A survey of the seafloor near BP's blown-out well in the Gulf of Mexico has turned up dead and dying coral reefs that were probably damaged by the oil spill. Further study is needed to conclusively link the coral die-off to the spill. "There's a lot of work to be done to see if there's been some sublethal effect on these corals," said Erik Cordes, a marine biologist at Temple who has been studying reefs in the gulf in the aftermath of the spill.