shallow marine environment extending from mean low water down to 200-metre (660-foot) depths, generally corresponding to the continental shelf. Neritic waters are penetrated by varying amounts of sunlight, which permits photosynthesis by both planktonic and bottom-dwelling organisms. The zone is characterized by relatively abundant nutrients and biologic activity because of its proximity to land. Coarse, land-derived materials generally constitute the bottom sediments, except in some low-latitude regions that favour production of calcium carbonate sediments by such organisms as algae, bacteria, and corals.