Seasonal dynamics of the jellyfish Rhizostoma pulmo between the two estuaries of Oued Ghis and Oued Nekkour, Al Hoceima Bay (Moroccan Mediterranean coast)

Abstract

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.