Overview
Salinity affects both biological and physical components of the ocean ecosystem, including growth rates of marine organisms and vertical stratification (Environment and Canada 2019; Feindel et al. 2013).
Different species and life stages have preferred salinity conditions, outside of which they experience harmful physiological effects, including mortality (Brennan et al. 2016; Feindel et al. 2013). Many organisms are expected to shift their spatial distribution to avoid poor environmental conditions (Nye et al. 2009), although sessile and cultured organisms have limited to no ability to do so. Salinity is of particular concern for shellfish aquaculture. For example, two cultured species in Nova Scotia (blue mussels and oysters) can tolerate a wide range of salinity for short periods of time, but prolonged exposure to low salinity (e.g., from freshwater pulses) can result in reduced growth and reproduction, higher disease prevalence, and eventually death (Feindel et al. 2013; Howarth et al. 2021).
Like temperature, salinity is directly related to seasonal ocean stratification. Freshwater inputs in the spring and summer contribute to a fresh, warm surface layer that is broken down by wind-driven mixing in the fall and winter. Salinity is also influenced by rates of evaporation and precipitation, melting and freezing of sea ice, and ocean circulation (Environment and Canada 2019).
Surface waters around Canada, including off the coast of Nova Scotia, are generally becoming fresher due to climate change and natural variability (Environment and Canada 2019). This trend is expected to continue as a result of the projected increase in precipitation and ice melt (Environment and Canada 2019; Howarth et al. 2021). In contrast, deep waters in the Gulf of St. Lawrence are becoming more saline as a result of a northward shift of subtropical currents bringing in saltier waters (Environment and Canada 2019; Howarth et al. 2021).