Etude des intermattes des herbiers à Posidonia oceanica

Among Mediterranean marine ecosystems, Posidonia oceanica (L.)
Delile seagrass meadows form a habitat playing an important ecological
and economical role. They form heterogeneous seascapes influenced by
the impact of natural and anthropogenic phenomenon (of which the
anchoring of leisure ships). These impacts lead to the formation of sand
and bare mat patches called ‘intermattes’.
By describing and using intermatte characteristics observed in Calvi Bay
and more widely around Corsica, these PhD works precisely described
intermatte and P. oceanica seascape dynamics in order to develop new
methods of analysis.
On the one hand, natural sandy intermattes formed by bottom currents
show two types of border. Each has its own characteristics at the level of
the sediments biogeochemistry. On the other hand, anthropogenic
intermattes generated by anchoring (bare mat) present different sizes
and shapes resulting from specific dynamics. They are not recolonized
when the anchoring pressure remains high. A depletion of the substrate
chemical quality occurs after the mechanical destruction.
A new cartographic seascape index, the Patchiness Source Index, was
created using the size and the nature of intermattes at large spatial scale.
After a comparison of methods used for the study of intermattes, two new
indices (Map Anchoring Index and Anchoring Index) for managers of
coastal areas were developed to evaluate the impact of anchoring within
P. oceanica meadows.