The distribution of salt marsh macrophyte species in relation to physicochemical variables

- Distribution of 11 macrophyte species in 14 estuaries was assessed in relation to sediment and groundwater variables.
- Common salt marsh species were poor bioindicators as they occurred over a broad range of measured physicochemical variables.
- Rare species need to be studied so that they can be used as indicators of environmental change.
- Useful data on the ecological requirements of salt marsh species and habitats spanning a regional scale were provided.

The aim of this study was to explore how estuarine salt marsh macrophytes are distributed in relation to physicochemical variables. This information was examined to determine whether macrophyte species are associated with a specific range of physicochemical variables and so could be used as bioindicators. The distribution of eleven macrophyte species in fourteen estuaries across the South African temperate coast was assessed in relation to sediment (moisture content, organic content, electrical conductivity, pH and redox potential) and groundwater (electrical conductivity, salinity and depth of the groundwater) variables. A univariate and multivariate approach showed that common salt marsh species were poor bioindicators as they occurred over a broad range of values across the measured physicochemical variables (i.e. Bassia diffusa, Juncus kraussii, Sarcocornia pillansii, Sarcocornia tegetaria and Sporobolus virginicus). It is therefore suggested that rare species (Sarcocornia capensis, Frankenia pulverulenta, Poeciolepis ficoidea, S. decumbens, Plantago carnosa, Triglochin elongata, Spergularia media, Suaeda fruticosa and S. inflata) be studied further to establish relationships with physicochemical variables as these may be useful indicators to monitor responses to sea level and other environmental changes. This study provides useful data on the ecological requirements of species and habitats in response to diverse physiochemical conditions across various estuaries spanning a regional scale.