Raashi Mohan - Dead Zones

“Dead zones” are areas of large bodies of water, typically occurring in the ocean, that lack the necessary amount of dissolved oxygen to support marine life. Historically, many of these sites were naturally occurring. However, recently there have been increased instances of these zones expanding and new ones being created. This is likely triggered by the process of eutrophication, caused by an excess of plant nutrients due to runoff from the land. These excess nutrients often cause rapid increases in the density of phytoplankton, a phenomenon known as an algal bloom, which allows small heterotrophs, such as zooplankton, to proliferate. Eventually, as phytoplankton and zooplankton die, the large amount of decomposition exhaust the water’s supply of dissolved oxygen.

Low levels of oxygen have several different effects on marine organisms. Many fish face reproductive problems, such as low egg counts and a lack of spawning. This occurs because the hypoxic (low-oxygen) conditions activate certain genes that lead to smaller reproductive organs. Additionally, bottom-dwelling organisms, such as clams and lobsters are unable to escape the potential suffocation, as they are quickly rendered unconscious and too slow to flee. However, jellyfish thrive in these situations, often present in vast numbers. Unfortunately, the mass amounts of jellyfish produce excess mucus and waste.

Fortunately, dead zones are reversible if their causes are largely reduced or eliminated. For example, after a large decline in the number of chemical fertilizers used in Russia, a large dead zone in the Black Sea mostly disappeared. Additionally, in the U.S., dead zones have been reduced in the Hudson River and San Francisco Bay as a result of major clean-up efforts. The Mississippi Basin/Gulf of Mexico Water Nutrient Task Force has been busy monitoring the large dead zone in the Gulf of Mexico and recommending ways to reduce it. However, as industrial and agricultural activity continues to increase, these clean-up efforts have an increasingly important job.

Food for Thought:
What are some ways in which people can reduce the occurrence of these "dead zones"?
In what ways can these zones have economic ramifications?
What are some other factors (other than runoff) that cause these zones?

Sources:
https://www.sciencedaily.com/terms/dead_zone_(ecology).htm
https://www.cbc.ca/news/technology/gulf-of-oman-marine-dead-zone-1.4645018
https://www.scientificamerican.com/article/ocean-dead-zones/