In order to maintain the shore protection systems of Odessa the renourishment of sand beaches in the Gulf of Odessa was organized in 2007. We analyzed the sand grain size of the splash zone at monitoring sites before the beach renourishment, in one year and 5 years after renourishment. Simultaneously, on the monitoring sites the microscopic algae were studied. The algae are indicators of the ecological state of the littoral zone.

A comparison of particle size of sand beaches before the renourishment and after showed that the median diameter of sand sediment significantly decreased, and its sorting code increased after renourishment on most sites. Median diameter decreased threefold. The mediumsize sand with a dash of coarse-size sand, which is natural for Odessa coastal beaches, actually was replaced by clean well sorted fine sand. Five years after the renourishment as a result of the wave rewashing of beach sediments the grain size of the sand splash zone has changed. A huge amount of renourished sand was washed into the sea and beaches width declined sharply. The mediumgrained sand began to prevail in the sediments. The content of coarse fraction increased. The median diameter of the sand increased by 1.4 times. Therefore, the lithodynamic balance began to recover. The sand grain composition of the deposits corresponding to natural hydrodynamic conditions was formed.

Sand renourishment in the Gulf of Odessa let us to investigate the response of algae community to changed habitat parameters. The beach renourishment led to higher organic matter content in the pore water, which affected taxonomical composition of microalgae. Groups of flagellates, which are capable to utilize organic matter, began to actively develop. In 2012, the total abundance of micro-algae decreases again, showing similar conditions on beaches with natural and artificial sand and indicating that the recovery of microorganisms is occurred.

Monitoring of sand grain composition changes showed that the western coast of the Gulf of Odessa is characterized by hydrodynamic processes where the medium-grained sands are persistent. The projects on beach zones development should take into account the granulometric features of the deposits on the shore that will provide the economical viability and sustainability.

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