Ocean acidification narrows the acute thermal and salinity tolerance of the Sydney rock oyster Saccostrea glomerata

- The impact of ocean acidification on oyster thermal & salinity tolerance was tested.
- Ocean acidification led to reduced upper thermal and lower salinity tolerance.
- Metabolic depression and greater extracellular acidosis was observed.

Coastal and estuarine environments are characterised by acute changes in temperature and salinity. Organisms living within these environments are adapted to withstand such changes, yet near-future ocean acidification (OA) may challenge their physiological capacity to respond. We tested the impact of CO2-induced OA on the acute thermal and salinity tolerance, energy metabolism and acid-base regulation capacity of the oyster Saccostrea glomerata. Adult S. glomerata were acclimated to three CO2 levels (ambient 380 μatm, moderate 856 μatm, high 1500 μatm) for 5 weeks (24 °C, salinity 34.6) before being exposed to a series of acute temperature (15-33 °C) and salinity (34.2-20) treatments. Oysters acclimated to elevated CO2 showed a significant metabolic depression and extracellular acidosis with acute exposure to elevated temperature and reduced salinity, especially at the highest CO2 of 1500 μatm. Our results suggest that the acute thermal and salinity tolerance of S. glomerata and thus its distribution will reduce as OA continues to worsen.