Modern pollen–vegetation relationships in saltmarsh habitats along a salinity gradient of a fluvial estuary

• Plant-pollen-spores relationship was studied in vegetated habitats of salt marshes.
• TWINSPAN analysis of the plant cover characterizes five vegetated habitats.
• Pollen frequencies of dominant families were highly correlated with plant cover.
• Higher taxa diversity of pollen than plants makes habitats poorly distinguishable.
• Widespread indicator plants produce high pollen quantities with high dispersibility.

The classification of vegetated habitats and the palynological study of surface sediments are used to evaluate the plant-pollen relationship in the saltmarshes of the Chuí River (southern Brazil). The visual plant cover was recorded in five transects perpendicular to the river's margins and positioned along 4.5 km of the estuarine gradient. Two-way Indicator Species Analysis (TWINSPAN) of the plant cover in 65 sampled quadrats was used to characterize five vegetated habitats. These habitats were distinguished by their elevation in the intertidal zone and their location in the estuarine gradient. The salinity of surface water that flooded low marshes decreased from 20 to 4 between transect 1 and transect 5. A total of 10 surface soil samples from marsh habitats were taken in the same transects as for the study of vegetation, and pollen and spores were identified. The pollen frequencies of dominant families (Cyperaceae, Poaceae, Chenopodicaeae, Juncaceae and Asteraceae) on the surface of marsh habitats show high correlations with the parent plant cover (0.66 to 0.81), but pollen taxa show a higher richness in the plant taxa. The most frequent spores (massulae) encountered in all samples belong to the aquatic fern Azolla filiculoides, followed by spores of the moss Phaeoceros. The palynological data obtained are consistent with the regional vegetation cover characteristics of saltmarshes, but it is difficult to distinguish different habitat types (Discriminant Analysis results). This low discrimination of pollen-spore assemblages is related to the widespread distribution of the indicator plant species, mostly taxa known to produce large quantities of (primarily) wind-dispersed pollen, which are also redeposited or transferred by tides or freshwater influxes. The low taxonomic resolution of pollen grains of dominant taxa, such as Cyperaceae and Poaceae, also creates difficulties to distinguish the vegetated marsh habitats based on pollen assemblages. The widespread presence of pollen from introduced plants such as Pinus species near the saltmarshes emphasizes the anthropogenic impact on this region.