Oil Spill Effects on Marine Life

Oil spills are one of the most notable catastrophes that occur in the ocean but actually only account for only a small percentage of oil that enters the ocean. The effects to marine life and habitat however are not small. Documented oil spills have release thousands or even hundreds of thousands of metric tones of oil into the ocean. The effect on marine life as a result of an oil spill can vary greatly depending on many different conditions and factors that are present at the time of spill, the type of oil, and also the type of marine life that is present. While marine life is not always affected in the same way by an oil spill, they will all be negatively affected by the contamination of oil into the marine habitat.

Conditions in the ocean and type of oil

The weather conditions at the site of the spill will affect the severity of the impact on marine life. Sometimes the spill can be greatly diluted just by the weather and currents in the ocean which will limit how much oil marine life is exposed to. Exposure to sunlight, wave action, air exposure, and even microscopic organisms can all help to reduce the toxic effects of an oils spill.

The type of oil is also a factor in the spill. While oil is very persistent in the environment and contaminates the environment, some oils are not as bad as others. The lighter crude oils are not nearly as bad as the medium and heavy crude oils. The lighter oils (such as jet fuel and gasoline) are highly volatile and will readily evaporate. This is also true of light oils and light crude which are moderately volatile. These lighter oils will also dilute more and only affect the upper water column in the ocean. The medium oils and heavier oils don’t mix nearly as much with water and cause severe as well as prolonged contamination. They are will evaporate much less than the lighter oils and weather slowly.


Oil can affect fish by being taken in through the gills, ingested through food, and even impact or kill eggs and larva. When exposed to oil through any of these pathways, fish may suffer heart or respiratory problems, an enlarged liver, reduction in growth potential, fin erosion, and reduced or impaired reproduction. Fish eggs or larvae will likely experience reduced survival rates and the success of each spawning by impaired fish will be reduced as well.

Invertebrates of the ocean

An oil spill can actually smother invertebrates or cause alterations in the formations of their shells and changes in feeding rates. The invertebrates that can be especially vulnerable are the ones that live on the bottom of the ocean. The sediments near the shore can absorb oil and oil can be washed in to the shoreline from wave action. While invertebrates can survive the contamination, they are likely to pass on the contamination to larger predators through bioaccumulation.

Birds and near-shore marine mammals

Birds and marine mammals such as otters can suffer from an oil spill in several different ways. Because of their feathers or fur, as well as their presence on the surface of the water where oil typically sits, they are physically exposed to oil which will cling to their feathers and fur. The oil reduces the insulation of the fur or feathers and reduces these animals’s ability to keep in their body heat. Thus they can suffer from hypothermia. Birds may also lose their buoyancy and ability to fly because of being weighted down by the oil. This can actually lead to birds drowning because they cannot stay on the surface of the water.

These animals will also try and clean the oil off of them as part of normal grooming and in an attempt to remove the substance. However, his can very detrimental as it causes the animals to ingest the oil. Ingestion of a large amount of oil can cause immediate death or lead to problems and damage to the internal organs which can also result in death at a later point. The long-term health effects for these animals are not understood but studies have shown that birds and marine mammals can suffer damage to the adrenal and immune system as well as behavioral changes. An oil spill can also affect birds and mammals that do not have a habitat near the ocean but that eat fish or other animals which were exposed to the oil. The ingestion of the oil contaminated food has been known to cause death or reproductive impairment.


Some plants and algae in the ocean may actually be the one type of marine life that are the exception to the statement that all marine life are negatively affected. These few types can actually respond positively to an oil spill and grow in number. However the remaining members of this category are all negatively affected but can recover quite quickly after a cleanup. For those species and type of plants that are negatively affected, this is due to the oil inhibiting growth and reproduction of the plants.