Spatio-temporal quantification and distribution of diatoms and dinoflagellates associated with algal blooms and human activities in Algiers Bay (Algeria) using Landsat-8 satellite imagery

Abstract Quantifying phytoplankton and its changes in coastal waters is an important aspect of marine ecosystems. Synoptic observations of phytoplankton communities became possible with remote sensing technologies and spatial analysis methods. Using these advancements would assist the scientific community to gain better understanding of marine ecosystem dynamics and consequently contribute in sustaining and maintaining these valuable ecosystems. Thus, this study aimed to evaluate the water quality and aquatic ecosystem status of Algiers Bay, Algeria, through the quantification of diatoms and dinoflagellates species using in-situ measurements and Landsat images. We developed empirical models to assess phytoplankton abundance by comparing in-situ measurements of diatoms and dinoflagellates with various spectral bands and band ratioing products derived from Landsat-8 OLI images acquired in 4 April 2017 and 9 May 2018. The results showed a wide variation between coastal and offshore stations. The number of diatoms was less than that of dinoflagellates. These two algae communities illustrated a different spectral behavior. Diatoms showed a significant relationship with one of the ratioing products (i.e., log B7/log B2), whereas dinoflagellates exhibited an insignificant relationship with the remotely sensed dataset. Also, we learned that the southeastern area of the bay can be influenced by harmful algae blooms developed offshore because of hydrodynamic forces that push these blooms toward this area of the bay.