Beach meiofauna in brackish waters has received very little attention compared to fauna in fully marine and fresh water habitats. This study explores for the first time the species composition and seasonal dynamics of zoopsammon communities in the Gulf of Finland, the brackish Baltic Sea, and relates the observed patterns to the key environmental variables. The study communities consisted of rotifers, nematodes, ciliates, testaceans, tardigrades, oligochaetes, polychaetes, small crustaceans, gastrotrichs, turbellarians, and insect larvae. Regardless of environmental conditions, ciliates, nematodes, and rotifers were the most abundant taxa in all sampling sites. The total population densities varied largely within site, among sites, and seasons with different sites showing different seasonal patterns. The BRT models reproduced reasonably well the spatial patterns and seasonal dynamics of psammon communities and identified environmental variables that affected the psammon seasonality (temperature, sand organic content, human trampling) and spatial patterns (sediment characteristics, porewater, and pH). Our study also shows that the majority of psammon taxa had species-specific responses to their environment. This provides a strong conceptual argument for enhancing expertise in the taxonomy of psammon, especially when constructing predictive models of psammon in the brackish-water habitats.