Ocean deoxygenation
Ocean deoxygenation refers to the loss of oxygen from the oceans due to climate change (Keeling et al. 2010). Oxygen plays a key role in structuring marine ecosystems and controls the distribution of essentially all marine organisms (Gilly et al. 2013).
Local Stressors
Overfishing
Pollution
Pollution covers a broad range but the biggest source of this stressor is non-point source pollution which occurs as a result of runoff from urbanised areas (cars, trucks, septic tanks, farms, livestock ranches, and timber harvest) adding chemicals, heavy metals, oil and other pollutants which greatly affect the water quality. Plastic has also a important impact on the ocean directly affecting all the biota in the ocean \cite{Koelmans_2014}.
Hipoxia
The increasing frequency of blooms of nontoxic micro-algae and nuisance macro-algae is harmful because it dramatically reduces sunlight penetration in the water column. Large and long blooms can also draw a substantial amount of oxygen from the water column at night during respiration. Even though these events can occur seasonally, increasing water temperature and OA can change their frequency and intensity favouring the expansion of dead zones \cite{Sherman_2017}.
Interaction between stressors
Recent assessments of multistressor effects at global scales show that more than half of the world’s ocean has experienced an increase in cumulative human impact over a 5-y time span, predominantly driven by increasing climate stressors such as sea surface temperature, ocean acidification, and UV radiation \cite{Halpern_2015}.