Marine life and fisheries are threatened as the oceans lose oxygen

A new report that was presented at the UN Climate Change conference in Madrid claims that the loss of oxygen from the world's oceans is increasingly threatening fish species and disrupting ecosystems. The report claims that ocean oxygen loss is driven by climate change and nutrient pollution and notes that this is a growing threat to fisheries and species like tuna, marlin, and sharks.The report is titled "Ocean deoxygenation: Everyone's problem" and is the largest peer-reviewed study so far into causes, impacts, and possible solutions to ocean deoxygenation. Ocean regions that have low oxygen concentrations are expanding with the report claiming at around 700 sites globally are now affected by low oxygen conditions, up from only 45 in the late '60s.

Over that same duration, the volume of anoxic waters, which are areas depleted of oxygen, in the global ocean has quadrupled. The report claims that deoxygenation is starting to alter the balance of marine life favoring low-oxygen tolerant species like microbes, jellyfish, and some squid at the expense of those that are sensitive to oxygen levels like most fish.

Some of the most productive biomes in the ocean that support a fifth of the world's marine fish harvest are formed by ocean currents carrying nutrient-rich, but oxygen-poor water to coasts that line the eastern edges of the world's ocean basins. These areas are vulnerable to even small changes in ocean oxygen.

The report claims that impacts in those areas can ripple out to affect hundreds of millions of people. Large species of fish are particularly vulnerable, such as tuna, marlin, and sharks due to their large size and energy demands. According to the report by the year 2100, the oceans will lose 3-4% of its oxygen inventory in a business as usual situation.