Oceans, caught between devil and the deep blue sea… (Pun intended!) – X

Oil spills and their effects on marine ecology

Hi Friends, there is an old saying which says, “Of all the things you choose in life, you don’t get to choose what your nightmares are. You don’t pick them; they pick you”.    

The incidence of an oil spill is the worst nightmare shipping industry can ever have, and this nightmare always catches you on the wrong foot.  Because there are a lot of extremely complicated and tricky processes involved in getting oil from inside the Earth to, say, inside your car’s petrol tank; possibilities of oil spilling at every step are very high.  Oil can spill at any point during the oil production process, from drilling, refining, or storing to transporting. During transportation or shipping, oil may drop accidentally – when ships collide or when a vessel runs aground or catches fire (as happened a few days ago in case of Maersk Honam) or any such accident.  Remember, 800,000 liters of oil-spill in Mumbai seas, during MSC Chitra colliding with Khalija Express in August 2010? Fish lovers in Mumbai had to give up relishing seafood then, with a fear that they may consume some bunker fuel along with their favorite Bombay duck!  The amount of oil spilled during such accidents usually is enormous in thousands of tons. 

Pollutants entering oceans

As I had mentioned in earlier articles and as we can see in above pie-chart, marine pollution from marine transport amounts to 10% of the total pollutants entering the oceans.  And as we saw before, this includes –

  • Ballast water pollution
  • Atmospheric pollution
    • Conventional pollutants
    • GHG pollutants
  • Oil spills/bilge pollution
  • Greywater pollution
  • Blackwater pollution
  • Sound pollution
  • Wildlife collisions

We saw details of pollution through Ballast Water in the last article.  In the present section, we will throw light on Oil Spills.  

An oil spill, in brief, is the release of fossil fuel (like crude oil, bunker fuel, gasoline, diesel or its by-products and various derivatives) into oceans accidentally. Oil released through such accidents floats on ocean water and as a matter of course rapidly spreads out across vast surface of the water to form a thin layer that we call an oil slick. As the oil continues spreading, the layer becomes thinner and thinner, finally growing a fragile layer called a sheen, which often looks like a rainbow. (You may have seen sheens on roads or parking lots after rain.) The spilled oil chokes marine ecology in that region entirely, and the spread even reaches shores, covering beaches, rocky shores, marshlands, and mangroves.  The spill can have disastrous consequences for society; economically, environmentally, and socially and can have a long-lasting impact. 

The effects of an oil spill will depend on a variety of factors including, the quantity and type of oil spilled, and how it interacts with the marine environment. Prevailing weather conditions will also influence the oil’s physical characteristics and its behavior. Other key factors include the biological and ecological attributes of the area and the environmental significance of critical species and their sensitivity to oil pollution as well as the time of year.

Oil spills may impact the environment in the following ways:

  • Physical smothering of organisms: This is caused by oils with a high viscosity, in other words, heavy oils. Smothering will affect an organism’s physical ability to continue critical functions such as respiration, feeding, and thermoregulation.
  • Chemical toxicity: This is characteristic of lighter chemical components which are more bio-available, i.e., absorbed into organs, tissues, and cells, and can have sub-lethal or lethal toxic effects.
  • Ecological changes: This is caused by the loss of crucial organisms with a specific function in an ecological community. They can be replaced by different species undertaking similar tasks in which case the implications for the ecosystem as a whole may not be severe. However, more detrimental is the niche in the community being replaced with organisms performing entirely different functions thereby altering the ecosystem dynamics.
  • Indirect effects: Loss of shelter or habitat through oiling or clean-up operations.

Because of enormous magnitude of its effects, oil spill accidents have initiated intense media attention and political uproar, bringing many together in a political struggle concerning government response to oil spills and what actions can best prevent them from happening. 

oil spill 2

In next article, we will see a more detailed analysis of marine environmental damage because of oil spills. 


  • Alaska Oil Spill Commission report
  • Oil in the sea III; Inputs, Fates, and Effects
  • Website of Live Science
  • Wikipedia

Milind Joshi




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