Role of the type of boat traffic on the presence of sessile non-indigenous species (NIS) in marinas of southwestern Bay of Biscay

Role of the type of boat traffic on the presence of sessile non-indigenous species (NIS) in marinas of southwestern Bay of Biscay | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Role of the type of boat traffic on the presence of sessile non-indigenous species (NIS) in marinas of southwestern Bay of Biscay Alejandra GARCÍA-MADRID, Silvia CUESTA, Eduardo LÓPEZ This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7510059/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The aim of this study was to analyze the influence of the type of boat traffic on the settlement of sessile non-indigenous species (NIS) in marinas from southwestern Bay of Biscay. The research was conducted in two zones, and two marinas were selected in each zone. One marina was subjected to heavy traffic, with numerous large boats capable of making long trips, and the other was subjected to light traffic, with fewer and smaller boats of limited autonomy. At each port, 12 PVC plates were installed to favor the settlement of sessile organisms. Eleven out of the 36 identified species were NIS. The analysis of the faunal composition revealed that in the area where the two marinas were closer, it was not possible to distinguish a different community in relation to the type of traffic. The analysis of the ecological descriptors considering "traffic" and "zone" as explanatory factors indicated that the differences were significant only with respect to the second factor for most of them. Only NIS diversity was related to traffic, although its behavior was opposite in the two zones. Our results indicate that the type of traffic is not enough to explain the composition of the NIS communities in the region and that they tend to merge in the short term when small and large marinas are very close. recreational navigation non-indigenous species Bay of Biscay marinas Figures Figure 1 Figure 2 Figure 3 Figure 4 INTRODUCTION In recent years, non-indigenous species (NIS thereafter), which can possibly become invasive, has turned a major concern in marine ecosystems. They are involved in 33% of the most recent extinction events (Zamora-Marínet al. 2023) and are responsible for annual expenses of over 26.8 billion dollars (Cano-Barbacil et al . 2023). This issue is strongly related to human activities and practices in the sea that help the introduction and dispersal of such species (Png-González et al. 2023). Despite this, NIS continue expanding their areas to the point of being a great threat to autochthonous species survival and causing relevant impacts on local economies. Thus, control and supervision of NIS before their arrival through the several available methods is strongly needed, as once they are established, they are nearly impossible to eradicate (Cano-Barbacilet al. 2023). The only known successful case of eradication occurred because of early detection and quick response, since once identified the presence of NIS, the only effective treatment is hard population control (Giakoumiet al. 2019; Fernández-Gutiérrezet al. 2025). NIS are favored by several intentional and unintentional mechanisms to arrive at new habitats. The most common pathway, which causes 58% of new arrivals, is shipping because allochthonous species can settle on ship hulls or travel mixed with ballast water, where they stay alive until being freed in new locations (Kelleret al . 2011). Larger floating structures drifting in the sea, such as plastic masses, gosht nets or buoys, act as temporal habitats for encrusting sessile NIS, which can be transported to faraway locations (Fernández et al. 2022). On the other hand, aquaculture activities are a risk factor since some species can accidentally escape from facilities where they are raised and establish in nature (Geburzi & McCarthy 2018). Moreover, if they are not carefully disinfected, introduced specimens can act as vectors for parasites and pathogens (Kelleret al . 2011), and even as a translocation mechanism or a high number of small-sized accompanying NIS (Piló et al. 2021). Intentionally introduced alien species of aquacultural interest are even more prone to establish because the species selected usually have similar ecological needs to those of their native counterparts but are more resilient and have greater population growth rates (Grosholz et al. 2015). The last factor is the introduction of species related to pet trade that accidentally escape or are intentionally released in native waterbodies (Holmberget al. 2015). Many of the arriving NIS eventually become established. Those achieving it share several traits that explain their success, especially those related to their plasticity in behavior, physiology and several strategies (Devin & Beisel 2007). Most of these strategies are related to reproductive biology and are associated with short durations of sexual maturation, fast growth rates, and, in most cases, long planktonic stages (Geburzi & McCarthy 2018). Another frequent trait is their environmental plasticity, as they need to adapt to the changing conditions of the environment and differ from their native habitat in terms of salinity and/or temperature (Keller et al. 2011). Although only a small number of NIS that are introduced into new habitats are effectively established and even smaller amounts can achieve high population densities, the consequences are extremely harmful and have great ecological impacts on aquatic ecosystems (Gallardo et al. 2016). These include a decrease in the richness and abundance of native species due to predation or competition for resources by alien species, as well as the alteration of invaded habitats. On the other hand, it has been demonstrated that the larvae of many benthic species tend to avoid settling near dominant species, such as invasive NIS NISs, so the reproductive patterns of native species are altered (Rius et al. 2009). As the most dramatic consequence of these interactions, the extinction of native species can eventually occur (Boudouresque & Verlaque 2005; Cano-Barbacil et al. 2023). As indirect effects, alterations can be caused in the food webs of colonized ecosystems and in the behavior of predators (Rius et al. 2009). Similarly, ecosystems can also undergo physicochemical changes, such as increases in turbidity, nitrogen concentration, and organic matter, which also affect native species (Gallardo et al. 2016). Finally, the impacts of NIS not only affect natural systems but can also act as vectors of foreign pathogens and cause health problems, both to other marine species and to humans, and cause significant damage to the economy (Muñoz-Mas et al. 2021). The location of the Iberian Peninsula is extremely important from a biogeographical point of view since it connects Europe with Africa and the Mediterranean Sea with the Atlantic Ocean but also plays a capital role in maritime transportation. For this reason, it is a common gate for NIS, accounting for 182 introduced species in the Bay of Biscay since 1970 (Png-González et al. 2023). To address this growing issue, new laws have been enacted, such as law 42/2007 about Natural Heritage and Biodiversity, and several checklists on NIS have been performed, including the Spanish Checklist on Invasive Alien Species; however, the cost between 1997 and 2020 of the management of these species was calculated to be approximately 232.54 million euros (Angulo et al . 2021). Similarly, control of marine NIS is treated in European laws, such as the Marine Strategy Framework Directive (MSFD) (2008/56/EC), which seeks to assess the ecological status of the coasts of member states through 11 qualitative descriptors, one of which is the number of artificially introduced species (Png-González et al. 2023). As mentioned above, sea navigation, be it commercial or recreational, is a major pathway for NIS introduction. They travel from one port to another fouling ship hulls or mixed with ballast water and establish themselves in new localities, taking advantage of artificial structures, the number of which has increased in recent decades (Castro et al. 2022). Unlike ship hulls, these structures are usually not treated with antifouling chemicals to prevent colonization by sessile organisms, so they usually harbor a relatively high abundance and species richness of encrusting animals (Carmona-Rodríguez et al. 2024). Compared with native species, NIS have greater chances of successful establishment in these structures, as the former are usually not well adapted to such unstable and hostile substrates (Ferrario et al. 2017; Geburzi & McCarthy 2018). On the other hand, transitional waters between river mouths and true marine environments, where many ports are located irrespective of their size or activity, are very vulnerable because factors typical of both kinds of environments act in combination and make them easily colonizable by species capable of quickly adapting to everchanging salinity and other environmental conditions, such as NIS (Zamora-Marín et al. 2023). Although poorly understood yet, the effects of recreational boating as an introduction pathway for marine NIS received considerable attention in recent years (Ulman et al. 2019). In contrast to commercial ships, recreational boats usually stay