International Society for Reef Studies Statement on Diseases on
Terry Done <
tdone at aims.gov.au
Thu Feb 4 14:43:03 EST 1999
Coral Reefs
Sender: owner-coral-list
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Reply-To: Terry Done <<tdone at aims.gov.au>
Dear Coral-listers,
Below is a statement on diseases of corals and other important coral reef
life
compiled by the International Society for Reef Studies and released
today.
The Society believes the statement is warranted at this time, following
its earlier
statement on Coral Bleaching published in its newsletter "Reef Encounter'
and on coral-list.
The International Society for Reef Studies (ISRS), consisting of over
750
members in over 50 countries, was founded in 1981 for the purpose of
promoting the production and dissemination of scientific knowledge and
understanding of coral reefs, both living and fossil. The ISRS
publishes
the scientific journal CORAL REEFS and holds periodic meetings around
the
world. Further information as well as membership details can be found
at:www.uncwil.edu/isrs.
For all correspondence regarding this statement or other ISRS matters,
please
contact Dr Richard Aronson, Corresponding Secretary, at:-
raronson at jaguar1.usouthal.edu.
Submitted on behalf of the Society by
Terry Done
President ISRS
___________________________________________
<bold><bigger><bigger><bigger>International Society for Reef Studies
Statement on Diseases on Coral Reefs
Released February 4 1999
</bigger></bigger></bigger></bold>
Diseases of corals and other organisms are having significant, negative
impacts on the structure and appearance of coral reefs. On some reefs,
the effects of disease have been of a similar magnitude to more familiar
disturbances, such as outbreaks of the crown-of-thorns starfish in the
Indo-Pacific and coral bleaching associated with elevated sea
temperatures. A new scientific awareness of diseases on coral reefs
leads to a host of questions about the novelty of recently discovered
syndromes, the importance of observed trends toward increasing infection
rates, and the extent to which human activities are responsible. This
statement, issued by the International Society for Reef Studies (ISRS),
summarizes current knowledge on the subject. It was compiled by an ad
hoc group of scientists in ISRS, composed of individuals who are directly
or indirectly considering disease as part of their research programs.
Disease is a natural process that has been poorly studied in the oceans
because of its ephemeral nature. Epidemics in animal populations,
called epizootics, are a serious threat to the health of coral reefs
worldwide. Recent observations of epizootics affecting sea urchins and
scleractinian corals show that diseases on reefs can devastate their
target populations and act as agents of rapid and dramatic community
change. Marine pathologists and microbiologists are attempting to
identify the causes of infection, but the pathogens responsible for most
diseases affecting reef organisms remain elusive. These difficulties are
complicating efforts by scientists and managers to study outbreaks and
decide if control measures are warranted. It is becoming clear, however,
that human activity is at least partially responsible for disease
outbreaks on coral reefs over the past decade.
Corals are colonial invertebrates related to sea anemones. They lay down
the limestone foundations of coral reefs, protecting tropical shorelines
and providing habitat for the many fish and invertebrate species that
feed a substantial proportion of the world's population. Like all living
organisms, corals are prone to diseases of various sorts. The incidence
of disease on coral reefs may be on the rise, but without historical,
baseline data it is difficult to determine if the observed increase is
real or simply a reflection of increased research activity. Recent
scientific reviews list four to six confirmed coral diseases in the
Caribbean region alone; other estimates, based only on observed symptoms,
run as high as fifteen. Bacteria, fungi, and cyanobacteria ("blue-green
algae") are known to cause diseases in corals. Sick and dying corals
are cause for concern, because coral death slows the rate of reef
construction. Reefs devastated by disease (or by other causes of coral
mortality) may not be able to keep up with sea-level rise, which is
naturally slow but may be accelerating due to global warming. And as
reefs degrade, fish and other seafood resources decline as well.
Three coral diseases--"white-band," "black-band," and "plague"-were
first reported in the Caribbean in the 1970s. The first documented,
regional-scale epizootic, however, affected the black-spined sea urchin,
Diadema antillarum. In 1983-84, a disease carried by ocean currents
killed more than 95 percent of the Diadema throughout the Caribbean.
This epizootic clearly demonstrated that diseases can have major impacts
on reef ecology. Before its mass mortality, Diadema was an important
herbivore: it ate fast-growing fleshy algae (seaweeds), keeping space
free for corals to survive and grow. After the urchins died, algae
increased dramatically on many Caribbean reefs. They colonized corals
that had been killed by hurricanes and by white-band disease.
