Because oil is usually floats, the animals affected most are those found at the surface - especially seabirds. The oil covers the birds and causes them to lose their waterproof coating. When they try to clean themselves, the oil sometimes poisons the birds. Some species of invertebrates and fish have the ability to remove small quantities of oil from their systems, but oil becomes toxic at higher levels. Young fish and roe are most susceptible to the effects of oil spills.
Adult fish are fairly mobile, and can usually move out of harms way.
They are also in danger of poisoning themselves with the oil. Seal pups are cleaned up using sorbents. As long as people are using oil, there will be a need to transport it and there will be a chance of oil spills. You can also volunteer with recovery crews. You could also choose a career that deals with marine biology and perform research that would improve restrictions, regulations, and clean up techniques.