longer at ports, providing more time for the establishment of translocated NIS, and can anchor in some marine protected areas that are forbidden for commercial vessels, favoring their colonization by alien species (Martínez-Laiz et al. 2019). Recreational boats are usually much slower than commercial boats but occasionally travel long distances and are very suitable vectors for NIS, an effect confirmed by several researchers. Thus, Clarke Murray et al. (2011) reported that 26% of the examined boats transported fouling NIS, and Martínez-Laiz et al. (2019) reported 56%. With respect to the Spanish case, it is important to emphasize that recreational navigation has increased heavily since 1960, causing an exponential growth in the number of marinas, from 131 in 1976 to 375 in 2015 (Cerchiello 2018), which highlights the importance of this challenge. Goals and hypotheses The goal of this research is to assess the influence of the type of recreational boat traffic on the settlement of sessile NIS in several marinas of southwestern Bay of Biscay. The main hypothesis is that in marinas that have heavier traffic and harbor larger boats capable of longer trips, a more diverse and abundant community of sessile NIS should be found because these ships act in long-distance transport for these species; consequently, overall biodiversity will be reduced due to the loss of native species. In contrast, marinas with lighter traffic and smaller boats that are unable to travel far away, should present the opposite situation, with a lower diversity and abundance of NIS and higher overall biodiversity. MATERIAL AND METHODS Study area All the studied locations are part of the Galician Rias system, a set of coastal embayments placed along the NW sector of Spain that usually function as partially mixed estuaries from a dynamic point of view (Álvarez-Salgado et al. 2000). Most of the Rias are located near the northern boundary of the East Atlantic Upwelling System, and experience wind-driven local upwelling events from March–April to September–October, whereas the prevailing winds promote downwelling processes throughout the rest of the year. In these events, Eastern North Atlantic Central Water (ENACW) masses influence the outer part of estuaries (Álvarez-Salgado et al. 2002). However, in smaller rias, such as those on the northern coast of Galicia, other drivers are responsible for estuary dynamics. The tide is the most energetic force, being semidiurnal and with a tidal range between 4 m in spring tides and 2 m in neap tides all over the northwest corner of Spain (Álvarez et al. 1997). In the rias associated with larger watercourses, river discharge is also an important force in the residual inner circulation (Piedracoba et al. 2005). For replicability, the study was conducted in two nearby zones in southwestern Bay of Biscay (Fig. 1). In each one, we selected a marina with larger boats, which could travel longer distances, and another marina with smaller boats, which usually stayed near the port. In the western zone, the marinas were Viveiro (43° 40’ 04” N - 7° 35’ 42” W), with 307 piers for larger boats, and Vicedo (43° 44’ 18” N - 7° 40’ 18” W), with 136 piers for smaller boats. Each marina is located in a different ria, and they are approximately 10.3 km away. The Ria de Viveiro is formed by a medium-sized river, the Landro River, whereas Ria del Barquero, where the marina of Vicedo lies, formed in the estuary of a much smaller stream, the Sor River (Lorenzoet al. 2003). The two marinas of the eastern zone are located in the same ria, which is formed by the Eo, one of the most abundant rivers in NW Spain (Piedracobaet al. 2005). In this case, the marinas of Ribadeo (43° 32’ 24” N - 7° 02’ 11” W), with 600 piers for larger boats, and Figueras (43° 32’ 13” N - 7° 01’ 25” W), with 146 piers for very small recreational boats, were selected; the two marinas are approximately 1.1 km away. Despite being included in the Nature 2000 Network for its great importance for birds, the Eo estuary is heavily industrialized, and a busy commercial port specializing in timber traffic, a mid-sized shipyard devoted to oceanic vessels, and numerous facilities for the NIS Japanese oyster Magallana gigas (Thunberg, 1793) aquaculture can be found. Sampling methods The sampling was based on the use of non-invasive passive devices that favor the settlement of sessile organisms but are easy to pick up. These devices (Fig. 2) were made of three horizontal PVC plates of 20x20 cm, plus a base of 30x30 cm made of the same material, all of which were joined by a core metal rod; the plates were separated from each other by a piece of PVC pipe 10 cm long that prevented them from collapsing (Fig. 2A, B). Each plate ported an identification label where the number of device and the level where it was located (A, B or C depending on its distance from the base). The sampling device stayed fixed to the bottom by means of a concrete mooring and could be recovered owing to a small buoy tied to a shackle in the core rod. Four random sites were selected at each marina, providing 16 sampling points, where the devices were placed for nearly four months (from 5–6 June to 18–19 October 2024), allowing the organisms enough time to colonize the PVC plates (Diem et al. 2023). Considering the size of the devices, the depth was greater than 1 m at all the sites, even with the most extreme low tides. Similar passive devices have been used in previous studies and have been shown to be most effective in terms of species richness and coverage (Tamburiniet al. 2021). After that time, the devices with the settled sessile organisms (Fig. 2C) were collected, and each plate was separated and stored in a ZIP plastic bag with 70% ethanol for adequate preservation until arriving at the laboratory. Data analysis For species identification, only the lower surface of each PVC plate was used, as most target organisms are sciophilous and the upper surface tended to be clogged with sediment. Identification was conducted by examining the entire plates through a binocular microscope, in most cases at the species level (Annex 1), via identification guides (Reverter-Gilet al. 2016; Hayward and Ryland 2017; Trigoet al. 2018; Cepedaet al. 2022) and regional taxonomic publications (Fernández-Rodríguez et al. 2022; López-Alonso et al. 2022). Assignation to the NIS category was based on the checklist by Png-González et al. (2023). Based on the identifications, an abundance (expressed as a percentage of cover per plate) matrix was created considering each plate as a sample. To graphically analyze the similarity in faunal composition between sessile communities inhabiting each marina, a non-metric multidimensional scaling (nMDS) plot was generated by applying the inverse Bray‒Curtis index calculated from the abundance matrix. To measure biodiversity, several ecological descriptors were computed from the abundance data: the number of species (SpR) and the Simpson (1-D), Shannon (H’) and Margalef (Mg) indices. The amount of NIS was described through the Richness Contamination Index (RCI), defined as the percentage of the NIS on the total diversity, and the Abundance Contamination Index (ACI), defined as the ratio of coverage of the NIS to total coverage expressed as a percentage (Fernández-Gutiérrez et al. 2025). To analyze the significance of the differences between the values of the descriptors for the four studied marinas, a two-way ANOVA was conducted, using “traffic” as predictor Factor 1 (two levels: “haevy” and “light”) and “zone” as predictor Factor 2 (two levels: “western” and “eastern”); both factors are fixed and orthogonal. We previously checked whether descriptor values fit a normal distribution via the Shapiro‒Wilk test. If they did not adjust, a more restrictive than usual criterion (p < 0.01) was used in our design, as in previous publications (Underwood 1997; Tamburini et al. 2021; Lekammudiyanse et al. 2024; Pradoet al. 2024). To check which pairs of marinas presented significant differences for each descriptor, Tukey’s post hoc test was applied. All the analyses were performed with the statistical package PAST 4.16c (Hammer 2024). RESULTS Owing to poor weather conditions, only 15 out of 16 sampling devices were recovered, resulting in a total of 45 plates. Thirty-six species of fouling sessile animals belonging to eight phyla were identified. The most abundant phylum was Bryozoa, with a mean coverage of 35.27 ± 2.16% (standard error), followed by Porifera (14.01 ± 1.26%) and Arthropoda (11.27 ± 0.79%). Among these 36 species, 11 were NIS: Austrominius modestus (Darwin, 1854); Balanus improvisus Darwin, 1854; Balanus trigonus Darwin, 1854; Botrylloides violaceus Oka, 1927; Bugula neritina (Linnaeus, 1758); Clavelina lepadiformis (Müller, 1776); Corella eumyota Traustedt, 1882; Didemnum vexillum Kott, 2002; Magallana gigas (Thunberg, 1793); Tricellaria inopinata D'Hondt and Occhipinti Ambrogi, 1985; and Watersipora subatra (Ortmann, 1890). The most abundant species (mean coverage > 5%) were W. subatra, with a mean coverage of 22.55 ± 3.24%; Dercitus bucklandi (Bowerbank, 1858), with 13.06 ± 2.77%; B. trigonus , with 7.82 ± 1.56%; D. vexillum , with 6.55 ± 1.63%; and Spirorbis spirorbis (Linnaeus, 1758), with 6.42 ± 1.04%. Notably, three of them are NIS. The nMDS plot (Fig. 3) shows the results