Characterizing the vulnerability of intertidal organisms in Olympic National Park to ocean acidification

Ocean acidification (OA) will have a predominately negative impact on marine animals sensitive to changes in carbonate chemistry. Coastal upwelling regions, such as the Northwest coast of North America, are likely among the first ecosystems to experience the effects of OA as these areas already experience high pH variability and naturally low pH extremes. Over the past decade, pH off the Olympic coast of Washington has declined an order of magnitude faster than predicted by accepted conservative climate change models. Resource managers are concerned about the potential loss of intertidal biodiversity likely to accompany OA, but as of yet, there are little pH sensitivity data available for the vast majority of taxa found on the Olympic coast. The intertidal zone of Olympic National Park is particularly understudied due to its remote wilderness setting, habitat complexity, and exceptional biodiversity. Recently developed methodological approaches address these challenges in determining organism vulnerability by utilizing experimental evidence and expert opinion. Here, we use such an approach to determine intertidal organism sensitivity to pH for over 700 marine invertebrate and algal species found on the Olympic coast. Our results reinforce OA vulnerability paradigms for intertidal taxa that build structures from calcium carbonate, but also introduce knowledge gaps for many understudied species. We furthermore use our assessment to identify how rocky intertidal communities at four long-term monitoring sites on the Olympic coast could be affected by OA given their community composition

Design of multifactorial experiment with 12 treatments testing aggregation of the diatom <i>T. weissflogii</i> in the presence or absence of bacteria at two temperatures and three <i>p</i>CO₂ scenarios.

<p>Xenic treatments contained the bacterium <i>M. adhaerens</i> HP15. Each treatment was prepared in triplicate; one replicate was harvested initially (t = 0) and two after 96 hr. incubation on roller tables in the dark. See text for specifics on <i>p</i>CO₂ treatments. Ax  =  axenic, HP  =  <i>M. adhaerens</i> HP15 added, Am  =  Ambient, F1  =  Future 1, F2  =  Future 2.</p><p>Design of multifactorial experiment with 12 treatments testing aggregation of the diatom <i>T. weissflogii</i> in the presence or absence of bacteria at two temperatures and three <i>p</i>CO₂ scenarios.</p

Relationship between <i>p</i>CO₂ determined from DIC and pH or TA vs. <i>p</i>CO₂ determined from pH and TA.

<p>Data stems from 50 random samples from the experiment, where the carbonate chemistry was over-determined.</p

Effect of autoclaving on the carbonate chemistry of seawater.

<p>Effect of autoclaving on the carbonate chemistry of seawater.</p

Production of Transparent Exopolymer Particles (TEP) during the incubations in all treatments, calculated as net change during the 96 hrs. experiment, and errors calculated using error propagation.

<p>Production of Transparent Exopolymer Particles (TEP) during the incubations in all treatments, calculated as net change during the 96 hrs. experiment, and errors calculated using error propagation.</p

Exponential growth of <i>T. weissflogii</i> and pH range during the acclimatization phase.

<p>Exponential growth of <i>T. weissflogii</i> and pH range during the acclimatization phase.</p

Comparison of average TEP production (µg GXeq. L⁻¹) and aggregation, as measured by total aggregate volume (Agg. Vol.), combining treatments with the same temperature, carbonate conditions, or state of axenicity, respectively.

<p>N =  number of treatments, each in duplicate.</p><p>*: averages significantly (p<0.05) different from each other, paired t-test.</p><p>Comparison of average TEP production (µg GXeq. L⁻¹) and aggregation, as measured by total aggregate volume (Agg. Vol.), combining treatments with the same temperature, carbonate conditions, or state of axenicity, respectively.</p

TEP in Aggregates, absolute amount and fraction.

<p>TEP in Aggregates, absolute amount and fraction.</p

Total aggregate volume after the incubations in all treatments; error bars represent the range of replicates.

<p>Total aggregate volume after the incubations in all treatments; error bars represent the range of replicates.</p

Initial and final <i>p</i>CO₂ during the incubations at 15°C and 20°C.

<p>Initial and final <i>p</i>CO₂ during the incubations at 15°C and 20°C.</p