Ocean Acidification at High Latitudes: Potential Effects on Functioning of the Antarctic Bivalve Laternula elliptica

Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO3) to generate shells or skeletons. Studies of potential effects of future levels of pCO2 on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO2 levels of their natural environment (430 µatm, pH 7.99; based on field measurements) with those predicted for 2100 (735 µatm, pH 7.78) and glacial levels (187 µatm, pH 8.32). Adult L. elliptica basal metabolism (oxygen consumption rates) and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS), a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify in seawater undersaturated in aragonite (ΩAr = 0.71), the CaCO3 polymorph of which their shells are comprised. The different response variables were influenced by pH in differing ways, highlighting the importance of assessing a variety of factors to determine the likely impact of pH change. In combination, the results indicate a negative effect of ocean acidification on whole-organism functioning of L. elliptica over relatively short terms (weeks-months) that may be energetically difficult to maintain over longer time periods. Importantly, however, the observed changes in L. elliptica CHS gene expression provides evidence for biological control over the shell formation process, which may enable some degree of adaptation or acclimation to future ocean acidification scenarios

Fertilisation and larval development in an Antarctic bivalve, Laternula elliptica, under reduced pH and elevated temperatures

Elevated temperatures associated with ocean warming and acidification can influence development and, ultimately, success of larval molluscs. The effect of projected oceanic changes on fertilisation and larval development in an Antarctic bivalve, Laternula elliptica, was investigated through successive larval stages at ambient temperature and pH conditions (-1.6°C and pH 7.98) and conditions representative of projections through to 2100 (-0.5°C to +0.4°C and pH 7.80 to pH 7.65). Where significant effects were detected, increased temperature had a consistently positive influence on larval development, regardless of pH level, while effects of reduced pH varied with larval stage and incubation temperature. Fertilisation was high and largely independent of stressors, with no loss of gamete viability. Mortality was unaffected at all development stages under experimental conditions. Elevated temperatures reduced occurrences of abnormalities in D-larvae and accelerated larval development through late veliger and D-larval stages, with D-larvae occurring 5 d sooner at 0.4°C compared to ambient temperature. Reduced pH did not affect occurrences of abnormalities in larvae, but it slowed the development of calcifying stages. More work is required to investigate the effects of developmental delays of the magnitude seen here in order to better determine the ecological relevance of these changes on longer term larval and juvenile success

High resolution microscopy reveals significant impacts of ocean acidification and warming on larval shell development in Laternula elliptica.

Environmental stressors impact marine larval growth rates, quality and sizes. Larvae of the Antarctic bivalve, Laternula elliptica, were raised to the D-larvae stage under temperature and pH conditions representing ambient and end of century projections (-1.6°C to +0.4°C and pH 7.98 to 7.65). Previous observations using light microscopy suggested pH had no influence on larval abnormalities in this species. Detailed analysis of the shell using SEM showed that reduced pH is in fact a major stressor during development for this species, producing D-larvae with abnormal shapes, deformed shell edges and irregular hinges, cracked shell surfaces and even uncalcified larvae. Additionally, reduced pH increased pitting and cracking on shell surfaces. Thus, apparently normal larvae may be compromised at the ultrastructural level and these larvae would be in poor condition at settlement, reducing juvenile recruitment and overall survival. Elevated temperatures increased prodissoconch II sizes. However, the overall impacts on larval shell quality and integrity with concurrent ocean acidification would likely overshadow any beneficial results from warmer temperatures, limiting populations of this prevalent Antarctic species

Linking Ross Sea Coastal Benthic Communities to Environmental Conditions : Documenting Baselines in a Spatially Variable and Changing World

Understanding the functionality of marine benthic ecosystems, and how they are influenced by their physical environment, is fundamental to realistically predicting effects of future environmental change. The Antarctic faces multiple environmental pressures associated with greenhouse gas emissions, emphasizing the need for baseline information on biodiversity and the bio-physical processes that influence biodiversity. We describe a survey of shallow water benthic communities at eight Ross Sea locations with a range of environmental characteristics. Our analyses link coastal benthic community composition to seafloor habitat and sedimentary parameters and broader scale features, at locations encompassing considerable spatial extent and variation in environmental characteristics (e.g., seafloor habitat, sea ice conditions, hydrodynamic regime, light). Our aims were to: (i) document existing benthic communities, habitats and environmental conditions against which to assess future change, (ii) investigate the relationships between environmental and habitat characteristics and benthic community structure and function, and (iii) determine whether these relationships were dependent on spatial extent. A very high percentage (>95%) of the between-location variability in macro- or epifaunal community composition was explainable using multi-scale environmental variables. The explanatory power varied depending on the scale of influence of the environmental variables measured (fine and medium-scale habitat, broad scale), and with community type. However, the inclusion of parameters at all scales produced the most powerful model for both communities. Ice duration, ice thickness and snow cover were important broad scale variables identified that directly relate to climate change. Even when using only habitat-scale variables, extending the spatial scale of the study from three locations covering 32 km to eight locations covering ~340 km increased the degree of explanatory power from 18–32 to 64–78%. The increase in explanatory power with spatial extent lends weight to the possibility of using an indirect “space for time” substitution approach for future predictions of the effects of change on these coastal marine ecosystems. Given the multiple and interacting drivers of change in Antarctic coastal ecosystems a multidisciplinary, long term, repeated observation approach will be vital to both improve and test predictions of how coastal communities will respond to environmental change.Peer reviewe

Spectroscopic study of the ternary complex of beta-cyclodextrin, pyrene, and triton X-100

The increased fluorescence intensity of pyrene due to indirect excitation by the nonionic surfactant Triton X-100 is discussed. Sensitization is quantitatively shown to occur in mixed solutions of pyrene, Triton X-100, and β-cyciodextrin (β-CD). A ternary complex is formed below the critical micelle concentration (CMC). Above the CMC, pyrene is displaced from the β-CD cavity. This is accompanied by a subsequent incorporation of pyrene into the interior of the micelle. Evidence is given that ternary complexation occurs among pyrene, CD, and TX-100. © 1993 Society for Applied Spectroscopy

Effects of reduced pH and elevated temperatures on shell sizes.

<p>a) Shell height and b) shell length on prodissoconch I (PI) and c) on growth of prodissoconch II. Letters indicate significance as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0175706#pone.0175706.g002" target="_blank">Fig 2</a>. The temperature/pH combination of 0.4°C/7.80 was not used. NS = no significant differences between treatments, n = 3. Error bars are standard error.</p

SEM images of D-larvae from various experimental treatments.

<p>(a) normally developed D-larva from the control treatment (pH 7.98 and -1.6°C, x370), and (b-e) damaged and/or malformed larvae from reduced pH (7.65) treatments at various temperatures (d: -1.6°C, x430, b: -0.5°C, x450, c and e: 0.4°C, x400), (f) extremely malformed (left) and uncalcified (right) larvae from pH 7.65, -1.6°C (x450). PI: prodissoconch I; PII: prodissoconch II. All scale bars are 50 μm.</p

Seawater conditions for all experimental treatments.

<p>Seawater conditions for all experimental treatments.</p

SEM image (x370) of the shell of a <i>L</i>. <i>elliptica</i> D-shape larva.

<p>Showing prodissoconch I (PI), the boundary (B) between PI and prodissoconch II (PII) and the narrow band of PII. H and L indicate measurements of shell height and length, respectively, of PI. Scale bar as indicated.</p

Summary table of 2-way ANOVA.

<p>Summary table of 2-way ANOVA.</p