of the comparison of the faunal compositions of the samples. In this figure, a first segregation by zones can be observed, with samples from the western zone grouped in the left section of the plot and those from the eastern zone to the right. In turn, a second segregation by marinas is noticeable among the eastern zone samples, with samples from Vicedo and Viveiro clearly separated. However, the samples from the two marinas from the eastern zone (Figueras and Ribadeo) appear interspersed. Thus, it cannot be inferred from the results that in the region distinct communities of sessile organisms inhabit large and small marinas on the basis of the type of boat traffic. With respect to the values of the ecological descriptors (Fig. 4), although Figueras was the subject of light boat traffic, the values were the worst, with the lowest values for species number and the Simpson, Margalef and Shannon indices, as well as the highest value for RCI (proportion of NIS species); the highest value for ACI (relative abundance of NIS) was found in Viveiro within the same estuary. In general, the NIS were very diverse across the region, with a mean RCI value of 45.44 ± 1.35% in the samples. Similarly, coverage by the NIS was very high, with a mean ACI value of 61.13 ± 3.02% and above 50% across all the marinas except Vicedo, indicating a high degree of colonization. After the Shapiro‒Wilk test was applied, the values of the Shannon and Margalef indices, as well as the RCI, fit a normal distribution, whereas the remaining descriptors (number of species, Simpson index and ACI) did not, so the more restrictive criterion of significance described in the methods was applied in the two-way ANOVA test. The results of this analysis (Tab. 1) revealed that the values of the ecological descriptors were more strongly affected by the factor “zone” than to “traffic”, except for those related to the presence of the NIS, since the ACI was influenced by the intersection of the two factors and the RCI by “traffic” and the intersection. However, Tukey’s post hoc test revealed that, whereas the prediction of the NIS being more abundant in the larger marina was fulfilled in the western zone, the situation was the opposite in the eastern zone. Thus, it was impossible to conclude that heavier boat traffic always corresponds to higher diversity and abundance of NIS. DISCUSSION The interpretation of drivers influencing benthic communities in port environments, even those that are less complex, is troublesome because of the complex array of human activities associated with them (Tempesti et al. 2022). However, their important role as arriving points for NIS makes them a major, if not the most important, kind of habitat in terms of understanding the mechanisms underlying their entrance and settlement. In this way, recreational boating has received much less attention than commercial shipping has, although several studies have pointed out in recent years a relevant role in the arrival of NIS, especially in their dispersion at a regional scale (Azmi et al. 2015). In terms of NIS abundance, the results obtained as a whole are similar to the 33% RCI reported by Canning-Clodeet al . (2013) and the 44.7% RCI reported by Gestoso et al . (2017) and are clearly higher than the 16% RCI reported by Diemet al . (2023). This highlights the strong exposure of the study area to the arrival of the NIS and the important role of marinas as hotspots for colonization by these species (Tempesti et al. 2022). However, although previous studies reported that an increase in boat traffic implies a greater number and abundance of NIS and detected a positive correlation between two factors (Mooreet al. 2014; Soutoet al. 2016; Ramalhosaet al. 2017), the results of our research did not support this assumption. In the western zone, where the distance between the selected marinas was greater, communities of sessile organisms clearly differed, as shown in the nMDS plot. The diversity indices (SpR, 1-D, H’ and Mg) were relatively high, and the presence of (RCI and ACI) was relatively low in marina with light traffic, as predicted in our initial hypothesis, although the difference was significant only for NIS coverage. In contrast, it was impossible to distinguish different sessile communities between marinas with heavy and light traffic, as the samples were interspersed in the nMDS plot. With respect to differences in the ecological descriptors and the diversity and abundance of NIS, the hypothesis was not supported in this zone, where the results were opposite those expected. The most negative situation (lowest values for biodiversity and greater presence of NIS) was found at the smallest marina. To understand these results, it is important to consider that the two marinas in the eastern zone are located close to one another, so the situation suggests that, irrespective of the greater marina being the actual entrance point of the NIS, dispersal occurred very quickly and strongly. This model corresponds well with the hub and spoke model (Azmi et al. 2015; Iacarella et al. 2020), in which ports with higher levels of traffic are the first receptors of NIS that subsequently scatter regionally to smaller localities by means of secondary maritime traffic. Thus, the communities of sessile NIS quickly merge if the smaller ports are located in proximity to larger ones, so the distribution of these species seems more strongly influenced by geographical factors related to port distribution than by the size or type of use of each marina (López-Legentil et al. 2015; Tempesti et al. 2022). This fact would explain the greater difference between the marinas in the western study zone and the clear similarity of those in the eastern zone. The existence of a shipyard specialized in building oceanic vessels intended for boreal waters next to Figueras might also influence the abundance of alien species in the locality, although no identified species are typical of high latitudes. Similarly, the intense aquaculture activity of the invasive Japanese oyster M. gigas throughout the whole Eo estuary, especially in the proximity of Figueras, might also be related to important biocontamination by NIS, since this type of activity has frequently been reported to involve the introduction of alien species (Bishop et al. 2015). In fact, the effect of aquaculture as a major pathway for these species has been specifically reported for recreational ports by Ulman et al. (2019). The abundance of NIS in this locality was greater than that reported in a previous study (Miralles et al. 2016), and their diversity increased with the appearance of A. modestus , B. improvisus , B. trigonus , D. vexillium and T. inopinata . The increase in the abundance and diversity of NISNISs in several localities in northern Spain has already been confirmed in other investigations (Miralles et al. 2021). Some authors have reported that freshwater inputs are adverse for the settlement of sessile species, both native (Fernández-Gutiérrez et al. 2025) and alien (Foster et al. 2016; Ulman et al. 2019). Three of the studied localities are located near the mouths of their estuaries, so the influence of freshwater from the associated riverine systems was irrelevant. Only in Viveiro, the staff of the marine area reported that a superficial layer of freshwater occurred during the rainy season, which caused the upper intertidal zone to nearly lack sessile fauna during the campaign to install the sampling devices. However, they were anchored deeper, where more dense saltwater accumulated, and the colonization process took place during the dry season, so this negative effect was not observed. Eleven NIS were found in the samples, and the bryozoan W. subatra , the cirriped B. trigonus and the tunicate D. vexillum were the most abundant in the area. Watersipora subatra , usually misidentified in the region as W. subtruncata (Vieira et al. 2014), is a fouling bryozoan that recently colonized the European Atlantic coasts; it has already been observed in several localities in the eastern half of the northern Spanish coast, mainly thriving on artificial structures (Reverter-Gil and Souto 2019). This species outcompetes the native ones because of its ability to quickly occupy the available surface and to grow over other organisms (Pageet al. 2019). This allowed it to occur at commercial and recreational ports in Europe and eastern North America (Viola et al. 2018), where it displaces native species and causes loss of biodiversity. Moreover, some studies have reported the association of W. subrata with the Japanese oyster M. gigas (Fernández-Rodríguez et al. 2022), which explains the high coverage of this species in the eastern zone of study, where this mollusk is subjected to intense aquaculture. Balanus trigonus is native to the Indo-Pacific but is frequent on both sides of the Northern Atlantic and is expanding into the Mediterranean (Carmona-Rodríguezet al. 2024). This species can settle on a wide variety of substrates and surfaces, such as ship hulls and port artificial structures, with the only limitation being low winter temperatures (Chapman et al. 2013). To date, there are no serious environmental issues related to this species, but its high dispersal and colonization capacity make it a potentially harmful invasive species (Piló et al. 2021). Finally, of