The Romanian North Western coastal and shelf zones of the Black Sea and Danube delta are a mosaic of complex, interacting ecosystems, rich natural resources and socio-economic activity. Dramatic changes in the Black Sea's ecosystem and resources are due to natural and anthropogenic causes (increase in the nutrient and pollutant load of rivers input, industrial and municipal wastewater pollution along the coast, and dumping on the open sea). A scientific management system for protection, conservation and restoration must be based on reliable information on bio-geophysical and geomorphologic processes, coastal erosion, sedimentation dynamics, mapping of macrophyte fields, water quality, climatic change effects. A multitemporal data set consisting of LANDSAT MSS, TM and SAR ERS-1 images was used for comparing and mapping landcover change via change detection. Synergetic use of quasi-simultaneously acquired multi-sensor data may therefore allow for a better approach of change detection of coastal area. The main aim of this paper is to conduct a comprehensive analysis based on existing historical and more recent in situ and remote sensing data to establish the link between phytoplankton bloom development, increasing erosion and diminishing of beaches and related coastal zone harmful phenomena.