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Spectrophotometric pH measurements of seawater (pHspec) are routinely made by the oceanographic community for a wide variety of studies. However, obtaining consistent measurements between laboratories that meet stringent thresholds such as the "weather" (± 0.02) and "climate" (± 0.003) standards, has been a challenge. One of the main sources of error for pHspec measurements is gas exchange of carbon dioxide during sample handling. Here, we present a simple method where pHspec measurements on the total scale are made directly in the sampling bottle, which minimizes sample handling errors because the solution is not transferred during analysis. We compared the performance of this method to a standard automated benchtop system on a hydrography cruise, and the two methods were consistent to 0.003 ± 0.0033 (1σ). This demonstrates that this simple method can produce pHspec that approaches climate quality, and comfortably meets weather quality standards. Additional benefits include high sample throughput, and the ability to rapidly quantify dye perturbation effects for each sample. The latter should be particularly useful for low salinity samples such as those taken from estuaries, insofar as modifications specific to the pHspec measurements of estuarine waters are employed. [ABSTRACT FROM AUTHOR]

Spawning market squid lay embryo capsules on the seafloor of the continental shelf of the California Current System (CCS), where ocean acidification, deoxygenation and intensified upwelling lower the pH and [O2]. Squid statolith geochemistry has been shown to reflect the squid's environment (e.g., seawater temperature and elemental concentration). We used real-world environmental levels of pH and [O2] observed on squid-embryo beds to test in the laboratory whether or not squid statolith geochemistry reflects environmental pH and [O2]. We asked whether pH and [O2] levels might affect the incorporation of element ratios (B:Ca, Mg:Ca, Sr:Ca, Ba:Ca, Pb:Ca, U:Ca) into squid embryonic statoliths as (1) individual elements and/or (2) multivariate elemental signatures, and consider future applications as proxies for pH and [O2] exposure. Embryo exposure to high and low pH and [O2] alone and together during development over four weeks only moderately affected elemental concentrations of the statoliths, and uranium was an important element driving these differences. Uranium:Ca was eight-times higher in statoliths exposed to low pHT (7.57-7.58) and low [O2] (79-82 μmol∙kg-1) than those exposed to higher ambient pHT (7.92-7.94) and [O2] (241-243 μmol∙kg-1). In a separate experiment, exposure to low pHT (7.55-7.56) or low [O2] (83-86 μmol∙kg-1) yielded elevated U:Ca and Sr:Ca in the low [O2] treatment only. We found capsular effects on multiple elements in statoliths of all treatments. The multivariate elemental signatures of embryonic statoliths were distinct among capsules, but did not reflect environmental factors (pH and/or [O2]). We show that statoliths of squid embryos developing inside capsules have the potential to reflect environmental pH and [O2], but that these "signals" are generated in concert with the physiological effects of the capsules and embryos themselves. [ABSTRACT FROM AUTHOR]

Natural variation and changing climate in coastal oceans subject meroplanktonic organisms to broad ranges of pH and oxygen ([O2]) levels. In controlled-laboratory experiments we explored the interactive effects of pH, [O2], and semidiurnal pH fluctuations on the survivorship, development, and size of early life stages of two mytilid mussels, Mytilus californianus and M. galloprovincialis. Survivorship of larvae was unaffected by low pH, low [O2], or semidiurnal fluctuations for both mytilid species. Low pH (<7.6) resulted in delayed transition from the trochophore to veliger stage, but this effect of low pH was absent when incorporating semidiurnal fluctuations in both species. Also at low pH, larval shells were smaller and had greater variance; this effect was absent when semidiurnal fluctuations of 0.3 units were incorporated at low pH for M. galloprovincialis but not for M. californianus. Low [O2] in combination with low pH had no effect on larval development and size, indicating that early life stages of mytilid mussels are largely tolerant to a broad range of [O2] reflective of their environment (80-260 μmol kg−1). The role of pH variability should be recognized as an important feature in coastal oceans that has the capacity to modulate the effects of ocean acidification on biological responses. [ABSTRACT FROM AUTHOR]