Bar graphs showing histograms of Ω_<i>arag</i> observations at APSH.

<p>The center panel is the data shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130384#pone.0130384.g004" target="_blank">Fig 4</a> with 2014 atmospheric pCO₂ levels (398 μatm; gray). Top and bottom panels are Ω_<i>arag</i> computed using total CO₂ (TCO₂) adjusted to atmospheric pCO₂ levels of 280 (blue) and 500 (red) μatm, respectively, following the approach of Harris et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130384#pone.0130384.ref017" target="_blank">17</a>] by assuming sea-air CO₂ disequilibria and the processes that determine TA, temperature and salinity variability are constant in time. The vertical dashed black line in all panels is the sub-optimal 1.5 Ω_<i>arag</i> threshold where some early life stages of marine bivalves become stressed [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130384#pone.0130384.ref007" target="_blank">7</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130384#pone.0130384.ref008" target="_blank">8</a>]. An atmospheric pCO₂ of 500 is expected by 2040 if the IPCC AR5 RCP 8.5 emissions trajectory is realized.</p

On the Frontline: Tracking Ocean Acidification in an Alaskan Shellfish Hatchery

<div><p>The invasion of anthropogenic carbon dioxide (CO₂) into the ocean is shifting the marine carbonate system such that saturation states of calcium carbonate (CaCO₃) minerals are decreasing, and this is having a detrimental impact on early life stages of select shellfish species. The global, secular decrease in CaCO₃ saturation states is occurring on top of a backdrop of large natural variability in coastal settings; progressively shifting the envelope of variability and leading to longer and more frequent exposure to adverse conditions. This is a great concern in the State of Alaska, a high-latitude setting vulnerable to rapid changes in the marine carbonate system, where an emerging shellfish industry plans major growth over the coming decades. Currently, the Alutiiq Pride Shellfish Hatchery (APSH) in Seward, Alaska is the only hatchery in the state, and produces many shellfish species with early life stages known to be sensitive to low CaCO₃ saturation states. Here we present the first land-based OA measurements made in an Alaskan shellfish hatchery, and detail the trends in the saturation state of aragonite (Ω<i>_arag</i>), the more soluble form of CaCO₃, over a 10-month period in the APSH seawater supply. These data indicate the largest changes are on the seasonal time scale, with extended periods of sub-optimal Ω<i>_arag</i> levels (Ω<i>_arag</i> < 1.5) in winter and autumn associated with elevated water column respiration and short-lived runoff events, respectively. The data pinpoint a 5-month window of reprieve with favorable Ω<i>_arag</i> conditions above the sub-optimal Ω<i>_arag</i> threshold, which under predicted upper-bound CO₂ emissions trajectories is estimated to close by 2040. To date, many species in production at APSH remain untested in their response to OA, and the data presented here establish the current conditions at APSH as well as provide a framework for hatchery-based measurements in Alaska. The current and expected conditions seen at APSH are essential to consider for this developing Alaskan industry.</p></div

Temperature (°C)–salinity diagram with contours of seawater potential density anomaly (σ_t) and Ω_<i>arag</i> as colored dots.

<p>Note the two areas of sub-optimal Ω_<i>arag</i> (Ω_<i>arag</i> < 1.5; warm colors) at the lowest salinities (<29) and coldest temperatures (< 7°C).</p

Image_1_Examining the impacts of elevated, variable pCO2 on larval Pacific razor clams (Siliqua patula) in Alaska.pdf

