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1. Contrasting responses of commercially important Northwest Atlantic bivalve species to ocean acidification and temperature conditions

   https://doi.org/10.1371/journal.pclm.0000509  

   McMahon, Teagan; Thatcher, Diana; Williams, Branwen; Wanamaker, Alan; Jellison, Brittany; Franklin, Heidi; Guay, Katherine; Whitney, Nina M; Stewart, Joseph A; LaVigne, Michèle (November 2024, PLOS Climate)

   Cyr, Frédéric (Ed.)

   Modern calcifying marine organisms face numerous environmental stressors, including overfishing, deoxygenation, increasing ocean temperatures, and ocean acidification (OA). Coastal marine settings are predicted to become warmer and more acidic in coming decades, heightening the risks of extreme events such as marine heat waves. Given these threats, it is important to understand the vulnerabilities of marine organisms that construct their shells from calcium carbonate, which are particularly susceptible to warming and decreasing pH levels. To investigate the response of four commercially relevant bivalve species to OA and differing temperatures, juvenileMercenaria mercenaria(hard shell clams), juvenileMya arenaria(soft shell clams), adult and juvenileArctica islandica(ocean quahog), and juvenilePlacopecten magellanicus(Atlantic sea scallops) were grown in varying pH and temperature conditions. Species were exposed to four controlled pH conditions (7.4, 7.6, 7.8, and ambient/8.0) and three controlled temperature conditions (6, 9, and 12°C) for 20.5 weeks and then shell growth and coloration were analyzed. This research marks the first direct comparison of these species’ biological responses to both temperature and OA conditions within the same experiment. The four species exhibited varying responses to temperature and OA conditions. Mortality rates were not significantly associated with pH or temperature conditions for any of the species studied. Growth (measured as change in maximum shell height) was observed to be higher in warmer tanks for all species and was not significantly impacted by pH. Two groups (juvenileM.arenariaand juvenileM.mercenaria) exhibited lightening in the color of their shells at lower pH levels at all temperatures, attributed to a loss of shell periostracum. The variable responses of the studied bivalve species, despite belonging to the same phylogenetic class and geographic region, highlights the need for further study into implications for health and management of bivalves in the face of variable stressors. 

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2. Drivers of Biogeochemical Variability in a Central California Kelp Forest: Implications for Local Amelioration of Ocean Acidification

   https://doi.org/10.1029/2020JC016320  

   Hirsh, Heidi K.; Nickols, Kerry J.; Takeshita, Yuichiro; Traiger, Sarah B.; Mucciarone, David A.; Monismith, Stephen; Dunbar, Robert B. (November 2020, Journal of Geophysical Research: Oceans)

   Abstract Kelp forests are among the world's most productive marine ecosystems, and they have the potential to locally ameliorate ocean acidification (OA). In order to understand the contribution of kelp metabolism to local biogeochemistry, we must first quantify the natural variability and the relative contributions of physical and biological drivers to biogeochemical changes in space and time. We deployed an extensive instrument array in Monterey Bay, CA, inside and outside of a kelp forest to assess the degree to which giant kelp (Macrocystis pyrifera) locally ameliorates present‐day acidic conditions which we expect to be exacerbated by OA. Temperature, pH, and O₂variability occurred at semidiurnal, diurnal (tidal and diel), and longer upwelling event periods. Mean conditions were driven by offshore wind forcing and the delivery of upwelled water via nearshore internal bores. While near‐surface pH and O₂were similar inside and outside the kelp forest, surface pH was elevated inside the kelp compared to outside, suggesting that the kelp canopy locally increased surface pH. We observed the greatest acidification stress deeper in the water column where pCO₂reached levels as high as 1,300 μatm and aragonite undersaturation (Ω_Ar < 1) occurred on several occasions. At this site, kelp canopy modification of seawater properties, and thus any ameliorating effect against acidification, is greatest in a narrow band of surface water. The spatial disconnect between stress exposure at depth and reduction of acidification stress at the surface warrants further assessment of utilizing kelp forests as provisioners of local OA mitigation. 

