Fish Threatened By Spike In Ocean Oxygen Exodus

Oceans across the globe are losing oxygen at an unprecedented rate, which is putting marine life in a serious bind, according to a new report released by the International Union for Conservation of Nature.

The report, which collated the work of 67 scientists from 17 countries, shows oxygen levels in the ocean have declined by about 2 percent since the 1950s while the volume of water completely depleted of oxygen has quadrupled since the 1960s. Back then, only a few dozen sites suffered from low oxygen levels, but that number skyrocketed to 700 in 2011.

Researchers say ocean warming from the burning of fossil fuels as well as excessive algae growth are the two main culprits in deoxygenation.

Warmer oceans hold less oxygen and are more buoyant than cooler water. That makes it difficult for oxygen to make its way to deeper waters and raises the oxygen demands of sea creatures. Plant life is also rapidly growing as a result of fertilizer and animal waste run-off, as well as other factors, leading to a lack of oxygen and higher animal mortality rates.

While nutrient runoff has been recognized as a threat to oceans for decades, climate change more recently began to aggravate the issue. The resulting rapid decline in oxygen is now posing a direct threat to many species of fish, including tuna, marlin and sharks.

Even small changes can impact fish ecosystems in a significant way. For example, waters with less oxygen favor species such as jellyfish. As jellyfish flourish while other species die off in the adverse conditions, there is less competition for food and jellyfish become dominant predators. The result is that they feast on fish eggs and larvae.

Researchers warn that continuing without a change in the approach to emissions, global oceans are expected to lose as much as 4 percent of their oxygen by 2100.

The study was the largest of its kind.

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