Climate change, nutrient pollution driving oxygen from oceans; threaten fish species

A  study by conservation group IUCN has revealed that climate change and nutrient pollution are reducing the oxygen from our oceans and threatening many species of fish.  As per the report, around 700 ocean sites are now suffering from low oxygen, compared with 45 in the 1960s. Aquatic species including tuna, marlin, and sharks are at stake with the depletion. Nitrogen and phosphorus from farms and industry discarded in the sea waters form the major portion of the nutrient runoffs. Yet climate change poses a higher threat than the runoff in recent days.

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Aquatic species at threat due to Climate Change

Global warming i.e. increase in carbon emission enhancing the greenhouse effect leads to a higher temperature and much of the heat is absorbed by the oceans. This warmer water holds less oxygen and scientists estimate that between 1960 and 2010, the amount of gas dissolved in the oceans declined by 2 per cent. The depletion is concentrated in many tropical locations with losses upto 40 per cent. Waters with less oxygen favour species such as jellyfish, but is bad for fast-swimming species like tuna. Minna Epps from IUCN told the media that they had earlier known about the phenomenon of de-oxygenation but were not aware of linkages to climate change. The decline of oxygen quadrupled in the past 50 years, she quoted. According to the authors, the bigger fishes with more energy needs will have to move to the shallow waters where more gas is dissolved. Yet this will make the species much more vulnerable to over-fishing. 

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Oxygen depletion will also affect the cycling of elements

The world's oceans are expected to lose 3-4 per cent of their oxygen by the year 2100 if the emissions are not controlled. In the tropics, more loss is expected in the top 1,000 metres of the water column, which is the richest in biodiversity. Moreover, depletion of oxygen is also bad for basic processes like the cycling of elements crucial for life on Earth, including nitrogen and phosphorous. Minna Epps said that running out of oxygen would mean habitat loss and biodiversity loss and a slippery slope down to slime and more jellyfish. It will also change the energy and the biochemical cycling in the oceans, she added.

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