"It doesn't seem like much, but this small change will have huge ramifications".
Those species are then driven to other areas not affected by deoxygenation, but that can leave them susceptible to over-fishing by commercial operations. It will also have an [influence] on habitats.
The ocean absorbs about a quarter of all fossil fuel emissions, but as the global demand for energy continues to grow, it is feared that the seas of the world will eventually reach saturation point.
On current trends, oceans are expected to lose 3-4 percent of their oxygen globally by 2100. But the report says the losses are predicted to be more concentrated in the upper 1000m of the water column which is the highest in marine diversity.
"With this report, the magnitude of the damage caused by climate change on the ocean is clearly highlighted", said IUCN Acting Director Grethel Aguilar.
'As the warming ocean loses oxygen, the delicate balance of marine life is thrown into disarray. The study "Ocean deoxygenation: Everyone's problem" indicates that ocean's oxygen loss is related to the warming and acidification of the oceans caused by the increase of carbon dioxide (CO2), which is in turn outcome of greenhouse gas (GHG) emissions and ocean fertilization.
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.
"We are now seeing increasingly low levels of dissolved oxygen across large areas of the open ocean".
"[The results] here will ultimately ripple out and [influence] hundreds of millions of people", the IUCN said.
The group published this year a historical assessment of the planet's natural habitats, clearly concluding that human activity threatened up to a million species of extinction.
Oceans are already struggling with warmer temperatures, rampant overfishing, and plastic pollution.
IUCN Global Marine and Polar Programme Director Minna Epps added: 'Choices taken on the continuing local climate convention will resolve whether our ocean continues to preserve a rich diversity of life, or whether liveable, oxygen-rich marine areas are more and more, gradually and irrevocably misplaced'.
"To stop the worrying expansion of oxygen-poor areas, we need to decisively curb greenhouse gas emissions, as well as nutrient contamination from agriculture and other sources".
World leaders will gather in Marseille in June for the IUCN's World Conservation Congress.
Policy makers are now negotiating at the COP25 climate summit in Madrid to ratify a comprehensive settlement for the 2015 Paris agreement.
'The potentially dire effects on fisheries and vulnerable coastal communities mean that the decisions made at the ongoing UN Climate Change Conference are even more crucial'.