Fishing trawlers are causing serious damage to fragile deep-sea coral reefs, which scientists have only begun to study in earnest in the last 10 years. As fisheries in shallower waters are depleted, the massive trawlers drag their large nets along the seafloor in deeper areas, trapping fish and clearing everything in their paths. Surveys off the coast of Norway indicate that one third to one half of the charted deep-sea reefs have been harmed by fishing. Damaged corals can take hundreds of years to regrow. Biologists, who say the diversity of deep-sea coral systems rivals that of better-known tropical coral reefs, are alarmed at the destruction and are calling for expansions of national and international marine protected areas to shield the corals from harm.