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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.


The experimental set up.Seawater collected from the study site was pumped from the source-water tank through the system at a constant rate of about 0.5 l. min−1. Oxygen concentration (mg. l−1) and pH were recorded upstream and downstream the coral chambers every 5 min. 6,500 lux light (i.e. about 120 µ mol. m−2 .s−1) was provided by an artificial sunlight lamp (Dymax Rex-2). Water temperature was controlled by heaters (Lauda E100, with accuracy of ± 0.1 ° C) and a chiller (Aqua medic Titan 1500, with accuracy of ±0.5 °C). Net photosynthesis or respiration rate of corals was calculated in light and dark conditions as the difference in O2 concentration between the upstream and downstream chamber multiplied by the flow rate. The measured metabolic fluxes were not affected by gas exchange with the atmosphere since the measurement and sample chambers were in a closed circuit and water was exposed to air only in the source tank.
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fig-1: The experimental set up.Seawater collected from the study site was pumped from the source-water tank through the system at a constant rate of about 0.5 l. min−1. Oxygen concentration (mg. l−1) and pH were recorded upstream and downstream the coral chambers every 5 min. 6,500 lux light (i.e. about 120 µ mol. m−2 .s−1) was provided by an artificial sunlight lamp (Dymax Rex-2). Water temperature was controlled by heaters (Lauda E100, with accuracy of ± 0.1 ° C) and a chiller (Aqua medic Titan 1500, with accuracy of ±0.5 °C). Net photosynthesis or respiration rate of corals was calculated in light and dark conditions as the difference in O2 concentration between the upstream and downstream chamber multiplied by the flow rate. The measured metabolic fluxes were not affected by gas exchange with the atmosphere since the measurement and sample chambers were in a closed circuit and water was exposed to air only in the source tank.

Mentions: Autotrophic performance of corals was evaluated by the oxygen anomaly technique, which has the advantage of not being affected by micro-scale variability of photosynthetic activity along surfaces and can be used for estimating net metabolic performance of coral colonies or other macro-photosynthetic organisms (McCloskey, Wethey & Porter, 1978; e.g., Levy et al., 2004). Our semi-closed temperature-regulated aquarium setup illustrated in Fig. 1 is a modified version of the flow-based setups used to measure net photosynthesis of corals in the natural environment and mesocosms (McCloskey, Wethey & Porter, 1978; Jokiel, Jury & Ku’ulei, 2014). The metabolic fluxes were not affected by gas exchange with the atmosphere, since the water was in a closed circuit from the time it was pumped out from the source container until it passed all the measurement and sample chambers and returned to the source tank (Fig. 1).


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)

The experimental set up.Seawater collected from the study site was pumped from the source-water tank through the system at a constant rate of about 0.5 l. min−1. Oxygen concentration (mg. l−1) and pH were recorded upstream and downstream the coral chambers every 5 min. 6,500 lux light (i.e. about 120 µ mol. m−2 .s−1) was provided by an artificial sunlight lamp (Dymax Rex-2). Water temperature was controlled by heaters (Lauda E100, with accuracy of ± 0.1 ° C) and a chiller (Aqua medic Titan 1500, with accuracy of ±0.5 °C). Net photosynthesis or respiration rate of corals was calculated in light and dark conditions as the difference in O2 concentration between the upstream and downstream chamber multiplied by the flow rate. The measured metabolic fluxes were not affected by gas exchange with the atmosphere since the measurement and sample chambers were in a closed circuit and water was exposed to air only in the source tank.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493696&req=5

fig-1: The experimental set up.Seawater collected from the study site was pumped from the source-water tank through the system at a constant rate of about 0.5 l. min−1. Oxygen concentration (mg. l−1) and pH were recorded upstream and downstream the coral chambers every 5 min. 6,500 lux light (i.e. about 120 µ mol. m−2 .s−1) was provided by an artificial sunlight lamp (Dymax Rex-2). Water temperature was controlled by heaters (Lauda E100, with accuracy of ± 0.1 ° C) and a chiller (Aqua medic Titan 1500, with accuracy of ±0.5 °C). Net photosynthesis or respiration rate of corals was calculated in light and dark conditions as the difference in O2 concentration between the upstream and downstream chamber multiplied by the flow rate. The measured metabolic fluxes were not affected by gas exchange with the atmosphere since the measurement and sample chambers were in a closed circuit and water was exposed to air only in the source tank.
Mentions: Autotrophic performance of corals was evaluated by the oxygen anomaly technique, which has the advantage of not being affected by micro-scale variability of photosynthetic activity along surfaces and can be used for estimating net metabolic performance of coral colonies or other macro-photosynthetic organisms (McCloskey, Wethey & Porter, 1978; e.g., Levy et al., 2004). Our semi-closed temperature-regulated aquarium setup illustrated in Fig. 1 is a modified version of the flow-based setups used to measure net photosynthesis of corals in the natural environment and mesocosms (McCloskey, Wethey & Porter, 1978; Jokiel, Jury & Ku’ulei, 2014). The metabolic fluxes were not affected by gas exchange with the atmosphere, since the water was in a closed circuit from the time it was pumped out from the source container until it passed all the measurement and sample chambers and returned to the source tank (Fig. 1).

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.