An increase in anthropogenic carbon dioxide is driving oceanic chemical shifts resulting in a long-term global decrease in ocean pH, colloquially termed ocean acidification (OA). Previous studies have demonstrated that OA can have negative physiological consequences for calcifying organisms, especially during early life-history stages. However, much of the previous research has focused on static exposure to future OA conditions, rather than variable exposure to elevated pCO2, which is more ecologically relevant for nearshore species. This study examines the effects of OA on embryonic and larval Pacific razor clams (Siliqua patula), a bivalve that produces a concretion during early shell development. Larvae were spawned and cultured over 28 days under three pCO2 treatments: a static high pCO2 of 867 μatm, a variable, diel pCO2 of 357 to 867 μatm, and an ambient pCO2 of 357 μatm. Our results indicate that the calcium carbonate polymorphism of the concretion phase of S. patula was amorphous calcium carbonate which transitioned to vaterite during the advanced D-veliger stage, with a final polymorphic shift to aragonite in adults, suggesting an increased vulnerability to dissolution under OA. However, exposure to elevated pCO2 appeared to accelerate the transition of larval S. patula from the concretion stage of shell development to complete calcification. There was no significant impact of OA exposure to elevated or variable pCO2 conditions on S. patula growth or HSP70 and calmodulin gene expression. This is the first experimental study examining the response of a concretion producing bivalve to future predicted OA conditions and has important implications for experimentation on larval mollusks and bivalve management.</p

Image_5_Examining the impacts of elevated, variable pCO2 on larval Pacific razor clams (Siliqua patula) in Alaska.pdf

An increase in anthropogenic carbon dioxide is driving oceanic chemical shifts resulting in a long-term global decrease in ocean pH, colloquially termed ocean acidification (OA). Previous studies have demonstrated that OA can have negative physiological consequences for calcifying organisms, especially during early life-history stages. However, much of the previous research has focused on static exposure to future OA conditions, rather than variable exposure to elevated pCO2, which is more ecologically relevant for nearshore species. This study examines the effects of OA on embryonic and larval Pacific razor clams (Siliqua patula), a bivalve that produces a concretion during early shell development. Larvae were spawned and cultured over 28 days under three pCO2 treatments: a static high pCO2 of 867 μatm, a variable, diel pCO2 of 357 to 867 μatm, and an ambient pCO2 of 357 μatm. Our results indicate that the calcium carbonate polymorphism of the concretion phase of S. patula was amorphous calcium carbonate which transitioned to vaterite during the advanced D-veliger stage, with a final polymorphic shift to aragonite in adults, suggesting an increased vulnerability to dissolution under OA. However, exposure to elevated pCO2 appeared to accelerate the transition of larval S. patula from the concretion stage of shell development to complete calcification. There was no significant impact of OA exposure to elevated or variable pCO2 conditions on S. patula growth or HSP70 and calmodulin gene expression. This is the first experimental study examining the response of a concretion producing bivalve to future predicted OA conditions and has important implications for experimentation on larval mollusks and bivalve management.</p

Relationship between total alkalinity (TA; μmol kg^-1) and salinity in the northern Gulf of Alaska calculated using the data described in Fig 1.

<p>The linear fit (gray line) for these data is: TA = 48.7709*S + 606.23 μmol kg^<b>-1</b> (r^<b>2</b> = 0.94, root mean square error = 17.21 μmol kg^<b>-1</b>). This fit was calculated using the MathWorks MATLAB robust linear regression algorithm with only salinity data < 33.6 (blue dots). Measurements above this salinity range are deep samples collected over the outer continental shelf that have a steeper TA-salinity relationship (black dots). Twenty-three validation TA measurements (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130384#pone.0130384.s001" target="_blank">S1 Table</a>) were made and are shown here as red dots.</p

Image_4_Examining the impacts of elevated, variable pCO2 on larval Pacific razor clams (Siliqua patula) in Alaska.pdf

An increase in anthropogenic carbon dioxide is driving oceanic chemical shifts resulting in a long-term global decrease in ocean pH, colloquially termed ocean acidification (OA). Previous studies have demonstrated that OA can have negative physiological consequences for calcifying organisms, especially during early life-history stages. However, much of the previous research has focused on static exposure to future OA conditions, rather than variable exposure to elevated pCO2, which is more ecologically relevant for nearshore species. This study examines the effects of OA on embryonic and larval Pacific razor clams (Siliqua patula), a bivalve that produces a concretion during early shell development. Larvae were spawned and cultured over 28 days under three pCO2 treatments: a static high pCO2 of 867 μatm, a variable, diel pCO2 of 357 to 867 μatm, and an ambient pCO2 of 357 μatm. Our results indicate that the calcium carbonate polymorphism of the concretion phase of S. patula was amorphous calcium carbonate which transitioned to vaterite during the advanced D-veliger stage, with a final polymorphic shift to aragonite in adults, suggesting an increased vulnerability to dissolution under OA. However, exposure to elevated pCO2 appeared to accelerate the transition of larval S. patula from the concretion stage of shell development to complete calcification. There was no significant impact of OA exposure to elevated or variable pCO2 conditions on S. patula growth or HSP70 and calmodulin gene expression. This is the first experimental study examining the response of a concretion producing bivalve to future predicted OA conditions and has important implications for experimentation on larval mollusks and bivalve management.</p