the three species, the colonial ascidian D. vexillum is the most noxious because of its wide global distribution and the ecological and economic problems it causes (Legrand et al. 2024). Once established, it forms encrusting colonies that cover all kinds of benthic substrata and displaces all the native species, so any naturally heterogeneous surface becomes monospecific (Long and Grosholz 2015). The expansión of W. subrata has been linked with navigation and with the culture of M. gigas , both of which have the same biogeographical origin (Prentice et al. 2024). Our results highlight the complexity of the drivers influencing the colonization of recreational ports by NIS, in which an array of different environmental, geographical and historical factors act in combination, in addition to the translocation of individuals. The development of future studies on the role and weight of the several involved drivers and their interactions is of paramount importance to implement the best procedures to limit and even avoid the increasing presence of NIS on our coasts. With respect to the management of sessile NIS, our results suggest that, in addition to the periodical control of hulls and ballast of ships reaching larger ports and arriving from distant locations, the traffic of small boats moving among little marinas also needs to be monitored. Declarations Funding declaration This study was funded entirely by the Department of Biology of the Universidad Autónoma de Madrid within the framework of its Research Grant Program (BIOUAM 02-2023). Ethics and Consent to Participate Not applicable References Álvarez E, Pérez B, Rodríguez I (1997) A description of the tides in the Eastern North Atlantic. Prog Oceanog 40:217–244. https://doi.org/10.1016/S0079-6611(98)00003-2 Álvarez-Salgado XA, Gago J, Miguez BM, Gilcoto M, Pérez FF (2000) Surface waters of the NW Iberian Margin: upwelling on the shelf versus outwelling of upwelled waters from the Rías Baixas. Estuar Coast Shelf Sci 51:821–837. https://doi.org/10.1006/ecss.2000.0714 Álvarez-Salgado XA, Beloso S, Joint I, Nogueira E, Chou L, Pérez FF, Groom SB, Cabanas JM, Rees AP, Elskens M (2002) New production of the NW Iberian shelf during the upwelling season over the period 1982-1992. 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Mar Pollut Bull 191:114893.https://doi.org/10.1016/j.marpolbul.2023.114893 Table Table 1. Results of the two-way ANOVA test for the ecological descriptors; the bold type indicates significant relationships. test results corresponding to a normal distribution are indicated in italics. Abbreviations: 1-D = Simpson index; ACI = Abundance Contamination Index; df = degrees of freedom; H’ = Shannon index; Mg = Margalef index; MS = mean square; n.s. = non-significant; RCI = Richness Contamination Index; SpR = number of species Source df SpR 1-D H' MS F MS F MS F Traffic 1 0.117 0.018 0.011 1.300 0.113 1.473 Zone 1 191.671 29.41 0.254 29.94 4.168 54.12 Traffic x Zone 1 0.942 8.341 . 0.001 0.173 0.111 1.446 . Error 41 6.518 0.008 0.077 Shapiro-Wilk test 0.943 0.838 0.965 Source df Mg RCI ACI MS F MS F MS F Traffic 1 0.085 0.154 . 446.256 10.700 1638.950 6.507 Zone 1 15.662 28.500 275.508 6.608 . 16.802 0.067 Traffic x Zone 1 1.550 2.820 1143.200 27.420 6081.920 24.140 Error 41 0.555 41.691 251.894 Shapiro-Wilk test 0.951 0.973 . 0.946 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7510059","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":526356580,"identity":"7b989571-c14d-4be6-9f8d-4739794e4f7d","order_by":0,"name":"Alejandra GARCÍA-MADRID","email":"","orcid":"","institution":"Autonomous University of Madrid","correspondingAuthor":false,"prefix":"","firstName":"Alejandra","middleName":"","lastName":"GARCÍA-MADRID","suffix":""},{"id":526356581,"identity":"d54ab8ee-6c7a-4861-a4bf-e8cc72238b4a","order_by":1,"name":"Silvia CUESTA","email":"","orcid":"","institution":"Consultores \u0026 Ingenieros Albio Ltd","correspondingAuthor":false,"prefix":"","firstName":"Silvia","middleName":"","lastName":"CUESTA","suffix":""},{"id":526356582,"identity":"4cc1b681-2102-4c7a-a63c-011b5eeda05a","order_by":2,"name":"Eduardo LÓPEZ","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3UlEQVRIiWNgGAWjYFCCBCBmY2DgA3MqSNHCBuacIVkLYxsRGvjZcww/V5TZMLCx9x58+HPeYXndBubDH/Bpkex5Yyx55lwaAxvPuWQDyW2HDbcdYEuTwKfF4EaOgWRj22EGNokcMwnDbYcZtx3gMcPrMPsbOcY/oVrMfyTOOWy/7QD/Z7wOMwAaDreF4WDD4USgLQx4HSZx5lmZZcO5NB6QXyQbjqUnbzvMZoZXC3978uabDWU2cvzAEPv4o8badtvx5sd4HQYDPGAEBszEqIfrGgWjYBSMglGADQAAMT5GdtqbuW8AAAAASUVORK5CYII=","orcid":"","institution":"Autonomous University of Madrid","correspondingAuthor":true,"prefix":"","firstName":"Eduardo","middleName":"","lastName":"LÓPEZ","suffix":""}],"badges":[],"createdAt":"2025-09-01 15:38:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7510059/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7510059/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":93703945,"identity":"4fe7fe48-5a07-4c41-99f1-aa8f0cf1f522","added_by":"auto","created_at":"2025-10-16 16:04:14","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":21284170,"visible":true,"origin":"","legend":"\u003cp\u003eMap of the study area. Orthophotos obtained from PNOA ceded © Instituto Geográfico Nacional, Spain. Scale bar for details of marinas = 150 m\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-7510059/v1/e22914451e43c3b3f6c29466.png"},{"id":93703946,"identity":"ad67febc-c670-40f4-a601-87af98b45466","added_by":"auto","created_at":"2025-10-16 16:04:14","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":38882444,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA.\u003c/strong\u003e Construction plan of a non-invasive sampler. \u003cstrong\u003eB. \u003c/strong\u003eAssembled sampling device before installation. \u003cstrong\u003eC.\u003c/strong\u003e The same device after removal. \u003cstrong\u003eD.\u003c/strong\u003eDetails of the plates dismantled before fixation.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-7510059/v1/ec94492d1301af71bd170c95.png"},{"id":93703942,"identity":"c12dc5b4-36f8-4862-b140-0cba7e74a76a","added_by":"auto","created_at":"2025-10-16 16:04:13","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":5920214,"visible":true,"origin":"","legend":"\u003cp\u003eNon-metric Multidimensional Scaling (nMDS) ordination plot based on Bray-Curti similarities calculated from species composition for sessile species communities across sampling stations. Abbreviations: FIG = Figueras; RIB = Ribadeo; VIC = Vicedo; VIV = Viveiro.\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-7510059/v1/a4873d81f300ae5b4718b7e2.png"},{"id":93703943,"identity":"006c27e6-6f07-4aea-a63b-c86da0c51aba","added_by":"auto","created_at":"2025-10-16 16:04:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":5777432,"visible":true,"origin":"","legend":"\u003cp\u003eEcological descriptors; box-and-whisker plots for values from each marina. The whiskers represent the minimal and maximal values without outliers, the outer edges of the boxes represent the 25th and 75th percentiles, and the horizontal line within the boxes represents the median. The vertical axis units are as described in the methods section. Abbreviations: 1-D = Simpson index; ACI = Abundance Contamination Index; FIG = Figueras; H’ = Shannon index; Mg = Margalef index; RCI = Richness Contamination Index; RIB = Ribadeo; SpR = number of species; VIC = Vicedo; VIV = Viveiro\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-7510059/v1/d8bf0482e3b8491c2daa30a3.png"},{"id":93704892,"identity":"af701684-8631-4a63-ac48-77b5682bb02e","added_by":"auto","created_at":"2025-10-16 16:12:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":66659650,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7510059/v1/36143534-3c16-46ab-a150-72076b4fec38.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Role of the type of boat traffic on the presence of sessile non-indigenous species (NIS) in marinas of southwestern Bay of Biscay","fulltext":[{"header":" INTRODUCTION","content":"\u003cp\u003eIn recent years, non-indigenous species (NIS thereafter), which can possibly become invasive, has turned a major concern in marine ecosystems. They are involved in 33% of the most recent extinction events\u0026nbsp;(Zamora-Marínet al. 2023) and are responsible for annual expenses of over 26.8 billion dollars (Cano-Barbacil et al\u003cem\u003e.\u003c/em\u003e 2023). This issue is strongly related to human activities and practices in the sea that help the introduction and dispersal of such species (Png-González et al. 2023). Despite this, NIS continue expanding their areas to the point of being a great threat to autochthonous species survival and causing relevant impacts on local economies. Thus, control and supervision of NIS before their arrival through the several available methods is strongly needed, as once they are established, they are nearly impossible to eradicate (Cano-Barbacilet al. 2023). The only known successful case of eradication occurred because of early detection and quick response, since once identified the presence of NIS, the only effective treatment is hard population control (Giakoumiet al. 2019; Fernández-Gutiérrezet al. 2025).