THE EFFECT OF SALINITY ON THE DOMINANCE-DIVERSITY RELATIONS OF EXPERIMENTAL COASTAL MACROPHYTE COMMUNITIES

Salinity and water regime have previously been recognised as the main environmental factors controlling the abundance of coastal submerged m acrophytes in temporarily-flooded marshes in the Camargue. The effects of these environmental variables, which are considered interrelated, are tested experimentally by subjecting experimental macrophyte commun ities from six temporarily flooded marshes to different levels of sali nity (from 0 to 6 g/l Cl). Communities subjected to high salinity leve ls (4 and 6 g/l Cl-) showed a decrease in species richness and in biom ass of all species involved. The species that most frequently dominate these communities, Chara aspera and Zannichellia pedunculata, are tol erant of salt and dominate over the entire salinity range. Three speci es groups can be distinguished based on the distribution of their biom ass and centre of gravity of distribution over the salinity range: (1) non-salt-tolerant species, 'glycophytes', (2) moderately salt-toleran t species and (3) very tolerant species ('halophytes'). A species ordi nation based on the experiments appeared to give results close to thos e previously obtained from field data.