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20 December 2012

Gasping for oxygen

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How continuous monitoring of coastal ecosystems, such as the Black Sea, could help understand oxygen depletion affecting fish populations and better manage fisheries

In 2010, nearly two tons of fish was found dead due to lack of oxygen on the coastal line of the Romanian Black Sea.  Oxygen depletion, or hypoxia, occurring in the water is thought to be responsible. Relying on historical data and on that obtained as a partner to an EU project, “we wanted to carry out an in depth analysis on how the ecosystem is disrupted by the oxygen shortage and to identify the means of post-hypoxia recovery,” Dan Secrieru tells He is a senior scientist at Romania’s National Research and Development Institute for Marine Geology and Geoecology GeoEcoMar, Constanta.

To have a better understanding of the causes of hypoxia, scientists have gathered under the umbrella of the EU funded HYPOX project. Their aim is to foresee its consequences in places such as the Black Sea, the Baltic Sea, the Arctic sea and fjords, lagoons and lakes. A persistent hypoxia can lead to the loss of biodiversity, loss of living resources, the degradation of the ecosystem, the collapse of fisheries, according to Traian Gomoiu, the Romanian project team leader working for GeoEcoMar.

The oxygen gets depleted along all the Romanian coastal line of the Black Sea close to human settlements and industrial plants and along the shipping routes, scientists found. Hypoxia, they discovered, may be due, among others, to chemical pollution. This combined with a large influx of freshwater brought by floods in the Danube that hinders the oxygen penetration to the bottom layers of the sea. In addition, the freshwater brings agricultural fertilizers, resulting in algae developing at the surface of the water. Their decomposition, in turn, consumes oxygen, following their death caused by high water temperature linked to global warming.

Secrieru recognises, however, that ecological pressures declined on the Black Sea in the last 20 years. This is due to lesser aggressive farming methods, the closure of a seaside fertiliser factory and the decline of industrial activity due to the economic slowdown. Nevertheless, he points out: “the health of ecosystems is still precarious and, it is difficult to predict further developments without [a monitoring programme].”

Some scientists question its feasibility.  “It would be ideal to do this monitoring regularly; especially when the temperature is increasing, or decreasing in order to make predictions either for the fundamental research or for economic assessments,” Brigitte Raval tells She is a hydrobiologist at Creocean, a Consultancy specialised in coastal and marine environment and oceanography, located in La Rochelle, France. However, she warns, from her own experience of working in this field, that “everything depends on the funding”.   

Others, such as Nicolae Papadopol, recognise the difficulty in intervening and making immediate changes. As the scientific director of the Museum of Natural Sciences at the seaside resort of Constanta, Romania, he still believes that they are means to control hypoxia. When continuous monitoring signals that it has reached alarming levels, “people in charge [of environmental] preservation must take urgent measures to reduce emissions, [and] to set up or improve water treatment plants,” he suggests.

By contrast, this monitoring could prove useful in fisheries management.  “These [monitoring] data are precious information for the fishing sector. If you have clean water, you can expect valuable fish species coming close to the coastal line,” Papadopol remarks. Verena Tunnicliffe concurs from her own seabed monitoring experience at the University of Victoria, British Columbia, Canada: “Monitoring is revealing a tremendous amount about ocean behavior,” adding: “we are finding that animals respond quickly and migrations are affected by the oxygen levels.  Thus, commercial fisheries for animals such as shrimp and crabs can be better managed.” provides its content to all media free of charge. We would appreciate if you could acknowledge as the source of the content.