Shallow-water gorgonian forests along the Moroccan Atlantic Coast

Abstract This study is the first comprehensive documentation of the distribution and fauna of gorgonian forests along the Atlantic Coast of Morocco. The presence of shallow water gorgonian ecosystems was mapped in 2020 using ROV as part of the FAO-NANSEN habitat mapping program. The seabed was visually mapped at depths from 27 to 112 m using an ROV at 37 localities and 400 m in long video transect was conducted at each locality. The recorded megafauna and substrate were annotated using the software “VideoNavigator”. Video-transects were subdivided into 109 sampling units based on substratum and fauna patterns were identified using the multivariate analysis TWINSPAN and DCA. The relation to 10 environmental variables was indicated by correlation with DCA ordination axes. In total, 28,919 organisms and 143 taxa were recorded, with the highest diversity linked to the presence of hard substratum. Eight fauna-groups were identified that related mainly to a gradient in depth and mud along ordination Axis 1 and degrees north and sand along Axis 2. Six of the fauna-groups were gorgonian garden ecosystems on hard substratum and two were sea pen and gorgonian ecosystems associated with soft sediments. Hard substratum at 27–76 m, Group III and IV, were dominated by Leptogorgia viminalis, Eunicella species and E. paraplexaurides. Hard substratum at 59–75 m, Group V, was dominated by E. verrucosa, E. labiata, and Leptogorgia species and E. paraplexaurides. Hard substratum at 76–112 m, Group I and II, was dominated by Ellisella paraplexaurides and sponges. Soft sediments at 38–75 m, Group IV and VIII, were dominated by Pennatula rubra. Soft sediments at 72 m, Group VII was characterized by E. verrucosa and P. rubra. An observed threat to the gorgonian ecosystems were the sand that due to strong swell covered the hard bottom in many places where gorgonians forest occurs. The moving sand threatens both to bury the colonies and damage the tissue on lower parts of the colonies. This emphasizes the importance of conservation efforts to protect these delicate ecosystems.