Understanding and Assessing Impacts
Acute stressor events in marine environments are increasing in duration and frequency due to climate change. Of particular concern are heatwaves, which can lead to various detrimental impacts, most notably mass die-offs of shellfish. In July 2021, as a recent example, a heatwave in western Canada caused a mass die-off of shellfish along the coast of British Columbia. In addition to thermal stress, warming events cause oxygen limitation due to forced rises in organismal metabolic rates and oxygen demand and parallel reductions in water oxygen concentration, thereby magnifying challenges to survival. According to the literature, under current climate change projections, dissolved oxygen in the oceans is also forecast to decline and an increased incidence of hypoxic events is predicted for coastal areas. However, the impact of heatwaves and hypoxia on marine species is poorly understood and mitigation techniques remain largely nonexistent. In recent years, cultured Pacific oysters have demonstrated a high susceptibility to summer mortality. Mortality rates typically range from at least 30% but can extend to near total loss. Recent research has shown mortality in the field to typically occur when summer temperatures reach >19–20°C. There is also growing awareness that heatwaves are a contributing factor, but an in-depth investigation is still required. Likewise, the role of oxygen limitation during these events is poorly understood. Similarly to Pacific oysters, declines in population abundance due to decreased recruitment of juveniles and increased mortality of adults have been observed in natural populations of Pacific razor clams.
For additional climate information, look at the Resources section of this example (below).