Oil spills and the marine environment

Wherever oil is being extracted from under the ocean or transported across it, there is always the danger that a spill will occur.

Shipwrecked tankers like the Amoco Cadiz (above) can cause environmental disaster if oil leaks from the ship

The marine environment is made up of complex interrelations between plant and animal species and their physical environment. Harm to the physical environment will often lead to harm for one or more organisms in a food web, which may lead to damage for other organisms further up the web. Oil spills are a serious threat to the marine environment. They have an enormous impact on surface resources and a wide range of subsurface organisms that are linked in complex food webs including human food resources.

Spilled oil can harm the environment in many ways:

Oil on the water affects marine animals

Seabirds are affected since many species spend long periods sitting on the water. The oil is soaked up by their feathers losing their insulating properties and preventing them from floating. They can’t fly, feed or preen themselves. They die of starvation, cold, poisoning or shock.

A dead gannet (left) and dead kittiwake (right) washed up on the beach at Hurst Spit, Hampshire in 2002.
Both birds are heavily oiled, having been conrtaminated somewhere offshore. Sadly, this is not an uncommon sight.
Images courtesy Russell Wynn.

Even if the fish stocks aren’t affected by the oil spill, fishing will stop because of the oil on the water - this will result in economic loss.

Oil in the water affects plankton, fish, aquaculture, and marine mammals.

Plankton is the basis of all marine food webs. It is very sensitive to the toxic oils and many planktonic species will die if the oil is found at high concentrations. Many other organisms in the food webs will be affected by the decrease in plankton numbers.

Fish have sense organs that can detect oil so they are able to leave the contaminated area unless they are trapped in some way. However, juvenile fish are more vulnerable and if they are affected there will be long term impacts on adult fish stocks. Larger animals in the marine environment such as larger fish, birds and humans may then eat these contaminated fish. Predators that consume contaminated prey can be exposed to oil through ingestion. Because oil contamination gives fish and other animals unpleasant tastes and smells, predators will sometimes refuse to eat their prey and may begin to starve.

Aquaculture will be affected since the fish in the farms are unable to escape the oil contamination. Oil accumulates in their flesh and it becomes inedible

In open water, marine mammals such as whales have the ability to leave the area of the spill, reducing the likelihood that they will be harmed by even a big spill. Marine mammals that live closer to shore, such as seals and dolphins, risk contamination by oil that washes onto beaches or by consuming oil-contaminated prey.

Oil on the shore affects beaches, marinas, shorelines, shorebirds and water extraction.

Oil on amenity beaches and marinas has an impact on the tourist industry. The effect of the oil on the shoreline will depend on its ecological sensitivity.

Exposed shorelines are not usually of high conservation importance. Although oil can soak into sand and gravel, few organisms live full-time in these habitat, so the risk to animal life or the food chain is less than in other habitats, such as tidal flats.

Sheltered shorelines are very sensitive to oil pollution. They have very little wave action to encourage natural dispersion. If these areas are contaminated the oil may remain stranded on these beaches for years.

Tidal flats are broad, low-tide zones - they are very productive areas usually containing many plant, animal, and bird communities. Deposited oil may seep into the muddy bottoms of these flats, creating potentially harmful effects on the ecology of the area.

Salt marshes are found in sheltered waters in cold and temperate areas. They are feeding areas for birds and have a very low self cleaning potential. The oil can have very long term impacts on these areas. Marsh vegetation, especially root systems, is easily damaged by fresh light oils.

Mangrove forests are located in tropical regions and are home to a diversity of plant and animal life. Mangrove trees have long roots, called prop roots, that stick out well above the water level and help to hold the mangrove tree in place. A coating of oil on these prop roots can be fatal to the mangrove tree, and because they grow so slowly, replacing a mangrove tree can take decades.

Right: A mangrove forest drowning in oil

Find out more about conserving the marine environment:

Natural disasters
Oil spills
The cleanup operation
A fishy business...


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February 2007