- Zooxanthellae are expelled from corals during a process known as bleaching.

- Bleaching occurs when corals undergo stress, such as elevated temperatures, increased irradiance, or pollution.

- When corals are stressed, they produce reactive oxygen species (ROS) that damage the symbiotic relationship between the coral and its zooxanthellae.

- This damage leads to the expulsion of zooxanthellae, causing the coral to lose its color and become bleached.

2. Disease:

- Zooxanthellae can also be expelled from corals due to disease.

- Coral diseases can be caused by a variety of factors, such as bacteria, viruses, or fungi.

- When corals are infected with a disease, the zooxanthellae may be expelled as part of the coral's immune response.

3. Competition:

- In some cases, zooxanthellae may be expelled from corals due to competition with other organisms.

- For example, if a coral is overgrown with algae or other invertebrates, the zooxanthellae may be shaded out and eventually expelled.

4. Predation:

- Zooxanthellae can also be expelled from corals by predators.

- Certain species of fish, shrimp, and snails prey on corals and may consume the zooxanthellae along with the coral tissue.