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Photosynthetic response of Persian Gulf acroporid corals to summer versus winter temperature deviations.

Vajed Samiei J, Saleh A, Mehdinia A, Shirvani A, Kayal M - PeerJ (2015)

Bottom Line: Corals exposed to warming during summer showed a decrease in net photosynthesis and ultimately died, while corals exposed to cooling during winter were not affected in their photosynthetic performance and survival.Coral autotrophic capability Pn/R was lower at the warmer thermal level within eachseason, and during summer compared to winter.Our results suggest that the autotrophic performance of the Persian Gulf A. downingi is sensitive to the extreme temperatures endured in summer, and therefore its populations may be impacted by future increases in water temperature.

View Article: PubMed Central - HTML - PubMed

Affiliation: Iranian National Institute for Oceanography and Atmospheric Science , Tehran , Iran.

ABSTRACT
With on-going climate change, coral susceptibility to thermal stress constitutes a central concern in reefconservation. In the Persian Gulf, coral reefs are confronted with a high seasonal variability in water temperature, and both hot and cold extremes have been associated with episodes of coral bleaching and mortality. Using physiological performance as a measure of coral health, we investigated the thermal susceptibility of the common acroporid, Acropora downingi, near Hengam Island where the temperature oscillates seasonally in the range 20.2-34.2 °C. In a series of two short-term experiments comparing coral response in summer versus winter conditions, we exposed corals during each season (1) to the corresponding seasonal average and extreme temperature levels in a static thermal environment, and (2) to a progressive temperature deviation from the annual mean toward the corresponding extreme seasonal value and beyond in a dynamic thermal environment. We monitored four indictors of coral physiological performance: net photosynthesis (Pn), dark respiration (R), autotrophic capability (Pn/R), and survival. Corals exposed to warming during summer showed a decrease in net photosynthesis and ultimately died, while corals exposed to cooling during winter were not affected in their photosynthetic performance and survival. Coral autotrophic capability Pn/R was lower at the warmer thermal level within eachseason, and during summer compared to winter. Corals exposed to the maximum temperature of summer displayed Pn/R < 1, inferring that photosynthetic performance could not support basal metabolic needs under this environment. Our results suggest that the autotrophic performance of the Persian Gulf A. downingi is sensitive to the extreme temperatures endured in summer, and therefore its populations may be impacted by future increases in water temperature.

No MeSH data available.


Related in: MedlinePlus

Net photosynthesis of corals exposed to gradual temperature deviations.Coral net photosynthesis Pn as a function of positive (black) versus negative (grey) temperature deviation /dT/ from the annual mean value of 27.5 °C. Plot (A) shows raw data as recorded for each of the n = 5 replicate coral fragments within each treatment. The corresponding temperature ranges are indicated in italic on top of the plot. Plot (B) shows the fit from the Generalized Linear Mixed-effect Model (GLMM) in the linearized dimension (x = [dT]2). The equations of the linear regressions are provided in the form y = slope (±SE) x + intercept (±SE), and significant equation parameters are printed in bold character. Note the significant negative slope estimated for the summer heating treatment (p < 0.001) while the slope is not significantly different from zero in the winter cooling treatment (p = 0.171). Plot (C) illustrates results from the semi-parametric contrast curve (based on GLMM and penalized splines) identifying the domain of significant difference between the profiles obtained from the two treatments: the profiles are significantly different when the contrast curve ±CI (black-line ± shading) does not overlap with the y = 0 line (here for [dT]2 > 1. 6 ° C or dT = 1.3 °C; see vertical line in zoom insert). Black and grey dashed lines indicate the levels of the peak temperatures observed at the study site in summer (34.2 °C) and winter (20.2 °C), respectively.
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fig-3: Net photosynthesis of corals exposed to gradual temperature deviations.Coral net photosynthesis Pn as a function of positive (black) versus negative (grey) temperature deviation /dT/ from the annual mean value of 27.5 °C. Plot (A) shows raw data as recorded for each of the n = 5 replicate coral fragments within each treatment. The corresponding temperature ranges are indicated in italic on top of the plot. Plot (B) shows the fit from the Generalized Linear Mixed-effect Model (GLMM) in the linearized dimension (x = [dT]2). The equations of the linear regressions are provided in the form y = slope (±SE) x + intercept (±SE), and significant equation parameters are printed in bold character. Note the significant negative slope estimated for the summer heating treatment (p < 0.001) while the slope is not significantly different from zero in the winter cooling treatment (p = 0.171). Plot (C) illustrates results from the semi-parametric contrast curve (based on GLMM and penalized splines) identifying the domain of significant difference between the profiles obtained from the two treatments: the profiles are significantly different when the contrast curve ±CI (black-line ± shading) does not overlap with the y = 0 line (here for [dT]2 > 1. 6 ° C or dT = 1.3 °C; see vertical line in zoom insert). Black and grey dashed lines indicate the levels of the peak temperatures observed at the study site in summer (34.2 °C) and winter (20.2 °C), respectively.

