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For many historical and contemporary experimental studies in marine biology, seawater carbonate chemistry remains a ghost factor, an uncontrolled, unmeasured, and often dynamic variable affecting experimental organisms or the treatments to which investigators subject them. We highlight how environmental variability, such as seasonal upwelling and biological respiration, drive variation in seawater carbonate chemistry that can influence laboratory experiments in unintended ways and introduce a signal consistent with ocean acidification. As the impacts of carbonate chemistry on biochemical pathways that underlie growth, development, reproduction, and behavior become better understood, the hidden effects of this previously overlooked variable need to be acknowledged. Here we bring this emerging challenge to the attention of the wider community of experimental biologists who rely on access to organisms and water from marine and estuarine laboratories and who may benefit from explicit considerations of a growing literature on the pervasive effects of aquatic carbonate chemistry changes. [ABSTRACT FROM AUTHOR]

Ocean acidification is predicted to have negative effects on marine biota, resulting in the loss of biodiversity and changes in marine ecosystem structure and function. However, some species and life stages may be capable of thriving in low pH conditions, either due to their natural ability to tolerate stressful low pH-high pCO conditions and/or alteration of species interactions caused by changes in pH profiles, or due to evolutionary trade-offs. A better understanding of which species may be capable of tolerating ocean acidification can guide future research into the mechanisms for physiological and ecological resilience to future carbon dioxide (CO) conditions. We investigated the colonization of selected polychaete species along a pH gradient originating from shallow, coastal volcanic CO vents (Ischia, Italy). Colonization was quantified by exposing artificial invertebrate collectors attached to the substratum for 30 days during different periods of the year (late spring, fall and late winter). Three species, Amphiglena mediterranea, Platynereis dumerilii and Syllis prolifera, were present and abundant along the gradient throughout the year. All three species were significantly more abundant in the most acidified areas, confirming their high tolerance and capacity to cope with very low pH. Abundances of all three species were compared to data previously collected via collectors suspended in the water column. More individuals were found in the collectors attached to the substratum, suggesting that abundances may have previously been underestimated. This is likely due to the close proximity of these collectors with the natural rocky substratum. All three species exhibited similar temporal variability, consistent with their life cycle and reproductive biology. Our results demonstrate high tolerance of the species for low and variable pH and corroborate their use as robust models to explore the capacity to cope with low pH-high pCO conditions, both in the natural vent systems and in the laboratory. [ABSTRACT FROM AUTHOR]