Featured Image Credit: National Geographic
By Adam Trautwig
Over the past decade, climate change has become a larger and larger part of the public dialogue (finally). With scientists struggling to quantify what exactly climate change entails, we can easily let aspects that are even more difficult to quantify fall into obscurity.
Dissolved oxygen may be one of those factors. Dissolved oxygen is vital to marine life. When levels of dissolved oxygen are depleted the effects can be catastrophic.
While oxygen poor areas of the ocean (or Oxygen Minimum Zones) are naturally occurring, research suggests that these areas may be expanding. The effects are most severe on fish populations already threatened by overfishing. Natural resource managers face difficulties adequately accounting for its effects because it is hard to predict how “Oxygen Minimum Zones” will expand.
But the research does show that the effects of depleting oxygen (with the expansion of Oxygen Minimum Zones) include changing patterns of costal upwelling and restrictions on habitat for fish with high oxygen demands.
Costal upwelling is important to many microorganisms and the subsequent disruptions to the food web may have compounding effects. As dissolved oxygen levels continue to decrease, resources are diverted to the microbes that support the food web. The relationship between microbes and the larger cycles of ocean chemistry, as a whole, are strongly linked.
When resources are restricted, there are less areas that oxygen demanding species of fish can traverse. While these habitats are being compressed, it is possible that rates of harvest may temporarily improve. This could give the false impression that a fishery is rebounding when in actuality it is being more severely exploited.
Researchers led by Lothar Stramma at the Leibniz Institute of Marine Sciences in Kiel Germany have examined some of these effects in the eastern tropical Atlantic. They observed enormous losses of 15 percent of usable habitat from 1960 2010.
Other indirect effects of dissolved oxygen loss include exacerbation of ocean acidification. Excess carbon dioxide throws off this delicate balance particularly in the highly productive coastal ecosystems. Models constructed to estimate how oceans will change with the addition of carbon dioxide predict more severe effects on marine life than previously thought.
While ecosystems can tolerate slight changes and correct for those changes, over time sudden changes may have more damaging effects. The result is likely to be extirpation of less tolerant species. With those inflexible species also goes the unique ecosystem functions they perform.
With all of these potential effects the outcome is clear. Ocean chemistry will play a vital role in preservation of marine resources for future generations.
The source material used to write this article includes: “Expansion of oxygen minimum zones may reduce available habitat for tropical pelagic fishes” by Stramma et al. and “Future ocean acidification will by amplified by hypoxia in coastal habitats” by Melzner et al.
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