How does ocean acidification influence disease susceptibility of oyster Crassostrea gigas?

Chair: Sue-Ann Watson

Marine Fuhrmann (1)*, Bruno Petton (2), Flavia L. D. Nunes (3), Charlotte Corporeau (1), Fabrice Pernet (1)

1 UMR LEMAR Ifremer/CNRS/UBO/IRD, Technopole de Brest-Iroise, France, 29280
2 UMR LEMAR Ifremer/CNRS/UBO/IRD, Argenton, France, 29280
3 Institut Universitaire Europe en de la Mer, Université de Bretagne Occidentale, Technopole Brest-Iroise, France, 29280

Background
The amount of atmospheric CO2 penetrating the ocean is expected to increase over the next century and to cause a pH reduction estimated at 0.3/0.4 pH unit. Environmental change in the marine realm has been accompanied emerging diseases as new pathogens evolve to take advantage of hosts weakened by environmental stress. The effects of ocean acidification on immune response of marine organisms has only been recently investigated. Studies revealed that acidification negatively impacts bivalve immune of bivalves which can have dire consequences in the face of pathogen infection.

Methods
Here we examined the effects of ocean acidification on disease transmission and related mortality of oysters. Oysters were first acclimated for 6 days at two pH, 8.2 and 7.8. Then, oysters were exposed to Ostreid herpesvirus 1 (OsHV-1), a widespread pathogen in Europe. A subsample of oysters was infected in situ and moved back to the marine station in a flow-through system. The seawater surrounding these infected oysters used as source of infection and bathed at 7.8 or 8.2 before being distributed to oyster acclimated at 7.8 and 8.2. Survival of oysters was followed every day for 14 days.

Findings
At the onset of infection, oysters acclimated at 7.8 were smaller than those held at 8.2. When oysters and source of infection were at 7.8, survival of oysters was only 33.5% compared to 44.8% in animals and pathogens at 8.2. Survival of oysters at 8.2 exposed to a source of infection previously bath at 7.8 were intermediate at 41.2%.

Conclusions
Therefore, it seems that disease susceptibility in oyster increases with ocean acidification, likely reflecting increasing cost of life due to acclimation at low pH and/or immune depression. These hypotheses are currently being tested in the lab. Finally, acidification does not provide a physical barrier to pathogens transmission and disease expression.