First Record of Stranded Holopelagic Sargassum Morphotypes and Associated Fauna on the Moroccan Atlantic Coast

In early 2024, a large influx of holopelagic Sargassum were discovered drifting along the Atlantic coast of Morocco, marking the first recorded occurrence of these drifting macroalgae in the region. This event revealed a striking morphological diversity within the drifted biomass, with three distinct morphotypes identified: Sargassum natans morphotypes I and VIII, and Sargassum fluitans morphotype III. The biomass density reached 10 ± 3 ind/m², with S. natans VIII dominating at 58%. Alongside the algal masses, a diverse associated fauna was observed, including hydroids and crustaceans, highlighting the role of Sargassum mats as transient pelagic habitats. The diversity of morphotypes observed reflects complex dispersal dynamics and potentially multiple origins or developmental pathways, possibly shaped by environmental drivers. The arrival of these forms following the Nelson storm underscores the influence of extreme hydrometeorological events in facilitating long-distance transport from the tropical Atlantic to the North Atlantic coast of Africa. As climate change continues to intensify such events, the frequency and morphotype variability of holopelagic Sargassum blooms are likely to increase. This study highlights the importance of monitoring not just biomass but also morphological variability, which can influence ecological impact and inform future coastal management strategies.