Thanks to global warming and increased dumping of pollutants in the world’s oceans, nearly two percent of the world’s ocean is today oxygen depleted “dead zones”. This is excluding areas where the quantum of oxygen is far less than what it ideally should be.
The oxygen depleted and Dead Zones of the oceans represent the worst-case scenario for marine ecosystems, coastal biodiversity, and are the severest form of ocean habitat degradation.
Some of the consequences are:
1. Fish, squid, crabs, clams, and crustaceans cannot survive in dead zones of the ocean.
2. Oxygen less zones in the oceans lead to diminished biodiversity. For instance, the Black Sea, one of the worst affected areas had 26 commercial fish species in the 1960s but now has only five.
3. One indirect impact of such devastation of marine life is the reduced feeding ground for predatory fishes and other marine animals like humpback, blue, fin, sperm and southern right whales. Oxygen minimum zones also affect nutrient cycling, predator-prey relationships, and plankton migrations. Less oxygen also means skin diseases and other deficiencies for whales and other animals.
4. Another impact is the expanded distributions of organisms that have adapted to live in hypoxic or oxygen-poor waters. New organisms from plankton to shellfish thrive in oxygen-depleted waters.
5. A bigger danger caused by the depletion of oxygen relates to Phytoplankton, the sea-plant responsible for about the same amount of photosynthesis each year as all the plants on land combined. These plants require oxygen to survive, and as oceans warm and dissolves less oxygen, these microscopic plants grow even slower. This in turn reduces the food available to fish and other organisms, including marine birds and mammals, which depend on the ocean’s food chain.
6. Another disturbing result of reduced phytoplankton is that these plants consume atmospheric carbon dioxide. Reduced phytoplankton means that the oceans take in less carbon dioxide, which again speeds global warming, contributing to a vicious cycle of increased warming. The lack of oxygen will also affect other elemental cycles on the planet, such as nitrogen and carbon.
7.Coral reefs are the “rainforest’s of the ocean” and support aquatic organisms in complex, linked food chains. Reduction of oxygen in the Indian Ocean has already killed off 90 per cent of the coral reefs near the surface in only one year. The remaining 10 per cent could die in the next 20 years, devastating fish stocks, and tourism vital to coastal economies.
8. Coral reefs also form natural breakwaters, and their destruction leads to increased coastal erosion.
Research conducted by the University of Copenhagen reveal that ocean oxygen depletion led to some of the large extinction events in the Earth’s history, including the end of the Permian, some 250 million years ago.