“…In marine ecosystems, the respiration of organisms, the decomposition of organic matter by bacteria and the lack of water column mixing (for example, in bays and estuaries [ Diaz, 2001 ]), or the effect of tides exposing intertidal species to air or confining them in rockpools or sediments can create chronic hypoxia ( Mcmahon, 1988 ), associated with an increased production of DNA-damaging reactive oxygen species (ROS [ Hermes-Lima and Zenteno-Savín, 2002 ]). Exposure to ROS is linked to an increase in cancer risk ( Nechifor et al., 2012 ; Valko et al., 2006 ), which is mitigated by production of antioxidant molecules and enzymes, incurring an additional energetic cost compared with species inhabiting normoxic environments ( Hermes-Lima and Zenteno-Savín, 2002 ). Although chronic hypoxia is currently exacerbated by anthropogenic factors ( Diaz, 2001 ), sediment records and modeling indicates whole marine ecosystems had large areas exposed to climate-driven chronic hypoxia over geological-scale time periods ( Praetorius et al., 2015 ; Zillén et al., 2008 ).…”