Assessment of the Marine Thermal Signal in the El Jadida Coastal Region (Atlantic Morocco) and Potential Implications for Gelidium Populations

The El Jadida coastal region on the Moroccan Atlantic coast is affected by seasonal upwelling and has long-standing socio-economic relevance because of the exploitation of red seaweeds of the genus Gelidium, used for agar production. This study evaluates the marine thermal signal in this region and discusses its potential ecological implications for Gelidium populations. Monthly sea surface temperature (SST) series were extracted from NOAA OISST v2.1 for three points: B, an offshore reference point; D, a near-offshore point; and C, a targeted coastal point close to the Gelidium-relevant shore. The analysis covers 528 months from January 1982 to December 2025. Monthly climatologies, annual means, linear trends, seasonal anomalies, differences between early and recent periods, and spatial contrasts were computed. A Copernicus Marine Atlantic L4 reprocessed SST product at 0.05° resolution was also used to provide a complementary fine-scale spatial interpretation for February and August 2025. Annual warming was detected at the three points, with trends of +0.095 °C per decade at B, +0.060 °C per decade at C, and +0.130 °C per decade at D. The strongest seasonal warming occurred in spring, whereas summer showed the weakest trends, particularly at the coastal point C, where the summer trend was slightly negative (-0.018 °C per decade). Copernicus data confirmed that C was cooler than the offshore and near-offshore points, particularly in August 2025. These results suggest that the El Jadida coast is not characterized by a spatially uniform warming signal. Instead, the thermal regime is modulated by coastal processes, including summer upwelling. Because the present work focuses on SST alone, it should be interpreted as an environmental baseline rather than as a direct biological diagnosis of Gelidium beds. Its ecological relevance is supported by previous biological and ecological studies showing that temperature, often interacting with irradiance, nutrients, water movement, substrate conditions and harvesting pressure, can influence Gelidium population maintenance and recovery processes. The study therefore provides an initial climate-oriented diagnostic and a scientific basis for future field-based work on Gelidium habitats along the El Jadida coast.