Title: Coral Bleaching and Coral Diseases: An Overview
1Coral Bleaching and Coral Diseases An Overview
2Phylum Cnidaria
- Radial (or biradial) symmetry
- Diploblastic tissue organization
- Mesoglea between tissue layers
- Gastrovascular cavity
- Nerve net
- 2 body forms polyp medusa
- Cnidocytes (w/nematocysts)
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4Phylum Cnidaria
5Phylum Cnidaria
- 4 Classes
- Hydrozoa - hydroids
- Scyphozoa true jellies
- Cubozoa - Box jellies
- Anthozoa anemones corals
6Class Anthozoa
- Corals sea anemones
- All Marine
- Colonial (corals) or solitary (anemones)
- No medusa stage
- Polyps have a mesenteries and a pharynx leading
to the GV cavity - Amoeboid cells in the mesoglea
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9Zooxanthellae
- Algal symbionts
- Most cnidarians possess the dinoflagellate
Symbiodinium microadriaticum - Within the vacuoles of gastrodermal cells (about
50 dinoflagellates) - May contain as many as 30,000 symbionts per mm3
- The dinoflagellate enters the host in the egg or
larval stage or the adult may engulf free algal
cells.
10Zooxanthellae
- It is the pigments of the symbiotic algae that
give corals their coloration - In most cases, the symbiosis is obligate
- The host coral must live in shallow, clear waters
(lt75m) so the algae can photosynthesize. - Products of photosynthesis are translocated to
the coral as carbon compounds. - The algae utilizes the corals nitrogenous wastes
and acetate.
11Zooxanthellae
12Coral Bleaching
- Caused by the loss or large reduction in the
zooxanthellea (or their pigment). - White calcium carbonate skeleton of the the coral
becomes visible - Loss of zooxanthallea causes the corals to begin
to starve. - Large number of environmental factors that may
cause coral bleaching - Pollution, sedimentation, increased UV radiation,
freshwater runoff, salinity changes, changes in
atmospheric carbon dioxide - Strongest correlation has been found between sea
surface temperatures (usually linked to ENSO) and
bleaching
13Montastrea faveolata
14Coral Bleaching
- In most species, temps above 32C along with
increased UV radiation can trigger bleaching. - Although bleaching may be lethal, some corals do
recover. - They may regain their symbionts when conditions
return to normal (if timely) - During a bleaching event reproduction and growth
are negatively affected and corals tend to be
more susceptible to disease. - If conditions remain stressed for extended
periods, death individual coral colonies or
entire stretches of reef may occur.
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16Bleached section of The Great Barrier Reef off
the coast of Queensland, AU
171998 Massive Bleaching Event
- 1997-1998 experienced major bleaching events.
- Every coral region in the world effected by
bleaching in 1998 the first global bleaching
event - Triggered by severe ENSO conditions
- Summer 1997-1998 at The Great Barrier Reef was
the hottest on record - 67 inshore reefs showed high or extreme levels
of bleaching (14 offshore) - Sea temps were 1-2C above long-term averages
- On some reefs coral mortality reached up to 80
18More Recently
- 2002 ENSO conditions are thought to have
triggered this major bleaching event. - 2005 NOAA reported a major bleaching event in the
Caribbean. - Bleaching was reported from the entire area, the
Florida Keys, Texas coast, Costa Rica, Tobago,
Panama etc - Bleaching coincided with areas that experienced
levels of high thermal stress
19The DHW accumulates any HotSpots greater than 1
C over a 12- week window, thus showing how
stressful conditions have been for corals in the
last three months. It is a cumulative measurement
of the intensity and duration of thermal stress,
and is expressed in the unit C-weeks. DHWs over
4 C-weeks have been shown to cause significant
coral bleaching, and values over 8 C-weeks can
cause widespread bleaching and some mortality.
--NOAA Coral Reef Watch
20Coral Disease
- Viruses
- Bacteria
- Protozoan
- Fungi
- There are some diseases that appear to have no
known pathogen associated with them
21Rapid Wasting Disease
- First observed in 1996
- Leaves skeleton exposed with no living tissue
- Appears on the coral head first
- Although the skeleton appears normal, when
touched it simply crumbles - Cause is not yet confirmed, however
- There has been observation of a filamentous
fungus present on infected corals - Infected corals tend to be found where
unfavorable algal species occur, particularly
those that are often associated with excess
nutrients from runoff and sewage.
