They occupied gaps within taller perennial vegetation (Juncus maritimus formations), such as small pools temporarily inundated with brackish waters. marina were generally found in the sub-halophilous inner part of salt marshes. We carried out a phytosociological study at 21 sites along the south-western and southern coast of mainland Portugal to determine the ecology and syntaxonomical status of these communities, and to compare them to the Atlantic ones. coronopifolia dominated communities on the Atlantic coast of northern Portugal has already been described, this information was missing for the southern part of the country. The exotic annual forb Cotula coronopifolia has locally invaded salt marsh communities naturally dominated by Spergularia marina along large parts of the Iberian coastline. Soil mobilization from agricultural activities, on the other hand, is often related to the disappearance of these communities because in such circumstances no surface water accumulation occurs. Grazing can favour the occurrence of Isoetes spp. Both flooding period and land use were found to determine the occurrence of each of these communities. Ten groups corresponding to the following associations were recognized: Callitricho brutiae-Ranunculetum peltati, Bolboschoenetum maritimi, Glycerio declinatae-Eleocharitetum palustris, Eryngio corniculati-Preslietum cervinae, Peplido erectae-Agrostietum salmanticae, Isoeto velatae-Juncetum pygmaei, Pulicario uliginosae-Agrostietum salmanticae, Periballio laevis-Illecebretum verticillati, Loto subbiflori-Chaetopogonetum fasciculati and Trifolio resupinati-Caricetum chaetophyllae. A classification with the TWINSPAN program (Hill 1979) was also made. The relationships between species and environmental variables were studied through a canonical correlation analysis (CCA) applied to these relevés using the CANOCO program. A total of 104 relevés were undertaken according to the method of Braun-Blanquet (1979). The aim of this work is to study the relationship between land use and different seasonal pond communities, as well as their spatial and temporal distribution in the Guadiana Valley Natural Park (Mediterranean Iberian Peninsula).
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