Mise en place d'indicateurs opérationnels de suivi des couvertures de fucales dans le cadre de l'avant projet détaillé "REBENT"

Un-quantified observations seem to indicate a decrease in brown algae blanket in inter-tidal zones along several coastlines. The goal of this contract, which is CEVA's contribution to REBENT- Bretagne_ year 2003, regards the quantitative evaluation and long term follow up of fucales in inter-tidal zones. The work that was accomplished during a previous contract with CEVA had allowed defining a SPOT image processing protocol used to evaluate and follow up, in time, global vegetal blankets. A methodology form had been written up and two SPOT images from the Trégor region had been processed as a vegetal blanket. Results analysis showed how being able to isolate fucales, and for that matter, its various species, was necessary in order to create more pertinent follow up indicators. The work accomplished within the scope of this contract allows us to complete the methodology by setting up a fucale zone determination procedure, and for that matter of species themselves, based on in situ observations of altitudinal belt extension limits and on relief knowledge. Two paths, corresponding to two precise levels, have been explored: instantaneous coast line acquisition through ULM snapshots as well as using MNT Lidar for the acquired zones. The processing of a SPOT image acquired from the North Finistère coast between Roscoff and Porsall has allowed us to spread the approach geographically. This work can potentially contribute to defining a useful indicator within the scope of the "Directive Cadre -Eau- » set up and will allow putting into place detailed habitat maps especially useful for the follow up of the Natura 2000 sites involved. It will also contribute to a better understanding of the factors ruling over species distribution in tidal zones (individual contribution of emerging and exposition components), related to predictable modelling post-doc work and MESH contract.