Coral/algal Reefs III

1
Coral/algal Reefs III

• The future?

2
Utilitarian justification for reef conservation

• Therapeutic compounds from marine species
• Anti-virals from sponges, seagrass
• Anti-tumor compounds from tunicate, dogfish,
  bryozoan, sea hares, cyanobacteria, sponge
• Compounds to promote bone grafts from stony
  corals
• Tourism
• Food
• Impact on global climate, carbon exchange
• Models for scientific study

3
Processes important in reef dynamics what
maintains the reef structure?

• Symbiotic mutualism (and dissolution of
  associations)
• Competition
• Predation and grazing
• Disturbance recovery

4
Questions

• Are symbiotic relationships increasingly
  disrupted?
• What are the consequences?
• How are organisms linked through symbiosis?
• Are changes reversible?

5
Coral bleaching (Hoegh-Guldberg)
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Coral bleaching dissolution of symbiosis

• zooxanthellae expelled from tissue
• polyp can persist for a while
• new associations can be formed
• responses to stresses

7
A general introduction to symbiosis

• De Bary (1850s) The living together of
  different species for an extended period of
  time.
• Proximity, not outcomes, define symbiosis
• Variation in characterizing some associations,
  e.g., pollination

8
Symbiosis has many dimensions

• Form of physical association
• Types of organisms involved
• Nature of the exchange or influence
• Outcomes of the interaction (, 0, -)
• Degree of dependence
• Evolutionary derivation of the association

9
Physical nature of the association

• Close proximity, but physically independent
• External contact
• Internal

10
What taxa are associated?

• Algae-invertebrate
• Among animals
• Bacteria/archaea - animals

11
What is exchanged?
Capability Donor Recipient
photosynthesis algae, bacteria protists, inverts
chemosynthesis bacteria invertebrates
added nutrients bacteria many animals
methanogenesis bacteria, protists anaerobic protists
cellulose digestion bacteria, protists herbivores (terrest.)
luminescence Vibrio, Photobact. molluscs, fish
protection cnidaria fish
12
What are the outcomes of symbiotic associations?

• Recipient

- 0
-
0 amensalism commensal
parasitism mutualism
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Outcomes nutrient exchange

• What is the evidence for exchange with
  endosymbiotic dinoflagellates?
• Experiment remove zooxanthellae
• ammonium content of polyp rises
• For Tridacna clams
• experimentally enrich with ammonium
• algal symbiont increases in density

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What is the degree of dependence?

• Facultative
• Obligate (often has very specialized morphology
  and life history)
• Symmetry is not necessarily found

15
What is the evolutionary origin of the
association?

• Parasite-host may evolve to be mutualistic
• Predator-prey (coral/dinoflagellate)
• Close proximity may lead to coevolved relationship

16
How can we evaluate importance?

• Removal experiments, e.g., cleaner fish
• Alter background conditions Chlorella/Hydra
  experiment

17
Bleaching occurs with high SST
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How does heat ( light) disrupt mutualism?

• Symbiodinium is damaged by oxidative stress

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Coral Responses

• Polyp responds immunologically
• Apoptosis autophagy
• Zooxanthellae can be expelled
• Polyp switches to heterotrophy
• This is a short-term strategy

20
Sensitivity to SST varies

• Among genotypes of Symbiodinium
• Among colonies within coral species
• Between different coral species
• Geographically for the same coral species

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Variation in Florida Keys corals, 2005
22
Brandt, M. E. 2009. The effect of species and
colony size on the bleaching response of
reef-building corals in the Florida Keys during
the 2005 mass bleaching event. Coral Reefs
28911-924.

• Background
• Summer fall, 2005 high SST in ne Caribbean
• Mass bleaching documented
• Methods
• Monitor corals for 191 colonies in permanent
  quadrats

23
Bleaching was correlated with heating
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Bleaching prevalence varied among spp
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Bleaching incidence varied with colony size
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Why and whats next?

• Symbiont clades vary genetically
• Corals can switch
• Symbiodinium communities can vary across
  environmental gradients
• Degree of flexibility is debated
• Hosts (corals) also vary
• Different fluorescent proteins for protection
• Different abilities in heterotrophy
• Coral structure affects the light environment

27
Competitive dynamics

• Exploitation competition (for light)
• Upright, branching corals can shade massive
  corals
• Encrusting algae can spread over corals
• Interference competition (for space)
• External digestion by some corals
• Sweeper tentacles for some species
• Hierarchy of competitive dominance
• Algae easily overgrow most corals
• Among corals Pocillopora is nastiest

28
Dynamics of predation on coral reef species

• Coral-feeding fish are present but usually not
  devastating
• Territorial damselfish create safe zones (up to
  60 of surface area)
• Coral-feeders have their own predators
• Starfish, such as Crown-of-Thorns can be
  problematic
• Population outbreaks can damage living corals

29
Dynamics of grazing on algal reef species

• Urchins are major consumers (e.g., Diadema
  antillarum)
• Grazing by herbivorous fish can be specialized on
  algae (more impact than fish feeding on corals)
• Grazing can suppress competitively dominant algae
• Indirect effects can become important