June 22nd USGCRP Seminar: "Status of the Health of Coral Reefs: An Update"
tsocci at usgcrp.gov
Wed Jun 16 12:04:38 EDT 1999
U.S. Global Change Research Program Seminar Series
Status of the Health of Coral Reefs: An Update
What is known about emerging diseases and pathogens affecting the health of
coral reefs worldwide? What is known about the causes of these emerging
diseases? What is the relationship, if any, between the observed global
climate warming and other environmental stresses, and the ability of coral
ecosystems to resist and overcome diseases and pathogens (new and old) in
the marine environment? How do elevated sea-surface temperatures affect
coral reefs? Do coral reefs generally have a temperature threshold beyond
which they can suffer injury or mortality? If so, what is that threshold?
What impact did the record warmth of 1998 have on reef ecosystems? What is
the suspected cause of increased amounts of dust in the tropical oceans
derived from the African continent since the mid-1970s? Has this increase
in dust affected the health of reef ecosystems, and if so, how?
Tuesday, June 22, 1999, 3:15-4:45 PM
Hart Senate Office Bldg., Room 902
(Use the north bank of elevators on the 1st floor to get to room 902)
Dr. Laurie L. Richardson, Associate Professor of Biology, Florida
International University, Miami, FL
Dr. James W. Porter, Professor of Ecology & Marine Sciences, University of
Georgia, Athens, GA
Dr. Richard Barber, Director of the Duke University/University of North
Carolina Oceanographic Consortium, Durham, NC
Emerging Coral Diseases
Emerging coral diseases have increased dramatically in recent years, both
in terms of increases in disease outbreaks and in the occurrence of new,
previously undescribed diseases, worldwide. Four coral diseases have been
characterized to date. Black band disease, the first coral disease to be
discovered (1973), consists of a dark line, or band, that migrates across
coral tissue at rates up to 1 cm per day, completely degrading coral tissue
and leaving behind bare coral skeleton. The disease consists of a specific
community of bacteria that work together to produce and maintain a toxic
chemical environment that kills corals. While the disease normally is
present at low levels on reefs (an incidence of <1%) it is a serious threat
in that it targets slow growing (<1 cm/year), reef building corals and
routinely kills corals that are several hundreds to a thousand years old.
In the last 5 years this disease has spread to coral reefs on a global
basis. Coral plague, another bacterial disease discovered in 1977,
reemerged in a new, more virulent form in 1995 on reefs of the Florida
Keys. Within months it spread to infect 17 species of corals and affected
over 200 km of reef tract. This is one of the most severe coral diseases
in that it has been known to kill, by rapid tissue degradation, up to 38%
of the most susceptible coral species in a matter of weeks. Since 1996
this disease has spread throughout the Caribbean. Aspergillosis is a newly
discovered disease that affects sea fans, a soft form of coral. This
fungal, lesion-producing disease is responsible for a massive sea fan
die-off that occurred throughout the Caribbean and the Florida Keys,
killing >90% of sea fans in regional epidemics since 1996. This disease is
linked to an increased supply of dust from the African continent. The last
disease, white band disease, is also responsible for massive coral die-offs
via complete coral tissue degradation. It has killed over 95% of the
important, shallow reef-building staghorn and elkhorn corals throughout the
Caribbean and the Florida Keys, and to date, is the only disease shown to
have completely restructured a long-standing coral reef (4,000 years old)
in less than a decade. The white band pathogen is unknown. A number of
other emerging coral diseases (red band disease, rapid wasting disease,
white pox, yellow band, and others) are incompletely characterized at this
It is known that coral diseases represent a threat to coral reefs on a
global basis. While the environmental causes of these diseases are just
beginning to be understood, it is clear that multiple stressors are
involved. Black band and coral plague disease activities are correlated
with warmer water temperatures, thus supporting the notion that a global
warming is contributing to the observed increase in coral disease.
