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Coral diseases
on the Great Barrier Reef
By Cathie Page
Coral diseases are caused by microbial pathogens including a variety of bacteria, algae, and fungi and often result in small amounts of coral mortality on otherwise healthy coral reefs. While coral diseases have affected only a small proportion of coral colonies in most reef parts of the world and have had limited impact on coral communities, this is not true in the Caribbean. In large areas of the Caribbean coral diseases have increased in frequency of occurrence, geographic range and impact. Coral diseases are emerging as important agents structuring coral communities1.
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The first record of corals infected by diseases came from reefs of Belize and Florida in 19732. Diseases that affect both hard and soft corals have been
since been found on reefs in many regions including the Caribbean, the Red Sea, the Pacific and the Indo-Pacific3. Coral diseases were first reported from the Indo-Pacific in 19854 and from the Great Barrier Reef in 19965. Diseased corals have been seen during manta tow surveys on the Great Barrier Reef since 19935.
The AIMS Long Term Monitoring Program has been recording incidences of coral disease on the Great Barrier Reef since 1999 using permanent transects. 48 reefs are surveyed each year. Two disease categories, black band disease and white syndrome, are recorded within a 2m belt transect on the reef slope.
Information
about methods
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A tabulate Acropora with white syndrome
Chain forming cyano-bacteria
that cause black band disease
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Black band disease on the
Great Barrier Reef
Black band disease was the first coral disease reported from the Great Barrier Reef5. Black band disease is characterised by a black band or line, 5-40mm wide. The coral tissue on one side of this band is healthy, while on the other side of the band the white coral skeleton shows where the coral tissue has recently died. In Atlantic corals, the black band of dying tissue has been found to move slowly over the colony surface at approximately 4mm a day6. Black band disease was initially thought to be caused by the cyanobacterium Phormidium corallyticum. It is now thought to be caused by a complex microbial community, including P. corallyticum, the
sulfide-oxidising bacteria Beggiatoa spp., a sulfate reducing bacteria and other heterotrophic bacteria7.
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The AIMS Long Term Monitoring Program has recorded incidences of black band disease on reefs along the length of the Great Barrier Reef and on inner, mid and outer-shelf reefs. This disease has been recorded from 10 of 15 regions in the four surveys since 1999.
A Montipora colony with
black band disease
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Although diseases have been recorded throughout the Great Barrier Reef, the number of reefs on which infected corals have been found each year has remained low.
Infected colonies were seen on two reefs in 1999, six reefs in 2000 and 2001 and on four reefs in 2002. The number of infected colonies on each of these reefs has also remained
small. In three sectors (Cairns, Cooktown/Lizard Island and the Capricorn-Bunkers) only one coral colony with black band disease has been found in the four years of surveys. The maximum number of colonies found infected with black band disease on any one reef is three colonies over the
1500m2 area surveyed. While present throughout the entire Great Barrier Reef, black band disease has not increased in abundance or in its impact on coral communities over the four years of surveys.
White syndrome
Due to the difficulty of differentiating between the coral diseases which are white in appearance, both white band and white plague diseases are placed in one category: "white syndrome".
White band disease is characterised by either a distinct line or a band/zone of bleached but intact coral tissue between the exposed coral skeleton and the healthy coral tissue8. In the Bahamas, the cause of white band disease is thought to be an
assortment of gram-negative bacteria including Vibrio charcharii9.
White plague is characterised by a white line between the living healthy coral tissue and the exposed coral skeleton8. This disease is more virulent than white band disease and results in the rapid death of coral tissue. The line of necrosing tissue typically moves through a coral colony at a rate of up to 2cm per day7. White plague is caused by a single species of gram-negative bacterium closely related to the genus Sphingomonas8.
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Like black band disease, white syndrome is widely distributed throughout the Great Barrier Reef, having been recorded in 13 of 15 regions in the four surveys conducted by the AIMS Long Term Monitoring Program since 1999. White syndrome has not been seen on inshore reefs around Cairns or Townsville.
