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The influence of Environmental Variability On Mussel Aquaculture and adaptation in the context of global ocean change

Periodic Reporting for period 1 - EVOMA (The influence of Environmental Variability On Mussel Aquaculture and adaptation in the context of global ocean change)

Reporting period: 2017-11-16 to 2019-11-15

Predictions of global climate change are based on average trends. However, the natural environment is highly variable and this is ultimately what organisms respond to. How natural variability of seawater conditions influences marine organisms is not fully understood, although there is evidence that exposure to variability today can help species adapt to future conditions. One important stressor is pH, which is declining in a process called ocean acidification. As atmospheric carbon dioxide is increasing in the atmosphere, carbon dioxide is absorbed by surface oceans causing acidification. This project reviewed the influence of pH variability on marine organisms’ sensitivity to ocean acidification and addressed the influence of pH, temperature, and salinity variability on the Mediterranean mussel Mytilus galloprovincialis in the context of global change.

Understanding how current environmental variability shapes species tolerances or sensitivity to global change is necessary for deciding where to invest management strategies such as habitat protection and restoration efforts. The focal species, M. galloprovincialis, is a globally important aquaculture and this industry may need to adapt its practices in light of global change.

The objectives of this project were to review the literature on organismal responses to pH variability in the context of ocean acidification, perform experiments on M. galloprovincialis to quantify their sensitivity to pH, temperature, and salinity variability, and track pH variability at two aquaculture farms in Spain.
- A review of all studies investigating how marine organisms respond to variation in seawater pH was performed. Results indicate that exposure to low pH events in the field can make species more tolerant of future ocean acidification conditions, but this was only the case for non-photosynthetic calcifiers. Generally, marine species are able to cope well with pH variability. These results were published in 2019 in Global Change Biology and disseminated at OceanVisions Summit 2019.
- An experiment was performed testing the hypothesis that early exposure to a heat event would help prepare mussels for dealing with summer heat stress. Mussels were exposed to various temperature treatments in the lab, transferred to the field, and mortality was tracked during summer warming. Early heat exposure did not influence mussel sensitivity to warming. Heat stress in summer was too severe and beyond the range of physiological tolerance of mussels, regardless of thermal history prior to seasonal warming.
- How mussel larvae respond to variable pH and salinity was investigated in a series of laboratory experiments. Larval development was found to be sensitive during the trochophore stage for pH, but this developmental stage was unaffected by salinity stress. This suggests that salinity and pH affect different developmental processes. Experiments assessing the effect of different carbonate chemistry and salinity conditions on larval development were also performed. Part of these results are published in Kapsenberg et al., 2018, and are currently being prepared for publication in an additional manuscript.
- SeaFET pH sensors were deployed in the north and south bays of Delta de Ebro for over one year to track pH variability at two aquaculture farms. Results indicate that while pH variability differs between the bays, mussels are currently not exposed to pH stress at these sites. However, temperatures still reach lethal limits in summer. These results will be disseminated to IRTA, the governmental body managing the aquaculture activities in Delta de Ebro.
The environmental data from Delta de Ebro have advanced knowledge on local pH exposures in aquaculture farms in a productive area of Spain. The project has highlighted the importance of environmental monitoring, and IRTA has now purchased their own pH sensors to continue monitoring pH in the future. As ocean acidification progresses, monitoring pH is necessary to ensure the health of bivalve and aquaculture production.
Deployment of pH sensors in Delta de Ebro