Presentation on theme: "The Role of Zooxanthellae in the thermal tolerance of corals"— Presentation transcript:
1The Role of Zooxanthellae in the thermal tolerance of corals Emily WanerkaJuliet Blass
2Key WordsAcclimatization – an organism’s response to changes in its environmentTemperature change in our caseZooxanthellae – photosynthetic algae that live in coral tissues forming a symbiosis with the coralCoral BleachingClimate Change
3About the Authors Ray Berkelmans -Australian Institute of Marine Science (1999 – present)-climate change and coral reefsMadeleine J.H. van Oppen- Australian Institute of Marine Science (program leader 2005 – present)-Research scientist-Marine molecular ecologyBerkelmans:Research into climate change impacts and adaptation of coral reefs-particularly thermal stress causing the breakdown of symbiosis between corals and zooxanthellaeVan Oppen-understanding marine microbes and symbioses
4Background Information Projected increases in temperature due to global warming are a major threat to coral reefs.Survival depends largely on the corals’ ability to acclimatizeAlgal symbiosis between coral reefs and zooxanthellaeHeat stress results in bleaching of corals, and can lead to death of the coralAlgae provides the corals with its color and up to up to 90% of its nutrientsHeat causes the algae to be toxic to corals, so they eject the algae and appear to be white
5PurposeInvestigate the role of zooxanthellae in the thermal tolerance of coralsNecessary to understand whether symbiont change will affect the level of thermal tolerance in corals, with anticipated increases in sea surface temperatures in near futureAverage 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
6Experimental DesignAcropora millepora –a widespread Indo-Pacific hard coral speciesThree different populations of A. millepora were studied22 colonies from North Keppel Island (coolest)22 colonies from Davies Reef (middle temp)22 colonies from Magnetic Island (warmest)Location of Study: Magnetic IslandControl: Native colonies from each locationNorth Keppel – cool southern inshore reef- coolest of temperaturesDavies Reef – cool central offshore reef- temp is 1.3 degrees celsius warmer than KeppelsMagnetic Island – Central Barrier Reefcorals were kept here on mesh racks at the same depth that they were collecteddata loggers record temperatures here every half hour temp is 0.9 degrees celsius warmer than that at Davies
7Geography of Study Great Barrier Reef off Eastern Coast of Australia Davies much closer to magnetic island – possibly suggests its resisitance to change in zooxanthellae typeC2* zooxanthellae of Davies differed slightly in ribosomal DNA from C2
8Regional 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).
9Obtained Results Magnetic Island colonies: - most thermally tolerant population-only contained D zooxanthellaeKeppels 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 presentDavies colonies:- 13 suvived,(9 died)- all remaining corals either completely or partially bleached- The remaining corals contained C2 only
10ResultsThermal tolerance among native populations was strongly linked with locationRelative thermal sensitivity was demonstrated by contrasting and significantly different patterns of zooxanthella densityReduced algal density did not affect the thermal resistence of the individual corals associatedIncreased tolerance only proven with type Dhopeful, but not enough to help populations cope w/ potential increases in average tropical sea temps-type D magnetic Island
11Strengths/Weaknesses Keppels results support adaptive bleaching hypothesisTemperatures recorded in 3 areas every half hourTransplants - highly regulated (depths etc)WeaknessesMethod of symbiont change not certain (shuffling, switching)Davies – Inconsistent with link between acclimatization and locationABH Environment change loss of zooxanthellae followed by new formation of zooxanthellae more suited to apparent conditionsdepths remained constantDavies did not exhibit take up of new zooxanthella in its transplanted coloniesResults in control and transplant were similar
12Further Study Cell Biochemistry of the coral proteins Temperature limits in sustaining coral life, and biological changes of coral in response to changing temperaturesPhysiological characteristics of zooxanthellaProcess of Symbiont ChangeZooxanthellae– responses to temperature and light stress (as they are the weakest in the symbiont relationship)Stability of the thylakoid membrane in chloroplastsSymbiont change - shuffling of zooxanthellae or switching types?
13Referencesnid=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 Febnt/001/headlines-01.html