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Decoupling salinity and carbonate chemistry: low calcium ion concentration rather than salinity limits calcification in Baltic Sea mussels

Decoupling salinity and carbonate chemistry: low calcium ion concentration rather than salinity limits calcification in Baltic Sea mussels
Decoupling salinity and carbonate chemistry: low calcium ion concentration rather than salinity limits calcification in Baltic Sea mussels

The Baltic Sea has a salinity gradient decreasing from fully marine (<25) in the west to below 7 in the central Baltic Proper. Habitat-forming and ecologically dominant mytilid mussels exhibit decreasing growth when salinity >11; however, the mechanisms underlying reduced calcification rates in dilute seawater are not fully understood. Both [HCO 3 ] and [Ca2C] also decrease with salinity, challenging calcifying organisms through CaCO3 undersaturation (1) and unfavourable ratios of calcification substrates ([Ca2C] and [HCO 3]) to the inhibitor (HC), expressed as the extended substrate inhibitor ratio (ESIR). This study combined in situ monitoring of three southwest Baltic mussel reefs with two laboratory experiments to assess how various environmental conditions and isolated abiotic factors (salinity, [Ca2C], [HCO3 ] and pH) impact calcification in mytilid mussels along the Baltic salinity gradient. Laboratory experiments rearing juvenile Baltic Mytilus at a range of salinities (6, 11 and 16), HCO3 concentrations (300 2100 mol kg1) and Ca2C concentrations (0.5 4 mmol kg1) reveal that as individual factors, low [HCO3], pH and salinity cannot explain low calcification rates in the Baltic Sea. Calcification rates are impeded when aragonite 1 or ESIR 0.7 primarily due to [Ca2C] limitation which becomes relevant at a salinity of ca. 11 in the Baltic Sea. Field monitoring of carbonate chemistry and calcification rates suggest increased food availability may be able to mask the negative impacts of periodic sub-optimal carbonate chemistry, but not when seawater conditions are permanently adverse, as observed in two Baltic reefs at salinities <11. Regional climate models predict a rapid desalination of the southwest and central Baltic over the next century and potentially a reduction in [Ca2C] which may shift the distribution of marine calcifiers westward. It is therefore vital to understand the mechanisms by which the ionic composition of seawater impacts bivalve calcification for better predicting the future of benthic Baltic ecosystems.

1726-4170
2573–2590
Sanders, Trystan
4f3b5742-82bb-48d6-bcaa-0489c0880628
Thomsen, Joern
18d15704-6184-4e4b-b4e8-04ba8f81d125
Mueller, Jens Daniel
813cea5d-d833-4ba1-8750-e3be4b3cd758
Rehder, Gregor
c6d5ad66-f039-4f55-b985-07474cfc4b6a
Melzner, Frank
a67e5475-e6d7-4f7a-850a-0658cae2504d
Sanders, Trystan
4f3b5742-82bb-48d6-bcaa-0489c0880628
Thomsen, Joern
18d15704-6184-4e4b-b4e8-04ba8f81d125
Mueller, Jens Daniel
813cea5d-d833-4ba1-8750-e3be4b3cd758
Rehder, Gregor
c6d5ad66-f039-4f55-b985-07474cfc4b6a
Melzner, Frank
a67e5475-e6d7-4f7a-850a-0658cae2504d

Sanders, Trystan, Thomsen, Joern, Mueller, Jens Daniel, Rehder, Gregor and Melzner, Frank (2021) Decoupling salinity and carbonate chemistry: low calcium ion concentration rather than salinity limits calcification in Baltic Sea mussels. Biogeosciences, 18 (8), 2573–2590. (doi:10.5194/bg-18-2573-2021).

Record type: Article

Abstract

The Baltic Sea has a salinity gradient decreasing from fully marine (<25) in the west to below 7 in the central Baltic Proper. Habitat-forming and ecologically dominant mytilid mussels exhibit decreasing growth when salinity >11; however, the mechanisms underlying reduced calcification rates in dilute seawater are not fully understood. Both [HCO 3 ] and [Ca2C] also decrease with salinity, challenging calcifying organisms through CaCO3 undersaturation (1) and unfavourable ratios of calcification substrates ([Ca2C] and [HCO 3]) to the inhibitor (HC), expressed as the extended substrate inhibitor ratio (ESIR). This study combined in situ monitoring of three southwest Baltic mussel reefs with two laboratory experiments to assess how various environmental conditions and isolated abiotic factors (salinity, [Ca2C], [HCO3 ] and pH) impact calcification in mytilid mussels along the Baltic salinity gradient. Laboratory experiments rearing juvenile Baltic Mytilus at a range of salinities (6, 11 and 16), HCO3 concentrations (300 2100 mol kg1) and Ca2C concentrations (0.5 4 mmol kg1) reveal that as individual factors, low [HCO3], pH and salinity cannot explain low calcification rates in the Baltic Sea. Calcification rates are impeded when aragonite 1 or ESIR 0.7 primarily due to [Ca2C] limitation which becomes relevant at a salinity of ca. 11 in the Baltic Sea. Field monitoring of carbonate chemistry and calcification rates suggest increased food availability may be able to mask the negative impacts of periodic sub-optimal carbonate chemistry, but not when seawater conditions are permanently adverse, as observed in two Baltic reefs at salinities <11. Regional climate models predict a rapid desalination of the southwest and central Baltic over the next century and potentially a reduction in [Ca2C] which may shift the distribution of marine calcifiers westward. It is therefore vital to understand the mechanisms by which the ionic composition of seawater impacts bivalve calcification for better predicting the future of benthic Baltic ecosystems.

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Accepted/In Press date: 26 March 2021
Published date: 22 April 2021
Additional Information: Funding Information: Financial support. This research was supported by the Marie Curie Funding Information: ITN network “CACHE” (Calcium in a Changing Environment) European Union Seventh Framework Programme under grant agreement no. 605051. The position of Jens Daniel Müller was funded by BONUS, the joint Baltic Sea research and development programme (Art 185), and jointly by the European Union’s Seventh Programme for research, technological development and demonstration and the German Federal Ministry of Education and Research through grant no. 03F0689A (BONUS PINBAL) and grant no. 03F0773A (BONUS INTEGRAL). Publisher Copyright: © 2021 BMJ Publishing Group. All rights reserved.

Identifiers

Local EPrints ID: 448876
URI: http://eprints.soton.ac.uk/id/eprint/448876
ISSN: 1726-4170
PURE UUID: d2cbd567-1431-471d-93f7-5ca3e2c30016
ORCID for Trystan Sanders: ORCID iD orcid.org/0000-0002-7605-0747

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Date deposited: 07 May 2021 16:33
Last modified: 16 Mar 2024 12:07

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Contributors

Author: Trystan Sanders ORCID iD
Author: Joern Thomsen
Author: Jens Daniel Mueller
Author: Gregor Rehder
Author: Frank Melzner

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