\u003c/p\u003e\n\u003cp\u003eNIS are favored by several intentional and unintentional mechanisms to arrive at new habitats. The \u0026nbsp;most common pathway, which causes 58% of new arrivals, is shipping because allochthonous species can settle on ship hulls or travel mixed with ballast water, where they stay alive until being freed in new locations (Kelleret al\u003cem\u003e.\u003c/em\u003e 2011). Larger floating structures drifting in the sea, such as plastic masses, gosht nets or buoys, act as temporal habitats for encrusting sessile NIS, which can be transported to faraway locations (Fernández et al. 2022).\u0026nbsp;On the other hand, aquaculture activities are a risk factor since some species can accidentally escape from facilities where they are raised and establish in nature (Geburzi \u0026amp; McCarthy 2018). Moreover, if they are not carefully disinfected, introduced specimens can act as vectors for parasites and pathogens (Kelleret al\u003cem\u003e.\u003c/em\u003e 2011), and even as a translocation mechanism or a high number of small-sized accompanying NIS (Piló et al. 2021). Intentionally introduced alien species of aquacultural interest are even more prone to establish because the species selected usually have similar ecological needs to those of their native counterparts but are more resilient and have greater population growth rates (Grosholz et al. 2015). The last factor is the introduction of species related to pet trade that accidentally escape or are intentionally released in native waterbodies (Holmberget al. 2015).\u003c/p\u003e\n\u003cp\u003eMany of the arriving NIS eventually become established. Those achieving it share several traits that explain their success, especially those related to their plasticity in behavior, physiology and several strategies (Devin \u0026amp; Beisel 2007). Most of these strategies are related to reproductive biology and are associated with short durations of sexual maturation, fast growth rates, and, in most cases, long planktonic stages (Geburzi \u0026amp; McCarthy 2018). Another frequent trait is their environmental plasticity, as they need to adapt to the changing conditions of the environment and differ from their native habitat in terms of salinity and/or temperature (Keller et al. 2011).\u003c/p\u003e\n\u003cp\u003eAlthough only a small number of NIS that are introduced into new habitats are effectively established and even smaller amounts can achieve high population densities, the consequences are extremely harmful and have great ecological impacts on aquatic ecosystems (Gallardo et al. 2016). These include a decrease in the richness and abundance of native species due to predation or competition for resources by alien species, as well as the alteration of invaded habitats. On the other hand, it has been demonstrated that the larvae of many benthic species tend to avoid settling near dominant species, such as invasive NIS NISs, so the reproductive patterns of native species are altered (Rius et al. 2009). As the most dramatic consequence of these interactions, the extinction of native species can eventually occur (Boudouresque \u0026amp; Verlaque 2005; Cano-Barbacil et al. 2023). As indirect effects, alterations can be caused in the food webs of colonized ecosystems and in the behavior of predators (Rius et al. 2009). Similarly, ecosystems can also undergo physicochemical changes, such as increases in turbidity, nitrogen concentration, and organic matter, which also affect native species (Gallardo et al. 2016). Finally, the impacts of NIS not only affect natural systems but can also act as vectors of foreign pathogens and cause health problems, both to other marine species and to humans, and cause significant damage to the economy (Muñoz-Mas et al. 2021).\u003c/p\u003e\n\u003cp\u003eThe location of the Iberian Peninsula is extremely important from a biogeographical point of view since it connects Europe with Africa and the Mediterranean Sea with the Atlantic Ocean but also plays a capital role in maritime transportation. For this reason, it is a common gate for NIS, accounting for 182 introduced species in the Bay of Biscay since 1970 (Png-González et al. 2023). To address this growing issue, new laws have been enacted, such as law 42/2007 about Natural Heritage and Biodiversity, and several checklists on NIS have been performed, including the Spanish Checklist on Invasive Alien Species; however, the cost between 1997 and 2020 of the management of these species was calculated to be approximately 232.54 million euros (Angulo et al\u003cem\u003e.\u003c/em\u003e 2021). Similarly, control of marine NIS is treated in European laws, such as the Marine Strategy Framework Directive (MSFD) (2008/56/EC), which seeks to assess the ecological status of the coasts of member states through 11 qualitative descriptors, one of which is the number of artificially introduced species (Png-González et al. 2023).\u003c/p\u003e\n\u003cp\u003eAs mentioned above, sea navigation, be it commercial or recreational, is a major pathway for NIS introduction. They travel from one port to another fouling ship hulls or mixed with ballast water and establish themselves in new localities, taking advantage of artificial structures, the number of which has increased in recent decades\u0026nbsp;(Castro et al. 2022). Unlike ship hulls, these structures are usually not treated with antifouling chemicals to prevent colonization by sessile organisms, so they usually harbor a relatively high abundance and species richness of encrusting animals (Carmona-Rodríguez et al. 2024). Compared with native species, NIS have greater chances of successful establishment in these structures, as the former are usually not well adapted to such unstable and hostile substrates (Ferrario et al. 2017; Geburzi \u0026amp; McCarthy 2018). On the other hand, transitional waters between river mouths and true marine environments, where many ports are located irrespective of their size or activity, are very vulnerable because factors typical of both kinds of environments act in combination and make them easily colonizable by species capable of quickly adapting to everchanging salinity and other environmental conditions, such as NIS (Zamora-Marín et al. 2023).\u003c/p\u003e\n\u003cp\u003eAlthough poorly understood yet, the effects of recreational boating as an introduction pathway for marine NIS received considerable attention in recent years\u0026nbsp;(Ulman et al. 2019). In contrast to commercial ships, recreational boats usually stay longer at ports, providing more time for the establishment of translocated NIS, and can anchor in some marine protected areas that are forbidden for commercial vessels, favoring their colonization by alien species (Martínez-Laiz et al. 2019). Recreational boats are usually much slower than commercial boats but occasionally travel long distances and are very suitable vectors for NIS, an effect confirmed by several researchers. Thus, Clarke Murray et al. (2011) reported that 26% of the examined boats transported fouling NIS, and Martínez-Laiz et al. (2019) reported 56%. With respect to the Spanish case, it is important to emphasize that recreational navigation has increased heavily since 1960, causing an exponential growth in the number of marinas, from 131 in 1976 to 375 in 2015 (Cerchiello 2018), which highlights the importance of this challenge.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eGoals and hypotheses\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe goal of this research is to assess the influence of the type of recreational boat traffic on the settlement of sessile NIS in several marinas of southwestern Bay of Biscay. The main hypothesis is that in marinas that have heavier traffic and harbor larger boats capable of longer trips, a more diverse and abundant community of sessile NIS should be found because these ships act in long-distance transport for these species; consequently, overall biodiversity will be reduced due to the loss of native species. In contrast, marinas with lighter traffic and smaller boats that are unable to travel far away, should present the opposite situation, with a lower diversity and abundance of NIS and higher overall biodiversity.\u003c/p\u003e"},{"header":"MATERIAL AND METHODS","content":"\u003cp\u003e\u003cstrong\u003eStudy area\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the studied locations are part of the Galician Rias system, a set of coastal embayments placed along the NW sector of Spain that usually function as partially mixed estuaries from a dynamic point of view (Álvarez-Salgado et al. 2000). Most of the Rias are located near the northern boundary of the East Atlantic Upwelling System, and experience wind-driven local upwelling events from March–April to September–October, whereas the prevailing winds promote downwelling processes throughout the rest of the year. In these events, Eastern North Atlantic Central Water (ENACW) masses influence the outer part of estuaries (Álvarez-Salgado et al. 2002). However, in smaller rias, such as those on the northern coast of Galicia, other drivers are responsible for estuary dynamics. The tide is the most energetic force, being semidiurnal and with a tidal range between 4 m in spring tides and 2 m in neap tides all over the northwest corner of Spain (Álvarez et al. 1997). In the rias associated with larger watercourses, river discharge is also an important force in the residual inner circulation\u0026nbsp;(Piedracoba et al. 2005).