A year after the worst oil spill to strike U.S. waters, oyster beds are struggling along the Gulf of Mexico, the dolphin population is experiencing what the federal government calls an "unusual mortality event," and red snapper with rotting fins are showing up on fishing lines.

But scientists say it's far too soon to make definitive conclusions about the scale and scope of the marine disturbances. This uncertainty, which may not be resolved for years, is paving the way for...