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The Pontocaspian domain constitutes a vast region including the Black Sea, Caspian Sea, Aral Sea, Marmara Sea, and several Anatolian lakes. Over the last five million years, repeated variations in connectivity occurred between the marine Mediterranean and restricted Pontocaspian basins. The dynamic evolution of this system, recording limited, intermittent or non-existent marine connectivity, produced frequent and drastic environmental changes, which typically differed from the changes documented in the open ocean.

This thesis first explores the effects of limited marine connectivity on coastal environments. The interplay between the water/sediment input and geographical settings of the seas, comprising for example the water depth and slope gradient, is identified as the main internal driver in such restricted basins. Secondly, this thesis investigates the external forcing mechanisms driving environmental changes through time, such as orbital and glacial cycles.

This research suggests that glacially induced global sea-level changes constituted the main driver generating episodic rejoining between the Caspian Sea, the Black Sea and the ocean. Finally, this thesis inspects the effects of environmental changes on the endemic Pontocaspian mollusc fauna. Salinity variations, both natural and man-made, are identified as the main drivers for past and current biodiversity crises affecting the Pontocaspian shells. Overall, the research presented in this thesis offers valuable insights of the response of coastal environments under climatic fluctuations and the resulting biodiversity crises occurring in restricted basins.