Tanio: Impact
After two aerial missions (11 and 28 March), detailed maps of the polluted areas could be drawn up. Sedimentationists boarded reconnaissance planes and confirmed that the extent of the pollution was very large and included the islands bordering the Côtes d’Armor.
131 research stations were chosen between Guisseny and Saint Brieuc in order to determine the impact of the pollution. Samples were taken and analysed in 15 of these stations. Researchers noticed that the effect of this new oil spill added up to the remaining effect of the Amoco Cadiz incident.
Scientists reconstituted the events of the pollution and tried to
determine the role played by natural elements. They distinguished
three types of areas with the help of a vulnerability index, which
took into account the geomorphology and sedimentology of each area.
Out of 160 km of polluted areas:
- 50 km were heavily polluted, on Ile Grande, at Trégastel and at Ploumanac’h deposits were continuous and thick
- 35 km were fairly polluted, showing numerous discontinuous oil patches
- 75 km remained polluted to a small extent by scattered patches of thin films.
80 % of the damaged coasts were rocky.
By mid-April almost all the spilled oil had reached the shoreline.
Sea pollution
Toxicological analyses were implemented by laboratories from the medicine faculty of Brest. The aim was to determine whether the oil had a potential effect on swimmers. But these studies were limited and the results were not very representative.
The evolution of fuel retained in the sediments was followed to check the spreading of the pollution and to measure the degree of water pollution on several sites. Data from four research campaigns of CNEXO’s ships, from March to June, asserted that pollution was significant off the Morlaix-Lannion zone, in the Sept Iles area and off Le Trieux.
A fine proportioning method facilitated the creation of pollution cartography in the western part of the Channel, the Aber’s coastal area, the bays of Morlaix and Lannion and the area between Sept Iles and Le Trieux. It allowed responders to establish almost instantaneously whether a zone was polluted or not.
The seabed was explored to check that there was no contamination. From 25 to 30 March, the CNEXO’s ship the Thalia carried out a first measurement assignment. Samples were taken at different depths in the water column. From 24 to 26 March, the Roscoff biological station's vessel the Pluteus asserted that there was no effect on deep marine sediments between Triagoz and Sept Iles.
Impact studies
Impact studies were carried out on seaweed, plankton, bivalves,
crustaceans.
- Giant seaweed was oiled to a greater or lesser extent depending on their location. Pollution did not disturb their photosynthetic activity, whereas cleaning operations seemed to have more noticeable consequences. High and medium level seaweed were little affected. Even if Ascophyllum were affected in some areas, overall losses were limited. Laminarias, which represent the main part of seaweed biomass, were also little affected.
- Global impact on plankton was low as the plankton cycle is short. Some studies on copepods showed that certain areas were polluted.
- Death of cockles and clams was recorded on Grande island and periwinkles on polluted rocks suffered.
- Lobster larvae living at the sea surface were affected. But, on the whole, death of crustaceans due to the pollution was relatively rare. In Trégastel young bibs were found dead, their digestive tract gorged with oil. This fauna, which lived on rocks, suffered 80 % losses in Trégastel and Ploumanac’h (mid-April). Sand fleas which fed on beached seaweed survived.