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In recent decades, the global environmental balance has been disrupted due to new environmental conditions and increasing anthropogenic pressure. In this context, the increase in frequency and magnitude of jellyfish proliferation in the Mediterranean Sea can be examined as an indicator closely associated with potential impacts of global changes. Despite their importance in ecosystem function and services, current knowledge of jellyfish diversity and phenology is largely lacking in the southern Mediterranean Sea, particularly along the Moroccan Mediterranean coast. Rhizostoma pulmo is a large scyphozoan jellyfish endemic to the Mediterranean. It is the second dominant scyphozoan species in the jellyfish community of Al Hoceima Bay. In this article, we explore the seasonal dynamics of the jellyfish R. pulmo between the estuaries of Oued Ghis and Nekkour at Souani Beach. Due to the disparity between the visual abundance of jellyfish and their rare beaching along the shores of Al Hoceima Bay, we implemented a specific method for collecting R. pulmo. This approach involves the use of a coastal trawl, a fishing net 200 meters long with a mesh size of 5 cm, deployed 80 meters from the shore and pulled from both sides by fishermen. Sampling missions conducted throughout the year 2022 revealed that R. pulmo reaches its maximum abundance in summer. The results indicate a maximum abundance of 0.28 ind/m2 in July 2022, with a maximum umbrella diameter reaching 26 cm in August 2022. Under the jellyfish umbrellas, fry of two fish species and one crustacean species were observed, adding an ecological dimension to this study.

Cartilaginous fish are particularly vulnerable to anthropogenic stressors and environmental change because of their K-selected reproductive strategy. Accurate data from scientific surveys and landings are essential to assess conservation status and to develop robust protection and management plans. Currently available data are often incomplete or incorrect as a result of inaccurate species identifications, due to a high level of morphological stasis, especially among closely related taxa. Moreover, several diagnostic characters clearly visible in adult specimens are less evident in juveniles. Here we present results generated by the ELASMOMED Consortium, a regional network aiming to sample and DNA-barcode the Mediterranean Chondrichthyans with the ultimate goal to provide a comprehensive DNA barcode reference library. This library will support and improve the molecular taxonomy of this group and the effectiveness of management and conservation measures. We successfully barcoded 882 individuals belonging to 42 species (17 sharks, 24 batoids and one chimaera), including four endemic and several threatened ones. Morphological misidentifications were found across most orders, further confirming the need for a comprehensive DNA barcoding library as a valuable tool for the reliable identification of specimens in support of taxonomist who are reviewing current identification keys. Despite low intraspecific variation among their barcode sequences and reduced samples size, five species showed preliminary evidence of phylogeographic structure. Overall, the ELASMOMED initiative further emphasizes the key role accurate DNA barcoding libraries play in establishing reliable diagnostic species specific features in otherwise taxonomically problematic groups for biodiversity management and conservation actions. [ABSTRACT FROM AUTHOR]