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3. The combined effects of acidification and acute warming on the embryos of Pacific herring (Clupea pallasii)

   https://doi.org/10.3389/fmars.2023.1307617  

   Singh, Nicole R.; Love, Brooke; Murray, Christopher S.; Sobocinski, Kathryn L.; Cooper, W. James (December 2023, Frontiers in Marine Science)

   Anthropogenic climate change is projected to affect marine ecosystems by challenging the environmental tolerance of individuals. Marine fishes may be particularly vulnerable to emergent climate stressors during early life stages. Here we focus on embryos of Pacific herring(Clupea pallasii), an important forage fish species widely distributed across the North Pacific. Embryos were reared under a range of temperatures (10-16°C) crossed with twopCO₂levels (600 and 2000μatm) to investigate effects on metabolism and survival. We further tested how elevatedpCO₂affects critical thermal tolerance (CT_max) by challenging embryos to short-term temperature fluctuations. Experiments were repeated on embryos collected from winter and spring spawning populations to determine if spawning phenology corresponds with different limits of environmental tolerance in offspring. We found that embryos could withstand acute exposure to 20°C regardless of spawning population or incubation treatment, but that survival was greatly reduced after 2-3 hours at 25°C. We found thatpCO₂had limited effects onCT_max. The survival of embryos reared under chronically warm conditions (12°, 14°, or 16°C) was significantly lower relative to 10°C treatments in both populations. Oxygen consumption rates (MO₂) were also higher at elevated temperatures andpCO₂levels. However, heart contraction measurements made 48 hours afterCT_maxexposure revealed a greater increase in heart rate in embryos reared at 10°C compared to 16°C, suggesting acclimation at higher incubation temperatures. Our results indicate that Pacific herring are generally tolerant ofpCO₂but are vulnerable to acute temperature stress. Importantly, spring-spawning embryos did not clearly exhibit a higher tolerance to heat stress compared to winter offspring. 

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4. New insights into the mechanisms of carbon dioxide mineralization by portlandite

   https://doi.org/10.1002/aic.17160  

   Falzone, Gabriel; Mehdipour, Iman; Neithalath, Narayanan; Bauchy, Mathieu; Simonetti, Dante; Sant, Gaurav (January 2021, AIChE Journal)

   Abstract Portlandite (Ca(OH)₂; also known as calcium hydroxide or hydrated lime), an archetypal alkaline solid, interacts with carbon dioxide (CO₂) via a classic acid–base “carbonation” reaction to produce a salt (calcium carbonate: CaCO₃) that functions as a low‐carbon cementation agent, and water. Herein, we revisit the effects of reaction temperature, relative humidity (RH), and CO₂concentration on the carbonation of portlandite in the form of finely divided particulates and compacted monoliths. Special focus is paid to uncover the influences of the moisture state (i.e., the presence of adsorbed and/or liquid water), moisture content and the surface area‐to‐volume ratio (s_a/v, mm⁻¹) of reactants on the extent of carbonation. In general, increasing RH more significantly impacts the rate and thermodynamics of carbonation reactions, leading to high(er) conversion regardless of prior exposure history. This mitigated the effects (if any) of allegedly denser, less porous carbonate surface layers formed at lower RH. In monolithic compacts, microstructural (i.e., mass‐transfer) constraints particularly hindered the progress of carbonation due to pore blocking by liquid water in compacts with limited surface area to volume ratios. These mechanistic insights into portlandite's carbonation inform processing routes for the production of cementation agents that seek to utilize CO₂borne in dilute (≤30 mol%) post‐combustion flue gas streams. 

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5. Ocean acidification effects on in situ coral reef metabolism

   https://doi.org/10.1038/s41598-019-48407-7  

   Doo, Steve S.; Edmunds, Peter J.; Carpenter, Robert C. (August 2019, Scientific Reports)

   Abstract The Anthropocene climate has largely been defined by a rapid increase in atmospheric CO_2,causing global climate change (warming) and ocean acidification (OA, a reduction in oceanic pH). OA is of particular concern for coral reefs, as the associated reduction in carbonate ion availability impairs biogenic calcification and promotes dissolution of carbonate substrata. While these trends ultimately affect ecosystem calcification, scaling experimental analyses of the response of organisms to OA to consider the response of ecosystems to OA has proved difficult. The benchmark of ecosystem-level experiments to study the effects of OA is provided through Free Ocean CO₂Enrichment (FOCE), which we use in the present analyses for a 21-d experiment on the back reef of Mo’orea, French Polynesia. Two natural coral reef communities were incubatedin situ, with one exposed to ambient pCO₂(393 µatm), and one to high pCO₂(949 µatm). Our results show a decrease in 24-h net community calcification (NCC) under high pCO₂, and a reduction in nighttime NCC that attenuated and eventually reversed over 21-d. This effect was not observed in daytime NCC, and it occurred without any effect of high pCO₂on net community production (NCP). These results contribute to previous studies on ecosystem-level responses of coral reefs to the OA conditions projected for the end of the century, and they highlight potential attenuation of high pCO₂effects on nighttime net community calcification. 

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