EN
The abundance of culturable heterotrophic microorganisms (bacteria, fungi, yeasts, actinomycetes) and their spatial and vertical variability were studied in marine-bay (“Sopot”) and open-sea (“Czołpino”) sandy beaches (southern Baltic Sea). Among studied microorganisms, halotolerant (13.4 – 308.4 × 10³ CFU g⁻¹ dry wt. of sand) and limnotolerant (7.4 – 69.2 × 10³ CFU g⁻¹ dry wt. of sand) bacteria predominated in the sand of both beaches. Filamentous fungi, yeasts, and actinomycetes constituted only a slight percentage (0.2–3.0%) of all isolated heterotrophic microorganisms. The numbers of all studied microorganisms were much higher on marine-bay beach characterized by a high level of accumulation of organic matter (4.1 mg g⁻¹ dry wt. of sand) than in the sand of the open-sea beach, where the content of organic matter was lower (1.9 mg g⁻¹ dry wt. of sand). There were marked differences in the horizonatal profile distribution of heterotrophic microorganisms inhabiting marine-bay and open-sea beaches. In both studied beaches higher numbers of microorganisms were determined in the surface (0–5 cm) than in subsurface (5–10cm) sand layer.