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An IMEDEA (UIB-CSIC) research concludes the number of «dead» coastal areas grows a five percent per year caused by the human action


Two out of three marine species will see its population halved due to falls in the oxygen concentration below 2 ml oxygen per litre

This study is the result of Raquel Vaquer’s PhD thesis, advised by Dr. Carlos Duarte, Malaspina expedition coordinator

Agua hipóxicas en Portocolom, MallorcaThe so-called «dead zones» are coastal areas depleted of most of the living resources as a consequence oxygen concentration decline (phenomenon known as hypoxia). These hypoxic zones have increased at a rate of the five percent per year due to human action, according to research conducted by Dr. Raquel Vaquer-Sunyer in her PhD thesis, Changes in coastal marine dissolved oxygen due to anthropogenic disturbances and consequences for marine life. The PhD thesis advisor is Dr. Carlos Duarte, Malaspina expedition coordinator. Raquel Vaquer’s PhD thesis also warns that increased human perturbations to coastal ecosystems during the last century are threatening coastal ecosystems, their biodiversity and ecosystems functioning.  The increase in anthropogenic nutrients inputs to the coastal ocean (phenomenon known as eutrophication), and global warming are the two principal pressures affecting coastal ecosystems.

New hypoxia definition
A hypoxic area is an area that registers insufficient oxygen levels for marine life. During 1980 the scientific community defined hypoxia as waters with oxygen levels bellow 2 mg O2/l. According Dr. Vaquer’s study, more than half of marine species will be affected by oxygen reduction below this value. Therefore, Dr. Vaquer proposes in her PhD thesis to increase the current threshold to define waters as hypoxic, to protect marine biodiversity. She recommends the use of 3,5 mg O2/l as a new operational oxygen threshold to designate hypoxic waters.

Consequences for the marine biodiversity
Organisms need more oxygen to live when temperature increases and, at the same time, oceans lose oxygen when water heats. Therefore, considering that: 1) global warming will reduce the dissolved oxygen concentration, and 2) the oxygen requirements of organisms will increase, the consequences for marine biodiversity may be catastrophic.

The PhD thesis also shows that the survival time of organisms exposed to low oxygen concentrations are reduced 74%, and the oxygen content that they need to survive increases 16% when the marine organisms are exposed to higher temperatures.

If current warming continues, the survival time of the marine organisms exposed to hypoxia will be reduced by 36% by the end of 21st century, and the oxygen needed to survive will increase by 25%.

Regarding mortality, two thirds of marine species will reduce their populations to a half at oxygen concentration below 2 mg of oxygen per litre. These percentages imply a risk for the marine biodiversity considerably higher than hitherto believed by the scientific community. Dr. Vaquer-Sunyer highlights that hypoxia is emerging a major threat for the marine biodiversity.


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Proyecto financiado por el Ministerio de Educación, Cultura y Deporte en el marco del Programa Campus de Excelencia Internacional

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