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First published online March 14, 2008
Journal of Experimental Biology 211, 1050-1056 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013284
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The effect of thermal history on the susceptibility of reef-building corals to thermal stress

Rachael Middlebrook*, Ove Hoegh-Guldberg and William Leggat{dagger}

Centre for Marine Studies and ARC Centre of Excellence for Coral Reef Studies, University of Queensland, St Lucia, QLD 4072, Australia


Figure 1
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  		Fig. 1 (A) Thermal stress profiles simulated in the experiment using Acropora aspera. Experimental temperature regimes are shown for the three different treatments, H2, H1, H0, and a control group (C). On day 2 (08:00 h), treatment H2 was heated to 31°C for 48 h and then returned to ambient temperature. On day 8 (08:00 h), treatment H1 was heated to 31°C for 48 h and then returned to ambient temperature. On day 14, H2, H1 and H0 were heated to an average of 34°C for 5 consecutive days simulating a bleaching event. (B) The table shows the experimental design, which was replicated twice in two tank systems. PS II (photosystem II efficiency), HPLC (pigment analysis including xanthophyll and chlorophyll a) and Symbiodinium density were measured 3 times per treatment, per replicate.

 

Figure 2
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  		Fig. 2. Changes in the (A) dark-adapted quantum yield (18:00 h) and (B) Symbiodinium cell density within the coral Acropora aspera during a simulated bleaching event. Coral colonies preheated 2 weeks prior (H2; filled circles), 1 week prior (H1; filled triangles), not preheated (H0; open diamonds), and controls (open squares) are indicated. Error bars, although not always visible, represent ± s.e.m., N=10. *Significant difference (post-hoc LSD analysis, P<0.05) between treatment and control on the same day; {dagger}significant difference (post-hoc LSD, P<0.05) between treatments on the same day.

 

Figure 3
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  		Fig. 3 Light induction recovery curves for effective quantum yield of photosystem II and NPQ for Symbiodinium within colonies of the reef-building coral Acropora aspera recorded at 18:00 h. (A) Amount of photosynthetically active radiation (PAR) that the coral branches were exposed to throughout the light induction recovery curve. (B) Effective quantum yield measurements for day 18. (C) The actinic light period showing the gradual saturation of photosystem II. (D) NPQ measurements for day 18. Corals preheated 2 weeks prior- (H2; filled circles), 1 week prior (H1; filled triangles), and not preheated (H0: open diamonds) were then subjected to a simulated bleaching event (control; open squares). Error bars shown, but not always visible, represent ± s.e.m., N=10. *Significant difference (post-hoc LSD analysis, P<0.05) between treatment and control on the same day; {dagger}significant difference (post-hoc, LSD, P<0.05) between treatments on the same day.

 

Figure 4
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  		Fig. 4. Changes in (A) dark-adapted NPQ, control from day 16 missing due to Imaging Pam malfunction, (B) chlorophyll a, (C) xanthophyll pool size and (D) daily light dosage (open circles) and xanthophylls cycling in Symbiodinium within the tissues of the coral Acropora aspera during a simulated bleaching event. Coral colonies preheated 2 weeks prior (H2; filled circles), 1 week prior (H1; filled triangles), and not preheated (H0; open diamonds) and controls (open squares) are indicated. Error bars shown, but not always visible, represent ± s.e.m., N=10. *Significant difference (post-hoc LSD analysis, P<0.05) between treatment and control on the same day; {dagger}significant difference (post-hoc LSD, P<0.05) between treatments on the same day. N=10 for A, N=6 for B,C.

 

Figure 5
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  		Fig. 5. Sea surface temperature recorded on Heron Island reef crest (HIRS, 23°33'S, 151°54'E) from the 9th to the 13th January 2006. Arrows indicate logger data where SST exceeded 32°C on two consecutive days for periods over 4 h.

 

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© The Company of Biologists Ltd 2008