An Acropora colony with
white syndrome
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The number of reefs with incidences of white syndrome has increased over the four survey years. In 1999 infected colonies were found on only
seven reefs, in 2002 this number had increased to 33
reefs (Figure 1). On most of these reefs white syndrome is present at low levels (1-2 colonies per reef), however, the number of infected colonies has been increasing on outer-shelf reefs in the Cooktown/Lizard Island and Capricorn-Bunker sectors over the past
four years.
| Figure 1. LTMP survey reefs where white syndrome has been
observed per survey year. |
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In 2002 surveys, the highest number of infected colonies was recorded at Carter Reef, an outer shelf reefs in the Cooktown/ Lizard Island sector. 101 colonies were infected with white syndrome within a
1500m2 area on this reef. In the Cooktown/ Lizard Island sector the total number of infected colonies ranged between 41 and 101 colonies per
1500m2 in 2002. In the Capricorn Bunker group the total number of infected colonies ranged between 17 and 77 colonies per
1500m2. In these two regions White syndrome appears to cause total mortality of infected colonies and appears to be resulting in declines in hard coral cover on these reefs.
The number of colonies infected with white syndrome on reefs within these two regions is still a small proportion of the total. Tropical cyclones or outbreaks of
crown-of-thorns starfish have been much more destructive to date.
Causes of increasing incidences of
white syndrome on some outer-shelf reefs
It is not known why some reef areas have higher incidences of coral diseases than others. In the Florida Keys and the Red Sea, incidences of diseased corals correlate with pollution10 or with large numbers of corallivorous Drupella gastropods11. If coral diseases were increasing as a result of anthropogenic pollution on the Great Barrier Reef, the highest levels of coral disease should occur on inner-shelf reefs. In fact, incidences of disease on the Great Barrier Reef have been increasing on outer-shelf reefs. These reefs are approximately 60km from the Queensland coast and are far from most anthropogenic sources of pollution. Coral cover on these reefs is the highest seen on any of the reefs surveyed since 1993. In the absence of cyclones and crown-of-thorns starfish, coral disease appears to be limiting the cover of hard corals on these reefs. There also does not appear to be a relationship between populations of Drupella and incidences of coral diseases on reefs of the Great Barrier Reef.
Are there other coral diseases on the Great Barrier Reef
A number of other potential diseases have been reported from other reef regions around the world. These diseases include shut-down-reaction, yellow band, yellow blotch, red band, rapid wasting disease, dark spot disease, white pox, and skeleton eroding band7.
The causes of these and other potential diseases are still being determined. The AIMS Long Term Monitoring Team records corals infected with these and other potential diseases
on the Great Barrier Reef.
For more information
about coral diseases open a new window to the coral
disease web site.
 Coral
diseases
References
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Porter J.W., Dunstan, P., Jaap, W.C., Patterson, L., Kosmynin, V., Meier,
O.W., Patterson, M.E., Parson, M. (2001) Patterns of spread of coral disease in the Florida keys. Hydrobiologia 460:1-24
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Antonius in: Kuta, K.G. and Richardson, L.L. (1996) Abundance and distribution of black band disease on coral reefs in the Northern Florida Keys. Coral reefs 15:219-223
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Kuta, K.G. and Richardson, L.L. (1996) Abundance and distribution of black band disease on coral reefs in the Northern Florida Keys. Coral reefs 15:219-223
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Antonius, (1995) A. Coral disease in the
Indo-Pacific: A first record. PSZNI Mar. Ecol 6(3):197-218
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Miller, I. (1996). Black band disease on the Great Barrier Reef. Coral Reefs15:58
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Rutzler, K. Santavy, D.L., Antonius, A. (1983) The black band disease of Atlantic coral reef corals. III. Distribution, ecology and development.
PSZNI: Mar Ecol 4(4):329-358
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Richardson, L. (1998) Coral disease: what is really known. TREE 13(11):438-443
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Richardson and Aronson, (in press) Infections diseases of coral reefs. Proc.9th Int. Coral Reef
Symp.
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Ritchie, K. and Smith, G. (1998) Description of type II white band disease in acroporid corals. Rev.Biol.Trop.46 (Suppl.5):199-203
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Harvell, C.D., Kim, K, Burkholder, J.M. Colwell, R.R, Epstein,
P.R, Grimes, D.J, Hofmann, E.E, Lipp, E.K., Osterhaus, A.D.M.E., Overstreet,
R.M., Porter, J.W., Smith, G.W., Vasta, G.R. (1999) Emerging marine diseases-Climate links and anthopogenic influence. Science 285:1505-1510
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Antonius, A., Riegl, B. (1998) Coral disease and Drupella cornus invasion in the Red sea. Coral reefs 17:48
May
2002
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