Presentation by Abimarie Otaño

1. Potential Costs of
Acclimatization to a
Warmer Climate: Growth
of a Reef Coral with Heat
Tolerant vs. Sensitive
Symbiont Types
Alison Jones1*, Ray Berkelmans2
1Centre for Environmental Management, Central Queensland University, Rockhampton, Queensland,
Australia, 2Australian Institute of Marine Science, Townsville,
Queensland, Australia
Environmental Science Graduate Program
CIAM 6117 Coastal Environment
Abimarie Otaño

2. Introduction
 Coral reefs are vulnerable to climatic change.
 Coral survival rate depends on acclimatization to
warmer conditions by shuffling symbiotic
zooxanthellae algae, from thermal sensitive to a heat
resistant genotype.
 To increase heat tolerance in a particular reef it must
occur zooxanthellae community shift of multiple coral
species.
 Coral depends on the symbiont energy1 to carry
calcification process. External ion transport and
eventually CaCo3 precipitation.
1.Zooxanthellaefunction in the cora (rETRmax)l: Facilitates the nutrients needed for the secretion of calcium
carbonate skeleton. Produce 95% of the coral energy requirements through photosynthesis.

3. Scleractinian order
 Scleractinian are hard skeleton corals which polyps secrete
a high rate of carbonate, distinguishing as the primary reef
builder.
 Benefits: coastal protection, carbon sink, provides habitat
for marine organism and touristic attractions.
 Growth rate of this species determines reef resilience and
regeneration after extreme events (i.e. bleaching, hurricane
impacts, anthropogenic pressures).
 Fast regeneration prevents phase shift directed to macro-
algae and soft corals dominance.
 Study objectives: Determine physiological comparison
between type C2 (thermal sensitive) and type D (thermal
tolerant) symbiont function in Acropora millepora corals of
the Keppel island in the Great Barrier Reef, Australia.

4. Scleractinian Acroporidae family
4 genera, >160 species of Acropora in the Indo-Pacific
Acropora millepora: Near threatened species
1 genera, 2 species of Acropora in the Caribbean
Acropora palmata Acropora cervicornis
Listed as Endangered specie in the 2006. (ESA, 2006).
Acropora porifera

5. Methods
Field study, at reef slope of Miall Island,
NE Australia
 43 pieces (15-20cm) of A. millepora colonies where cut
and pruned to similar sizes.
 Symbiodinum genotyped with Single Stranded
Conformational Polymorphism(SSCP) analysis of the
algal nuclear ribosomal DNA. Only colonies with intense
bands where selected. March 2004 and May 2006.
 Buoyant coral weight measurement, every 3 months from
March to December 2005.
 Growth measurement experiment after bleaching event in
February 2006.
 C2 and D colonies where placed in racks to allow
recovery.

6. Results: Field study
First experiment – before bleaching event in 2006
Growth rate of D colonies 38% lower that C2 (figure 3).
Growth varied with season, 71% higher in spring than in
winter (figure 4).
Figure 3. Growth of A. millepora in the field Figure 4: Seasonal growth

7. Results: Field study
Second experiment- after bleaching event in February 2006.
 Gained half of buoyant weight (figure 5).
 Overall growth rate was 47% lower. Symbiodium was retained.
 Highest growth rate rate in spring (76% lower than 2005).
 Lowest growth rate in autumn and winter.
Figure 5. Seasonal growth rate before and after bleaching.

8. Methods
Laboratory Australian Institute of Marine Science
 16 colonies where transplanted from Keppel Islands to
Magnetic island to allow recovery and acclimatization.
 6 explants (9 colonies type C2 and 7 type D) where cut and
distributed in three tanks.
 Controlled temperature conditions 23oC (spring/autumn non-
stressful) and 29oC (summer stressful conditions).
 Coral where fixed to plastic stand and rotated 180o daily to
allow enough light exposure.
 Approximate natural diurnal light cycle: 3.5h shaded light, 5h
un-shaded, 3.5h shaded and 12h darkness.
 Photosynthetically active radiation measurements F0 and Fm.
Fluorumeter (Fv/Fm): to monitor health of explant after dark-adapted max yield, assessed each morning after 8 hours of darkness.

9. Methods: Laboratory
Zooxanthellae densities and pigments:
 Explants where frozen (-20oC) and tissues where
stripped with air gun. Volume was homogenized for 20s
 Zooxanthellae count on 8 independent drops with a
compound light microscope.
 Centrifugation for 5s at 4oC separated algal pellet.
 Absorbance was measured with a spectrophotometer.
 Total Chlorophyll a was calculated from the equation of
Jeffrey and Haxo.

10. Results: Laboratory study
 Buoyant weight gained in explants was 29% less in
colonies with type D symbiont than in type C2 (figure
1).
 Zooxanthellae density for type D colonies was 22%
lower.
 Zooxanthellae density at 29oC density was 21% lower
than 23oC.
 Chlorophyll a in type D was 16% lower.
 Chlorophyll c2 in type D was 17% lower.
 Concentration of chlorophyll a and chlorophyll c2 at
29C was 20% and 19%, respectively, higher than 23C.

11. Figure 1. Growth rate in the laboratory
Figure 2. Algal density and chlorophyll pigments

12. Points to discuss:
1. In your opinion, corals zooxanthellae shift to thermal resistant
genotype is beneficial or prejudicial to the reef community?
2. What are the main environmental factors that might influence
the laboratory and field studies? Which method provides the
most reliable results?
3. What can be done to ensure the coral reef diversity and
functions taking into consideration climate change
projections?

13. Discussion
Growth rate is affected by:
1. Symbiont shuffling to thermally tolerant type after thermal
stress.
2. Bleaching stress.
✽Type D symbiodinium colonies had lower growth rate in
comparison with type C2, even in non-stressful conditions.
✽Shuffling to type D and C1 thermal tolerant symbiont
ocurred in A. millepora at Miall Island after bleaching event in
2006.
✽Coral growth reduced by 56% after bleaching.
✽Acclimation by shuffling to thermal resistant symbiont
reduce growth but improve heat tolerance and survival.

14. ✽ Growth differed by a 50% in juvenile A. millepora between
type D and C1 symbiont (Mieog et. Al. ).
✽ rETRmax 87% higher in juvenile corals with type C1, correlates
with a double 14C fixation.
Lower rETRmax and growth in type D symbiont:
✽ Result of the retaining of photosynthetically fixed carbon for
metabolism and repair.
✽ Increased use of energy for respiration.
✽ Increased rate of photo-inhibition and reduces
photosynthesis.

15. Conclusion
 Growth rate of A. millepora is affected by the shift to
thermal-resistant zooxanthela.
 In the long term, heat tolerance and resilience
benefits are much greater due to the expected
climatic change.
 Further research is required to truly quantify the effect
of symbiont genotypes on diverse coral growth as
they acclimatize to climate change.
 Evidence is needed to determine if there exist a
correlation between thermally sensitive symbiont and
a reduce photosynthesis carbon fixation in other
scleractinian corals.