Different hydro climatic conditionsat and above a continental shelf have significant effects on the ecology of theenvironment (temperature, nutrient richness and pelagic production). Indeed,bioclimatic changes defined clearly reflects the prevailing conditions imposedabove the continental shelf. Based on contributions made to the sea (rainfall,temperature, wind ...) and those put together by the internal dynamics can bedistinguished marine years that correspond to low enrichment in terms of anychange in continental and marine conditions generally short and strongenrichment of years corresponding to eventful years and transformations ofcontinental and marine conditions, strong shifts in time. Thus, a hot or coldbut very fluctuating period influence the marine ecosystem and phytoplankton growth. Also, the impact of development on the coastal and marine environmentis localized mainly in the coastal metropolitan areas characterized by highurbanization and concentration of activities. Keywords:climate change; environmental variability; Ecosystem vulnerability; West coastof Algeria.