Organische Strandwälle und Nehrungen in korsischen Rias

Abstract

In the 'classic monofluvial rias’ of the granite upland regions of Corsica, mid-bay bars (Nehrungen), from 20 to 350 metres long and up to 90 metres wide, have been formed, especially where a westerly attitude and exposed funnel-shaped sites allow an extended Posidonietum oceanicae. Through gradual accumulation they develop a seaweed cover up to 3,5 metres thick on and around a very low inorganic core. These Nehrungen are thrown up and moulded by frontally swelling waves of translation on the inner boundary of the extended, recently abraded 'estuarine aureoles' (Mündungshöfe). Probably only the winter storm tides repeatedly break open the outer part of this accumulation of marine plants, elastic, tightly packed and anchored in the sand, and deposit fresh seaweed. While the material is largely replaced, the location and form of the Nehrung complexes remain largely unchanged for decades. If Nehrungen normally accelerate the silting-up of constricted bays, the seaweed Nehrungen delay the fossilisation of the rias which, through the lack of effective tides and fresh-water inflow as well as the massive influx of marine plants are usually quickly filled up right to the edge of the Mündungshöf. Where the width is sufficient, a zonally divided and recurrent plant-society complex develops on the seaweed Nehrungen which reflects the striplike ecologic changes derived from the frontally-swelling origin of the Nehrungen. Seaweed Nehrungen, as a special Biotope and carrier of a special ‘Phytozönose’ growing out of dead associations, form a Holocene (in the sense of J. Schmithusen 1961 p. 80) which varies in its development, is rare in occurrence but is nevertheless typical and can be regarded as an Ecotope of the Corsican coastal landscape.