Impacts of ocean acidification on predator – prey interactions of molluscs

Elevations in atmospheric carbon dioxide (CO2) are anticipated to lead to the acidification of the world’s oceans over the next century. This thesis sought to understand the fate of the predator-prey interactions between the endemic predator, the Mulberry whelk Tenguella marginalba (Blainville, 1832) and their prey the native Sydney rock oyster Saccostrea glomerata (Gould, 1850) and the recently introduced Pacific oyster Crassostrea gigas (Thunberg, 1793) in a marine environment increasingly affected by elevated pCO2. It was predicted that predator-prey relationships will be altered by exposure to elevated pCO2 because 1) the energetic costs for T. marginalba to survive in an acidified environment will increase causing them to compensate by increasing their consumption rate of prey; 2) growth and physiological defences of S. glomerata and C. gigas will decrease and greater energy will be required for the maintenance of acid-base balance. It was also predicted that responses will vary between oyster species and within populations of oysters. This study provides evidence that alterations in predator-prey relationships will be complex. Responses of oysters to elevated CO2 were variable and dependent on the species, family line, ploidy and size which in some cases interacted with the presence of the whelk. This thesis provides evidence that utilising triploid breeding programs to produce oysters which can divert a greater proportion of their energy budget into growth and acid-base balance, may be a viable option to reduce the predicted impacts of elevated pCO2 on oyster aquaculture over this century. Preliminary evidence for selecting oyster family lines that are resilient to both elevated pCO2 and predation suggests that this may be a challenge and more research is required to determine whether this is a feasible option to help ‘climate-proof’ aquaculture industries and oyster populations in Australia and around the world