Abstract
The invasive macroalga Rugulopteryx okamurae represents an unprecedented case of bioinvasion by marine macroalgae facing the European coasts. Since the first apparition of the species in the Strait of Gibraltar in 2015, its fast dispersion along the introduced habitats constitutes a real challenge to develop monitoring strategies that ahead of its impacts. The present study uses three different approaches to address impacts on the benthic ecosystems, at the same time offers relevant data for future management actions in El Estrecho Natural Park (PNE). Information obtained by monitoring permanent sentinel stations revealed a significant loss in resident species coverage after the moment of maximum growth in 2017. Thus, despite coverage of R. okamurae did not strongly varied in the latter years, impacts generated remain high in the habitats studied. Estimations of the invasive species coverage by combining cartographic image analysis and in situ data predicted a major occupation (over 85% coverage) between 10 and 30 m, coinciding with the maximum rocky surface areas (m2) mapped on the PNE. Furthermore, a Citizen Science research collaboration evidenced impacts on the benthic seascape through an ad hoc exploration of images that allowed a “before” and “after” comparison of the invasion process in the same geographic locations. This has made it possible to graphically demonstrate severe changes in the underwater seascape and, therefore, the general impact of this new biological invasion. The spatial colonization estimations combined with the impacts reported by both scientific [Sessile Bioindicators in Permanent Quadrats (SBPQ) sentinel stations] and civilian (Citizen Science) monitoring methodologies claim the urgent development of further studies that allow the design of monitoring strategies against R. okamurae expansion across the Mediterranean and Atlantic waters.
Highlights
The Strait of Gibraltar is a hot spot area for marine biodiversity in the Atlantic-Mediterranean waters with great biogeographic importance due the coalesce of the Lusitanian, Mediterranean and Mauritanian regions (Ekman, 1953; Briggs, 1974; GarcíaGómez, 2002)
We considered winters as the season of the year most appropriate to test whether the Sessile Bioindicators in Permanent Quadrats (SBPQ) methodology is minimally robust, since it is the time when it is expected that the development and growth of the invasive macroalga is lower (this has been supported by pers. obs. and growth data for R. okamurae in Japan (Agatsuma et al, 2005), with similar north latitude to Spain: between 20◦ and 40◦)
The present study determined that impacts derived from R. okamurae establishment remain high in the rocky habitats studied of the PNE
Summary
The Strait of Gibraltar is a hot spot area for marine biodiversity in the Atlantic-Mediterranean waters with great biogeographic importance due the coalesce of the Lusitanian, Mediterranean and Mauritanian regions (Ekman, 1953; Briggs, 1974; GarcíaGómez, 2002). Its species richness and habitat diversity is influenced by the littoral physiographic complexity, which has led to the co-occurrence and dominance of different biological strategies and affecting the composition of benthic communities (Zabala and Ballesteros, 1989) The biodiversity of this area has been largely assessed by a list of references in terms of foundation species [macroalgae (Flores-Moya et al, 1995a,b; Conde et al, 1996; Adama et al, 2021) and sessile macroinvertebrates as ascidians (Carballo et al, 1997) or molluscs (García-Gómez, 2002; Gofas et al, 2011)] and associated fauna (e.g., García-Raso, 1993; Conradi et al, 2000; Castello and Carballo, 2001; Guerra-García et al, 2009; García-Raso et al, 2011). This implies a threat due to marine bioinvasions since ballast waters and boat hulls fouling are recognized as potential transport vectors for non-indigenous species (NIS) (Ribera-Siguan, 2003)
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