EAPSI: Understanding the response of a natural system to long-term acidification using Sydney rock oysters and mud crabs as a model predator-prey system

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Ocean acidification is the gradual decrease in ocean pH as a result of carbon dioxide (CO2) uptake, and it is expected to have detrimental effects on the shell formation of calcified organisms such as oysters. The effect of ocean acidification on multiple interacting species should be explored to understand impacts on ecosystem dynamics. Mangrove estuaries experiencing acidic soil runoff near Sydney, Australia provide a natural laboratory for the study of ocean acidification and its effects on the ecosystem. This study will examine the effect of ocean acidification on a crab-oyster predator-prey system through a caging experiment and a laboratory experiment using a natural population of oysters that have been exposed to acidification for generations. This research will be conducted in collaboration with Dr. Melanie Bishop, an expert on community ecology of mangrove invertebrates, at Macquarie University in Sydney, Australia. In the source estuaries, Sydney rock oysters (Saccostrea glomerata) grown in either acidified or normal pH conditions will be enclosed in cages with mud crab predators (Scylla serrata) in both acidified and normal pH water for one week. The relationship between oyster mortality, the presence of mud crabs, and pH will be examined using linear models. In a separate laboratory experiment, oysters from acidified and normal pH sites will be exposed to mud crab predation, and video of predator behavior will be used to calculate handling time (the time a predator spends manipulating or eating a prey item). The effect of acidification on handling time and oyster mortality will be examined using ANOVAs. This study expands upon ocean acidification research by examining the effect of global change on interactions between two commercially important species, and by using oysters that have had generations to adapt to long-term acidification in nature. This NSF EAPSI award is funded in collaboration with the Australian Academy of Science.