Seasonal dynamics of associated epifaunal families with the endangered fucoid Gongolaria nodicaulis along the Atlantic coast of Morocco.

The structure and composition of epifaunal communities are closely linked to the ‎characteristics of their host species and environmental fluctuations. This study investigates the ‎diversity and seasonal variation of macro epifaunal families associated with Gongolaria ‎nodicaulis, collected from the Atlantic coast of Morocco over four seasons. Sampling was ‎carried out seasonally using standardized collection methods, and organisms were identified ‎to the family level under a stereomicroscope using standard taxonomic keys, with ‎confirmation through WoRMS and other online databases. Our results revealed a total of 67 ‎epifaunal families belonging to four major taxonomic groups, including 44 Arthropod, 19 ‎Molluscan, 2 Echinoderm and 2 Annelid. Arthropods were the most diverse and abundant ‎group across all seasons. The highest epifaunal diversity was recorded during spring with 28 ‎Arthropod, 11 molluscans and 3 families representing other groups. Moreover, the overall ‎epifauna abundance peaked in Autumn, with 250 ± 10 individuals/10 g of seaweed dry ‎weight, followed by Spring and Summer (187 ± 19 and 137 ± 28 ind./10 g dw, respectively) ‎and reached its lowest level in winter (119 ± 16 ind./ 10 g dw). This seasonal variation was ‎significantly associated with fluctuations in nutrient concentrations (nitrate, nitrite and ‎orthophosphate), salinity and conductivity (p<0.05). ‎The high abundance observed in autumn ‎may reflect favorable physicochemical conditions and post recruitment, while temperature-‎related metabolic activity, primary productivity and enhanced reproductive ‎cycles ‎of both the ‎host species and associated fauna may also contribute to this seasonal patterns. Conversely, ‎the low abundance detected in winter could be attributed to lower temperatures, reduced ‎primary productivity and biological activity, limited food availability, and harsher ‎environmental conditions affecting both colonization and survival of associated fauna. Five ‎dominant families (e.g., Gammaridae, Calliopiidae, Calyptraeidae, Nassariidae and ‎Nereididae) exhibited significant seasonal variation in abundance, indicating their sensitivity ‎to environmental factors such as temperature, food availability, and the phenology of the host ‎species. This study underscores the ecological significance of Gongolaria nodicaulis as a ‎habitat provider and epifaunal biodiversity hotspot. These findings highlight the ecological ‎importance of conserving this marine forest, given its role in supporting diverse epifaunal ‎communities and potentially contributing to the maintenance of coastal biodiversity. ‎