Coral Reefs Support Quarter Of Marine Life

Often called the 'rainforests of the sea,' coral (Deals) reefs create bustling underwater cities in otherwise barren ocean landscapes. The secret to their incredible biodiversity lies in their complex, three-dimensional structure. Built by colonies of tiny animals, the intricate skeletons form a maze of caves, crevices, and ledges. This architecture provides countless niches for shelter (Review), hunting, and raising young, attracting an astonishing diversity of organisms from tiny invertebrates and algae to large predatory fish. This physical complexity is the primary reason such a small fraction of the seafloor can become a haven for so many different forms of life.

The engine powering this entire ecosystem is a remarkable partnership. Each coral is not a plant, but a colony of minuscule animals called polyps. Living within their tissues are microscopic algae called zooxanthellae. The algae use sunlight to photosynthesize, providing the coral with up to 90% of its food. In return, the coral provides the algae with a protected home and essential nutrients. This symbiotic relationship is so efficient that it allows reefs to flourish in clear, nutrient-poor tropical waters, forming the foundation (Review) of a vast and vibrant food web that ultimately supports a quarter of all known marine species.