22Lethal Orange Disease
- Attacks the reef-building coralline algae
Porolithon onkodes - Proceeds in an orange band leaving behind the
white skeleton - Forms upright filaments and globules similar to
slime molds - Coralline lethal disease is probably related but
lacks the orange band - Believe to be a bacterial pathogen
23Dark Spot Disease
- Circular or irregular shaped dark spots appear on
the surface of coral - Usually begins as purple or gray lesions
- Sediment accumulates in the center of these
patches - Cause is unknown, possibly a combination of
pathogens
24Coral Viruses (Vega, 2008)
- Corals do not just have zooxanthellea as
symbionts, they also have an array of microbial
flora fauna, much like we do - The coral holobiont refers to the coral,
zooxanthellea this normal flora fauna. - Viruses present as a part of this normal state
are often those that infect protozoans,
metazoans, bacteria archaea - Certain viruses and bacteria may be detrimental
in times of stress - Temperature, nutrient levels, DOM
25Herpes Viruses
- Elevated abundance when temperature stress is
applied - Herpes viruses tend to be under control as long
as the coral is not stressed - Once stressed or compromised, the viruses become
much more active - Positive correlation has been found between
herpes genes and presence of coral tumors
26Geminivirus
- Single stranded DNA plant virus
- Increased abundance with increased nutrients
levels (ie fertilization runoff) - Symbiodinium abundance is negatively correlated
with certain Geminiviruses - Zooxanthellea being reduced or lysed as a result
of viral infection
27Bdellovibrio Phages
- Virus that infects bacterivorous bacteria
- Increased numbers in the presence of increased
DOM (carbon source) - Negative correlation between Bdellovibrio phages
and heterotrophic bacteria - Suggests that Bdellovibrio phages kill the good
bacteria that eat the bad
28Coral Bacterial Infections
- The good-guys on 1 cm2 of coral, there may be 10
million bacteria and 1 billion archaea. - Many are part of the normal flora and are
symbiotic - Control populations of harmful bacteria
29White Band Disease I
- Slow acting (1 cm/day)
- Attacks Acroporid (branching) corals only
- Tissue slowly peels off
- White bands found at the base and middles of the
coral - Gram negative rod shaped bacteria has been
associated with the disease.
30White Band Disease II
- Fast acting (up to 10 cm/day)
- Affects all corals Acroporid and non-Acroporid
- Bleaching edge that precedes the dead egde
- Bleaching edge may arrest and necrosis may catch
upif so, WBD I II look very similar - Bacteria in the genus Vibrio have been found in
the bleaching edge
31Black Band Disease
- Affects a large variety of corals
- Slow acting
- Black ring about a cm wide moving across the
coral surface. - Leave behind bare skeleton
- Caused by a number of bacteria resemblinga
bacterial mat - Sulfur-reducers
- Cyanobacteria
32Red Band Disease
- Host corals are limited to stag, star brain
corals - Brick red or dark brown microbial mat that
advances across the surface of corals - Bacterial components of the microbial mat seem to
differ from those found in black band disease
33Black Aggressive Band Disease
- Attacks a large variety of corals
- Similar to BBD, but the band is much thinner
- Actually a gray band
- Cyanbacterium from the genus Spirolina is the
most probable cause - Although others such as Ballesteros sp. have not
been entirely ruled out
34Yellow Band Disease
- Yellow botch disease
- Yellow pox disease
- Distinctive yellow band that proceeds across the
surface of the coral - Leaves behind a skeleton that is stained yellow
(penetrates a few mm) - Bacterial pathogen is Vibrio sp.
35Skeleton Eroding Band A protozoan
- Novel type of coral disease
- Caused by Halofolliculina corallasia, eukaryotic
protozoan - Damages not only the living tissue but also the
skeleton of the coral. - Attacks a variety of corals
- Colonies of black loricea (shields or houses)
- When they reproduce asexually, they release
chemicals toxic to the coral tissue.
36Aspergillus A fungus
- Aspergillus is a ubiquitous genus of Ascomycetes
soil fungiin terrestrial ecosystems - Has been found in marine environments including
coral reefs - Now known as the cause of brown sea fan disease
- First observed in 1995 when a large percentage of
purple sea fans appeared stuffed with material
and were turning brown. - That material was fungal hyphae
37Scolecobasidium A fungus (Raghukumar 1991)
- In the Bay of Bengal, 5 species of coral were
regularly found with necrotic patches - Sections of the patches showed a dark brown
hyphal network - Scolecobasidium a basidiomycete fungus was the
causative agent - In contrast to most marine fungi identified to
date being Ascomycetes
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39Citations
- Raghukumar, Chandralata Raghukumar, S. Fungal
Invasion of Massive Corals. 1991 Marine Ecology
12 (3)251-260 - Kohlmeyer, B Kohlmeyer, J. Mycological Research
News, Letters Fungi from Coral Reefs A
Commentary. 2003. Mycological Research 107 (4)
385-387 - Bruno, John F., Petes, Laura E., Harvell, C.
Drew, Hettinger, Annaliese. Nutrient Enrichment
can Increase the Severity of Coral Diseases.
2003. Ecology Letters 6 1056-1061 - Vega Thurber, R., Barott, K., Rodriguez-Brito,
B., Liu, H., Hall, D., Edwards, R.A., Desnues,
C., Angly, F., Haynes, M., Wegley, L., and
Rohwer, F. MetagenomicAnalysis Indicated that
Stressors Induce Production of Herpes-like
Viruses in the Coral Porites compressa. (in
review, PNAS) - http//www.noaanews.noaa.gov/stories2005/s2526.htm
- http//www.reef.crc.org.au/publications/brochures/
1998event.htm - http//www.marinebiology.org/coralbleaching.htm
- www.sbg.ac.at/ipk/avstudio/pierofun/aqaba/disease1
.htm - http//www.livescience.com/environment/070620_micr
obes_corals.html