39
Coral Bleaching and Coral Diseases: An Overview J. Kilic

Coral Bleaching and Coral Diseases: An Overview

  • Upload
    phyre

  • View
    111

  • Download
    0

Embed Size (px)

DESCRIPTION

Coral Bleaching and Coral Diseases: An Overview. J. Kilic. Phylum Cnidaria. Radial (or biradial) symmetry Diploblastic tissue organization Mesoglea between tissue layers Gastrovascular cavity Nerve net 2 body forms – polyp & medusa Cnidocytes (w/nematocysts). Phylum Cnidaria. - PowerPoint PPT Presentation

Citation preview

Page 1: Coral Bleaching and Coral Diseases: An Overview

Coral Bleaching and Coral Diseases: An Overview

J. Kilic

Page 2: Coral Bleaching and Coral Diseases: An Overview

Phylum Cnidaria

• Radial (or biradial) symmetry • Diploblastic tissue organization• Mesoglea between tissue layers• Gastrovascular cavity• Nerve net• 2 body forms – polyp & medusa• Cnidocytes (w/nematocysts)

Page 3: Coral Bleaching and Coral Diseases: An Overview
Page 4: Coral Bleaching and Coral Diseases: An Overview

Phylum Cnidaria

Page 5: Coral Bleaching and Coral Diseases: An Overview

Phylum Cnidaria• 4 Classes

– Hydrozoa - hydroids– Scyphozoa – true jellies– Cubozoa - Box jellies– Anthozoa – anemones &

corals

Page 6: Coral Bleaching and Coral Diseases: An Overview

Class 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

Page 7: Coral Bleaching and Coral Diseases: An Overview
Page 8: Coral Bleaching and Coral Diseases: An Overview
Page 9: Coral Bleaching and Coral Diseases: An Overview

Zooxanthellae• 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.

Page 10: Coral Bleaching and Coral Diseases: An Overview

Zooxanthellae

• 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

(<75m) so the algae can photosynthesize.• Products of photosynthesis are translocated to the

coral as carbon compounds. • The algae utilizes the coral’s nitrogenous wastes

and acetate.

Page 11: Coral Bleaching and Coral Diseases: An Overview

Zooxanthellae

Page 12: Coral Bleaching and Coral Diseases: An Overview

Coral 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

Page 13: Coral Bleaching and Coral Diseases: An Overview

Montastrea faveolata

Page 14: Coral Bleaching and Coral Diseases: An Overview

Coral 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.

Page 15: Coral Bleaching and Coral Diseases: An Overview
Page 16: Coral Bleaching and Coral Diseases: An Overview

Bleached section of The Great Barrier Reef off the coast of Queensland, AU

Page 17: Coral Bleaching and Coral Diseases: An Overview

1998 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%

Page 18: Coral Bleaching and Coral Diseases: An Overview

More 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”

Page 19: Coral Bleaching and Coral Diseases: An Overview

“The 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

Page 20: Coral Bleaching and Coral Diseases: An Overview

Coral Disease

• Viruses• Bacteria• Protozoan• Fungi• There are some diseases that appear to have

no known pathogen associated with them

Page 21: Coral Bleaching and Coral Diseases: An Overview

Rapid 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.

Page 22: Coral Bleaching and Coral Diseases: An Overview

Lethal 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

Page 23: Coral Bleaching and Coral Diseases: An Overview

Dark 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

Page 24: Coral Bleaching and Coral Diseases: An Overview

Coral 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

Page 25: Coral Bleaching and Coral Diseases: An Overview

Herpes 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

Page 26: Coral Bleaching and Coral Diseases: An Overview

Geminivirus

• 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

Page 27: Coral Bleaching and Coral Diseases: An Overview

Bdellovibrio 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”

Page 28: Coral Bleaching and Coral Diseases: An Overview

Coral 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

Page 29: Coral Bleaching and Coral Diseases: An Overview

White 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.

Page 30: Coral Bleaching and Coral Diseases: An Overview

White 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 up…if so, WBD I & II look very similar– Bacteria in the genus Vibrio have been found in

the bleaching edge

Page 31: Coral Bleaching and Coral Diseases: An Overview

Black 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

Page 32: Coral Bleaching and Coral Diseases: An Overview

Red 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

Page 33: Coral Bleaching and Coral Diseases: An Overview

Black 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

Page 34: Coral Bleaching and Coral Diseases: An Overview

Yellow 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.

Page 35: Coral Bleaching and Coral Diseases: An Overview

Skeleton 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.

Page 36: Coral Bleaching and Coral Diseases: An Overview

Aspergillus – A fungus

• Aspergillus is a ubiquitous genus of Ascomycetes soil fungi…in 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

Page 37: Coral Bleaching and Coral Diseases: An Overview

Scolecobasidium – 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

Page 39: Coral Bleaching and Coral Diseases: An Overview

Citations• 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_microbes_corals.html