Additional, recently proven stressors (for black band disease) include
increased nutrients and lowered salinities, with a positive correlation of
disease incidence with lower coral diversity. While the environmental
factors contributing to other disease outbreaks are not known at this time,
factors such as prolonged elevated water temperature, increased turbidity,
increased nutrient input and lower salinity are known to increase coral
susceptibility to disease.
Unpredictable Effects of Global Climate Change: Coral Bleaching, Coral
Disease, and Coral Response to Elevated C0-2
Corals are photosynthetic. Based on the presence of symbiotic algae within
their tissues, reef-building corals produce more oxygen than they consume.
Survival and reproduction of shallow-water coral is dependent on
maintaining a Production/Respiration ratio in excess of one. Factors that
significantly lower the P/R ratio kill corals. Like most tropical marine
organisms, corals exist much closer to their upper tolerance level in terms
of water temperature than to their lower tolerance level. Elevated oceanic
temperatures of as little as 2.7 degrees F (1.5 degrees C) over the average
summer temperature destroy the symbiotic algae resident in corals.
Resultant loss of this pigmented algae causes the coral animal to become
transparent, revealing the white limestone coral skeleton beneath, hence
the term "coral bleaching." If bleaching persists for an extended period of
time, the likely outcome is reef mortality. While several stresses can cause
bleaching, virtually all known examples of mass bleaching to date have been
caused by elevated water temperature. Although the onset of coral
bleaching is a response to elevated water temperatures, it does not prove
the existence of a global warming. However, a global climate warming best
explains the recent occurrence of mass bleaching worldwide. 1998 was the
warmest year on record, and recent reports from the Indian Ocean suggest
that up to 70% of all corals there died as a result of these
record-breaking temperatures. There is considerable concern that any
additional, future global warming will cause an increase in both the
frequency and severity of coral bleaching.
Elevated sea surface temperatures may also contribute to an increase in the
reported incidence of marine diseases from both tropical and temperate
oceans. For instance, some reefs in the Florida Keys have experienced a
loss of coral cover and biodiversity due to disease (caused by a host of
new pathogens). As a result of extensive surveys throughout the Florida
Keys it has been discovered that there has been a quadrupling of the number
of stations exhibiting disease, and a tripling of the number of coral
species afflicted by disease. One locality, the deep (65 feet) reef at
Carysfort Light, has experienced a 62% reduction of living coral cover
during the three-year survey due, in part, to coral disease.
The 1995 Intergovernmental Panel on Climate Change's "business as usual"
scenario (IS92a) projects that anthropogenic production of greenhouse gases
will result in a doubling of the current atmospheric C0-2 concentration from
355 ppm (parts per million) to nearly 700 ppm by the end of the next
century. Recent research on corals suggests that by the middle of the next
century, such elevated levels of CO-2 will reduce by 30-40%, the ability of
corals (and other tropical marine organisms) to deposit their limestone
skeletons and to calcifv normally. Adding to the influence of elevated C0-2
on global temperatures, new research suggests that elevated CO-2
concentrations will likely have serious consequences with regard to corals,
resulting from the direct effects of elevated CO-2.
The Coral Response to Climate Change
Worldwide episodes of coral bleaching, coral disease outbreaks and
macroalgal overgrowth of coral are increasing in frequency, intensity and
range. These deleterious events occur in all regions supporting reefs
including the Indo-Pacific, the Western Atlantic and the Caribbean.
Surprisingly, both inhabited and uninhabited regions are affected. These
recent coral reef changes have been attributed to (in order of assumed
importance) global warming, oxygen starvation, sediment loading,
overfishing of plant-eating animals and increased UV radiation. Only
global warming and increased UV radiation (resulting from ozone depletion)
have the global-scale influence that is characteristic of the scale of the
coral responses observed. In addition to a global vs. local issue, there
is a temporal enigma that may well provide a key to understanding causality
- many changes to coral ecosystems began very abruptly in the mid-1970s.