Although the infective agent of white-band disease remains unknown, there
is some evidence that it is bacterial. White-band disease infected
populations of staghorn and elkhorn coral (Acropora cervicornis and
Acropora palmata) throughout the Caribbean region in the 1980s and 1990s,
inflicting enormous losses. Because Diadema also disappeared, seaweeds
rapidly colonized the dead coral skeletons, and as a result large areas
of Caribbean reefs have been covered with fleshy algae for over a
decade. Paleontologists working in Belize recently uncovered evidence
that the epizootic of white-band disease is without historical precedent:
staghorn coral has not died off before on a regional basis in at least
several thousand years. Staghorn and elkhorn corals are major
constructors of reef framework, and their loss could slow the rate of
reef growth in the Caribbean.
Many marine scientists suspect that human activities, such as pollution
and changing patterns of land use, promoted the spread of white-band
disease in Florida and the Caribbean. There is little evidence for a
human connection, however, other than the historical novelty of the
outbreak. Eutrophication, the enhanced input of nutrients by humans, may
be an important source of stress to reef organisms. Eutrophication may
compromise disease resistance, allowing opportunistic infections to take
hold and new diseases to emerge. A fungal infection of sea fans appears
to provide a link to human activity. The fungus, Aspergillus sydowii,
has infected large populations of sea fans in the Florida Keys and
throughout the Caribbean. Aspergillus sydowii is thought to be a
land-based fungus that has invaded the marine environment via the
sediment in terrestrial runoff.
Reliable information exists for two other diseases: black-band disease
and "plague type II." Black-band disease, caused by a consortium of
bacteria (including cyanobacteria) attacks and kills massive,
head-forming corals. Black-band disease could pose a serious threat to
populations of brain corals and star corals, which, like the Acropora
species, are important components of reef framework in the Caribbean.
Plague type II attacks head corals in Florida, but it has also been
observed elsewhere in the Caribbean. In this case, rigorous
microbiological work showed that the disease is caused by a single
bacterium, a new species of Sphingomonas.
Other epizootics are killing corals and many other important species on
reefs of the Pacific, Indian and Atlantic Oceans. Black-band disease and
white-band disease have now been identified on reefs throughout the
tropical Indo-Pacific, including the Red Sea, Mauritius, the Philippines,
Papua New Guinea, and the Great Barrier Reef of Australia. In the
Arabian Gulf, the newly discovered yellow-band disease is affecting up to
75 percent of the coral colonies in local populations. In addition,
diseases of algae, sponges, and fish have been and continue to be
identified.
Reefs throughout the world were stressed by unusually high sea
temperatures in 1997-98, and the worldwide episode of coral bleaching
that resulted may render corals more susceptible to disease. In the
Mediterranean, bacterial infections are associated with bleaching, and
disease outbreaks have been linked to predation by coral-eating snails in
the Red Sea. The causal connections among bleaching, predation, and
disease remain obscure, however.
The role of disease on coral reefs and possible interactions with
environmental influences should be a research priority over the next
several years. Despite the frustrating inability to identify pathogens
in most cases, reef scientists have detected symptoms that could
represent over a dozen new diseases. Diseases are now recorded as part
of standardized reef monitoring programs throughout the world, including
the Caribbean Coastal Marine Productivity (CARICOMP) Program, the
worldwide Reef Check, the Atlantic and Gulf Reef Assessment (AGRA)
Program, and a variety of government and private programs in Australia.
Because corals grow slowly, live for decades to centuries, and reproduce
sporadically, today's epizootics will probably have consequences that
reach far into the future. Multidisciplinary efforts, combining
microbiology, coral physiology and pathology, ecological monitoring, and
paleontology, will be necessary if we are to understand what is happening
and devise management strategies in response. The International Society
of Reef Studies endorses existing government and private funding of
multidisciplinary programs to promote research on the changing nature of
coral reefs. The Society recognizes the need for an increased level of
support if the many threats to reefs worldwide are to be understood and
mitigated.
</excerpt><<<<<<<<
Dr Terry Done
Australian Institute of Marine Science
PMB #3 Mail Centre,
Townsville Qld 4810
Australia
Phone 61 7 47 534 344
Fax 61 7 47 725 852
email: tdone at aims.gov.au
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