\u003c/p\u003e\n\u003cp\u003eFor replicability, the study was conducted in two nearby zones in southwestern Bay of Biscay (Fig. 1). In each one, we selected a marina with larger boats, which could travel longer distances, and another marina with smaller boats, which usually stayed near the port. In the western zone, the marinas were Viveiro (43° 40’ 04” N - 7° 35’ 42” W), with 307 piers for larger boats, and Vicedo (43° 44’ 18” N - 7° 40’ 18” W), with 136 piers for smaller boats. Each marina is located in a different ria, and they are approximately 10.3 km away. The Ria de Viveiro is formed by a medium-sized river, the Landro River, whereas Ria del Barquero, where the marina of Vicedo lies, formed in the estuary of a much smaller stream, the Sor River (Lorenzoet al. 2003). The two marinas of the eastern zone are located in the same ria, which is formed by the Eo, one of the most abundant rivers in NW Spain (Piedracobaet al. 2005). In this case, the marinas of Ribadeo (43° 32’ 24” N - 7° 02’ 11” W), with 600 piers for larger boats, and Figueras (43° 32’ 13” N - 7° 01’ 25” W), with 146 piers for very small recreational boats, were selected; the two marinas are approximately 1.1 km away. Despite being included in the Nature 2000 Network for its great importance for birds, the Eo estuary is heavily industrialized, and a busy commercial port specializing in timber traffic, a mid-sized shipyard devoted to oceanic vessels, and numerous facilities for the NIS Japanese oyster \u003cem\u003eMagallana gigas\u0026nbsp;\u003c/em\u003e(Thunberg, 1793) aquaculture can be found.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSampling methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe sampling was based on the use of non-invasive passive devices that favor the settlement of sessile organisms but are easy to pick up. These devices (Fig. 2) were made of three horizontal PVC plates of 20x20 cm, plus a base of 30x30 cm made of the same material, all of which were joined by a core metal rod; the plates were separated from each other by a piece of PVC pipe 10 cm long that prevented them from collapsing (Fig. 2A, B). Each plate ported an identification label where the number of device and the level where it was located (A, B or C depending on its distance from the base). The sampling device stayed fixed to the bottom by means of a concrete mooring and could be recovered owing to a small buoy tied to a shackle in the core rod. Four random sites were selected at each marina, providing 16 sampling points, where the devices were placed for nearly four months (from 5–6 June to 18–19 October 2024), allowing the organisms enough time to colonize the PVC plates (Diem et al. 2023). Considering the size of the devices, the depth was greater than 1 m at all the sites, even with the most extreme low tides. Similar passive devices have been used in previous studies and have been shown to be most effective in terms of species richness and coverage (Tamburiniet al. 2021).\u003c/p\u003e\n\u003cp\u003eAfter that time, the devices with the settled sessile organisms (Fig. 2C) were collected, and each plate was separated and stored in a ZIP plastic bag with 70% ethanol for adequate preservation until arriving at the laboratory.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFor species identification, only the lower surface of each PVC plate was used, as most target organisms are sciophilous and the upper surface tended to be clogged with sediment. Identification was conducted by examining the entire plates through a binocular microscope, in most cases at the species level (Annex 1), via identification guides (Reverter-Gilet al. 2016; Hayward and Ryland 2017; Trigoet al. 2018; Cepedaet al. 2022) and regional taxonomic publications (Fernández-Rodríguez et al. 2022; López-Alonso et al. 2022). Assignation to the NIS category was based on the checklist by Png-González et al. (2023).\u003c/p\u003e\n\u003cp\u003eBased on the identifications, an abundance (expressed as a percentage of cover per plate) matrix was created considering each plate as a sample. To graphically analyze the similarity in faunal composition between sessile communities inhabiting each marina, a non-metric multidimensional scaling (nMDS) plot was generated by applying the inverse Bray‒Curtis index calculated from the abundance matrix.\u003c/p\u003e\n\u003cp\u003eTo measure biodiversity, several ecological descriptors were computed from the abundance data: the number of species (SpR) and the Simpson (1-D), Shannon (H’) and Margalef (Mg) indices. The amount of NIS was described through the Richness Contamination Index (RCI), defined as the percentage of the NIS on the total diversity, and the Abundance Contamination Index (ACI), defined as the ratio of coverage of the NIS to total coverage expressed as a percentage (Fernández-Gutiérrez et al. 2025). To analyze the significance of the differences between the values of the descriptors for the four studied marinas, a two-way ANOVA was conducted, using “traffic” as predictor Factor 1 (two levels: “haevy” and “light”) and “zone” as predictor Factor 2 (two levels: “western” and “eastern”); both factors are fixed and orthogonal. We previously checked whether descriptor values fit a normal distribution via the Shapiro‒Wilk test. If they did not adjust, a more restrictive than usual criterion (p \u0026lt; 0.01) was used in our design, as in previous publications (Underwood 1997;\u0026nbsp;Tamburini et al. 2021; Lekammudiyanse et al. 2024; Pradoet al. 2024). To check which pairs of marinas presented significant differences for each descriptor, Tukey’s \u003cem\u003epost hoc\u003c/em\u003e test was applied. All the analyses were performed with the statistical package PAST 4.16c (Hammer 2024).\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003eOwing to poor weather conditions, only 15 out of 16 sampling devices were recovered, resulting in a total of 45 plates. Thirty-six species of fouling sessile animals belonging to eight phyla were identified. The most abundant phylum was Bryozoa, with a mean coverage of 35.27 ± 2.16% (standard error), followed by Porifera (14.01 ± 1.26%) and Arthropoda (11.27 ± 0.79%). Among these 36 species, 11 were NIS: \u003cem\u003eAustrominius modestus\u0026nbsp;\u003c/em\u003e(Darwin, 1854); \u003cem\u003eBalanus improvisus\u003c/em\u003e Darwin, 1854; \u003cem\u003eBalanus trigonus\u003c/em\u003e Darwin, 1854; \u003cem\u003eBotrylloides violaceus\u003c/em\u003e Oka, 1927; \u003cem\u003eBugula neritina\u0026nbsp;\u003c/em\u003e(Linnaeus, 1758); \u003cem\u003eClavelina lepadiformis\u003c/em\u003e (Müller, 1776); \u003cem\u003eCorella eumyota\u003c/em\u003e Traustedt, 1882; \u003cem\u003eDidemnum vexillum\u003c/em\u003e Kott, 2002; \u003cem\u003eMagallana gigas\u003c/em\u003e (Thunberg, 1793); \u003cem\u003eTricellaria inopinata\u003c/em\u003e D'Hondt and Occhipinti Ambrogi, 1985; and\u003cem\u003e\u0026nbsp;Watersipora subatra\u003c/em\u003e (Ortmann, 1890). The most abundant species (mean coverage \u0026gt; 5%) were \u003cem\u003eW. subatra,\u003c/em\u003e with a mean coverage of 22.55 ± 3.24%; \u003cem\u003eDercitus bucklandi\u003c/em\u003e (Bowerbank, 1858), with 13.06 ± 2.77%; \u003cem\u003eB. trigonus\u003c/em\u003e, with 7.82 ±\u0026nbsp;1.56%; \u003cem\u003eD. vexillum\u003c/em\u003e, with 6.55 ± 1.63%; and \u003cem\u003eSpirorbis\u0026nbsp;\u003c/em\u003e\u003cem\u003espirorbis\u003c/em\u003e (Linnaeus, 1758), with 6.42 ± 1.04%. Notably, three of them are NIS.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe nMDS plot (Fig. 3) shows the results of the comparison of the faunal compositions of the samples. In this figure, a first segregation by zones can be observed, with samples from the western zone grouped in the left section of the plot and those from the eastern zone to the right. In turn, a second segregation by marinas is noticeable among the eastern zone samples, with samples from Vicedo and Viveiro clearly separated. However, the samples from the two marinas from the eastern zone (Figueras and Ribadeo) appear interspersed. Thus, it cannot be inferred from the results that in the region distinct communities of sessile organisms inhabit large and small marinas on the basis of the type of boat traffic.\u003c/p\u003e\n\u003cp\u003eWith respect to the values of the ecological descriptors (Fig. 4), although Figueras was the subject of light boat traffic, the values were the worst, with the lowest values for species number and the Simpson, Margalef and Shannon indices, as well as the highest value for RCI (proportion of NIS species); the highest value for ACI (relative abundance of NIS) was found in Viveiro within the same estuary. In general, the NIS were very diverse across the region, with a mean RCI value of 45.44 ± 1.35% in the samples. Similarly, coverage by the NIS was very high, with a mean ACI value of 61.13 ± 3.02% and above 50% across all the marinas except Vicedo, indicating a high degree of colonization. After the Shapiro‒Wilk test was applied, the values of the Shannon and Margalef indices, as well as the RCI, fit a normal distribution, whereas the remaining descriptors (number of species, Simpson index and ACI) did not, so the more restrictive criterion of significance described in the methods was applied in the two-way ANOVA test. The results of this analysis (Tab. 1) revealed that the values of the ecological descriptors were more strongly affected by the factor “zone” than to “traffic”, except for those related to the presence of the NIS, since the ACI was influenced by the intersection of the two factors and the RCI by “traffic” and the intersection. However, Tukey’s \u003cem\u003epost\u003c/em\u003e\u003cem\u003e\u0026nbsp;hoc\u003c/em\u003e test revealed that, whereas the prediction of the NIS being more abundant in the larger marina was fulfilled in the western zone, the situation was the opposite in the eastern zone. Thus, it was impossible to conclude that heavier boat traffic always corresponds to higher diversity and abundance of NIS.