5 Major Effects of Oil Spills on Marine Ecosystems

The harmful effects of an oil spill are felt immediately and the long term damage can last for years, even decades in cases.

In March of 1989  the Exxon Valdez cargo ship ran aground off the coast of Alaska spilling 37,000 tons of oil and affecting 1,300 miles of Alaskan shoreline. 

Even now over 30 years later it’s possible to strike oil when digging into the ground. 

The effects of an oil spill cascade from the top right down to the bottom of the food chain as toxic substances enter it and get passed from prey to predator.

As well as the environmental impact,  there is also an economical impact on coastal activities, affecting the businesses and people whose livelihood may rely on these resources.

From the water’s surface to the seabed, and from the ocean to the coastline, here are 5 ways in which a marine ecosystem is affected by an oil spill. 

  1. Impact on Marine Animals

Oil which is not dispersed will remain on the ocean’s surface, and if the current carries it to the shoreline, then the coastal area the oil may affect the birds, mammals and more coastal organisms like invertebrates.

If the oil is not dispersed, it will affect fish, plankton and larvae will be greatly affected by oil toxicity

Typically when you picture an oil spill you think of the hundreds, if not thousands of animals coated in slick oil.

A great many species of marine animal are vulnerable to the effects of an oil spill.

Besides direct contact to the oil itself, Inhalation of toxic fumes and ingestion are two other very serious dangers to these animals.

During the early stages of an oil spill, marine animals who spend time at the surface of the water are likely to be affected.

As the tide brings the oil to shore, animals who come to the shore to nest or to forage will be greatly impacted, and once the oil begins to disperse from the surface of the water and into the water column, there begins its impact on the creatures, and reefs below the surface.

Below is a list of some of the animals who may be affected by an oil spill and how:


Sea turtles are at great risk if there is an oil spill and can be affected by physical contact, inhalation and ingestion.

Turtles can mistake the oil for food, or ingest food which has been contaminated. The ingestion of oil can lead to many digestion complications, and the development of ulcers, bleeding, diarrhoea, and kidney damage.

Sea turtles are air breathers and need to come to the surface in order to breathe. At the surface they are at risk of inhalation of toxic fumes, which can cause serious respiratory inflammation, irritation, pneumonia or even emphysema.

Oil Spills can also affect nesting turtles – Eggs and hatchlings are susceptible to direct contact from the oil, and may suffer from direct absorption.

Thinner egg shells, lower growth rates and and other developmental defects often occur, as well as 

the threat of cleanup operations disrupting or harming their nests also.


Adult fish do have a tendency to avoid oil, however this avoidance has an impact on the food chain as their predators then must compete for the remaining food supply.  

Those that are directly impacted by an oil spill can suffer from enlarged livers and changes in heart and respiratory rates.

Juvenile fish and fish eggs are much more greatly affected as toxicity at even low levels can harm them, causing growth deformities or death.

Oysters & Shellfish

Oysters and shellfish can accumulate high levels of toxins which are then passed on up the food chain as they are consumed. 

An oil spill can penetrate deep within the sediment for years, sometimes decades and can therefore cause long term contamination.

Seals, Otters

Furred mammals like seals and otters are affected when physically coming into contact with oil.

It affects their ability to regulate body heat and their buoyancy putting them at risk of drowning or succumbing to hypothermia. 

Oil may also be ingested by them as they attempt to clean/preen themselves and result in poisoning.

Dolphins & Whales

Dolphins and whales also spend a lot of time at the surface of the water. 

As well as potentially inhaling toxic fumes when surfacing, oil can also clog their blowholes making it hard, (or even impossible) for them to breathe, as well as potentially disrupting their form of communication.

Those who manage to escape being harmed via direct contact may still be affected by a contaminated food supply.

2. Effects on Coral Reefs 

Coral Reefs are extremely important to the marine environment for a multitude of reasons. Reefs also help the local economy by supporting tourism and fisheries.

The importance of our coral reefs cannot be understated. They act as shelter for fish, shrimp and other marine creatures and provide an important and diverse ecosystem where fish and other animals can feed, reproduce and seek protection from predators. 

They also provide much needed protection for our coastal shorelines.

Coral reefs are sensitive and can suffer harm in a number of ways – sea temperature increases, human interaction (via touch), and toxic substances from sunscreen are all ways in which reefs suffer damage.

An oil spill to a coral reef can unfortunately be devastating and the time until recovery (if recovery can be achieved), can take a long time. The grounding of a vessel on a reef itself can also cause substantial damage to it.

3. The Effects on Marine Plant Life

When vegetation perils in the event of an oil spill, this loss of food for some species will result in the relocation of animals which were reliant on it as a food source.

Of the animals remaining this will cause greater competition for the now limited food source which remains.

Oil can harm the growth of sea plant life, and destroy other marine plant life entirely. Plankton for example, are often killed during an oil spill due to the lack of sunlight which is unable to penetrate through the oil.

4. Shorelines and Coastal Effects

Sea birds are of particular high risk during an oil spill – They often swim and dive underwater in search of food and can therefore suffer from direct exposure, and also by ingestion.

When the feathers of a sea bird become oiled, the bird loses its ability to insulate itself and becomes at risk of hyperthermia. 

It can also lose its buoyancy, and is susceptible to drowning, and it may also ingest the oil whilst preening and cleaning itself.

Or, the oil may impede the bird from being able to fly, therefore placing it at risk of not being able to flee a predator, or impede it in its ability to catch its own prey.

Oil can also be spread from the bird to its nest, thereby affecting its young. An estimated 30,000 birds were oiled by the Exxon Valdez spill off the in Alaska in 1989

5. The Environmental Effects of Oil Spill Clean Ups

Oil spill clean ups bring their own complications to an affected site, as quite often clean-up operations themselves can also be very damaging .

Sometimes the clean up operation can be as damaging, or even more so than the oil spill itself.

Chemical dispersants for example, which are spread over the oil spill to accelerate its disbursement into the sea are extremely damaging to coral reefs.

The cost of an oil spill clean up can also be substantial. This includes the cost of cleaning up the spill, but also the cost of penalties and legal claims which may ensue.


Oil spills have become less common over the years as stringent measures are put in place to reduce or prevent them.

Double hulled tankers and the designation of protected marine areas

It is clear from recent events in Mauritius, with the Japanese cargo ship running  aground just off the coast, that while spectacular oil spills are far less common than in the 60’s and 70’s, they are unfortunately not entirely preventable.

There are many varying factors at play which can determine the severity and the impact of an oil spill on the marine environment.

The devastating effects of an oil spill can be felt for years to come, decades in some cases. Some species in fact have never fully recovered from the Exxon Valdez spill.

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Gia Halliday

Hey, my names Gia! My biggest passions are food, travel and basically anything to do with being in the water. Combine all of that with an addiction for buying gear and you end up with with this website!