Major development projects are taking place in oceans across the globe all the time, enterprises that will provide shelter and food for a vast number of fish, mussels, urchins, and other marine life.
While credit is regularly and duly given to the visible construction crew — coral polyps — recognition is also due the polyps’ invisible, but very active algal partners, the zooxanthelle.
These algae (a type called dinoflagellates) live inside the body tissues of coral polyps. Coral polyps take care of some of their nutritional needs on their own by catching tiny protists and organic matter that drift past their tentacles. Their partnership with the chlorophyll-containing algae enable them to also get food from sunlight as if they were plants.
The zooxanthelle do the actual work of converting the sunlight into energy via photosynthesis. The by-products they generate (organic carbons such as glycerol and sugars) are excellent nutrients for their polyp hosts.
The zooxanthellae supply much of the polyps’ energy needs. In turn, the polyps provide the algae a protected, stable environment and nutrients they need for growth, such as nitrates and phosphates. Zooxanthellae also increase the rate of coral calcification, the growth of the hard shells that form the actual reef structures.