SUMMARY
Chlorophyll-a concentration in water is an indicator of phytoplankton density, which in turn is crucial, as it represents the base of the ecological life in seas and oceans. Any increase or decrease in the number of phytoplankton may contribute to disruption to the ecological cycle in the seawater. The density of phytoplankton is also an important indicator of water quality. Traditionally, water samples are collected in the field and analysed in the laboratory to find the density of phytoplankton in a specified amount of water. Recently, remote sensing has led to the development of advanced and remote methods to detect phytoplankton density, chiefly by extracting near-surface chlorophyll-a concentrations. In this study, MODIS (Aqua) Level 3 data (64 images) were used to extract average chlorophyll-a concentration at time points from 2004 to 2019 (over 16 years) for the Arabian Gulf, where the Level 2 (11 images) data were used to determine the accuracy of the estimated values via MODIS (Aqua) using field data taken from the waters of the State of Kuwait (25 points). The results showed good accuracy for MODIS (RMSE = 1.066), and it also shows that the temporal seasonal averages change in a annual-cycles, and that the trend decreased from 2004 to 2019, by about 0.7 mg/ .