Coral Bleaching Animation— HHMI BioInteractive Video

Recent questions

• What are corals made of?

  Corals are made of colonies of genetically identical polyps. These small animals form structures that can be seen from space, and each polyp has essential features such as a mouth, tentacles, and gonads. This unique structure allows corals to live, reproduce, and grow effectively in their marine environments. The collective behavior of these polyps contributes to the formation of coral reefs, which are vital ecosystems supporting diverse marine life.

• Why do corals have vibrant colors?

  The vibrant colors of corals are primarily due to symbiotic organisms known as dinoflagellates, which live within the coral's gastrodermis. These dinoflagellates contain chloroplasts that enable them to perform photosynthesis, capturing light energy and converting it into chemical energy. This process not only provides energy for the dinoflagellates but also supplies 75-80% of the energy required for the coral's survival, contributing to the coral's bright and colorful appearance.

• What causes coral bleaching?

  Coral bleaching occurs when environmental stressors, such as increased temperature and light intensity, overwhelm the dinoflagellates living within coral cells. Under these stressful conditions, the dinoflagellates break down, leading to their expulsion from the coral. This loss of symbiotic organisms results in a significant reduction of energy available to the coral, causing it to lose its vibrant color and turn white. Bleaching is a critical process that can threaten coral survival, as the corals become unable to produce their skeletons and face a high risk of mortality.

• How do dinoflagellates help corals?

  Dinoflagellates play a crucial role in the survival of corals by providing them with the majority of their energy needs. These symbiotic organisms reside within the coral's gastrodermis and utilize photosynthesis to convert light energy into chemical energy. This energy is essential for the coral's growth and reproduction, as it accounts for 75-80% of the energy required for these processes. Without dinoflagellates, corals would struggle to survive, as they rely heavily on these symbionts for their energy and overall health.

• What happens to corals without dinoflagellates?

  Without dinoflagellates, corals face severe challenges to their survival. The expulsion of these symbiotic organisms leads to a significant energy deficit, as dinoflagellates provide 75-80% of the energy that corals need to thrive. This lack of energy prevents corals from producing their skeletons, which are essential for their structure and growth. As a result, corals become more vulnerable to mortality and may struggle to recover from environmental stressors, ultimately threatening the health of coral reefs and the diverse marine ecosystems they support.