The kelp Undaria pinnatifida is considered one of the 100 worst invasive species in the world. The presence of Undaria in Portugal was reported more than 20 years ago, but there is not recent detailed information about its distribution and impacts. The aims of this study are to provide updated data about the distribution of Undaria in marinas and natural habitats along the north Portuguese coast, to afford insights about Undaria impacts on native macroalgae and to test the efficiency of mitigation actions based on Undaria removal. Mitigation measures were implemented in a marina where a native kelp was recently displaced by Undaria. The results showed stable populations of Undaria in marinas, but few ephemeral ones on natural rocky shores. The observed distribution pattern suggests an important role of salinity and wave exposure in shaping the distribution of Undaria. Moreover, Undaria was able to displace a native kelp and overgrow mussels in marinas, while on natural rocky shores, it was able to overgrow Gongolaria baccata but not native kelps. Finally, mitigation actions resulted in a partial recolonization by the native kelp.

The number of recreational marinas has recently increased due to the growing demand for leisure boating. Floating pontoons of marinas provide novel habitats to fouling assemblages, specially to sessile habitat-forming species, that increase heterogeneity creating new habitats for mobile and sessile epibionts. Therefore, sessile species play a crucial role in sustaining biodiversity in urban areas. Despite the relevance of sessile fouling assemblages, the role of environmental factors in shaping the structure of these assemblages has not been comprehensively studied. In the present study, the abundance, richness and multivariate structure of sessile fouling assemblages associated with floating pontoons were studied in marinas under two different environmental conditions (brackish and marine), and the influence of environmental variables (salinity, temperature and dissolved oxygen) on fouling assemblages was tested. Our results showed that univariate variables and assemblage composition significantly differed between environments, with lower values of abundance and richness under brackish conditions. This pattern could result from the influence of freshwater inputs in brackish marinas, that also showed a higher level of multivariate dispersion. Results also pointed out that salinity was the most important factor, explaining 46 %, 56 % and 37 % of abundance, richness and multivariate structure of sessile fouling assemblage, respectively. The sessile assemblage in marine and brackish marinas was dominated in terms of abundance by the native habitat-forming species Mytilus galloprovincialis, which harboured most of the collected sessile epibiont species. These findings highlight the role of floating pontoons to support sessile invertebrates in urban areas where biodiversity may be heavily impacted.

The number of recreational marinas has increased in recent years due to the growing demand for leisure boating. Recreational marinas are key points for the introduction of non-indigenous species (NIS), which are considered a source of biocontamination. However, there is scarce knowledge on the influence of environmental features on NIS fouling assemblages, especially regarding different salinity conditions. The aim of this study is to explore the effect of salinity on the structure of NIS fouling assemblages and biocontamination levels. Therefore, fouling assemblages associated with floating pontoons were studied in recreational marinas located in fully marine and brackish habitats on the Northern Portuguese coast. Twenty-four NIS were found, of which arthropods and bryozoans represented the most abundant taxa. Except for NIS abundance, univariate and multivariate analyses showed that NIS assemblage structure was shaped by salinity conditions. Thus, NIS richness and the ratio between NIS richness and total richness were significantly higher in marine than in brackish habitats. Similarly, consistently higher biocontamination levels were found in marine habitats, compromising their ecological status. Quantitative data provided here will be useful in the development of NIS management strategies. Thus, in Northern Portugal, efforts should be focused on marinas under fully marine salinity conditions because they harbor a greater number of NIS and, consequently, a worse ecological status.

Recreational marinas are raising worldwide attention because of the public appeal for recreational activities such as boating. Their floating pontoons provide substrate for fouling assemblages, which include many ecosystem engineers such as the mussel Mytilus galloprovincialis. However, knowledge on vagile assemblages in floating pontoons under different salinity conditions and its drivers is still very limited. In this study, vagile fouling assemblages were investigated in six marinas along the northern coast of Portugal (three brackish and three marine) to test if the M. galloprovincialis population (abundance, size structure) and the vagile fouling assemblage (abundance, taxon richness, multivariate structure) differed between marine and brackish conditions. Furthermore, we tested if there was a relationship between mussel abundance and the aforementioned features of the assemblage. Mussel abundance was about three times greater in marine than in brackish marinas; the former also showed a more diverse mussel size structure. Richness in marine habitats was about twice in comparison to brackish ones. Seventy-six species were exclusively found in marine habitats whereas 27 species were found only in brackish marinas. Moreover, the multivariate assemblage structure showed an average dissimilarity of 81% between brackish and marine conditions. Mussel abundance and salinity interplayed in the structure of vagile fouling assemblages. Salinity potentially has a direct effect on the vagile fauna by influencing their composition according to each species’ tolerance to salinity, but also an indirect effect through its influence on mussels. Our findings suggest that mussels could be useful if the goal is to increase biodiversity in marinas under marine conditions since richness increased with mussel abundance. However, future experimental studies will be necessary to elucidate the role of mussels as biodiversity enhancers.