Download Session 3 Summary: Coral Holobionts, Black Band Disease and

Session 3 Summary: Coral Holobionts, Black Band Disease and Oyster Reefs
February 4th, 2010
Lauren Walsh Kinne
I.
Dr. Ester Peters (Coral Holobionts)
a. Outputs: (Dr. Peter’s Lecture)
 Overview of research
1. lots of research on symbioses
2. R.E. Brown (1997) discusses impacts of temperature and UV
radiation on coral (bleaching)
3. Rosenberg (2007) discusses role of a variety of
microorganisms on coral health (most recent/important) and
also puts forth hologenome idea
4. Leggat (2007) rebuttal of Rosenberg’s hologenome theory
(Dr. Peters does not agree w/this article)
5. Rohwer (2002) discusses diversity of bacteria that live on
coral
6. Peters (1986) discusses a protozoan found on coral
 Overview of Disease
1.
Disease-impairment of organisms vital functions resulting
from a biotic/abiotic source
2. Health-state of an organism when it functions optimally
w/out evidence of disease/abnormality
3. Controversy: Can there be a separation between coral health
and coral reef health?
4. Criteria for disease: pathogen, signs/symptoms, consistent
anatomical alterations
5. Many factors can detrimentally affect organisms including
biotic factors (fungi, bacteria, protozoa) and abiotic factors
(viruses, pollutants, light-intensity, temp.)
6. Pathogenic microorganisms cause disease/death of a host
7. A host’s susceptibility to the disease is related to the
virulence of the pathogen and other environmental factors
that can stress the host organism
8. Optimum envelope-much like a homeostatic plateau-health
of an organism is an aggregate of a lot of different aspects of
homeostasis including exposure to a variety of environmental
factors
9. Lesion-wound/injury (pathogenic change in tissue) may be
external or internal
10. Lesions are often morphological changes caused by cellular
injury; pathogen may have attacked a cellular processes such
as ability to photosynthesize or protein synthesis
11. Disease is caused by a complex interplay between
biomarkers, exposure to toxicants/microorganisms
12. Diseases are major denominators of population dynamics
13. Disease may lead to changes in ecosystems that will alter
trophic relationships/community interactions (Ex: Loss of
honey bees affecting pollination)


Diversity of Scleractinia
1. Color of coral based on dinoflaggellate algae (brownish tint)
2. Corals are made up of connected polyps consisting of sacs
with a single oral opening; retractable tentacles contain
cnidocytes (stinging cells); if you make a microscope slide of
a tentacle tip you can see the dinoflaggellates which live
inside coral and are part of an important mutualistic
relationship (coral protects algae, algae provides coral with
products of photosynthesis)
3. Specifically, algae is found in cells lining the gastrodermis,
which lines the interior of polyp (gastrovascular cavity)
Animal/Algal Symbioses
1. Algae that are part of the animal (coral) and algal symbioses
are called zooxanthellae
2. This type of algae uses coral waste (CO2, NH4) which
detoxifies potentially harmful (to the coral) molecules and it
also does photosynthesis producing small organic
carbohydrates like G3P and triose phosphate
3. Algae lives in vacuoles inside corals which is notable
because they are not broken down by lysosomes inside the
coral cells
4. The energy products provided by the algae allow the coral to
build bigger/better skeletons
5. Corals produce these skeletons by causing pH changes in the
coral cell layer next to the coral skeleton which allows
CaCO3 to crystallize (calcify)
6. Growth rates can be measured using dye (Dr. Peters did this
work for her post-doc research at the Smithsonian)
7. Corals can reproduce sexually or asexually
8. Many other types of organisms live in or on the outside of the
coral including other types of algae, fungi, worms, bivalves,
bacteria and protozoans
9.
10. http://www.columbia.edu/itc/eeeb/baker/N0316/Lecture%20
2/Images/anatomy-fig.jpg


