Using MERIS data to assess the spatial and temporal variability of phytoplankton in coastal areas

This study aims to highlight how satellite data can be used for an improved understanding of ecological processes in a narrow coastal bay. The usefulness of the Medium Resolution Imaging Spectrometer MERIS data 2003–2011 as a complement to the in situ monitoring in Himmerfjarden HF bay is used as an example that can also be applied to other coastal areas. HF bay is one of the most frequently monitored coastal areas in the world, allowing for a rigorous comparison between satellites and ship-based monitoring data. MERIS data was used for the integration of chlorophyll-a chl-a over each waterbody in the HF area, following the national waterbody classification by the Swedish Meteorological and Hydrological Institute SMHI. Chl-a anomaly maps were produced for the bay and its adjacent areas. The maps could be used to show events with high chl-a, both with natural causes e.g. a Prymnesium polylepis bloom observed in summer 2008 and of anthropogenic causes e.g. failure in the local sewage treatment plant resulting in a strong spring bloom in 2006. Anomaly maps thereby allow to scan larger coastal stretches to discriminate areas that may require additional sampling by ship, or to identify areas that do not differ much from the median value of the MERIS time series.