Factors affecting the population dynamics of Suaeda maritima at initial stages of development

This study describes life history and population dynamics of the annual hal ophyte Suaeda maritima, at initial stages of seedling development, in salt- marshes of the Mont-Saint-Michel Bay. Effects of salinity on seed germinati on and seedling development were studied both in the laboratory and in the field. Salinity was measured as sediment electrical conductivity. Experimen ts in the laboratory showed that Suaeda maritima was relatively tolerant to salinity during the germination stage. In the field, germination occurred when soil salinity was minimal. Almost all seeds germinated in the field; t his may explain the absence of a persistent seed bank. Salinity did not see m to affect the growth of seedlings either. Mortality in the field was attr ibuted to physical factors such as anoxia during temporary immersion, buria l by sediment and tidal uprooting. The intensity of these effects varied ac cording to the location of Suaeda maritima seedlings: in hollows, along the edge of tidal creeks, in gaps among dense vegetation cover, or in pattern with Puccinellia maritima. Perennial vegetation did not restrict Suaeda mar itima germination. In contrast, perennials such as Puccinellia maritima and Halimione portulacoides limited the development of Suaeda maritima seedlin gs since only a small number of this annual emerged beneath their canopies. The fate of seedlings depended to a great extent on the permeability of th e perennial canopy to light. Thus, disturbance resulting in bare patches in side the perennial vegetation seemed essential for the development of this annual species. Suaeda maritima can grow in the presence of Puccinellia mar itima so long as the latter present as an open matrix. Suaeda maritima may also benefit from protection against desiccation and tidal action where thi s occurs.