Remote sensing techniques for monitoring algal blooms in the area between Jeddah and Rabigh on the Red Sea Coast

Abstract

The Red Sea is known to host and facilitate the growth and reproduction of several species of phytoplankton and algae. The degree of density and distribution of these organisms differ with region. However, very few studies have been conducted on algal blooms in this region. Hence, this study aimed to identify the effectiveness of remote sensing techniques in monitoring and controlling algal blooms in the area extending between the cities of Jeddah and Rabigh on the Red Sea coast. A series of satellite images were used to study algae from January 2020 to March 2021. All study data were subjected to processing and analysis using spectral indices [chlorophyll a (Chl-a); Concentration and Sea Surface Temperature (SST); Normalized Difference Turbidity Index (NDTI); Surface Scum Index (SSI); Surface Algal Bloom Index (SABI); Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI)], and the classification, overlay, and buffer methods. We found that the rate of chlorophyll a (Chl-a) increased in February 2021 and decreased in May 2020, with the algal bloom dwindling with increasing distance from the shores of the Red Sea. Furthermore, despite the varying effectiveness of the spectral indices in estimating the distribution and density of algae in the Red Sea, Landsat SSI was the most effective. One of the primary results of the study was that algal blooms more frequently occur in the winter (February). The study produced a digital map of algal blooms in the study area. Algal blooms exhibited medium inverse correlations with temperature and specific humidity, and strong direct correlation with wind speed. Valley estuaries, close to the beaches, were found to be the most suitable area for the concentration and growth of algae. The study's findings emphasize the need for close monitoring and controlling changes in the components of the marine environment using remote sensing techniques, in order to track the changes that marine plants (algae) are exposed to in the Red Sea.