Impacts of coral bleaching on pH and oxygen gradients across the coral concentration boundary layer: a microsensor study

Verena Schoepf, Christopher E. Cornwall, Svenja M. Pfeifer, Steven A. Carrion, Cinzia Alessi, Steeve Comeau, Malcolm T. McCulloch

Research output: Contribution to journalArticle

Abstract

Reef-building corals are surrounded by complex microenvironments (i.e. concentration boundary layers) that partially isolate them from the ambient seawater. Although the presence of such concentration boundary layers (CBLs) could potentially play a role in mitigating the negative impacts of climate change stressors, their role is poorly understood. Furthermore, it is largely unknown how heat stress-induced bleaching affects O2 and pH dynamics across the CBLs of coral, particularly in branching species. We experimentally exposed the common coral species Acropora aspera to heat stress for 13 d and conducted a range of physiological and daytime microsensor measurements to determine the effects of bleaching on O2 and pH gradients across the CBL. Heat stress equivalent to 24 degree heating days (3.4 degree heating weeks) resulted in visible bleaching and significant declines in photochemical efficiency, photosynthesis rates and photosynthesis to respiration (P/R) ratios, whereas dark respiration and calcification rates were not impacted. As a consequence, bleached A. aspera had significantly lower (− 13%) surface O2 concentrations during the day than healthy corals, with concentrations being lower than that of the ambient seawater, thus resulting in O2 uptake from the seawater. Furthermore, we show here that Acropora, and potentially branching corals in general, have among the lowest surface pH elevation of all corals studied to date (0.041 units), which could contribute to their higher sensitivity to ocean acidification. Additionally, bleached A. aspera no longer elevated their surface pH above ambient seawater values and, therefore, had essentially no [H+] CBL. These findings demonstrate that heat stress-induced bleaching has negative effects on pH elevation and [H+] CBL thickness, which may increase the overall susceptibility of coral to the combined impacts of ocean acidification and warming.
LanguageEnglish
JournalCoral Reefs
DOIs
Publication statusE-pub ahead of print - 9 Aug 2018

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coral bleaching
corals
coral
boundary layer
oxygen
bleaching
heat stress
seawater
Acropora
breathing
branching
photosynthesis
respiration
heating
heat
calcification
reefs
reef
warming
climate change

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Schoepf, Verena ; Cornwall, Christopher E. ; Pfeifer, Svenja M. ; Carrion, Steven A. ; Alessi, Cinzia ; Comeau, Steeve ; McCulloch, Malcolm T. / Impacts of coral bleaching on pH and oxygen gradients across the coral concentration boundary layer: a microsensor study. In: Coral Reefs. 2018.
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title = "Impacts of coral bleaching on pH and oxygen gradients across the coral concentration boundary layer: a microsensor study",
abstract = "Reef-building corals are surrounded by complex microenvironments (i.e. concentration boundary layers) that partially isolate them from the ambient seawater. Although the presence of such concentration boundary layers (CBLs) could potentially play a role in mitigating the negative impacts of climate change stressors, their role is poorly understood. Furthermore, it is largely unknown how heat stress-induced bleaching affects O2 and pH dynamics across the CBLs of coral, particularly in branching species. We experimentally exposed the common coral species Acropora aspera to heat stress for 13 d and conducted a range of physiological and daytime microsensor measurements to determine the effects of bleaching on O2 and pH gradients across the CBL. Heat stress equivalent to 24 degree heating days (3.4 degree heating weeks) resulted in visible bleaching and significant declines in photochemical efficiency, photosynthesis rates and photosynthesis to respiration (P/R) ratios, whereas dark respiration and calcification rates were not impacted. As a consequence, bleached A. aspera had significantly lower (− 13{\%}) surface O2 concentrations during the day than healthy corals, with concentrations being lower than that of the ambient seawater, thus resulting in O2 uptake from the seawater. Furthermore, we show here that Acropora, and potentially branching corals in general, have among the lowest surface pH elevation of all corals studied to date (0.041 units), which could contribute to their higher sensitivity to ocean acidification. Additionally, bleached A. aspera no longer elevated their surface pH above ambient seawater values and, therefore, had essentially no [H+] CBL. These findings demonstrate that heat stress-induced bleaching has negative effects on pH elevation and [H+] CBL thickness, which may increase the overall susceptibility of coral to the combined impacts of ocean acidification and warming.",
author = "Verena Schoepf and Cornwall, {Christopher E.} and Pfeifer, {Svenja M.} and Carrion, {Steven A.} and Cinzia Alessi and Steeve Comeau and McCulloch, {Malcolm T.}",
year = "2018",
month = "8",
day = "9",
doi = "10.1007/s00338-018-1726-6",
language = "English",
journal = "Coral Reefs",
issn = "0722-4028",
publisher = "Springer-Verlag London Ltd.",

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Impacts of coral bleaching on pH and oxygen gradients across the coral concentration boundary layer: a microsensor study. / Schoepf, Verena; Cornwall, Christopher E.; Pfeifer, Svenja M.; Carrion, Steven A.; Alessi, Cinzia; Comeau, Steeve; McCulloch, Malcolm T.

