Potential Effects of Climate Change on Offshore Aquaculture of the Mediterranean Mussel (Mytilus galloprovincialis, Lamarck, 1819) in Portugal

ABSTRACT There is increasing concern on how future climate change (CC) will affect fish and shellfish populations. The European Union funded the Climate change and European aquatic RESources (CERES) consortium to collaborate with industry and policy stakeholders to test CC scenarios through 24 “storylines” linked to specific regional fisheries or aquaculture activities. For this study, the focus is on “storyline 7” related to offshore longline aquaculture for Mediterranean (Med) mussel (Mytilus galloprovincialis, Lamarck, 1819) along the Atlantic coast at Sagres, Southern Portugal. CERES has compared two greenhouse gas emission scenarios in terms of Representative Concentration Pathways (RCP) 4.5 and 8.5 W m–2 for projected mean sea surface temperature (SST) and mean net primary production (PP) comparing the period 2000 to 2019 to the period 2080 to 2099. With regard to SST in the Algarve, the prediction is for an increase of up to 1°C and under RCP 4.5 and up to 2°C under RCP 8.5 by the end of the century, while the projected changes for net PP are much more variable, with a trend for a slight increase for both RCP 4.5 and 8.5. Some of the key research activities included an experimental study testing the combined effects of temperature (3°C, 8°C, 15°C, 20°C, 25°C) and chlorophyll (2.10 µg–1), the data from which was used for a WinShell mass balance model based on an individual Med mussel grown offshore at Sagres and then incorporated into the local-scale Farm Aquaculture Resource Management model to provide data for projecting climate-driven changes on production potential. Mussel weight at harvest and production yield at Sagres are similar under both emission scenarios, RCP 4.5 and 8.5 at periodic time periods between the years 2000 and 2099. The Med mussel was able to adapt to SST up to 25°C provided the PP was reasonable. A core activity of CERES is engagement with stakeholders, with the help of bow-tie analysis to reflect stakeholder concerns about the current and future factors affecting Med mussel production, as well as the development of a probabilistic Bayesian Belief Network model linking biological projections with economic consequences and policy measures to test whether current management systems can adapt to identified risks under CERES scenarios. Initial interactions with stakeholders showed that they were much more concerned with day-to-day issues, including failure of mussel spat recruitment, reduced mussel condition, and periodic closures due to harmful algal blooms, rather than any hypothetical future problems arising from CC. Nonetheless, there was much more interest when potential scenarios arising from CC were presented. The Med mussel does seem to be better adapted to higher SST compared with the blue mussel (Mytilus edulis).