Researchers are warning that the Gulf of Mexico oil spill is a bigger mess than the government claims and that a lot of crude is lurking deep below the surface, some of it settling perhaps in a critical undersea canyon off the Florida Panhandle.

The evidence of microscopic amounts of oil mixing into the soil of the canyon was gathered by scientists at the University of South Florida, who also found poisoned plant plankton — the vital base of the ocean food web — which they blamed on a toxic brew of oil and dispersants.