Since the mid-1970s there have been increases in the frequency, intensity
and range of outbreaks of a wide spectrum of "invader" micro-organisms,
including numerous pathogens that affect coral, other invertebrates,
amphibians and humans, and outbreaks of harmful algal blooms.
Global warming has a complex relationship to coral bleaching. Bleaching
occurs during episodes of elevated temperature that appear to be the result
of a combination of natural phenomena and human-induced changes to the
climate system. Global warming appears to elevate seasonal temperatures
while natural, short-lived climate phenomena such as El Nino, add to the
new seasonal maxima resulting in temperatures that can be lethal to coral
ecosystems, especially if sustained over a significant increment of time.
Thus, the combined effects of a long-term climate warming, superimposed on
the operation of short-term climate phemonena like El Nino, seem to best
explain the current epidemic of coral bleaching which was especially
widespread in 1998. These complex interactions are likely involved in the
increased incidence of disease outbreaks because bleaching weakens the
coral's ability to resist pathogens or competitors.
In addition, the observed global mean temperature increase may now be
acting in concert with other recent climate-induced changes. For example,
around 1976 there was a relatively abrupt climate shift in the Northern
Hemisphere that was reflected most clearly in the change in the North
Pacific and North Atlantic pressure systems. One consequence of this shift
was a prolonged drought in the Sahel region of Africa that resulted in an
increase by about a factor of five, the global supply of dust in the
atmosphere. Because this dust is iron-rich, and because the productivity
in tropical oceans is ordinarily limited by the lack of iron (which also
serves as a nutrient in tropical waters), its transport to typically
iron-poor regions of the tropical oceans leads to the reduction or removal
of an otherwise natural limitation or check on microbial growth. Thus,
this extra supply of iron may have spurred the growth of a variety of
invader organisms harmful to coral ecosystems. The timing of this
increased supply of atmospheric dust may help account for the peculiar
timing of the change in the rate of disease outbreaks in coral ecosystems
beginning in the mid-1970s.
As scientists struggle to understand the plight of coral, several ideas
seem particularly noteworthy:
1) In order to better understand the global decline in coral it will be
necessary to investigate coral ecosystems, global warming and marine
diseases and pathogens simultaneously, as a system, as opposed to isolated,
2) Anthropogenic climate change and natural climate variability occurring
together may produce a biological response that is quite different from
that of either process taken alone.
3) Significant ecological changes are probably already underway in the
ocean. In order to better understand and predict the response of marine
ecosystems, diseases and pathogens to climate-induced changes, it will be
necessary to gain a better understanding of marine ecosystems and
biological processes, and incorporate that knowledge into a more integrated
climate model. Even more fundamentally, complex environmental problems
such as this, require a research plan that is both strategic and integrated
- a systems approach.
Dr. Laurie L.Richardson is an Associate Professor of Biology at Florida
International University (FIU) in Miami, FL. Prior to her arrival at FIU
in 1990, she spent three years in the Ecosystems Science and Technology
Branch of NASA's Ames Research Center, California, first as a National
Research Council Fellow and then as a senior research scientist.
Dr. Richardson's area of specialization is the relationship between
microorganisms and the aquatic environment. She is particularly interested
in how microbial metabolism affects aquatic chemistry, and the
environmental cues that control the behavioral and mobility patterns of
microorganisms. Her research has been conducted in hot spring outflows,
lakes, hypersaline ponds, coastal and estuarine environments, and most
recently coral reefs.
In recent years Dr.Richardson has focused her research efforts on
identifying and understanding the biological mechanisms associated with
coral diseases. This work involves characterizing pathogens of newly
emerging coral diseases, determining the interactions between coral disease
and reef degradation (reef stresses), and investigating the relationships
between environmental perturbations and coral disease incidence. She is
also actively involved in research in the area of remote sensing of aquatic
ecosystems, including coral reefs.
Dr. Richardson received her Ph.D. in microbial ecology and physiology in
1985, at the University of Oregon, Eugene, OR.
