Phytoplankton phenology in algerian continental shelf and slope waters using remotely sensed data

摘要

Understanding the dynamics of phytoplankton provides important information on the health and richness of a marine ecosystem. In the Mediterranean Sea, significant phytoplankton variability has been observed between the western and eastern basins and between open ocean and coastal waters. In this study, we used eleven years' (2003-2013) MERIS and MODIS sea surface chlorophyll-a (Chla) data to investigate the spatial and temporal variability of phytoplankton in the Algerian shelf and slope waters (ASW), in the southwestern part of the Mediterranean Sea. We assessed the inter-annual and seasonal variability of phytoplankton biomass, retrieved thirteen pixel-based phenology metrics using TIMESAT algorithms, and determined the influence of precipitation on phytoplankton dynamics. Our results reveal differences between the western and eastern parts of ASW. In the eastern part of the coast, the production season starts one month later than in the western region. It also peaks about 15 days earlier and ends one month earlier as compared to the west. As a result, the productive season is shorter in the east than in the west. The area between Be ' jaia and Skikda stands out, with the highest Chla values and the highest variability. These findings show that the phytoplankton dynamics varies also at the scale of ASW in timing and magnitude, which is complementary with studies previously conducted at the Mediterranean Sea scale. Correlation analysis shows that rainfall influences phytoplankton biomass and some phenology metrics' variability. However, other physical and biogeochemical variables should be investigated for a more complete understanding of the plankton dynamics and to assess the impact of this variability on species abundance and diversity.