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe interpretation of drivers influencing benthic communities in port environments, even those that are less complex, is troublesome because of the complex array of human activities associated with them (Tempesti et al. 2022). However, their important role as arriving points for NIS makes them a major, if not the most important, kind of habitat in terms of understanding the mechanisms underlying their entrance and settlement. In this way, recreational boating has received much less attention than commercial shipping has, although several studies have pointed out in recent years a relevant role in the arrival of NIS, especially in their dispersion at a regional scale (Azmi et al. 2015).\u003c/p\u003e\n\u003cp\u003eIn terms of NIS abundance, the results obtained as a whole are similar to the 33% RCI reported by Canning-Clodeet al\u003cem\u003e.\u003c/em\u003e (2013) and the 44.7% RCI reported by Gestoso et al\u003cem\u003e.\u003c/em\u003e (2017) and are clearly higher than the 16% RCI reported by Diemet al\u003cem\u003e.\u003c/em\u003e (2023). This highlights the strong exposure of the study area to the arrival of the NIS and the important role of marinas as hotspots for colonization by these species (Tempesti et al. 2022). However, although previous studies reported that an increase in boat traffic implies a greater number and abundance of NIS and detected a positive correlation between two factors\u0026nbsp;(Mooreet al. 2014; Soutoet al. 2016; Ramalhosaet al. 2017), the results of our research\u0026nbsp;did not support this assumption. In the western zone, where the distance between the selected marinas was greater, communities of sessile organisms clearly differed, as shown in the nMDS plot. The diversity indices (SpR, 1-D, H’ and Mg) were relatively high, and the presence of (RCI and ACI) was relatively low in marina with light traffic, as predicted in our initial hypothesis, although the difference was significant only for NIS coverage. In contrast, it was impossible to distinguish different sessile communities between marinas with heavy and light traffic, as the samples were interspersed in the nMDS plot. With respect to differences in the ecological descriptors and the diversity and abundance of NIS, the hypothesis was not supported in this zone, where the results were opposite those expected. The most negative situation (lowest values for biodiversity and greater presence of NIS) was found at the smallest marina. To understand these results, it is important to consider that the two marinas in the eastern zone are located close to one another, so the situation suggests that, irrespective of the greater marina being the actual entrance point of the NIS, dispersal occurred very quickly and strongly. This model corresponds well with the hub and spoke model (Azmi et al. 2015; Iacarella et al. 2020), in which ports with higher levels of traffic are the first receptors of NIS that subsequently scatter regionally to smaller localities by means of secondary maritime traffic. Thus, the communities of sessile NIS quickly merge if the smaller ports are located in proximity to larger ones, so the distribution of these species seems more strongly influenced by geographical factors related to port distribution than by the size or type of use of each marina (López-Legentil et al. 2015; Tempesti et al. 2022). This fact would explain the greater difference between the marinas in the western study zone and the clear similarity of those in the eastern zone.\u003c/p\u003e\n\u003cp\u003eThe existence of a shipyard specialized in building oceanic vessels intended for boreal waters next to Figueras might also influence the abundance of alien species in the locality, although no identified species are typical of high latitudes. Similarly, the intense aquaculture activity of the invasive Japanese oyster \u003cem\u003eM. gigas\u003c/em\u003e throughout the whole Eo estuary, especially in the proximity of Figueras, might also be related to important biocontamination by NIS, since this type of activity has frequently been reported to involve the introduction of alien species (Bishop et al. 2015). In fact, the effect of aquaculture as a major pathway for these species has been specifically reported for recreational ports by Ulman et al. (2019). The abundance of NIS in this locality was greater than that reported in a previous study (Miralles et al. 2016), and their diversity increased with the appearance of \u003cem\u003eA. modestus\u003c/em\u003e, \u003cem\u003eB. improvisus\u003c/em\u003e, \u003cem\u003eB. trigonus\u003c/em\u003e, \u003cem\u003eD. vexillium\u003c/em\u003e and \u003cem\u003eT. inopinata\u003c/em\u003e. The increase in the abundance and diversity of NISNISs in several localities in northern Spain has already been confirmed in other investigations (Miralles et al. 2021).\u003c/p\u003e\n\u003cp\u003eSome authors have reported that freshwater inputs are adverse for the settlement of sessile species, both native (Fernández-Gutiérrez et al. 2025) and alien (Foster et al. 2016; Ulman et al. 2019). Three of the studied localities are located near the mouths of their estuaries, so the influence of freshwater from the associated riverine systems was irrelevant. Only in Viveiro, the staff of the marine area reported that a superficial layer of freshwater occurred during the rainy season, which caused the upper intertidal zone to nearly lack sessile fauna during the campaign to install the sampling devices. However, they were anchored deeper, where more dense saltwater accumulated, and the colonization process took place during the dry season, so this negative effect was not observed.\u003c/p\u003e\n\u003cp\u003eEleven NIS were found in the samples, and the bryozoan \u003cem\u003eW. subatra\u003c/em\u003e, the cirriped \u003cem\u003eB. trigonus\u003c/em\u003e and the tunicate \u003cem\u003eD. vexillum\u003c/em\u003e were the most abundant in the area. \u003cem\u003eWatersipora subatra\u003c/em\u003e, usually misidentified in the region as \u003cem\u003eW. subtruncata\u003c/em\u003e (Vieira et al. 2014), is a fouling bryozoan that recently colonized the European Atlantic coasts; it has already been observed in several localities in the eastern half of the northern Spanish coast, mainly thriving on artificial structures (Reverter-Gil and Souto 2019). This species outcompetes the native ones because of its ability to quickly occupy the available surface and to grow over other organisms (Pageet al. 2019). This allowed it to occur at commercial and recreational ports in Europe and eastern North America (Viola et al. 2018), where it displaces native species and causes loss of biodiversity. Moreover, some studies have reported the association of \u003cem\u003eW. subrata\u003c/em\u003e with the Japanese oyster \u003cem\u003eM. gigas\u003c/em\u003e (Fernández-Rodríguez et al. 2022), which explains the high coverage of this species in the eastern zone of study, where this mollusk is subjected to intense aquaculture. \u003cem\u003eBalanus trigonus\u003c/em\u003e is native to the Indo-Pacific but is frequent on both sides of the Northern Atlantic and is expanding into the Mediterranean (Carmona-Rodríguezet al. 2024). This species can settle on a wide variety of substrates and surfaces, such as ship hulls and port artificial structures, with the only limitation being low winter temperatures (Chapman et al. 2013). To date, there are no serious environmental issues related to this species, but its high dispersal and colonization capacity make it a potentially harmful invasive species (Piló et al. 2021). Finally, of the three species, the colonial ascidian \u003cem\u003eD. vexillum\u003c/em\u003e is the most noxious because of its wide global distribution and the ecological and economic problems it causes (Legrand et al. 2024). Once established, it forms encrusting colonies that cover all kinds of benthic substrata and displaces all the native species, so any naturally heterogeneous surface becomes monospecific (Long and Grosholz 2015). The expansión of \u003cem\u003eW. subrata\u003c/em\u003e has been linked with navigation and with the culture of \u003cem\u003eM. gigas\u003c/em\u003e, both of which have the same biogeographical origin (Prentice et al. 2024).