History of Coral Bleaching (Trouble in Paradise)
1. 1980: 1st report of coral bleaching
2. 1982: Caribbean bleaching (El Nino event)
3. 1987: Major bleaching events (blamed on sea temperature,
light intensity)
4. 1997: Worldwide mass bleaching (finally linked to climate
change)
5. 2000: Adaptive bleaching hypothesis (zooxantellae are
replaced by more resistant algae)
6. 2000+: Bleaching linked to pathogenic bacteria
Reasons for Bleaching
1. Bleaching could be due to loss of photosynthetic pigments
inside the algae leading to atrophy of tissues or…
2. Expulsion of zooxantellae from gastrodermal cells (possibly
due to exocytosis from corals)
3. http://www.gbrmpa.gov.au/__data/assets/image/0006/13749/
Bleaching-and-mortality-dia.gif
4. Loss of the photosynthetic ability of the algae leads to tissue
atrophy, reduced growth and reduced gonadal development
of corals; often it can also lead to colony death
5. Interestingly, there is differential susceptibility within in the
colony, often between individuals of the same species (this
related back to the idea of adaptive bleaching in which
bleached coral can become recolonized by more heat tolerant
algae
6. Question: How do zooxantellae get into the coral tissue?
7. Question: What causes patching bleaching? Possibility that
it relates to protozoans that are evolutionarily related to
zooxantellae
8. Not all bleaching indicates disease; coral found deep under
Bay waters does not have associations w/algal whereas coral
closer to the surface does
9. Often bleaching is caused by a bacteria in the genus Vibrio
(Vibrio shiloi in Mediterrannean coral, Vibrio coralliliyticus
in Indo-Pacific coral) which enters mucocytes in the coral
and excretes toxins. As it cannot survive in cold water
temperatures it “winters” in the fire worm which is
considered its vector


10. Scientists have found a close relationship between quality of
mucus and types of microorganisms (mucus is affected by
changes in temperature, chemical contaminants, sediment)
Coral Holobiont: This is the idea that the dynamic interplay between
microorganisms should be looked at as one entity as well as a group
of interrelated organisms
Coral Hologenome: This is the idea that genes in different organisms
evolve in concert with each other and that natural selection acts on a
composite of these organisms and not on each individually
b. Impacts: (Questions/Discussion)
 Questions:
1. What are some of the difficulties associated with studying
coral bleaching?
a. Returning to the same spot, resource availability to
return year after year (have started to use markers
w/buoys to help mark a specific coral location)
2. Is there coral in the Bay that exhibit these mutualistic
relationships?
a. No, however, Hydra in the bay can develop
symbioses with green algae.
3. What is the effect of ocean acidification on coral bleaching?
a. Ocean acidification does not affect coral bleaching,
however, due to its effect on ocean pH it does slow
down coral growth by preventing calcification
 Link to previous lecture (and a question): Do the coral polyps
squeeze photosynthetic products out of the algae they are associated
much like the fungi associated with the algae in lichens do?
 Discussion/Link to PRV: This lecture is linked to Dr. Jonas’s lecture
and our study of the PRV in the conclusion section below.
II.
Dr. Jonas (Black Band Disease)
a. Outputs: (Dr. Jonas’s Lecture)
 History and Effects of Black Band Disease
1. Black band disease is the first disease identified with coral
(in the 1970’s) Question: Why wasn’t it seen before?
2. Black band disease is a non-traditional microbial mat (only
1mm thick) that can move up to 10 cm a year on coral
3. Black band disae takes away all living tissue, leaving behind
a skeleton only (recolonization has never been seen, however,
algae sometimes grows on the denuded surface)
4. Black band disease is a composite of
several unique type of organisms that are
non-pathogenic when grown individually
but become intensely pathogenic when
growing/interacting together as part of a
“pathogenic mutualism”
5. http://earthobservatory.nasa.gov/Features/Coral/Images/black
_band_detail.jpg

