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The term anoxia means lack of oxygen. In our own bodies it can lead to organ failure and death. In marine systems the results are similar. Fish and other organisms cannot breathe and die off. Studies have found that widespread anoxia was associated with at least four of the “big five” mass extinctions in the past. Today anoxic dead zones have quadrupled since 1950. Sharks, tuna and other large fish species that need more oxygen to survive are at particular risk with oxygen levels reported to be dangerously low in over 700 areas globally.

There are naturally occurring areas in the open ocean that have low oxygen levels. This is particularly true off the west coast of continents due to how the rotation of the earth affects currents. Global warming during the past few decades has amplified this, causing the large expansion of dead zones in the north east Pacific, off the west coast of North America. Our fisheries have suffered. Following is a quote by Maya Elrick, at The University of New Mexico, lead author of a study of marine animal and plant fossils taken from Anticosti Island in the St. Lawrence seaway: “We are warming and acidifying the oceans today and warmer oceans hold less and less oxygen. Some marine organisms can handle the heat and the acidity, but not the lack of oxygen” Elrick said. “All these things are happening today and the results from the Late Ordovician study indicate the potential severity of marine anoxia as an extinction driver for many of the past and ongoing biologic extinction events.” “Abrupt global-ocean anoxia during Late Ordovician-early Silurian detected using uranium isotopes of marine carbonates,” was published in Proceedings of the National Academy of Sciences (PNAS), May 22, 2018. The only way to avert further catastrophic damage is to reduce and then reverse our human-caused GHG pollution in the seas and atmosphere.
The other main cause of anoxia is pollution flowing into coastal waters. Monoculture farming, such as massive soy, corn and wheat production, causes depletion of nitrogen in the soil. To make up for this, farmers apply nitrogen fertilizers to their crops. Researchers have found that only 17% of the nitrogen is absorbed by crops. Most of the rest makes its way to rivers and eventually to the sea. (Fowler, 2013; Ribaudo, 2011) Industrial meat production leads to even greater quantities of nitrogen in manure leaching out via rivers to the sea.[1] Scientists have blamed meat production for the world’s largest dead zone in the Gulf of Mexico. The U.S. industrial meat industry is huge. Just five companies produce most of the meat in the U.S. The biggest, Tyson, “slaughters 125,000 head of cattle, 35 million chickens, and 415,000 hogs every week.”29 They say that people can help the situation by cutting back on meat. This is one of the most effective actions an individual can do to both lower personal GHG emissions and help the sea recover. “The scale and environmental impact of the meat industry is enormous: more than a third of all land in the continental U.S. is dedicated to growing feed crops and providing the pastures to raise meat.”29 Blaming individual consumers for the bad practices of the industrial meat industry is the wrong way to attack the problem, though. The whole industry needs to be reformed. Hopefully the fledgling consumer movement to support meat substitutes and lab-grown meat will eventually reduce the meat industry’s powerful hold on public opinion and government policy.

The nitrogen at the mouths of rivers and marine estuaries causes marine algae to bloom. In a healthy system the algae feed off the nutrients and release oxygen through photosynthesis. As the algae die their bodies sink to the ocean floor and are consumed by bacteria. This process consumes oxygen, but plants on the ocean floor benefit and provide oxygen to the water. However, when too much nitrogen enters the water, column algae proliferate until sunlight cannot reach the ocean floor. Photosynthesis stops and oxygen levels can fall disastrously. This process is called eutrophication and the resulting lack of oxygen is called hypoxia.

