Optical remote sensing was used to provide scientific information to support environmental management in the Gulf of Gabes located on the southeastern coast of Tunisia. This region is characterized by a shallow continental shelf with semi-diurnal tides. Since the early 1970s, industrial activity in this area may have contributed to the degradation of ecosystem biodiversity due to problems of eutrophication and the disappearance of benthic and planktonic species. Previous studies assessing the long term effects of anthropogenic and natural discharges on the Gulf of Gabes were based on regular seaborne measurements of total suspended matter, Secchi depth, turbidity, chlorophyll and temperature. However, these are often costly and difficult to obtain. The objective of this study is to carry out an optical remote sensing analysis with supporting in situ measurements of chlorophyll to monitor water quality and the impact of industrial discharges in the Gulf of Gabes. To start with, data provided both by the optical sensor and by our in situ sampling methods is described. Then, semi-empirical algorithms (OC3, OC5) are presented which are used to process Moderate Resolution Imaging Spectrometer MODIS data for retrieval of chlorophyll (CHL) and a validated algorithm for TU. A comparison was made between the derived estimates CHL and TU and the concurrent bio-optical in situ measurements at stations representing the coast and open ocean and produced significant correlations. The results obtained therefore confirm the high sensitivity and useful spatial coverage of MODIS data to provide a significant tool to accurately assess water quality parameters.
