The future of modern reefs Modern reefs are under assault from a variety of human activities, including over-fishing, sedimentation caused by agriculture and logging, high-impact tourism, and pollution resulting from coastal development. The decline of reefs can be linked to the current biodiversity crisis, in which a large number of species are becoming extinct because of human modification of the environment. The geologic record offers two insights into the future of reefs. Local decline of reefs is reversible if environmental conditions in an area become favorable again. Global extinction of reefs would be an ecologic catastrophe; once the world's reefs are eliminated, millions of years would be necessary for reef communities to re-evolve.