Marie Nordström, a member of the ICES Workshop to Review the Marine Strategy Framework Directive Descriptor 4, explains hypoxia.
'Hypoxia essentially means 'low oxygen'. Aquatic animals need oxygen to breathe, just like terrestrial ones. When seawater contains very low levels of oxygen there are detrimental effects on fishes as well as other animals living on the seafloor.
Hypoxia alters species physiology and behaviour, and eventually, mobile animals flee the hostile conditions, but the rest die, leaving only bacteria capable of thriving in low-oxygen environments. Whereas some areas experience natural hypoxia, human activities exacerbate the occurrence, frequency and severity of hypoxic events by over-enrichment of nutrients in coastal waters throughout the world.
In my work on food webs, I study the links between species – who feeds on whom – and the importance of these interactions for maintaining a functioning ecological community. Hypoxia affects interactions between species, as well as the structure and functioning of entire communities.'