Final answer:
The relationship between protist zooxanthellae and the polyps of reef-building corals can be classified as mutualistic symbiosis. Both organisms benefit from the relationship, as the zooxanthellae supports the coral with nutrition from photosynthesis while the coral provides a protective environment and compounds necessary for photosynthesis.
Step-by-step explanation:
The relationship between the protist zooxanthellae and the polyps of reef-building corals are best described as mutualistic symbiosis. This is because both the protist and the coral benefit from the relationship. Zooxanthellae, a type of photosynthetic protist, resides within the coral polyps and provide nutrition through the process of photosynthesis. In return, the corals offer zooxanthellae a secure and protective environment and provide the compounds necessary for photosynthesis. This relationship is especially crucial in nutrient-poor underwater environments.
For instance, reef-building corals cannot live in waters deeper than 20 meters because there is insufficient light for the dinoflagellates to perform photosynthesis. If dinoflagellate symbionts are absent, corals lose their algal pigments, a process known as coral bleaching, and they eventually die.
Conclusively, mutualistic symbiosis like the one between zooxanthellae and corals is not only beneficial for the co-existing species but also plays an instrumental role in maintaining the ecosystem, as in the case of coral reefs.
Learn more about Symbiotic Relationships