Role of zooxanthellae in the thermal tolerance of corals, Great Barrier Reef

Brief description

The acclimatization potential of Acropora millepora was investigated through transplantation and experimental manipulation. Twenty-two colonies were sourced from each of a cool southern inshore reef (North Keppel Island) and a cool central offshore reef (Davies Reef) and transplanted to a warm inshore bay (Magnetic Island). A further 22 colonies from each of Magnetic Island, Davies Reef and North Keppel Island were kept at their respective 'native' reefs until their thermal tolerance limits could be experimentally tested together with the transplanted corals kept at Magnetic Island for 9 (Keppels) and 14 months (Davies).Corals were sampled for zooxanthella genotyping at the time of transplantation and again just before the temperature experiments. Zooxanthellae were identified based on the nuclear ribosomal DNA internal transcribed spacer 1 (ITS1) region using single stranded conformation polymorphism (SSCP) and sequencing analysis.Twelve nubbins (3-5 cm long) were cut from each of 6 colonies of A. millepora from each of 5 populations (Magnetic Island, North Keppel Island native, North Keppel Island transplants, Davies Reef native and Davies Reef transplants) and distributed equally among 4 temperature treatments (27.5, the non-bleaching control treatment; 30; 31 and 32°C each with 3 treatment replicates) in an indoor aquarium system.The fluorescence yield (dark-adapted) of zooxanthellae was measured using a Diving-PAM. Dead corals and white bleached corals that could not return a reliable yield were assigned a value of 0. Corals were designated healthy, bleached, dead.Data loggers have continuously recorded temperatures at half-hourly intervals at Magnetic Island since 1992, and at Davies Reef and Halfway Island (about 15 km from North Keppel Island) since 1995. To investigate the role of zooxanthellae in the thermal tolerance of the stony coral, Acropora millepora, in a large scale transplantation experiment.To show that thermal tolerance in this species is inextricably linked to the type of algal symbionts harboured. To show that individual corals can change their predominant algal symbiont types.To show that the potential for a change in algal symbiont may be population-specific and that increased tolerance resulting from symbiont change is limited inregard to expected future temperature increases. The first study to show thermal acclimatization is causally related to symbiont type.

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Maintenance and Update Frequency: notPlanned

Notes

Credit
Berkelmans, Ray WC, Dr (Principal Investigator)