| Summary: | The South African abalone, Haliotis midae, is an economically important species. H. midae is the largest of the five endemic abalone species in South Africa and is especially valuable in Asian markets. Over-fishing, increased predation (due a geographical shift in lobster populations), and prolific poaching of this commercially valuable species have depleted natural populations. Commercial abalone aquaculture began as a means to meet the market demand for H. midae and currently accounts for 77 % of South Africa's aquaculture revenue. Despite marked growth in this industry over the past decade, further increases will be challenged by the predicted threat of climate change, particularly ocean acidification. Calcifying organisms, such as abalone, are particularly susceptible to the impacts of ocean acidification and its resultant alteration in seawater carbonate chemistry. Most calcifying organisms display reduced calcification and growth in response to ocean acidification, with possible alterations to acid-base regulation, development, gonadal maturation and behaviour, as well as reduced larval and gamete survival. A further potential challenge to abalone aquaculture is global warming. The effects of temperature change depend on the organism's level of sensitivity, taxonomy, distribution and life history. The distribution of H. midae ranges from Saldanha Bay (cool-temperate) to Riet Point (warm-temperate), with the majority of commercial aquaculture production occurring in Hermanus (cool-temperate). Abalone aquaculture facilities will need to adapt to these environmental changes and assess potential mitigation strategies. This study investigated the long-term (12 months) impact that ocean acidification and warming will have on the South African abalone, Haliotis midae, by incorporating the natural variability of seawater pH and temperature in Hermanus. Ambient seawater retained natural pH and temperature variability and acidified seawater was offset to natural pH variability using CO2/O2 diffusion and a ...
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