[en] The Mediterranean seagrass Posidonia oceanica forms meadows and develops a
complex of rhizomes, roots and sediment which is called “matte”. P. oceanica meadows
show discontinuity patterns in the form of sand or dead matte (matte without living shoots)
patches, called “intermattes”, which can have natural or anthropogenic origins. Mechanical
processes (e. g. currents, anchoring) can initiate intermattes formation but their dynamic
after creation seems to be linked with the sediment chemistry, especially with S cycle. P.
oceanica plays an important role in controlling coastal belowground biogeochemistry, in
particular by oxidizing sediments through the release of O2 by roots. This process allows
creating more suitable condition for plant growth and colonization. The lack of H2S oxidation
in SO4 2- can lead to limitation of the plant development or its regression.
In order to investigate the effect of oxidation condition in sediments on intermattes
dynamic and the neighboring meadow, we initiate, in December 2013, a study on six
intermattes (three natural, three anthropogenic) at different depths in Calvi Bay, in Corsica
(France). We hypothesize that redox potential and H2S concentration in sediments play an
important role in the regression of P. oceanica meadows, particularly after a mechanical anthropic impact like anchoring. It also may be possible that two different kinds of processes
are involved for each type of intermatte. Regular samplings throughout two years are planed
with the aim of evaluating the seasonal variations of physicochemical parameters.
