COP25: Marine life, Fisheries Threatened by Ocean Oxygen Loss

blue marlin
blue marlin

Published Dec 7, 2019 5:47 PM by The Maritime Executive

The loss of oxygen from the world’s ocean is increasingly threatening fish species and disrupting ecosystems, a new International Union for Conservation of Nature (IUCN) report warns. 

Ocean oxygen loss, driven by climate change and nutrient pollution, is a growing menace to fisheries and species such as tuna, marlin and sharks, according to the report released on Saturday at the COP25 UN Climate Change conference in Madrid.

The review report "Ocean deoxygenation: Everyone's problem" is the largest peer-reviewed study so far into the causes, impacts and possible solutions to ocean deoxygenation. Ocean regions with low oxygen concentrations are expanding, with around 700 sites worldwide now affected by low oxygen conditions – up from only 45 in the 1960s. In the same period, the volume of anoxic waters – areas completely depleted of oxygen – in the global ocean has quadrupled, according to the report.

Deoxygenation is starting to alter the balance of marine life , favoring low-oxygen tolerant species (e.g. microbes, jellyfish and some squid) at the expense of low-oxygen sensitive ones (many marine species, including most fish). Some of the ocean’s most productive biomes – which support one fifth of the world’s wild 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. As naturally oxygen-poor systems, these areas are particularly vulnerable to even small changes in ocean oxygen. 

Impacts here will ultimately ripple out and affect hundreds of millions of people, states the report. Species groups such as tuna, marlin and sharks are particularly sensitive to low oxygen because of their large size and energy demands. These species are starting to be driven into increasingly shallow surface layers of oxygen-rich water, making them more vulnerable to over-fishing. 

Very low ocean oxygen can also affect basic processes like the cycling of elements crucial for life on Earth, such as nitrogen and phosphorous, the report warns.

The ocean is expected to lose three to four percent of its oxygen inventory globally by the year 2100 under a business-as-usual scenario, but the global average masks local changes that are predicted to be, for example, more severe in mid to high latitudes. Most of the losses are predicted to be concentrated in the upper 1,000 meters of the water column, which is richest in marine biodiversity.

The major drivers of ocean oxygen loss are climate change and nutrient pollution, with the latter affecting coastal areas. As the ocean warms, its waters hold less oxygen and become more buoyant, resulting in reduced mixing of the oxygen-rich water near the surface with the ocean depths, which naturally contain less oxygen. Nutrient pollution causes oxygen loss in coastal waters as fertilizer, sewage, animal and aquaculture waste cause excessive growth of algae, which in turn deplete oxygen as they decompose.

The report is available here.

Analysis predicts huge coral reef tourism losses

Climate change could cause coral reef tourism revenue losses of more than 90 percent in Australia by 2100, another COP25 report predicts. The research, commissioned by the High Level Panel for a Sustainable Ocean Economy - a group of 14 heads of state, found that even if action is taken to cut carbon emissions, the industry is still expected to suffer economic losses of up to 66 percent.

The Great Barrier Reef tourism industry supports two million tourists a year, sustains 64,000 jobs and generates A$6 billion dollars annually. On the west coast of Australia, another World Heritage listed reef – Ningaloo – is visited by more than 200,000 people per year.

The High Level Panel analysis used new models to assess impacts at country and regional levels, identifying that coral reef tourism industries in Egypt, Indonesia, Mexico and Thailand will also be hit hard.

The paper calls for more conservation and restoration measures for coral reefs to aid resilience as well as actions that will reduce the climate impact of tourism.

The report is available here.