The decrease in oxygen content (deoxygenation) of coastal and oceanic waters worldwide has
worsened in recent decades. The main causes are climate change (warmer water holds less oxygen and causes increased stratification, which reduces ventilation, i.e. oxygen replenishment of the ocean interior and estuaries), and measurably higher nutrient concentrations (eutrophication) due to intensified human activities affecting coastal areas. Open-ocean deoxygenation, warming and ocean acidification are all driven by increased atmospheric carbon dioxide (CO2); they constitute multiple stressors for marine ecosystems, the socio-economic consequences of which are only just beginning to be appreciated.