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Negative response of photosynthesis to natural and projected high seawater temperatures estimated by pulse amplitude modulation fluorometry in a temperate coral

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ABSTRACT

Balanophyllia europaea is a shallow water solitary zooxanthellate coral, endemic to the Mediterranean Sea. Extensive field studies across a latitudinal temperature gradient highlight detrimental effects of rising temperatures on its growth, demography, and skeletal characteristics, suggesting that depression of photosynthesis at high temperatures might cause these negative effects. Here we test this hypothesis by analyzing, by means of pulse amplitude modulation fluorometry, the photosynthetic efficiency of B. europaea specimens exposed in aquaria to the annual range of temperatures experienced in the field (13, 18, and 28°C), and two extreme temperatures expected for 2100 as a consequence of global warming (29 and 32°C). The indicators of photosynthetic performance analyzed (maximum and effective quantum yield) showed that maximum efficiency was reached at 20.0–21.6°C, slightly higher than the annual mean temperature in the field (18°C). Photosynthetic efficiency decreased from 20.0 to 13°C and even more strongly from 21.6 to 32°C. An unusual form of bleaching was observed, with a maximum zooxanthellae density at 18°C that strongly decreased from 18 to 32°C. Chlorophyll a concentration per zooxanthellae cell showed an opposite trend as it was minimal at 18°C and increased from 18 to 32°C. Since the areal chlorophyll concentration is the product of the zooxanthellae density and its cellular content, these trends resulted in a homogeneous chlorophyll concentration per coral surface across temperature treatments. This confirms that B. europaea photosynthesis is progressively depressed at temperatures >21.6°C, supporting previous hypotheses raised by the studies on growth and demography of this species. This study also confirms the threats posed to this species by the ongoing seawater warming.

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Balanophyllia europaea. Regression and correlation analysis between mean maximum quantum yield (Fv/Fm) and temperature using a quadratic function model. Error bars represent the standard error. N number of temperature treatments.
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Figure 2: Balanophyllia europaea. Regression and correlation analysis between mean maximum quantum yield (Fv/Fm) and temperature using a quadratic function model. Error bars represent the standard error. N number of temperature treatments.

Mentions: Mean Fv/Fm was significantly different among temperature treatments (ANOVA, P < 0.001). The maximum value was obtained at 27°C, with a mean Fv/Fm of 0.550 (Table 2). When fitted with a quadratic function, mean Fv/Fm was correlated with temperature, whose variation explained 61% of Fv/Fm variance. According to the quadratic function, maximum Fv/Fm occurred at 21.6°C and while Fv/Fm decreased by 17.2% from 21.6 to 13°C, it decreased by 23.7% from 21.6 to 32°C (Figure 2).


Negative response of photosynthesis to natural and projected high seawater temperatures estimated by pulse amplitude modulation fluorometry in a temperate coral
Balanophyllia europaea. Regression and correlation analysis between mean maximum quantum yield (Fv/Fm) and temperature using a quadratic function model. Error bars represent the standard error. N number of temperature treatments.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4631832&req=5

Figure 2: Balanophyllia europaea. Regression and correlation analysis between mean maximum quantum yield (Fv/Fm) and temperature using a quadratic function model. Error bars represent the standard error. N number of temperature treatments.
Mentions: Mean Fv/Fm was significantly different among temperature treatments (ANOVA, P < 0.001). The maximum value was obtained at 27°C, with a mean Fv/Fm of 0.550 (Table 2). When fitted with a quadratic function, mean Fv/Fm was correlated with temperature, whose variation explained 61% of Fv/Fm variance. According to the quadratic function, maximum Fv/Fm occurred at 21.6°C and while Fv/Fm decreased by 17.2% from 21.6 to 13°C, it decreased by 23.7% from 21.6 to 32°C (Figure 2).

View Article: PubMed Central

ABSTRACT

Balanophyllia europaea is a shallow water solitary zooxanthellate coral, endemic to the Mediterranean Sea. Extensive field studies across a latitudinal temperature gradient highlight detrimental effects of rising temperatures on its growth, demography, and skeletal characteristics, suggesting that depression of photosynthesis at high temperatures might cause these negative effects. Here we test this hypothesis by analyzing, by means of pulse amplitude modulation fluorometry, the photosynthetic efficiency of B. europaea specimens exposed in aquaria to the annual range of temperatures experienced in the field (13, 18, and 28&deg;C), and two extreme temperatures expected for 2100 as a consequence of global warming (29 and 32&deg;C). The indicators of photosynthetic performance analyzed (maximum and effective quantum yield) showed that maximum efficiency was reached at 20.0&ndash;21.6&deg;C, slightly higher than the annual mean temperature in the field (18&deg;C). Photosynthetic efficiency decreased from 20.0 to 13&deg;C and even more strongly from 21.6 to 32&deg;C. An unusual form of bleaching was observed, with a maximum zooxanthellae density at 18&deg;C that strongly decreased from 18 to 32&deg;C. Chlorophyll a concentration per zooxanthellae cell showed an opposite trend as it was minimal at 18&deg;C and increased from 18 to 32&deg;C. Since the areal chlorophyll concentration is the product of the zooxanthellae density and its cellular content, these trends resulted in a homogeneous chlorophyll concentration per coral surface across temperature treatments. This confirms that B. europaea photosynthesis is progressively depressed at temperatures &gt;21.6&deg;C, supporting previous hypotheses raised by the studies on growth and demography of this species. This study also confirms the threats posed to this species by the ongoing seawater warming.

No MeSH data available.


Related in: MedlinePlus