\u003c/p\u003e\n\u003cp\u003eOur results highlight the complexity of the drivers influencing the colonization of recreational ports by NIS, in which an array of different environmental, geographical and historical factors act in combination, in addition to the translocation of individuals. The development of future studies on the role and weight of the several involved drivers and their interactions is of paramount importance to implement the best procedures to limit and even avoid the increasing presence of NIS on our coasts. With respect to the management of sessile NIS, our results suggest that, in addition to the periodical control of hulls and ballast of ships reaching larger ports and arriving from distant locations, the traffic of small boats moving among little marinas also needs to be monitored.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded entirely by the Department of Biology of the Universidad Autónoma de Madrid within the framework of its Research Grant Program (BIOUAM 02-2023).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics and Consent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003e\u0026Aacute;lvarez E, P\u0026eacute;rez B, Rodr\u0026iacute;guez I (1997) A description of the tides in the Eastern North Atlantic. 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Zootaxa 3857:151\u0026ndash;182. https://doi.org/10.11646/zootaxa.3857.2.1\u003c/li\u003e\n\u003cli\u003eViola SM, Page HM, Zaleski SF, Miller RJ, Doheny B, Dugan JE, Schroeder DM, Schroeter SC (2018) Anthropogenic disturbance facilitates a non-native species on offshore oil platforms. J Appl Ecol 55:1583\u0026ndash;1593. https://doi.org/10.1111/1365-2664.13104\u003c/li\u003e\n\u003cli\u003eZamora-Mar\u0026iacute;n JM, Herrero-Reyes AA, Ruiz-Navarro A, Oliva-Paterna FJ (2023) Non-indigenous aquatic fauna in transitional waters from the Spanish Mediterranean coast: A comprehensive assessment. Mar Pollut Bull 191:114893.https://doi.org/10.1016/j.marpolbul.2023.114893\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table","content":"\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Results of the two-way ANOVA test for the ecological descriptors; the bold type indicates significant relationships. \u0026nbsp; test results corresponding to a normal distribution are indicated in italics. Abbreviations: 1-D = Simpson index; ACI = Abundance Contamination Index; df = degrees of freedom; H\u0026rsquo; = Shannon index; Mg = Margalef index; MS = mean square; n.s. = non-significant; RCI = Richness Contamination Index; SpR = number of species\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"632\" class=\"fr-table-selection-hover\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSource\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e\u003cstrong\u003edf\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSpR\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1-D\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eH\u0026apos;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eF\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eF\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eF\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTraffic\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e0.117\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e0.018\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.011\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e1.300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e0.113\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e1.473\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eZone\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e191.671\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e29.41\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.254\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e29.94\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e4.168\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e54.12\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTraffic x Zone\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e0.942\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e8.341\u003csup\u003e.\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.173\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e0.111\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e1.446\u003csup\u003e.\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eError\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e6.518\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.008\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e0.077\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eShapiro-Wilk test\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e0.943\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.838\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cem\u003e0.965\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSource\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e\u003cstrong\u003edf\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRCI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eACI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eF\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eF\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eF\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTraffic\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e0.085\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e0.154\u003csup\u003e.\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e446.256\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e10.700\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e1638.950\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e6.507\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eZone\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e15.662\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e28.500\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e275.508\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e6.608\u003csup\u003e.\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e16.802\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e0.067\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTraffic x Zone\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e1.550\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e2.820\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e1143.200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e27.420\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e6081.920\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e24.140\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eError\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\n \u003cp\u003e41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\n \u003cp\u003e0.555\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e41.691\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\n \u003cp\u003e251.894\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eShapiro-Wilk test\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 47px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 63px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cem\u003e0.951\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cem\u003e0.973\u003c/em\u003e\u003csup\u003e.\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 76px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 65px;\"\u003e\n \u003cp\u003e0.946\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"recreational navigation, non-indigenous species, Bay of Biscay, marinas","lastPublishedDoi":"10.21203/rs.3.rs-7510059/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7510059/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"The aim of this study was to analyze the influence of the type of boat traffic on the settlement of sessile non-indigenous species (NIS) in marinas from southwestern Bay of Biscay. The research was conducted in two zones, and two marinas were selected in each zone. One marina was subjected to heavy traffic, with numerous large boats capable of making long trips, and the other was subjected to light traffic, with fewer and smaller boats of limited autonomy. At each port, 12 PVC plates were installed to favor the settlement of sessile organisms. Eleven out of the 36 identified species were NIS. The analysis of the faunal composition revealed that in the area where the two marinas were closer, it was not possible to distinguish a different community in relation to the type of traffic. The analysis of the ecological descriptors considering \"traffic\" and \"zone\" as explanatory factors indicated that the differences were significant only with respect to the second factor for most of them. Only NIS diversity was related to traffic, although its behavior was opposite in the two zones. Our results indicate that the type of traffic is not enough to explain the composition of the NIS communities in the region and that they tend to merge in the short term when small and large marinas are very close.","manuscriptTitle":"Role of the type of boat traffic on the presence of sessile non-indigenous species (NIS) in marinas of southwestern Bay of Biscay","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-16 16:04:09","doi":"10.21203/rs.3.rs-7510059/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"cc0673af-2e57-4090-9708-56712fafe5f4","owner":[],"postedDate":"October 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-30T07:38:25+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-16 16:04:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7510059","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7510059","identity":"rs-7510059","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}