Pathogenic mutualism (the specifics) Dr. Jonas has a theory
regarding the functions of the organisms involved in black band
disease:
1. 1st, a lesion or depression forms in the coral.
2. 2nd, filamentous blue-green algae start to knit a mat above the
hole.
3. 3rd, the blue-green algae (cyanobacteria) create anoxic
conditions and also makes sugars
4. 4th, the anoxic conditions allow anaerobic bacteria (such as
Vibrio) to thrive and break down those sugars to lactic acid
5. 5th, other bacteria called desulfovibrios use lactic acid to
produce H2S, a toxic acid which breaks down coral, killing it
6. 6th, the breakdown of the coral releases nitrogen and
phosphorus which are used by the cyanobacteria
7. 7th, another bacteria called Vegetoa uses H2S as an e- donor
which detoxifies it and prevents the cyanobacteria from being
killed off
8. These microorganisms work together to create ideal living
conditions for their partners. Also, hydrophobic components
of these microorganisms (possibly glycolipids?) allow them
to reassemble naturally when separated (for example, due to
wave action)
b. Impacts: (Questions/Discussion)
 Questions:
1. How did black band disease get started?
2. Was there some climactic or other environmental
stressor/pressure that caused black band disease to suddenly
become pathogenic?
 Discussion/Link to PRV: This lecture is linked to Dr. Peter’s lecture
and our study of the PRV in the conclusion section below.
III.
Julia Welch (Link to PRV, Oyster Reefs)
a. Outputs: (Julia’s Lecture)
 Mutualisms present in coral reefs include the red snapping shrimp
and the sea anemone as well as the clown fish and the sea anemone.
The sea anemone provides protection while the clown fish lures prey
back to the anemone. Other mutualisms include the previously
discussed relationships between zooxanthellae and coral.
 Anthropogenic effects including pollution, cyanide/blast fishing,
trawling, harvesting coral for jewelry, damage from ships and oil
spills are negatively impacting the mutualistic relationships that
allow organisms to survive and flourish in our “rainforest of the
sea”.
 One example of mutualism present in the Potomac River Valley
include sea nettles and oyster spat. Sea nettles eat but spit out oyster
spat. Sea nettles also eat comb jellies which helps oyster spat
because comb jellies are one of oyster spat’s primary predators.
 Anthropogenic effects include pollution, detrimental oyster catching
techniques, blast fishing, trawling and release of ballast water
allowing invasive species (such as the bacteria that cause MSX and
dermo) as well as oil to adversely affect mutualistic relationships in
the aquatic ecosystems associated with the PRV. For example, in
one season sea nettles lost their oral arms earlier than expected
possibly due to anoxic water conditions related to anthropogenic
stressors. This meant that they died off earlier leaving oyster spat
exposed to the predation of comb jellies.
b. Impacts: (Questions/Discussion)
 Questions:
1. What is the connection between infection rate of striped
bass (75% infected) and anthropogenic causes in the PRV?
 Discussion/Link to PRV: I feel that Julia did an excellent job linking
our discussion of coral reefs and the PRV and I have attempted to
expand on this discussion in my conclusion section below.
IV.
Conclusion: Summarize how coral holobiont and/or black band disease models
might be pertinent to our understanding of PRV aquatic ecosystems, ecosystem
engineers and their habitats
In the last 40 years, both coral reefs and the oysters of the Chesapeake Bay
have been greatly impacted by infections caused by pathogenic microorganisms
from a variety of different kingdoms. Bacteria from the genus Vibrio have caused
coral bleaching around the world just as bacteria in associations with other
microorganisms cause black band disease in coral and bacteria also cause MSX
and dermo disease in oysters. In each of these cases, these microorganisms are
more virulent due to a host of other environmental factors. For example, the
bacteria that cause coral bleaching are much more virulent at higher temperatures.
Increased sea temperatures not only increase the viability of these bacteria, they
also increase the susceptibility of coral to coral bleaching. For example, high sea
temperatures and increased irradiance compromise the innate immune system of
coral reefs leaving them more open to infection by these bacteria. Other stressors
including sediments kicked up by boats and dredging as well as chemical
contaminants can decrease the quality of mucus created by corals leading to
increased susceptibility to infection by Vibrio bacteria and also by the organisms
that cause black band disease. This can be directly linked to the Potomac River
Valley because an increase in salinities in the waters of the Chesapeake Bay (most
notably in 1987 and 1988) has been linked to MSX and dermo disease becoming
more infective. Furthermore, these bacteria could have been brought to the Bay
as a result of ballast water dumping that also brings toxins and oil scum which can
further lower the innate resistance of oysters to infection. Once again, we see the
link between environmental stressors weakening the defenses of our target
organism (coral, oysters) and at the same time increasing the virulence of the
pathogen in question (Vibrio, MSX, dermo).
Looking beyond the similarities in anthropogenic stressors and pathogenic
microorganisms between coral reefs and Bay oysters, a valuable lesson can be
learned from the “bad guys” aka, black band disease. The complex symbioses
involved in the organisms that perpetuate black band disease can also be linked to
our understanding of aquatic ecosystems in the Potomac River Valley. Each
organism that is a part of black band disease is part of a pathogenic mutualism
that slowly and methodically kills coral. Ecological engineers that seek to clean
up the Bay and protect its important but fragile ecosystem dynamics should look
at black band disease as a sort of “evil genius” that incorporates the ideas of
mutualism to its best advantage. If all of the human populations that surround the
Bay could work together as well as the microorganisms associated with black
band disease do to help preserve our natural resources, I feel confident that the
Bay would be ecologically sound in no time at all!
Finally, a quick look at the relationship between the holobiont/hologenome
ideas and the Chesapeake Bay… It makes sense to me to think of organisms that
work collaboratively (not necessarily in symbiosis but even as part of a united
food web) as a single (albeit complex) unit that evolves together. The idea of
natural selection working on an ecosystem as a whole is directly relatable to the
Chesapeake Bay when one thinks of the effects of invasive species on the bay.
For example, the zebra mussel (thought to have been brought to the Bay in the
ballast water of ships) is a very effective filter-feeder who is out-competing local
filter feeders (oysters) placing stress on an already damaged organism. Because
zebra mussels came in from outside the “Chesapeake Bay holobiont” it does not
have natural predators and thus affects the natural balance of the Chesapeake Bay.
More information can be found at the website below:
http://www.mdsg.umd.edu/issues/restoration/non-natives/workshop/