Abstract
Rising sea temperatures and ocean acidification pose a major threat to marine organisms, and this holds especially true for marine calcifiers. Although previous studies have highlighted the impact that these stressors have on the physiology of various marine molluscs, many of them focused on a single stressor at a time. As such, understanding on the underlying mechanisms that contribute towards the persistence of these organisms under multiple stressors is still lacking. This fact extends to one of South Africa’s most important farmed marine invertebrates, the abalone Haliotis midae. Climate change is predicted to continue for the next century and beyond, raising concerns about the long-term survival of the species. Gene expression presents a way of unravelling the mechanisms that allow organisms to adapt to environmental change. For this purpose, the complete transcriptome of the gill tissue of H. midae was assembled and annotated de novo, and changes in the gene expression profile in response to an increase in temperature, decrease in pH, and compound effects of both stressors were investigated. The results indicated that abalone exposed to multiple stressors had a unique transcriptomic response. Furthermore, this group experienced heightened stress compared to the single stressors, with evidence of metabolic and oxidative stress as well as reduced growth rates. The findings shed light on the complex biochemical pathways that modulate adaptive responses in marine organisms and indicate that the true physiological challenges that marine organisms will experience under anthropogenic climate change are not reflected in analyses of individual stressors.