Sunlit reef walls in the Caribbean’s so‑called pearl of the sea look like a single breathing organism, yet most of the architecture is mineral. The branching towers and boulder‑like domes are calcium carbonate skeletons left behind by coral polyps that have already died, turning living tissue into a rigid scaffold.
Each coral colony functions as a layered system. At the surface, a thin living skin of polyps extends tentacles to capture plankton and directs calcification, building new skeletal chambers on top of old ones. Packed inside their cells, symbiotic algae known as zooxanthellae perform photosynthesis, pumping sugars and oxygen into the polyps and, in return, receiving carbon dioxide and inorganic nutrients. This energy flow drives high primary productivity and supports a dense food web across fish, crustaceans and sponges.
Color and motion complete the illusion of a single, vibrant body. Pigments from zooxanthellae and coral tissues, plus fluorescent proteins, paint the skeleton in bright bands, while biofilms and turf algae coat bare rock. Schools of reef fish, grazing sea urchins and swirling plankton constantly traverse the structure, exploiting its surface area and crevices. The result is a biological palimpsest: layer upon layer of living communities occupying the enduring skeletons of past coral generations.
