LAUSR

Abstract The Mediterranean is one of the most biodiverse and anthropogenically impacted seas and the coralligenous is one of its most diverse habitats. Its presence is indicative of well-preserved areas and its associated species are considered among the best bioindicators for monitoring nearshore rocky habitats. This study aims to report the temporal fluctuations of the coralligenous community in the marine protected area of Jbel Moussa (Strait of Gibraltar) in a period concomitant with the rapid expansion of the non-indigenous species Rugulopteryx okamurae (E.Y.Dawson) I.K.Hwang, W.J.Lee & H.S.Kim in the area. From year 2015 to 2019, an area covering 36 m2 of the coralligenous habitat was monitored across three sites, including temperature logs from 2017 to 2019. After its first record in the area in 2017, R. okamurae became the most abundant species in only one year, followed by a change in the coralligenous community structure and a regression of the bioindicator species Paramuricea clavata (Risso, 1826) and Mesophyllum expansum (Philippi) Cabioch & M.L.Mendoza. These species are sensitive to increases in water temperature and were already under a gradual regression due to anthropogenic disturbances and previous biological invasions, all of which could have reduced niche competition in the area and favoured the impacts caused by R. okamurae in the area. Results highlight the need of a rapid administrative response to increase mitigation efforts on this protected habitat. Due the potential expansion of this non-indigenous invasive species to the Mediterranean Sea, the present study could provide valuable information for future monitoring, conservation and management actions.