6.6: Oil Spills and Marine Life

According to the National Oceanic and Atmospheric Association, there are thousands of oil and chemical spills each year. The Ocean Service’s Office of Response and Restoration is the first to come to the scene and assess the impacts that a spill may have, identify risks, and recommend different cleanup methods. However, when oil spills occur, the first organisms to come into contact with the oil are marine organisms. Many of the issues that occur for marine life are due to the bioaccumulation of oil components by organisms. Biological organisms lower in food chains such as zooplankton accumulate the oil’s chemicals within their tissues. When these zooplankton are consumed by organisms such as fish at higher trophic levels, the concentration of chemicals is magnified. With each successive trophic level, this biomagnification continues and the concentrations of the chemicals can be extremely dangerous especially for apex predators causing health and reproductive problems.

The effects of oil spills are varied across species, the distance from the spill, how big the spill is, and where the oil disperses. Organisms such as shellfish can be unaffected by oil or only slightly. This is because most of the oil floats within the water column and the amount that sinks to the ocean floor is limited, although thereare still some circumstances where the oil spill has a large effect on the shellfish. Oil spills that are in shallow or confined waters are the most at risk for effects. Oxygen depletion can occur due to the formation of oil slicks at the surface of the water.

“Louisiana_Oil_Spill” by US Coast Guard, under public domain

Oil slicks in deeper water can also have an effect. For example, the BP Oil spill in the Gulf of Mexico had well leaks at deep depths. Organisms such as shellfish that don’t move often or far and are filter-feeders, are unable to avoid exposure to oil. Juvenile and adult fish are much more mobile, are more selective in what foods they eat, and they also have a variety of enzymes that allow them to detoxify many oil compounds. As a result, they are often better suited to limited oil exposure and related impacts. In spite of this, many fish are killed as a result of light oils and petroleum in shallow water. Also, oil spills can completely kill or wipe out fish egg populations.

“Port Sulphur, La. (Nov. 29)–An aerial view of a section of the Mississippi River containing a dense amount of the Nigerian ‘sweet’ crude oil spilled by the M/V Westchester Nov. 28, 2000 by USCG” by PA1 Jeff Hall

Effects of oil spills can be direct or indirect. Direct impacts include when oil directly touches, is consumed, or is injected through a cut in the skin. When these things happen they can deteriorate the thermal insulation of some organisms. They can also result in changes in the behavior and reproductive systems of those organisms that come into contact with the oil. Indirect effects of oil spills are those that result from consuming individuals who have direct contact with the oil as well as effects from the mass mortality and decomposition that occurs during oil spills such as oxygen depletion. Another indirect effect can be losing a major food source which could result in the death or extinction of one or more species.

Another factor that can affect marine organisms is the type of oil that is spilled. Light oils and petroleum products can cause acute toxicity in fish, but the toxic event is generally over fairly quickly. Heavier oils sometimes do not affect fish, however they can be detrimental to fish that are in the larval and spawning stages. The type of oil and the timing of the release influences the severity of oil effects on fish. Heavier oils can have great impacts on sea birds. This is because the feathers on birds are naturally waterproof, and in order to maintain this, the feathers on the birds bodies must be aligned. This is so the water cannot leak through the microscopic barbs, and barbules that are part of the vane of each feather. The bird, through a process referred to as preening, distributes natural oils on the feathers to keep the feathers in place. The oil floating in the ocean water sticks onto the birds feathers, causing it to become matted. The matting causes the feathers to separate ultimately making the feathers no longer waterproof. The bird then suffers from hypothermia or hyperthermia when it can no longer protect itself from extreme temperatures. Birds react to the presence of oil by preening, and by doing so the birds end up ingesting the oil that is toxic to them. During this time all of the birds energy is put into preening and they are left vulnerable and malnourished. Death, in most cases, is what the birds are facing without proper treatment. The washing treatment can not begin until the bird is at an acceptable weight, with good blood values while displaying active and alert behavior.

“Oiled Pelican 03 Dawn IBRRC 2010” by International Bird Rescue Research Center [CC by 2.0]

This information in this chapter is thanks to content contributions from Andrew Fuhs and Alana Olendorf.