Revision summary
Dead zones are hypoxic waters, often seasonal, driven by nutrient pollution and warming. Bottom animals die; mobile fish flee into crowded oxygenated belts. Food webs shift toward microbes and jellyfish and away from commercial stocks. Seagrass, coral, and mangrove nurseries suffer on eutrophic coasts. The Gulf of Mexico, Baltic, and parts of the Arabian Sea show the global spread.
Model answer
Flow diagram
flowchart TD N[Nutrient runoff] --> A[Algal bloom] A --> O[Oxygen used up] O --> D[Dead zone] D --> F[Fish flee benthos die] D --> C[Catch and nursery loss]
Conclusion
- Cut fertiliser runoff, treat sewage, and restore wetlands that trap nutrients before they reach the shelf.
- Treat warming seas as a partner of nutrient pollution, because a warmer ocean holds less oxygen and keeps the dead zone in place.
Spreading dead zones empty the seafloor of animals, push fish away, and shrink coastal nurseries. The marine ecosystem pays in diversity and in catch until nutrients and warming are both reduced.
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Students also ask
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"Caste system is assuming new identities and associational forms. Hence, caste system cannot be eradicated in India." Comment.
Next question in the 2018 paper (Q8). View answer →
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Are dead zones completely without life?
Almost for animals that need oxygen. Bacteria and some tolerant microbes remain. The ecosystem people use is gone.
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Can a dead zone recover?
Yes, if nutrient input falls and mixing returns oxygen, as parts of the Black Sea showed after fertiliser use dropped. Recovery of animals takes years.
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