Data from: Fluctuating seawater pH/ p CO 2 regimes are more energetically expensive than static pH/ p CO 2 levels in the mussel Mytilus edulis

Ocean acidification (OA) studies typically use stable open-ocean pH or CO2
values. However, species living within dynamic coastal environments can
naturally experience wide fluctuations in abiotic factors, suggesting
their responses to stable pH conditions may not be reflective of either
present or near-future conditions. Here we investigate the physiological
responses of the mussel Mytilus edulis to variable seawater pH conditions
over short- (6 h) and medium-term (2 weeks) exposures under both current
and near-future OA scenarios. Mussel haemolymph pH closely mirrored that
of seawater pH over short-term changes of 1 pH unit with acidosis or
recovery accordingly, highlighting a limited capacity for acid–base
regulation. After 2 weeks, mussels under variable pH conditions had
significantly higher metabolic rates, antioxidant enzyme activities and
lipid peroxidation than those exposed to static pH under both current and
near-future OA scenarios. Static near-future pH conditions induced
significant acid–base disturbances and lipid peroxidation compared with
the static present-day conditions but did not affect the metabolic rate.
These results clearly demonstrate that living in naturally variable
environments is energetically more expensive than living in static
seawater conditions, which has consequences for how we extrapolate future
OA responses in coastal species.