Psammon is diverse group of microscopic organisms living in the interstitial sandy habitat at the water’s edge. Psammon is not only important from the perspective of biodiversity, but may also significantly contribute to the transfer of energy and matter as the populations in beach sand can reach higher densities compared to other benthic habitats. Psammon communities have received very little attention compared to plankton or benthos. The objective of the thesis was to provide an overview of the species composition of zoopsammon communities, their spatial patterns and seasonal dynamics in relation to environmental parameters.The most common taxa that were found from all studied beaches were nematodes, rotifers, ciliates, testate amoebae and harpacticoids. A total of 159 taxa were determined, of which 80 taxa were new records for Estonia. The taxonomic richness and total zoopsammon abundance was much higher in lake beaches than in coastal beaches. Taxonomic richness was related to trophic state of and anthropogenic impact on the sampling site.The horizontal pattern is highly variable and poorly predictable. The vertical distribution was taxon-specific and depended on the sediment type. There was no clear seasonal pattern for the overall psammon abundance, however most taxon-rich season was summer. Sand structure, feeding conditions (sand organic matter and chlorophyll a content, vegetation cover at a transect) and human activities (e.g. trampling by swimmers) proved to be more important variables structuring the psammon communities than seasonality. The majority of psammon taxa had taxon-specific responses to their environment and differences occurred even within one genus. In coastal beaches the abundance of many taxa was related also with porewater pH and salinity. This thesis showed that the seemingly deserted beach habitat hosts a diverse community which can reach high population density, despite the unstable and very fluctuating environment in the habitat. The high abundance and taxonomic richness indicate the importance of psammon communities in the water ecosystem. |
