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Crab Mølen
Crab covered in oil on the pebbly beach Mølen in the wreck area. 
Photo: Øystein Paulsen
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Oil seek in small, very small and micro small organisms

Fish and shell fish are easily cut open and examined for oil in inner organs. But what method can be used to find out how much oil there is in a microscopic plankton?

By Marie Hauge

The tanker "Full City" ran aground off Langesund in the beginning of August. More than 306 cubic metres of spilled oil have so far been collected from the area.

Food and environment

The day after the wreck samples of common mussel and crab were collected from the wreck area. A week later The Institute of Marine Research received more than a 100 samples of fish and shell fish together with some water samples. Plankton is also sampled and sent to the institute.

Plankton, fish and shell fish as indicators

Stepan Boitsov is in charge of the fish and shell fish samples while Lars-Johan Naustvoll and Padmini Dalpadado are in charge of the phytoplankton and zooplankton analysis. 

Boitsov and his collagues are looking for certain oil compounds - PAHs (Polycyclic aromatic hydrocarbons) - in the entrails of common mussel and crab and in the liver, gall and fillets from fish.

- The oil compounds are more easily found in marine organisms than in water. Common mussel for instance filtrates the water. A chemical analyse of the entrail unveils the PAH values. They tell us something about the extent of the contamination, says Boitsov.  


The oil compounds are slowly extracted from the water samples by Kjell Westrheim at the Institute of Marine Research.

Photo: Marie Hauge

Plankton in formalin

While fish, crab and shell fish easily is dissected, the scalpel is not so useful when it comes to plankton. Phytoplanktons are microscopic. Zooplanktons measure from a fraction of a millimetre and up to a few millimetres.

The plankton is collected with net, fixed in formalin and then studied through the microscope.

- We study the species and the amount of organismes. Samples from different locations in the wreck area are compared, says Padmini Dalpadado.

The oil can affect the plankton directely or through the absorption of nutrient. Zooplankton is eaten by a lot of young fish, marine mammals and seabirds. If the level of mortality is high or the plankton is very toxic, this may effect the rest of the food chaine.

Don't know the consequences

Only a few hours after the tanker ran aground, seabirds and beaches were covered in oil. The long term consequences of an oil spill are more complicted to foresee. They depend on several different conditions: how vulnerable the affected area is, the periode of the year, how toxic the oil is, weather and temperature, the two scientists explaine.


Sample stations after the "Full City" wreck off Langesund.