The correct answer is (d). Global warming is the most significant factor in coral bleaching. Coral bleaching is a stress response that occurs when corals are exposed to elevated water temperatures. When corals bleach, they expel the algae that live in their tissues, which provide them with food and color. Bleached corals can recover if the water temperature drops, but if the stress continues, they can die.
Mining of coral rocks is a human activity that can damage coral reefs. Coral rocks are used in a variety of products, including jewelry, building materials, and aquarium decorations. Mining can damage coral reefs by removing coral rocks, disturbing the sediment, and introducing pollutants into the water.
Outbreak of coral diseases is a natural phenomenon that can also damage coral reefs. Coral diseases are caused by a variety of pathogens, including bacteria, viruses, and fungi. These pathogens can kill corals or weaken them, making them more susceptible to other stressors.
Siltation of seawater is a natural process that can also damage coral reefs. Siltation occurs when sediment is carried into the water by rivers, waves, or wind. This sediment can smother corals and prevent them from getting the sunlight they need to survive.
The following is a list of dams and the rivers they are located on:
- Grand Coulee Dam – Columbia River
- Hoover Dam – Colorado River
- Nurek Dam – Vakhsh River
- Cahora (Cobbora) Bassa Dam – Zambezi River
The dam that is not correctly matched is (c). Nurek Dam is located on the Vakhsh River in Tajikistan. The Vakhsh River is a tributary of the Amu Darya River.