Coral Reefs Support 25% of All Marine Species

The incredible biodiversity of coral (Deals) reefs is a direct result of the intricate structures they create, which provide shelter (Review), feeding, and nursery grounds for a vast array of marine life. These underwater cities are built by tiny animals called coral polyps, which form colonies and secrete hard calcium carbonate skeletons. Over time, these skeletons accumulate, creating the complex three-dimensional framework of the reef. This structure offers countless nooks and crannies that serve as homes and hiding places for organisms from small invertebrates to large predatory fish. The reefs act as a vital refuge, spawning area, and source of food for countless species.

The foundation (Review) of this vibrant ecosystem lies in a crucial symbiotic partnership between the coral polyps and microscopic algae called zooxanthellae. These algae live within the coral's tissues, and through photosynthesis, they provide the coral with essential nutrients like glucose, glycerol, and amino acids. In return, the coral provides the algae with a protected environment and the compounds necessary for photosynthesis. This mutually beneficial relationship is so vital that it provides up to 90% of the coral's energy needs and is also responsible for the brilliant colors of the reefs. The success of this symbiosis, which dates back hundreds of millions of years, is fundamental to the reef's ability to thrive in nutrient-poor tropical waters.

Beyond the well-documented threat of rising ocean temperatures which can cause coral bleaching—the expulsion of the vital algae—reefs face a multitude of other dangers. Pollution from land-based sources, including sediment, nutrients from fertilizers, and toxic (Review) substances, can smother corals and promote the growth of harmful algae. Destructive fishing practices, such as blast and cyanide fishing, can shatter the fragile reef structure, while overfishing can disrupt the delicate ecological balance. Furthermore, ocean acidification, a result of increased carbon dioxide absorption by the ocean, hinders the ability of corals to build their skeletons, making them more vulnerable to erosion and damage.