeMeyer, the director of the Marine Park in Bonaire and Dr. Rolf Bak of the Netherlands Institute for Sea Research. In Jan 1997, Marine Biologist James Cervino, and Dr. Thomas Goreau of the Global Coral Reef Alliance examined and identified this to be a new disease affecting one of the major reef builders in the Caribbean. RWD looks as if someone poured acid over the tops of the coral heads. The bright white skeleton is completely intact, with no living tissue. Touch the skeleton and it breaks up like granulated sugar. In Montastraea annularis, RWD can be seen on the tops of the coral heads and on Colpophyllia natans , it occurs around the rim and on a few areas throughout the coral structure. During the beginning stages of RWD, measurements show the spread to be one to two inches per day, then slowing after a month. There is no distinct boundary between the eroded skeleton and live tissue. Algae quickly overgrow the skeleton. Therefore when one sees skeleton, it indicates the recent occurrence of RWD. Our data show that the RWD and Yellow Pox Disease (YPD) occurs only at depths of 65 feet and above, predominantly in the shallows. Also, RWD and YPD are seen in areas where algal species, unfavorable to corals, occur. The presence of these algal species have been linked to excess nutrients from leaky septic tanks, poor sewage systems and high runoff from fertilizers.

Yellow Pox Disease:

Another disease affecting the same species in the Florida Keys and in the Netherlands Antillies, is Yellow Pox Disease. First discovered by Dr. Jim Porter (Univ. of Georgia) and Dr. Esther Peters (Tetratech) in 1996. This disease was also seen in close proximity to Rapid Wasting Disease in the Antillies region. Both affect the major reef builder Montastraea annularis. Yellow Pox is slow acting and can be seen with round yellow rings on the sides of the coral. The disease starts off with clear rings then turns into a yellow blotch around filamentous algae/sediment patches. This phenomenon has also been observed at low levels in pristine Bahamian waters by Tom McGrath of Earthwatch and myself.

White Plague Type II:

The only living reefs left in the United States are also being wiped out by numerous diseases, such as White Plague Type II (WP II). This disease was discovered in the Keys by Dr. Laurie Richardson and Dr. Steven Miller (Fla. Internat. Univ.) . It has been seen on non-acroporid corals (acroporid corals are branching and often look like large animal horns) like, Dichocoenia, Dendrogyra, Stephanocoenia, and Montastraea. WP II is fast acting, and spreading 1cm per day. A potential bacterial pathogen has been recently identified by Kim Ritchie of the University of North Carolina and myself. The bacterium is a newly discovered species and may represent an entire new genus. White Plague Type I A slower acting White Plague type I is also killing corals in the Keys, however this is not spreading as fast, Dr. Phil Dustan (Charleston Univ.) has been focusing on this disease since 1977, it also affects non-acroporid species like Colpohyllia, and Mycetophyllia. The type and role of the bacteria present in the tissues are still under investigation. Despite the lack of understanding of the origin of these diseases and their inter-relationships, their significance should not be ignored.

Black Band Disease (BBD):

Black Band Disease affects hard corals, fire corals, gorgonians, and has also been seen on acroporids on the Great Barrier Reef. Originally found in Bermuda and the Caribbean by Dr. Antonius, Dr. Garrett , and Dr. Ducklow in 1973. This disease is slow acting characterized by a black mat ring a few mm to cm wide on the surface of the coral tissue, moving across the surface of the skeleton, leaving the bare skeleton. The unaffected coral tissue appears normal in color, morphology, and behavior. Laurie Richardson and Debbie Santavy (EPA) have found that BBD is caused by a consortia of bacteria including sulfur-reducers, a cyanobacterium and other bacteria that resemble a microbial mat.

White Band Disease Type I:

White Band Disease (Type I) is also slow acting, only affecting Acroporid (branching) species of coral. First seen in the Caribbean, it has now been reported from reefs around the world. With Type I, coral tissue peels off slowly, with a white bands found at the base and middle of the coral. Ester Peters found bacterial aggregates present in Type I WBD.

White Band Disease Type II:

Type II WBD, described by Kim Ritchie and Garriet Smith, often progresses very quickly. With Type II WBD, a bleaching edge precedes the necrotic (dead) edge by up to nine centimeters per day. The bleaching edge can become arrested, allowing the necrotic edge to catch up. When this happens, Type I and II WBD appear very similar. A bacterium, similar to one previously isolated from sharks, appears to be the cause.

Abiotic and Biotic Factors in Coral Reef Destruction:

Coral reefs form and protect land masses in the tropical and sub-tropical seas around the world, and provide complete habitats to support fisheries and tourism industries. Coral mortalities have been occurring on a more frequent basis since the massive bleaching events of the 1980's. Bleaching, which can be caused by increased and decreased sea surface temperatures, over-exposure to UV radiation, sedimentation, and pollution, induces the expulsion of zooxanthellae (algae living inside the coral). The zooxanthellae provide the coral with their color and nutrition. However, in some cases, there is a clear distinction between bleaching and disease. Coral diseases, like WBD I, are distinct from bleaching says Dr. Esther Peters a marine scientist who has been researching diseases of marine organisms for more than 20 years. What takes place can only be described as a complete spontaneous disintegration of the coral tissue. The tissue sloths off, exposing the bare skeleton. On the other hand, Kim Ritchie and Garriet Smith showed a distinct bleaching phase associated with WBD II.


In addition to the diseases of hard corals, gorgonian (sometimes called soft corals) diseases have, at times, resulted in mass mortalities of extensive stands of sea fans. Ivan Negelkerkin (Carmabi Foundation, Curacao, N.A.) recently reported that sea fan disease is widespread throughout the Caribbean. Kim Ritchie and Garriet Smith reported that the cause is a species of the fungus Aspergillus. David Geiser (Univ. of California-Berkeley) indentified the pathogen as Aspergillus sydowii. The response of the sea fans to infection is being studied by Drew Harvell and Kiho Kim (Cornell Univ,). They have found that sea fans can produce an unknown anti-fungal compound which increases during the infection process. They also suspect this pathogen affects other gorgonians as well.

Politics of the Environment:

President Bill Clinton declared 1997 the "Year of The Reef". With this in mind, immediate action should be taken to understand the mechanisms behind coral reef mortalities and their possible interactions. Regular photographic or video monitoring is needed of selected coral heads and transects to determine changes in the abundance of coral diseases and their rates of spread. This objective can be met by a collaborative effort of the local people, volunteer monitoring programs, like Reef Relief in the Florida Keys, Global Coral Reef Alliance, and coral reef scientists. Earthwatch International (Watertown, MA) sponsors volunteer programs, like McGrath and Smith's Bahamian Reef Survey, designed to monitor the long-term health of specific reefs. However, more research is needed to determine the cause of these diseases through observational, field experimental lab analysis of tissue, and by attempting to culture an identify any possible disease causing microorganisms.

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