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Impact of nitrogen (N) and phosphorus (P) enrichment and skewed N:P stoichiometry on the skeletal formation and microstructure of symbiotic reef corals

Impact of nitrogen (N) and phosphorus (P) enrichment and skewed N:P stoichiometry on the skeletal formation and microstructure of symbiotic reef corals
Impact of nitrogen (N) and phosphorus (P) enrichment and skewed N:P stoichiometry on the skeletal formation and microstructure of symbiotic reef corals
Reported divergent responses of coral growth and skeletal microstructure to the nutrient environment complicate knowledge-based management of water quality in coral reefs. By re-evaluating published results considering the taxonomy of the studied corals and the N:P stoichiometry of their nutrient environment, we could resolve some of the major apparent contradictions. Our analysis suggests that Acroporids behave differently to several other common genera and show distinct responses to specific nutrient treatments. We hypothesised that both, the concentrations of dissolved inorganic N and P in the water and their stoichiometry shape skeletal growth and microstructure. We tested this hypothesis by exposing Acropora polystoma fragments to four nutrient treatments for >10 weeks: high nitrate / high phosphate (HNHP), high nitrate / low phosphate (HNLP), low nitrate / high phosphate (LNHP) and low nitrate / low phosphate (LNLP). HNHP corals retained high zooxanthellae densities and their linear extension and calcification rates were up to ten times higher than in the other treatments. HNLP and LNLP corals bleached through loss of symbionts. The photochemical efficiency (Fv/Fm) of residual symbionts in HNLP corals was significantly reduced, indicating P-starvation. Micro-computed tomography (µCT) of the skeletal microstructure revealed that reduced linear extension in nutrient limited or nutrient starved conditions (HNLP, LNHP, LNLP) was associated with significant thickening of skeletal elements and reduced porosity. These changes can be explained by the strongly reduced linear extension rate in combination with a smaller reduction in the calcification rate. Studies using increased skeletal density as a proxy for past thermal bleaching events should consider that such an increase in density may also be associated with temperature-independent response to the nutrient environment. Furthermore, the taxonomy of corals and seawater N:P stoichiometry should be considered when analysing and managing the impacts of nutrient pollution.
Acropora, nutrient enrichment, STOICHIOMETRY, linear extension, calcification, skeletal density
0722-4028
Buckingham, Michael, Christopher
fe08d09b-389e-4d25-b204-c4cbac92706b
D'Angelo, Cecilia
e6b94611-e6bb-4e02-9116-69d406f7550c
Chalk, Thomas
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Foster, Gavin
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Connelly, Zoe
b3694945-1b8d-4ea4-87d7-1ed47a5e4319
Saeed, Muhammad
ff93daec-06aa-4828-b444-97210e26dcf8
Olla, Carolina
f2b615a1-01c8-447a-91e8-947f08f511ba
Wiedenmann, Joerg
ad445af2-680f-4927-90b3-589ac9d538f7
Buckingham, Michael, Christopher
fe08d09b-389e-4d25-b204-c4cbac92706b
D'Angelo, Cecilia
e6b94611-e6bb-4e02-9116-69d406f7550c
Chalk, Thomas
0021bbe6-6ab1-4a30-8542-654d0f2d1a0a
Foster, Gavin
fbaa7255-7267-4443-a55e-e2a791213022
Connelly, Zoe
b3694945-1b8d-4ea4-87d7-1ed47a5e4319
Saeed, Muhammad
ff93daec-06aa-4828-b444-97210e26dcf8
Olla, Carolina
f2b615a1-01c8-447a-91e8-947f08f511ba
Wiedenmann, Joerg
ad445af2-680f-4927-90b3-589ac9d538f7

Buckingham, Michael, Christopher, D'Angelo, Cecilia, Chalk, Thomas, Foster, Gavin, Connelly, Zoe, Saeed, Muhammad, Olla, Carolina and Wiedenmann, Joerg (2022) Impact of nitrogen (N) and phosphorus (P) enrichment and skewed N:P stoichiometry on the skeletal formation and microstructure of symbiotic reef corals. Coral Reefs. (doi:10.1007/s00338-022-02223-0).

Record type: Article

Abstract

Reported divergent responses of coral growth and skeletal microstructure to the nutrient environment complicate knowledge-based management of water quality in coral reefs. By re-evaluating published results considering the taxonomy of the studied corals and the N:P stoichiometry of their nutrient environment, we could resolve some of the major apparent contradictions. Our analysis suggests that Acroporids behave differently to several other common genera and show distinct responses to specific nutrient treatments. We hypothesised that both, the concentrations of dissolved inorganic N and P in the water and their stoichiometry shape skeletal growth and microstructure. We tested this hypothesis by exposing Acropora polystoma fragments to four nutrient treatments for >10 weeks: high nitrate / high phosphate (HNHP), high nitrate / low phosphate (HNLP), low nitrate / high phosphate (LNHP) and low nitrate / low phosphate (LNLP). HNHP corals retained high zooxanthellae densities and their linear extension and calcification rates were up to ten times higher than in the other treatments. HNLP and LNLP corals bleached through loss of symbionts. The photochemical efficiency (Fv/Fm) of residual symbionts in HNLP corals was significantly reduced, indicating P-starvation. Micro-computed tomography (µCT) of the skeletal microstructure revealed that reduced linear extension in nutrient limited or nutrient starved conditions (HNLP, LNHP, LNLP) was associated with significant thickening of skeletal elements and reduced porosity. These changes can be explained by the strongly reduced linear extension rate in combination with a smaller reduction in the calcification rate. Studies using increased skeletal density as a proxy for past thermal bleaching events should consider that such an increase in density may also be associated with temperature-independent response to the nutrient environment. Furthermore, the taxonomy of corals and seawater N:P stoichiometry should be considered when analysing and managing the impacts of nutrient pollution.

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Accepted/In Press date: 15 January 2022
Published date: 20 April 2022
Keywords: Acropora, nutrient enrichment, STOICHIOMETRY, linear extension, calcification, skeletal density

Identifiers

Local EPrints ID: 456791
URI: http://eprints.soton.ac.uk/id/eprint/456791
ISSN: 0722-4028
PURE UUID: 99f76fc6-7b95-4835-abb7-f099ea796fd2
ORCID for Michael, Christopher Buckingham: ORCID iD orcid.org/0000-0002-8946-9854
ORCID for Thomas Chalk: ORCID iD orcid.org/0000-0002-2880-3847
ORCID for Gavin Foster: ORCID iD orcid.org/0000-0003-3688-9668
ORCID for Joerg Wiedenmann: ORCID iD orcid.org/0000-0003-2128-2943

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Date deposited: 11 May 2022 16:46
Last modified: 15 Jan 2023 05:01

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Contributors

Author: Cecilia D'Angelo
Author: Thomas Chalk ORCID iD
Author: Gavin Foster ORCID iD
Author: Zoe Connelly
Author: Muhammad Saeed
Author: Carolina Olla

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