The combined impacts of climate change induced environmental variation (salinity and temperature) and pollutant mixtures on stress response in a typi

Estuaries are highly dynamic ecosystems occupying unique locations between terrestrial and aquatic ecosystems, covered by intermittent or permanent shallow e water layers and exhibit exceptionally high biodiversity, productivity, and provide important habitats and essential ecosystem services, and are highlighted as being in urgent need of protection within UNSDGs. Estuaries can act as both sinks and secondary sources of pollutants. The high absorption potential of silt/clay particles contribute to the enrichment sedimentary estuarine environments with often persistent pollutants. Many species of bivalves occur in estuaries play important ecological roles, such as filtration and nutrient cycling. Bivalves have significant economic importance and are widely regarded as sensitive indicators of environmental health. In addition, their ability to bioaccummulate contaminants makes them important entry routes into the human food chain.
Despite the realisation that climate-related environmental change has the potential to impact contaminants in aquatic environments, empirical investigations into the effects of climate change related environmental drivers of pollutant impacts on biota are limited largely to single pollutant exposure experiments, with very few data available on complex mixtures in multi-stressor scenarios. Changes in rainfall patterns and seasonal temperature extremes in previously temperate climate zones are known to affect the salinity regimes in local coastal and estuarine environmenty. Salinity fluctuations, as a result of dilution and evaporation events, impose ionic stress on aquatic organisms. Whilst euryhaline species may be able to cope better under fluctuating salinity regimes, the associated stress is also likely to make organisms more sensitive to chemical pollutants, particularly if the salinity fluctuations influence bioavailability. In addition, 2014 IPCC report shows that the average sea surface temperature has been increasing at an average rate of 0.11 C per decade at most of the world's coastlines since 1971 and is predicted to continue. Furthermore, local heatwaves, increasing in frequency and intensity, are adding to stress in marine organisms and, in combination with salinity fluctuations are likely to make species more susceptible to contaminant exposure.
In the marine and estuarine environment, the blue mussel, Mytilus sp, is a well characterised bivalve genus widely used as a model organism in ecotoxicological research and environmental monitoring. Mytilid distribution across Europe ranges from the warm water Mediterranean mussel M. galloprovincialis in Southern Europe to the cold water blue mussel M. edulis extending to Northern Europe, with an overlap and potential hybridization zone in the Bay of Biscay to northern Scotland. However, wild populations of Mytilus sp are declining through a combination of climate-related factors, habitat loss, over exploitation and pollutant exposure. Euryhaline marine mussels face significant osmotic challenges during salinity fluctuations
Mytilus sp, a facultative euryhaline osmoconformer, applies energy consumptive aerobic physiological processes leading to oxidative stress. These increased stress levels are likely to make mussels more susceptible to contaminant exposure.

The objectives are:

1) To quantify baseline physiological stress levels in mussels under experimental fluctuating environmental conditions (salinity and temperature) without pollutant challenge.
2) To investigate the effects of salinity and temperature fluctuations on the bioavailability of contaminants to mussels.
3) Investigate the ecotoxicological effects of pollutant mixtures on mussels under the influence of salinity fluctuations and temperature regimes in a multi-stressor context.