Dynamics of benthic algal vegetation and environment in Dutch estuarine salt marshes studied by means of permanent quadrats

Summary Knowledge of the spatial structure of benthic algal vegetations in salt marshes, consisting of about 100 species of blue-green, green, brown and red algae, formed the basis of a detailed study into the dynamics of the algal mat.The temporal changes in algal vegetations and concomitant processes in their environment were studied in 27 permanent quadrats (PQs), plotted in tidal salt marshes and along brackish inland waters in the SW Netherlands. Once a month vegetation and environment of the PQs were examined over the period March 1968-February 1971. From the Spearman rank-correlation between vegetational and environmental parameters it appeared that in semiterrestrial and terrestrial environments the average number of algal species in a relevé and the average similarity between the species composition of successive relevés obtained from one PQ have a significant positive correlation with the stability of the substrate, and hardly any correlation with fluetuations in soil-moisture content and salinity of the soil moisture and with the maximum cover percentage of the phanerogams.Stable substrates tend to bear stable algal mats, as appeared from quantitative data. Small and moderate fluctuations in soil-moisture content and salinity of the soil moisture have no limiting influence on the algal cover degree. During periods of extremely high salinity and concomitant extremely low soil-moisture contents that coincide with evaporation surpluses, the green algal mat bleaches and decreases in cover in semi-terrestrial and terrestrial environments. Below 20% the soil-moisture content is limiting for the expansion of a mat of green algae (Rhizoclonium riparium, Percursaria percursa, Enteromorpha torta, E. prolifera) and Vaucheria species. The mat desiceates and bleaches but recovers after increase of the soil-moisture content above 20% within one month. Two weeks of severe frost (temperature down to – 10°C) do not influence the cover degree of the algal mat in aquatic branckish PQs, but the cover degree in semi-terrestrial PQs decreases. Short lasting soil-moisture salinities of 130–190 Cl^– have no limiting effect on the expansion of the algal mat.Nomenclature authorities are given in Table 3.Contribution to the Symposium of the Working Group for Succession Research on Permanent Plots, held at Yerseke, The Netherlands, October 1975.Communication No. 163 of the Delta Institute for Hydrobiological Research, Yerseke.