Dr. James W. Porter is Professor of Ecology and Marine Sciences in the
Institute of Ecology at the University of Georgia. After teaching at the
University of Michigan from 1973 to 1997, he joined the faculty at the
University of Georgia, where he has won both the University's Outstanding
Teaching Award and Creative Research Award. Dr. Porter has also served as
Editor of Ecology and Ecological Monographs from 1974 to 1978, as Graduate
Coordinator for the Institute of Ecology from 1990 until 1997, and as
Associate Director for the Institute from 1993 to 1997. He was later
selected as a Fellow of the American Association for the Advancement of
Dr. Porter has also been called upon to testify before Congress on several
occasions, most recently on coral reef conservation issues and the effects
of global climate change on coral reefs. He is currently collaborating
with the US Environmental Protection Agency on long-term monitoring of
coral reefs, studying the distribution of coral diseases from Key Largo,
Florida to the Dry Tortugas.
Dr. Porter received his B.S. degree from Yale in 1969, and his Ph.D. from
Yale in 1973.
Dr. Richard T. Barber is the Harvey W. Smith Professor of Biological
Oceanography in the Nicholas School of the Environment at Duke University.
He also serves as director of the Duke/University of North Carolina
Oceanographic Consortium, a program that operates R/V Cape Hatteras. Dr.
Barber's research focuses on the interrelationship of large-scale thermal
dynamics and oceanic productivity, emphasizing how biological/physical
coupling contributes to partitioning of carbon between the ocean and the
atmosphere. His interests also lie in the role of iron in the regulation
of primary production in Antarctic waters as well as the equatorial
Pacific. His interest in the global decline of coral reef ecosystems stems
from observations on the apparent relationship between episodic influxes of
iron to outbreaks of marine "invader" organisms.
Dr. Barber has chaired numerous advisory and editorial committees related
to national and global research programs. He served as an advisor on the
NASA SeaWiFS (Sea-Viewing Wide-Field Sensor) Science Team and Review Panel
and on the U. S. JGOFS (Joint Global Ocean Flux Study) Synthesis & Modeling
Project. On behalf of the National Academy of Sciences, he served on the
Committee on Ocean's Role in Global Change, the TOGA (Tropical Oceans and
Global Atmosphere) Advisory Panel, and the International Ocean Science
Dr. Barber's honors and awards include the John Holland Martin Medal of
Excellence from Stanford University, the National Science Foundation
Creativity Award, the Rosenstiel Award in Oceanographic Science from the
Rosenstiel School of Marine and Atmospheric Sciences, University of Miami,
and the Ecology Institute's Prize in Marine Ecology. He is a Fellow in the
American Association for the Advancement of Science, the American
Geophysical Union, and the California Academy of Science.
Dr. Barber received his B. S. in zoology and botany at Utah State
University in 1962, and a Ph.D. in biological science at Stanford
University in 1967. He later a postdoctoral fellowship at the Woods Hole
Oceanographic Institute (WHOI) from 1967-1968, was an Assistant Scientist
at WHOI in 1969, and joined Duke University in 1970, as an Associate
Professor. From 1987 to 1990, he was the founding Executive Director of
Monterey Bay Aquarium Research Institute, and in 1990, he rejoined Duke
University as the Harvey W. Smith Professor of Biological Oceanography.
The Next Seminar is scheduled for Tuesday, July 20, 1999
Tentative Topic: Origin, Impact, and Implications of the "Dead Zone" in the
Gulf of Mexico
For more information please contact:
Anthony D. Socci, Ph.D., U.S. Global Change Research Program Office, 400
Virginia Ave. SW, Suite 750, Washington, DC 20024; Telephone: (202)
314-2235; Fax: (202) 488-8681 E-Mail: TSOCCI at USGCRP.GOV.
Additional information on the U.S. Global Change Research Program (USGCRP)
and this Seminar Series is available on the USGCRP Home Page at:
http://www.usgcrp.gov. A complete archive of seminar summaries can also be
found at this site. Normally these seminars are held on the second Monday
of each month.
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