Image_6_Examining the impacts of elevated, variable pCO2 on larval Pacific razor clams (Siliqua patula) in Alaska.pdf

An increase in anthropogenic carbon dioxide is driving oceanic chemical shifts resulting in a long-term global decrease in ocean pH, colloquially termed ocean acidification (OA). Previous studies have demonstrated that OA can have negative physiological consequences for calcifying organisms, especially during early life-history stages. However, much of the previous research has focused on static exposure to future OA conditions, rather than variable exposure to elevated pCO2, which is more ecologically relevant for nearshore species. This study examines the effects of OA on embryonic and larval Pacific razor clams (Siliqua patula), a bivalve that produces a concretion during early shell development. Larvae were spawned and cultured over 28 days under three pCO2 treatments: a static high pCO2 of 867 μatm, a variable, diel pCO2 of 357 to 867 μatm, and an ambient pCO2 of 357 μatm. Our results indicate that the calcium carbonate polymorphism of the concretion phase of S. patula was amorphous calcium carbonate which transitioned to vaterite during the advanced D-veliger stage, with a final polymorphic shift to aragonite in adults, suggesting an increased vulnerability to dissolution under OA. However, exposure to elevated pCO2 appeared to accelerate the transition of larval S. patula from the concretion stage of shell development to complete calcification. There was no significant impact of OA exposure to elevated or variable pCO2 conditions on S. patula growth or HSP70 and calmodulin gene expression. This is the first experimental study examining the response of a concretion producing bivalve to future predicted OA conditions and has important implications for experimentation on larval mollusks and bivalve management.</p

Map showing the location of Alutiiq Pride Shellfish Hatchery (APSH) in Resurrection Bay, the position of the Gulf of Alaska OA (GAKOA) mooring at the mouth of Resurrection Bay.

<p>Red dots are locations of discrete total alkalinity (TA) and salinity measurements, with the number of measurements made during cruises in May and September from 2008 through 2013 shown in the insert.</p

Table_3_Examining the impacts of elevated, variable pCO2 on larval Pacific razor clams (Siliqua patula) in Alaska.pdf

An increase in anthropogenic carbon dioxide is driving oceanic chemical shifts resulting in a long-term global decrease in ocean pH, colloquially termed ocean acidification (OA). Previous studies have demonstrated that OA can have negative physiological consequences for calcifying organisms, especially during early life-history stages. However, much of the previous research has focused on static exposure to future OA conditions, rather than variable exposure to elevated pCO2, which is more ecologically relevant for nearshore species. This study examines the effects of OA on embryonic and larval Pacific razor clams (Siliqua patula), a bivalve that produces a concretion during early shell development. Larvae were spawned and cultured over 28 days under three pCO2 treatments: a static high pCO2 of 867 μatm, a variable, diel pCO2 of 357 to 867 μatm, and an ambient pCO2 of 357 μatm. Our results indicate that the calcium carbonate polymorphism of the concretion phase of S. patula was amorphous calcium carbonate which transitioned to vaterite during the advanced D-veliger stage, with a final polymorphic shift to aragonite in adults, suggesting an increased vulnerability to dissolution under OA. However, exposure to elevated pCO2 appeared to accelerate the transition of larval S. patula from the concretion stage of shell development to complete calcification. There was no significant impact of OA exposure to elevated or variable pCO2 conditions on S. patula growth or HSP70 and calmodulin gene expression. This is the first experimental study examining the response of a concretion producing bivalve to future predicted OA conditions and has important implications for experimentation on larval mollusks and bivalve management.</p