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The Role of Zooxanthellae in the thermal tolerance of corals

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Presentation on theme: "The Role of Zooxanthellae in the thermal tolerance of corals"— Presentation transcript:

1 The Role of Zooxanthellae in the thermal tolerance of corals
Emily Wanerka Juliet Blass

2 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

3 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 Berkelmans: Research into climate change impacts and adaptation of coral reefs -particularly thermal stress causing the breakdown of symbiosis between corals and zooxanthellae Van Oppen -understanding marine microbes and symbioses

4 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 Algae provides the corals with its color and up to up to 90% of its nutrients Heat causes the algae to be toxic to corals, so they eject the algae and appear to be white

5 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 -study in this field is becoming increasingly important based on projected temperature changes

6 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 North Keppel – cool southern inshore reef - coolest of temperatures Davies Reef – cool central offshore reef - temp is 1.3 degrees celsius warmer than Keppels Magnetic Island – Central Barrier Reef corals were kept here on mesh racks at the same depth that they were collected data loggers record temperatures here every half hour  temp is 0.9 degrees celsius warmer than that at Davies

7 Geography of Study Great Barrier Reef  off Eastern Coast of Australia
Davies much closer to magnetic island – possibly suggests its resisitance to change in zooxanthellae type C2*  zooxanthellae of Davies differed slightly in ribosomal DNA from C2

8 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).

9 Obtained Results Magnetic Island colonies:
- most thermally tolerant population -only contained D zooxanthellae Keppels colonies: -80% had C2 at transplantation, 20% had D present along with C2 -all bleached, 7 died (those that died all contained C) -surviving colonies regained color, and only had D zooxanthellae present Davies colonies: - 13 suvived,(9 died) - all remaining corals either completely or partially bleached - The remaining corals contained C2 only

10 Results 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 hopeful, but not enough to help populations cope w/ potential increases in average tropical sea temps -type D  magnetic Island

11 Strengths/Weaknesses
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 ABH Environment change  loss of zooxanthellae followed by new formation of zooxanthellae more suited to apparent conditions depths remained constant Davies did not exhibit take up of new zooxanthella in its transplanted colonies Results in control and transplant were similar

12 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 Zooxanthellae – responses to temperature and light stress (as they are the weakest in the symbiont relationship) Stability of the thylakoid membrane in chloroplasts Symbiont change - shuffling of zooxanthellae or switching types?

13 References nid=22A9E673BB4E173F062BBB20915F2B3E?partyId=  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): PubMed. 8 June Web. 17 Feb nt/001/headlines-01.html

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