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Monitoring the impacts of marine aggregate extraction

Robert Lafite
Michel Desprez


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1The SIEGMA programme has resulted in greater international knowledge on the impact of extraction and on the recolonisation process:

  • detailed understanding of the dynamics of the turbid plume generated by the dredge overspill;
  • confirmation of the physical impacts (morphology furrows, sedimentary evolution of the seabed) and of the restoration rates of habitats at different time-scales (year to decade).

2New results have been obtained concerning:

  • turbidity monitoring for various extraction methods and hydrodynamic conditions;
  • the relationship between extraction intensity and the different degrees of biological and morphosedimentary impacts;
  • the morphosedimentary typology of the seabed in connection with the extraction activity (intensive or not, recent or long-term, influenced or not by overflow);
  • the quantification of the impact on benthos and the benthos recolonisation rate after one year of extraction (fallow test in the Baie de Seine);
  • the fish communities inhabiting the extraction sites before, during and after the period of operation: in Dieppe and in the Baie de Seine the absence or scarcity of many species has been observed (gurnard, pouting, flounder). It has also been noticed that sole, cod and black seabream were attracted to the extraction areas and gurnards to the recolonised zones;
  • the trophic role of benthic communities for bottom-feeding fish species: apart from the studies conducted with the SIEGMA programme, there is very little information on the consequences of benthic food reduction for the trophic chain, including fish. The impact levels on fish abundance observed in Dieppe (-50%) are significantly lower than those observed in the Baie de Seine (-80 to-90%). In the latter location they have the same order of magnitude as those observed in benthos which is traditionally used as the indicator for ecosystem disturbance;
  • the indirect effects of oversanding on the nature of fish species frequenting the area of sediment deposition: sole, plaice and rays are attracted to this area where they can find easily-accessible preys.

© Presses universitaires de Rouen et du Havre, 2014

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