The Ecology of Coral Reefs

Coral reefs are among the most biodiverse and productive ecosystems on Earth. Often referred to as the "rainforests of the sea," these underwater structures are built by colonies of tiny animals known as coral polyps. Each polyp secretes a hard skeleton of calcium carbonate, and over many generations, these skeletons accumulate to form the massive, complex structures of the reef. Although coral reefs cover less than one percent of the ocean floor, they support an estimated 25 percent of all marine species, providing them with food, shelter, and breeding grounds.

The survival of reef-building corals depends on a crucial symbiotic relationship with microscopic algae called zooxanthellae. These algae live within the tissues of the coral polyps. Through photosynthesis, the zooxanthellae produce nutrients that provide the coral with up to 90% of its energy needs. In exchange, the coral provides the algae with a protected environment and the compounds necessary for photosynthesis. This partnership is also responsible for the vibrant colors of many corals; the pigments of the algae are visible through the transparent polyp tissue.

Unfortunately, coral reefs are highly sensitive to changes in their environment. One of the most significant threats is rising ocean temperatures, which can disrupt the symbiotic relationship between corals and their algae. When stressed by heat, corals expel the zooxanthellae from their tissues in a process known as coral bleaching. Without the algae, the corals turn white, lose their primary energy source, and become more susceptible to disease and death. Ocean acidification presents another major threat, hindering the ability of polyps to build their calcium carbonate skeletons.