Twenty-five percent of all species in the ocean live in coral reefs, which are created by tiny living organisms known as coral polyps. if conditions do not change, over half of the world's coral will be dead by 2050. most polyps live with algae in a symbiotic relationship—one that both organisms. these algae rely on sunlight for food. the coral needs access to flowing water for its own food as well as for the gases it and its algae need. runoff from farming, construction, and other human activities can carry silt far out into the ocean. what effects does this silt have on coral reefs?