11 Aug 2023
 | 11 Aug 2023
Status: this preprint is open for discussion.

Variability and drivers of carbonate chemistry at shellfish aquaculture sites in the Salish Sea, British Columbia

Eleanor Simpson, Debby Ianson, Karen Elizabeth Kohfeld, Ana C. Franco, Paul A. Covert, Marty Davelaar, and Yves Perreault

Abstract. Ocean acidification reduces seawater pH and calcium carbonate saturation states (Ω), which can have detrimental effects on calcifying organisms such as shellfish. Nearshore areas, where shellfish aquaculture typically operates, have limited data available to characterize variability in key ocean acidification parameters pH and Ω, as samples are costly to analyse and difficult to collect. This study collected samples from four nearshore locations at shellfish aquaculture sites on the Canadian Pacific coast from 2015–2018 and analysed them for dissolved inorganic carbon (DIC) and total alkalinity (TA), enabling the calculation of pH and Ω for all seasons. The study evaluated the diel and seasonal variability in carbonate chemistry conditions at each location and estimated the contribution of drivers to seasonal and diel changes in pH and Ω. Nearshore locations experience a greater range of variability and seasonal and daily changes in pH and Ω than open waters. Biological uptake of DIC by phytoplankton is the major driver of seasonal and diel changes in pH and Ω at our nearshore sites. The study found that freshwater is not a key driver of diel variability, despite large changes over the day in some locations. Shellfish mortality events coincide with highly favourable pH and Ω conditions during summer and are most likely linked to high surface temperatures and disease rather than ocean acidification. To reduce shellfish mortality, shellfish could be hung lower in the water column (5–20 m) to avoid high temperatures and disease, while still experiencing favourable pH and Ω conditions for shellfish.

Eleanor Simpson et al.

Status: open (until 30 Sep 2023)

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  • RC1: 'Comment on egusphere-2023-1553', Anonymous Referee #1, 22 Sep 2023 reply

Eleanor Simpson et al.

Data sets

NCEI Accession 0244177 Eleanor Simpson, Debby Ianson, Karen E. Kohfeld, Yves Perreault, André M. Comeau, Keith Reid, Marty Davelaar, Danielle Caleb, Kenny Scozzafava, and Paul Covert

Eleanor Simpson et al.


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Short summary
Shellfish aquaculture operates in nearshore areas where data on key ocean acidification (OA) parameters is limited. We show daily and seasonal variability in chemical properties at nearshore aquaculture sites in Canada and define drivers of these changes. Nearshore locations have greater variability than open waters and uptake of carbon by phytoplankton is the major driver of variability. Areas with high primary productivity are recommended for aquaculture as they will be less vulnerable to OA.