2.1. 5: Pyramids and Ecosystem Function

November 14th, 2010


Story of Minamata Bay.

Minamata is a small factory town in Japan, dominated by one factory, The Chisso Factory. Chisso make petrochemical based substances from fertilizer to plastics. Between 1932 and 1968 Chisso dumped an estimated 27 tons of mercury into Minamata Bay.

Beginning in the 1950’s, thousands of people started to suffer from mercury poisoning.

What had happened?

Some bacteria can change mercury to a modified form called methylmercury. Methylmercury is easily absorbed into the bodies of small organisms such as shrimp. When the shrimp are eaten by fish, the methylmercury enter the fish. The methylmercury does not break down easily and can stay in the fish bodies for a long time. As the fish eat more and more shrimp, the amount of methylmercury increases. The same increase in concentration happens when people then eat the fish. fish are a major part of the diet of people around Minamata bay. This process is known as bioaccumulation.

There is a slow magnitude build up along the food chain: Very many bacteria absorb very small amounts of mercury - many shrimp eat a lot of bacteria building up the mercury concentration - lots of fish eat lots of shrimp again building up the concentration and finally a small number of humans at the top of the food chain eventually eat a lot of fish and absorb high levels of methylmercury.

The end of the food chain

It is the often the highest trophic level in a food chain that is the most susceptible alterations in the environment. Another example of the effects of toxins on a food chain was DDT (a pesticide) and Peregrine folcans in Britain in the 1950’s and 60’s. Follow this link to find out more PEREGRINES IN YORKSHIRE

The top of the food chain is always vulnerable to the effects of changes further down the chain. Top carnivores often have a limited diet so a change in their food prey has a knock on effect. Their population numbers are low because of the fall in efficiency alone a food chain, therefore their ability to withstand negative influences is more limited than species lower in the food chain with larger populations.

The above animation was made by S Thomas

Biomagnification and bioaccumulation in Arctic ecosystems

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