This means that there are certain things that corals need to live. In order to understand these requirements, let's explain them more thoroughly. The water in the ocean is saline or salty.
Coral polyps require saline water.
They cannot live in parts of the ocean where there is water that has little or no salt at all, known as freshwater . Usually, freshwater flows into the ocean from the land via rivers and streams. Since corals polyps do not like freshwater, they do not grow near rivers or streams flowing into the ocean. Coral polyps require sunlight. As we learned in Lesson 10, during a process known as photosynthesis sunlight and excess coral polyp wastes combine to promote the growth of tiny plants called zooxanthellae-algae.