First Inventory of the Biodiversity, Abundance, and Distribution of Jellyfish (Cnidaria) in Relation to Depth in the Bay of Al Hoceima, North Coast of Morocco, the Mediterranean Sea

Jellyfish are considered the most important components of plankton in the oceans. However, in the Moroccan Mediterranean, data on jellyfish populations are scarce.  Jellyfish are organisms belonging to the phylum Cnidaria, characterized by the presence of cnidocysts, and stinging cells. In carrying out our research on the jellyfish that proliferate in Al Hoceima Bay over the period 2019 to 2022, great importance was placed on studying the diversity of jellyfish species present in the bay. This is due to the risks associated with their proliferation, particularly during the summer months. This study aimed to analyze the species composition, abundance,  and frequency of occurrence of the jellyfish community in the bay of Al Hoceima, located on the northern coast of Morocco. To achieve this objective, the gelatinous zooplankton sampling method was used, which enabled the researchers to collect samples in the epipelagic layer, between 0 and 80m depth, at nine different stations. In addition to this method, field surveys were carried out specifically for macromedusae. During this study, a total of 16 species of Hydromedusae and Scyphomedusae belonging to 15 genera were discovered in the study area. Among these, there were ten new records for the Moroccan Mediterranean and thirteen new records for the bay of Al Hoceima. The populations of Hydromedusae consisted of six species of Trchymedusae, three species of Anthomedusae, and four species of Leptomedusae. In terms of the Scyphomedusae populations, three species were identified: Pelagia noctiluca, Rhizostoma pulmo, and Rhizostoma luteum. Notably, Pelagia noctiluca and Rhizostoma pulmo formed dense aggregations in the bay during the summer periods.