In: Coral Reefs, 09.08.2018.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Impacts of coral bleaching on pH and oxygen gradients across the coral concentration boundary layer: a microsensor study

AU - Schoepf, Verena

AU - Cornwall, Christopher E.

AU - Pfeifer, Svenja M.

AU - Carrion, Steven A.

AU - Alessi, Cinzia

AU - Comeau, Steeve

AU - McCulloch, Malcolm T.

PY - 2018/8/9

Y1 - 2018/8/9

N2 - Reef-building corals are surrounded by complex microenvironments (i.e. concentration boundary layers) that partially isolate them from the ambient seawater. Although the presence of such concentration boundary layers (CBLs) could potentially play a role in mitigating the negative impacts of climate change stressors, their role is poorly understood. Furthermore, it is largely unknown how heat stress-induced bleaching affects O2 and pH dynamics across the CBLs of coral, particularly in branching species. We experimentally exposed the common coral species Acropora aspera to heat stress for 13 d and conducted a range of physiological and daytime microsensor measurements to determine the effects of bleaching on O2 and pH gradients across the CBL. Heat stress equivalent to 24 degree heating days (3.4 degree heating weeks) resulted in visible bleaching and significant declines in photochemical efficiency, photosynthesis rates and photosynthesis to respiration (P/R) ratios, whereas dark respiration and calcification rates were not impacted. As a consequence, bleached A. aspera had significantly lower (− 13%) surface O2 concentrations during the day than healthy corals, with concentrations being lower than that of the ambient seawater, thus resulting in O2 uptake from the seawater. Furthermore, we show here that Acropora, and potentially branching corals in general, have among the lowest surface pH elevation of all corals studied to date (0.041 units), which could contribute to their higher sensitivity to ocean acidification. Additionally, bleached A. aspera no longer elevated their surface pH above ambient seawater values and, therefore, had essentially no [H+] CBL. These findings demonstrate that heat stress-induced bleaching has negative effects on pH elevation and [H+] CBL thickness, which may increase the overall susceptibility of coral to the combined impacts of ocean acidification and warming.

AB - Reef-building corals are surrounded by complex microenvironments (i.e. concentration boundary layers) that partially isolate them from the ambient seawater. Although the presence of such concentration boundary layers (CBLs) could potentially play a role in mitigating the negative impacts of climate change stressors, their role is poorly understood. Furthermore, it is largely unknown how heat stress-induced bleaching affects O2 and pH dynamics across the CBLs of coral, particularly in branching species. We experimentally exposed the common coral species Acropora aspera to heat stress for 13 d and conducted a range of physiological and daytime microsensor measurements to determine the effects of bleaching on O2 and pH gradients across the CBL. Heat stress equivalent to 24 degree heating days (3.4 degree heating weeks) resulted in visible bleaching and significant declines in photochemical efficiency, photosynthesis rates and photosynthesis to respiration (P/R) ratios, whereas dark respiration and calcification rates were not impacted. As a consequence, bleached A. aspera had significantly lower (− 13%) surface O2 concentrations during the day than healthy corals, with concentrations being lower than that of the ambient seawater, thus resulting in O2 uptake from the seawater. Furthermore, we show here that Acropora, and potentially branching corals in general, have among the lowest surface pH elevation of all corals studied to date (0.041 units), which could contribute to their higher sensitivity to ocean acidification. Additionally, bleached A. aspera no longer elevated their surface pH above ambient seawater values and, therefore, had essentially no [H+] CBL. These findings demonstrate that heat stress-induced bleaching has negative effects on pH elevation and [H+] CBL thickness, which may increase the overall susceptibility of coral to the combined impacts of ocean acidification and warming.

U2 - 10.1007/s00338-018-1726-6

DO - 10.1007/s00338-018-1726-6

M3 - Article

JO - Coral Reefs

T2 - Coral Reefs

JF - Coral Reefs

SN - 0722-4028

ER -