Restoring the flat oyster Ostrea angasi in the face of a changing climate

Across the globe, restoration efforts are stemming the loss of native oyster reefs and the ecosystem services they provide, but these efforts will need to consider climate change in order to be sustainable. South-eastern Australia is the focus of restoring the once abundant oyster Ostrea angasi. This region is also a climate change 'hot spot' where the ocean is warming rapidly, with the potential to be exacerbated by marine heatwaves and coastal acidification. In this study, the impact of near-future (similar to 2050) elevated temperature and pCO(2) on O. angasi was determined and considered in context with concerns for the long-term sustainability of oyster reef restoration efforts. Oysters were exposed to ambient and elevated pCO(2) concentrations (mean +/- SE: 408 +/- 19.8 and 1070 +/- 53.4 mu atm) and ambient and elevated temperatures (22.78 +/- 0.17 and 25.73 +/- 0.21 degrees C) for 10 wk in outdoor flow-through mesocosms. Shell growth, condition index, standard metabolic rate (SMR), extracellular pH and survival were measured. Elevated temperature caused high mortality (36 %) and decreased the condition of oysters (33 %). Elevated pCO(2) increased SMR almost 4-fold and lowered the extracellular pH of O. angasi by a mean 0.29 pH units. In combination, elevated pCO(2) and temperature ameliorated effects on SMR and survivorship of oysters. O. angasi appears to be living near the limits of its thermal tolerance. Restoration projects will need to account for the temperature sensitivity of this species and its changing habitat to 'climate proof' long-term restoration efforts.