Abstract
Ocean acidification (OA) studies to date have typically used stable open-ocean pH and CO2 values to predict the physiological responses of intertidal species to future climate scenarios, with few studies accounting for natural fluctuations of abiotic conditions or the alternating periods of emersion and immersion routinely experienced during tidal cycles. Here, we determine seawater carbonate chemistry and the corresponding in situ haemolymph acid–base responses over real time for two populations of mussel (Mytilus edulis) during tidal cycles, demonstrating that intertidal mussels experience daily acidosis during emersion. Using these field data to parameterize experimental work we demonstrate that air temperature and mussel size strongly influence this acidosis, with larger mussels at higher temperatures experiencing greater acidosis. There was a small interactive effect of prior immersion in OA conditions (pHNBS 7.7/pCO2 930 µatm) such that the haemolymph pH measured at the start of emersion was lower in large mussels exposed to OA. Critically, the acidosis induced in mussels during emersion in situ was greater (ΔpH approximately 0.8 units) than that induced by experimental OA (ΔpH approximately 0.1 units). Understanding how environmental fluctuations influence physiology under current scenarios is critical to our ability to predict the responses of key marine biota to future environmental changes.
Highlights
In an era of unprecedented global ocean and climatic change, there is growing interest in understanding the physiological mechanisms by which environmental conditions influence species’ performance and how that varies over space and time
The combined field and laboratory data collected in this study reveals that periods of emersion have greater physiological impact on the acid –base balance of the intertidal mussel Mytilus edulis than submersion in high CO2/low pH seawater conditions
This is true both for conditions observed in the field currently and for predicted ocean acidification (OA) scenarios used in laboratory experiments
Summary
In an era of unprecedented global ocean and climatic change, there is growing interest in understanding the physiological mechanisms by which environmental conditions influence species’ performance and how that varies over space and time. Both populations showed similar acid–base status during periods of immersion in seawater (figure 2), as demonstrated when mussels from SC were transposed to PG during the July sampling (t-test comparing haemolymph acid–base parameters of the two populations at high tide point: pH T 1⁄4 21.5509, d.f. 1⁄4 87, p 1⁄4 0.1245; pCO2 T 1⁄4 1.83235, d.f. 1⁄4 88, p 1⁄4 0.0703; HCOÀ3 T 1⁄4 1.97844, d.f. 1⁄4 87, p 1⁄4 0.0510).
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