Transcript The Role of Zooxanthellae in the thermal tolerance of corals

THE ROLE OF ZOOXANTHELLAE IN THE
THERMAL TOLERANCE OF CORALS
Emily Wanerka
Juliet Blass
KEY WORDS

Acclimatization – an organism’s response to
changes in its environment

Temperature change in our case
Zooxanthellae – photosynthetic algae that live in
coral tissues forming a symbiosis with the coral
 Coral Bleaching
 Climate Change

ABOUT THE AUTHORS

Ray Berkelmans
-Australian Institute of Marine Science (1999 –
present)
-climate change and coral reefs

Madeleine J.H. van Oppen
- Australian Institute of Marine Science
(program leader 2005 – present)
-Research scientist
-Marine molecular ecology
BACKGROUND INFORMATION




Projected increases
in temperature due
to global warming
are a major threat to
coral reefs.
Survival depends
largely on the corals’
ability to acclimatize
Algal symbiosis
between coral reefs
and zooxanthellae
Heat stress results in
bleaching of corals,
and can lead to death
of the coral
PURPOSE



Investigate the role
of zooxanthellae in
the thermal
tolerance of corals
Necessary to
understand whether
symbiont change will
affect the level of
thermal tolerance in
corals, with
anticipated increases
in sea surface
temperatures in
near future
Average seawater
temperatures
predicted to increase
1-3°C over the next
100 years
EXPERIMENTAL DESIGN
Acropora millepora –a widespread Indo-Pacific
hard coral species
 Three different populations of A. millepora
were studied
 22 colonies from North Keppel Island (coolest)
 22 colonies from Davies Reef (middle temp)
 22 colonies from Magnetic Island (warmest)
 Location of Study: Magnetic Island
 Control: Native colonies from each location

GEOGRAPHY OF STUDY
REGIONAL TEMPERATURES
Figure 2. Average daily temperatures at Magnetic Island, Davies Reef and Halfway Island
(approximately 15 km from North Keppel Island) for the warmest austral summer months. Data are
averages of 48 readings per day over 15 years (Magnetic Island) and 10 years (Davies Rf and Halfway
Is) and were averaged over the reef flat (0 m at LAT) and slope (5 m at LAT). A 10 day smoothing
function is applied to indicate the general trend in summer temperatures. Temperatures differences
between Halfway Island and Nor th Keppel Island are less than 0.1 8C based on an 18 month period
when loggers were deployed at both sites (data not shown).
Obtained Results
RESULTS
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Thermal tolerance
among native
populations was
strongly linked with
location
Relative thermal
sensitivity was
demonstrated by
contrasting and
significantly
different patterns of
zooxanthella
density
Reduced algal
density did not
affect the thermal
resistence of the
individual corals
associated
Increased tolerance
only proven with
type D
STRENGTHS/WEAKNESSES
Strengths
 Keppels results support adaptive bleaching
hypothesis
 Temperatures recorded in 3 areas every half
hour
 Transplants - highly regulated (depths etc)
 Weaknesses
- Method of symbiont change not certain
(shuffling, switching)
- Davies – Inconsistent with link between
acclimatization and location

FURTHER STUDY
Cell Biochemistry of the coral proteins
 Temperature limits in sustaining coral life, and
biological changes of coral in response to
changing temperatures
 Physiological characteristics of zooxanthella
 Process of Symbiont Change

REFERENCES
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http://data.aims.gov.au/staffcv/jsf/external/view.jspx;jsessio
nid=22A9E673BB4E173F062BBB20915F2B3E?partyId=10
0000290
Berkelmans, Ray, and Madeleine J.H. Van Oppen. "The
Role of Zooxanthellae in the Thermal Tolerance of Corals: a
‘nugget of Hope’ for Coral Reefs in an Era of Climate
Change." Proceedings of The Royal Society B (2006): 2305312. PubMed. 8 June 2006. Web. 17 Feb. 2011.
http://www.aims.gov.au/docs/publications/waypoi
nt/001/headlines-01.html