Our Oceans Are Dying

Starting in the seventies, researchers began to document the existence of "dead zones" in the world's oceans. These are areas of low oxygen where marine life can no longer be supported. They are located in coastal areas, where the vast majority of aquatic life is normally located. In 2004, a UN study reported 146 dead zones in the world's oceans. In 2008, the journal Science reported a count of 405 dead zones, up to 70,000 square kilometres in size.

Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning. The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fuelled by riverine runoff of fertilizers and the burning of fossil fuels.

The first cause listed is the runoff of fertilizer. Modern agricultural methods produce much greater crop yields than traditional farming practices, but in order to do they must apply significant amounts of fertilizer. This usually contains nitrogen and phosphorus, much of which ends up as runoff in rivers and tributaries, which eventually lead to the ocean. The result is, in effect, the fertilization of the ocean, which results in ocean-based plant life (such as phytoplankton) growing much more rapidly than usual. The consequence of the resulting algal bloom is that oxygen is depleted, so that larger forms of life, such as fish, can no longer survive.

It is possible for dead zones to be reversible if fertilizer inputs are stopped or significantly reduced. A dead zone in the Black sea largely disappeared after the collapse of the Soviet Union. Many countries suffered extensive economic difficulties, with the consequence that they could not afford to use fertilizer. After some time fishing became possible once again.

The second cause listed by Science is the burning of fossil fuels. The issue here is that of global warming, caused by the emissions generated from the use of these fuels. There are several factors here. First, as levels of carbon dioxide increase in the atmosphere, the ocean begins to absorb more carbon dioxide as well. As this report details the increase in CO2 makes it harder for marine life to breath, and when combined with the reduction in oxygen caused by the dead zones, puts a double pressure on marine life. Another report describes how changes in ocean currents, caused by global warming, could lead to the dead zones growing by as much as a factor of 10.

It is clear that dead zones are a significant, and growing, problem for the world's oceans. Unfortunately, however, this is not the only stressor on marine life. Overfishing has also led to a great reduction in fish stocks worldwide, as well as species extinction. An article in Scientific American reports on a Nature article from 2003 which concludes that 90 percent of large fish have already disappeared from the ocean, largely as a result of overexploitation by industrial fisheries.

There is also significant pollution of the world's oceans, far and above the issue of fertilizer runoff. Habitat destruction, especially the loss of coral reefs, is another major factor. The destruction of the corals is largely being caused by ocean acidification, which is occurring because of the increase of CO2 levels in the oceans, as mentioned above. While any individual species might be able to survive one of these factors, the combination of all of them is frequently more than enough to cause extinction, and the general loss of biodiversity.

If we don't take action, it is possible that most salt-water fish could be extinct by as early as mid-century. Ocean life is extremely important for us and the biosphere as a whole. Of course, for many people in the world, fish and other sea creatures are a primary source of food, and one they are dependant on. Other land-based creatures also depend on ocean life, and its loss would dramatically impact them and terrestrial extinction rates as well.

There are several things that can be done to help prevent the death of our oceans. First, we must stop overfishing. In many areas, fishing may need to be banned outright (which has already happened in some areas). Failure to do this does fishermen no good, as the fish stocks they depend on have already been depleted in many cases, and others will become so quickly without any action taken. We also need to reduce the use of fertilizer as much as possible, and to try to capture as much runoff as possible. Obviously, we also need to urgently address global warming, for reasons that extend further than the health of the oceans.

If we fail to address these problems, and continue on our present course, there are many young people alive today that may live to see a world in which the oceans are devoid of fish entirely.