Storms kill most of the animals every year so they're adapted to re-colonise very quickly. According to Greenpeace scientist Paul Horseman, the impact of an oil spill can partly depend on the nature of the coastline and the weather. Oil is easier to get off rocky coasts than soft marsh of an estuary, for example. And in colder regions the fuel can stay around longer than it would in hot regions because it cannot evaporate so quickly. The type of oil will also make a difference.
Crude oil has a suffocating, toxic effect and is like a heavy tar.
Gasoline is generally more toxic but evaporates fairly quickly.