Ecological Impact of an Oil Spill: Utilization of Biological Indicators
One of the major difficulties for science today is still the understanding of how a whole ecosystem operates. However, perturbations affecting the normal functioning of an ecosystem can be evaluated and monitored in time, from trophic or dimensional points of view, by studying the macrofauna which is found in the middle of the trophic or dimensional hierarchies of the ecosystem. Organisms in this category are greater than 1 mm in size, and sampling is effected by means of quantitative grabs. Most of these organisms have life cycles generally ranging between 1 and 3 years. They are distinct from other fauna of larger size and longer life cycle, but they are also scattered, and are therefore difficult to sample. The effects of the “Amoco Cadiz” oil spill on the fine sand ecosystem are evaluated by means of macrofauna which represent medium hydrodynamic conditions. Different species were classified in ecological groups according to their sensitivity to hydrocarbons and to organic matter overload. The two parameters, specific richness and abundance per square meter, indicate the structure of the macrofauna population, and a third parameter, the biomass, can also be used. The study of these factors and their evolution in time, as well as the ecological groups, enables definition of the degradation, recolonization and restructuring conditions. Finally, predators such as fish juveniles regulate these communities; six years after the “Amoco Cadiz” oil spill, even if this fine sand ecosystem reaches a new equilibrium, it is still too early for the regulation processes by predators to take place.