Morpho-sedimentary characterization of intertidal seagrass Zostera noltii (Horneman, 1832) in relation to biometric indicators.

Zostera noltii (Horneman, 1832) intertidal seagrass is one of the two marine phanerogams species occuring along the North-Atlantic coasts. This seagrass growths on muddy-sand flats in sheltered environments such as estuaries and protected embayments. Z. noltii has a significant biomass which is varying with its geographical distribution. In North Brittany coast of France, the average biomass reaches 120 g.dw.m-2 with a productivity around 500 g.C.m-2.y-1. These biocoenoses are listed among the most productive marine ecosystems. The physical structure of the seagrass beds contributes to fine particles deposition, while locally reducing tidal currents. Temporal and spatial variations of seagrass beds structure depends on physical and biological factors. Alternating periods of erosion and sedimentation affect the superficial sediment stability and consequently the seagrass meadows development. After a strong erosion stage, the beds recovery is going on for 5 to 10 years. However, Z. noltii seems rather tolerant to the annual sediment budget fluctuations. Arenicola marina contributes to important bioturbation which can locally scraps the seagrass beds. The occurence of Z. noltii seagrass influences the morpho-sedimentary dynamic of the surrounding area, although, this sedimentary environment induces the seagrass meadows structure.