Since 1950 ocean dead zones starved of oxygen have quadrupled. The number of oxygen-starved sites near coasts has increased tenfold to over 400 documented globally. The dead zone in the Gulf of Mexico that has resulted from agricultural runoff had expanded to 6,400 square miles according to the EPA in 2016, and it has grown since then. The Po River flow has been staunched to a trickle after dams, cities, and crops have drunk their fill. Its estuary holds water long enough for dead, anoxic zones to form, choking life in the Adriatic Sea for thousands of square miles. Similarly, the Loire River in France and the Minjiang River Estuary in the Fujian, the southeast province in China, experience severe hypoxia. India may have the most polluted rivers due to its massive growth in population over the last 40 years to 1.35 billion people. The urban rivers are especially polluted, with 63% of sewage flowing into rivers untreated. There are large dead zones associated with the Ulhas, Mithi, Cooum, Yamuna and Ganges rivers. Since major extinction events, such as the Ordovician-Silurian extinction event (when nearly 85% of all marine species disappeared) experienced high levels of oxygen depletion, this is something that we should be very concerned about.
There has been some success in cleaning up dead zones in estuaries. I’ll briefly discuss two: one in a rich country, the other a developing country.

The Chesapeake Bay
The Chesapeake is by far the largest estuary in the U.S., covering 64,000 square miles with drainage from more than 150 rivers and streams. Its second biggest tributary, the Potomac, flows through Washington, DC. This was once one of the most biologically productive marine areas in the world, with over 300 species of fish, shellfish and crab species. The estuary absorbs the waste of nearly 18 million people, millions of acres of farms, and polluted air from coal-burning power plants in the Midwest (about a third of the pollution in Chesapeake Bay is caused by air pollution from cars, industry and power plants). By 1983 there were massive dead zones with toxic algae blooms and lost sea grass habitats.
Conservation began after that, with programs coordinated amongst federal, state, and municipal governments and agencies. Federal agencies provided more than half a billion dollars a year and billions more were spent by the six surrounding states and District of Columbia. Goals are to plant 8,000 miles of forests and grassy buffers along waterways and rebuild miles of oyster reefs. Oysters, which filter pollution from the water, are now at less than one percent of historical numbers. Water sampling by the U.S. Geological Survey shows that water quality is slowly improving and the estuary is gradually being brought back to past abundance. As this example demonstrates, restoration in a heavily populated area with large industrial farms and a reliance on fossil fuel power plants takes lots of time and big money. All of this is at risk. And none of this restoration should be necessary. A study by the UN human rights council in 2017 found that it is a myth that pesticides are necessary to feed the world. It accused the global manufacturers of pesticides of “systematic denial of harms”, aggressive unethical marketing tactics” and heavy lobbying of governments which has “obstructed reforms and paralysed global pesticide restrictions”. (Damian Carrington, Guardian, Tue, Mar 7, 2017)
One thing that stands out in all of this is that big, monoculture agri-business, as well as fossil fuel power plants, create big, expensive environmental problems. Either the environment suffers or taxpayers are forced to pay large amounts for cleanup. In this case, both.

Cuba and The Bahamas
Before the Cuban Revolution seventy percent of its agriculture was made up of sugar cane and coffee. Most of its exports went to the Soviet Union. This monoculture system was very vulnerable and during the revolution there were severe food shortages.

After the revolution, in order to increase the food supply, the government promoted even stronger monoculture farming with a tenfold increase in fertilizers. This led to polluted waterways and marine dead zones. The Cuban government somehow recognized that the way to deal with this was to break up the large state-owned farms and to promote sustainable farming practices while growing a wide variety of crops. Green manure instead of fertilizers was used with the resulting improvement in soil quality and reduced agricultural runoff. Food production is up and the marine environment has benefited. An article from the University of Illinois describes this and suggests that lessons learned in Cuba could be applied in the Bahamas as it seeks to increase its food security while preserving its unique coastal treasures.
The Bahamas (known officially as the Commonwealth of the Bahamas) imports 85% of its food supply. Relying on a monoculture system with heavy reliance on fertilizers would be a disaster for a country with so little land and so many beautiful marine areas. Sustainable farming practices, such as hydroponics, aquaponics[2] and green manure could increase crop yields greatly, without harming tourism and fisheries (mainly conch and spiny lobster).
[2] The most simple definition of Aquaponics is the combination of aquaculture (raising fish) and hydroponics (the soil-less growing of plants) that grows fish and plants together in one integrated system. The fish waste provides an organic food source for the plants, and the plants naturally filter the water for the fish.(

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