Mentions: Coral net photosynthesis Pn was differently affected by positive versus negative temperature deviations (GLMM, interaction Treatment × dT2, df = 1,088, t-value = −6.7, p < 0.001). Coral Pn remained relatively consistent in winter when water temperature was lowered from the annual mean value of 27.5 °C toward a minimum of 17 °C (estimated Pn of 0.12 ± 0.02 and 0.10 ± 0.01 SE mgO2 respectively), but decreased substantially in summer with equivalent positive deviation toward a maxima of 38 °C (estimated Pn of −0.03 ± 0.01 at 38 °C; Fig. 3B). Net photosynthesis was reduced by 50% at the summer maxima level of 34.2 °C (estimated Pn of 0.06 ± 0.01 mgO2), and was negative above a temperature of 36.8 °C (dT = 9.3 °C). Coral photosynthetic performance differed significantly between summer heating and winter cooling treatments for a temperature deviation /dT/ > 1.3 °C (dT2 > 1.6 °C). This domain of significant difference between the two treatments is identified by the contrast curve technique (see Durbán et al., 2005) and illustrated in Fig. 3C as the portion of the covariable ([dT]2) where the contrast curve and its confidence intervals do not overlap with the no-difference threshold y = 0.


Photosynthetic response of Persian Gulf acroporid corals to summer versus winter temperature deviations.

Vajed Samiei J, Saleh A, Mehdinia A, Shirvani A, Kayal M - PeerJ (2015)

