Large-scale changes in ocean temperature and pH driven by carbon emissions are negatively affecting the growth and survival of marine calcifiers. How these stressors influence disease virulence in marine shellfish is poorly understood. To understand this linkage, we conducted experiments investigating the effects of temperature and pH on disease susceptibility in the white abalone (Haliotis sorenseni), an ESA protected species that is captively bred as part of restoration efforts. This species is susceptible to withering syndrome (WS), a digestive disease caused by the Rickettsiales-like bacteria Candidatus Xenohaliotis californiensis (CaXc). To evaluate the impact of ocean warming and acid ification on CaXc virulence in H. sorenseni, we exposed white abalone to factorial combinations of temperature (12, 15, and 18°C), pCO2 (450 μatm and 1,080 μatm ), and CaXc pathogen (unexposed (U), exposed (E)) over the course of a 9-month experiment, simulating conditions experienced in wild and captive settings.
The combination of elevated temperature and CaXc exposure reduced white abalone survival by 73% and 84% at 15°C and 18°C, respectively, compared to survival rates observed in animals un-exposed to CaXc and held at 12°C. In contrast, exposure to high versus low CO2 did not influence survival. However, mean growth of animals held under high CO2 decreased by 29.4% when compared to animals held under low CO2 conditions. These impacts were modulated by the initial size of individuals entering the experiment, with larger animals showing a higher tolerance of climate stress. Interestingly, differences in these responses were observed among our F2 family groups, indicating that genetic lineage could confer some resilience to temperature, disease, and pH stress. These findings hold relevance for white abalone conservation aquaculture and for understanding how global climate change will impact disease dynamics and challenge the management of California abalone into the future.