Net photosynthesis of corals exposed to gradual temperature deviations.Coral net photosynthesis Pn as a function of positive (black) versus negative (grey) temperature deviation /dT/ from the annual mean value of 27.5 °C. Plot (A) shows raw data as recorded for each of the n = 5 replicate coral fragments within each treatment. The corresponding temperature ranges are indicated in italic on top of the plot. Plot (B) shows the fit from the Generalized Linear Mixed-effect Model (GLMM) in the linearized dimension (x = [dT]2). The equations of the linear regressions are provided in the form y = slope (±SE) x + intercept (±SE), and significant equation parameters are printed in bold character. Note the significant negative slope estimated for the summer heating treatment (p < 0.001) while the slope is not significantly different from zero in the winter cooling treatment (p = 0.171). Plot (C) illustrates results from the semi-parametric contrast curve (based on GLMM and penalized splines) identifying the domain of significant difference between the profiles obtained from the two treatments: the profiles are significantly different when the contrast curve ±CI (black-line ± shading) does not overlap with the y = 0 line (here for [dT]2 > 1. 6 ° C or dT = 1.3 °C; see vertical line in zoom insert). Black and grey dashed lines indicate the levels of the peak temperatures observed at the study site in summer (34.2 °C) and winter (20.2 °C), respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig-3: Net photosynthesis of corals exposed to gradual temperature deviations.Coral net photosynthesis Pn as a function of positive (black) versus negative (grey) temperature deviation /dT/ from the annual mean value of 27.5 °C. Plot (A) shows raw data as recorded for each of the n = 5 replicate coral fragments within each treatment. The corresponding temperature ranges are indicated in italic on top of the plot. Plot (B) shows the fit from the Generalized Linear Mixed-effect Model (GLMM) in the linearized dimension (x = [dT]2). The equations of the linear regressions are provided in the form y = slope (±SE) x + intercept (±SE), and significant equation parameters are printed in bold character. Note the significant negative slope estimated for the summer heating treatment (p < 0.001) while the slope is not significantly different from zero in the winter cooling treatment (p = 0.171). Plot (C) illustrates results from the semi-parametric contrast curve (based on GLMM and penalized splines) identifying the domain of significant difference between the profiles obtained from the two treatments: the profiles are significantly different when the contrast curve ±CI (black-line ± shading) does not overlap with the y = 0 line (here for [dT]2 > 1. 6 ° C or dT = 1.3 °C; see vertical line in zoom insert). Black and grey dashed lines indicate the levels of the peak temperatures observed at the study site in summer (34.2 °C) and winter (20.2 °C), respectively.
Mentions: Coral net photosynthesis Pn was differently affected by positive versus negative temperature deviations (GLMM, interaction Treatment × dT2, df = 1,088, t-value = −6.7, p < 0.001). Coral Pn remained relatively consistent in winter when water temperature was lowered from the annual mean value of 27.5 °C toward a minimum of 17 °C (estimated Pn of 0.12 ± 0.02 and 0.10 ± 0.01 SE mgO2 respectively), but decreased substantially in summer with equivalent positive deviation toward a maxima of 38 °C (estimated Pn of −0.03 ± 0.01 at 38 °C; Fig. 3B). Net photosynthesis was reduced by 50% at the summer maxima level of 34.2 °C (estimated Pn of 0.06 ± 0.01 mgO2), and was negative above a temperature of 36.8 °C (dT = 9.3 °C). Coral photosynthetic performance differed significantly between summer heating and winter cooling treatments for a temperature deviation /dT/ > 1.3 °C (dT2 > 1.6 °C). This domain of significant difference between the two treatments is identified by the contrast curve technique (see Durbán et al., 2005) and illustrated in Fig. 3C as the portion of the covariable ([dT]2) where the contrast curve and its confidence intervals do not overlap with the no-difference threshold y = 0.

Bottom Line: Corals exposed to warming during summer showed a decrease in net photosynthesis and ultimately died, while corals exposed to cooling during winter were not affected in their photosynthetic performance and survival.Coral autotrophic capability Pn/R was lower at the warmer thermal level within eachseason, and during summer compared to winter.Our results suggest that the autotrophic performance of the Persian Gulf A. downingi is sensitive to the extreme temperatures endured in summer, and therefore its populations may be impacted by future increases in water temperature.

View Article: PubMed Central - HTML - PubMed

Affiliation: Iranian National Institute for Oceanography and Atmospheric Science , Tehran , Iran.

ABSTRACT
With on-going climate change, coral susceptibility to thermal stress constitutes a central concern in reefconservation. In the Persian Gulf, coral reefs are confronted with a high seasonal variability in water temperature, and both hot and cold extremes have been associated with episodes of coral bleaching and mortality. Using physiological performance as a measure of coral health, we investigated the thermal susceptibility of the common acroporid, Acropora downingi, near Hengam Island where the temperature oscillates seasonally in the range 20.2-34.2 °C. In a series of two short-term experiments comparing coral response in summer versus winter conditions, we exposed corals during each season (1) to the corresponding seasonal average and extreme temperature levels in a static thermal environment, and (2) to a progressive temperature deviation from the annual mean toward the corresponding extreme seasonal value and beyond in a dynamic thermal environment. We monitored four indictors of coral physiological performance: net photosynthesis (Pn), dark respiration (R), autotrophic capability (Pn/R), and survival. Corals exposed to warming during summer showed a decrease in net photosynthesis and ultimately died, while corals exposed to cooling during winter were not affected in their photosynthetic performance and survival. Coral autotrophic capability Pn/R was lower at the warmer thermal level within eachseason, and during summer compared to winter. Corals exposed to the maximum temperature of summer displayed Pn/R < 1, inferring that photosynthetic performance could not support basal metabolic needs under this environment. Our results suggest that the autotrophic performance of the Persian Gulf A. downingi is sensitive to the extreme temperatures endured in summer, and therefore its populations may be impacted by future increases in water temperature.

No MeSH data available.


Related in: MedlinePlus