Habitat use of bryozoans in marinas across multiple spatial scales: the case of the Canary Islands (North-Eastern Atlantic)

Habitat use of bryozoans in marinas across multiple spatial scales: the case of the Canary Islands (North-Eastern Atlantic) Sofía Ruiz-Velasco a,* , Jos´ e M. Guerra-García a , Macarena Ros a , Carlos M. L´ opez-F´ e a , ´ Angela Izquierdo b , María Pastor-Montero a,b , Sabrina Clemente b a Laboratorio de Biología Marina, Departamento de Zoología, Facultad de Biología, Universidad de Sevilla, Avenida Reina Mercedes 6, 41012, Seville, Spain b Departamento de Biología Animal, Edafología y Geología. Universidad de La Laguna, Spain ARTICLE INFO Keywords: Bryozoa Colonization Buoys Artificial structures Non-indigenous species Ports ABSTRACT Marinas, as other maritime transport hubs, act as reservoirs for the introduction and secondary spread of nonindigenous bryozoans, which are key components of fouling communities. Although understanding habitat use patterns of these organisms could be very useful for implementing management strategies, the ecology of bryozoans in marinas has been greatly overlooked. To explore this issue, we sampled a total of 12 marinas on four islands of the Canarian archipelago (North-Eastern Atlantic). The occurrence of bryozoans (both total species and non-indigenous ones) was compared in contrasting zones within the marinas (i.e. interior and exterior) and types of floating artificial substrates (i.e. floating pontoons, buoys and ropes). We recorded a total of 23 bryozoan species, including 12 non-indigenous species. Both the type of substrate and the singularity of the marinas were the main factors driving the structure of bryozoan assemblages in marinas of the Canary Islands, while the sampled island had only a very subtle influence. Buoys showed the highest number of total and nonindigenous species of bryozoans, with some being registered only on this substrate. This finding supports buoys as a priority substrate in strategies for monitoring and detecting non-indigenous bryozoans in marinas. 1. Introduction The introduction of non-indigenous species is considered a great threat to global biodiversity (Pyˇ sek et al., 2020), having the potential to severely alter recipient ecosystems composition and functioning (Streftaris et al., 2005; Bellard et al., 2016). In marine ecosystems, these modifications are most often irreversible once species have established, with scarce evidence of successful eradications (Streftaris et al., 2005). Therefore, preventive management measures are a priority, promoting the early detection of newcomer species through monitoring programmes, horizon-scanning studies (O’Shaughnessy et al., 2023) and proper legislative support (Lehtiniemi et al., 2015). Biofouling, the growth of organisms that live attached to submerged artificial structures, is one of the major contributors to species introductions worldwide (Bailey et al., 2020). Despite its magnitude, this vector is still unregulated in areas considered as global hotspots for marine biological invasions (such as European waters) (IMO (International Maritime Organization), 2012). In fact, hull fouling of small recreational boats has been suggested as the largest unregulated vector for the introduction of non-indigenous species (Murray et al., 2011). The role of this on-growing vector is particularly crucial for secondary spread of established populations of non-indigenous species, but it can also be related to primary introductions (Ferrario et al., 2017). Recreational marinas act as recipients for travelling recreational boats, and as reservoirs for fouling species to be further spread once introduced in an area (Ferrario et al., 2017; Ulman et al., 2017). For these reasons, marinas are key points for the management of non-indigenous species, being a suitable environment for detecting these newcomer species (Lehtiniemi et al., 2015; Guerra-García et al., 2021). Furthermore, enclosed environmental pollution of marinas acts as a filter, facilitating the colonization of non-indigenous species due to their generalist and tolerant behaviour (Kenworthy et al., 2018). Indeed, fouling communities from different zones within a marina can differ greatly according to the environmental conditions they are exposed to, such as hydrodynamics, concentration of pollutants, among other variables (Kenworthy’s (2018); Oricchio et al., 2016). Artificial structures in marinas are structurally and compositionally diverse, offering a wider option of substrates (floating, fixed, horizontal, * Corresponding author. E-mail address: [email protected] (S. Ruiz-Velasco). Contents lists available at ScienceDirect Marine Environmental Research journal homepage: www.elsevier.com/locate/marenvrev https://doi.org/10.1016/j.marenvres.2025.107397 Received 14 May 2025; Received in revised form 26 June 2025; Accepted 23 July 2025 Marine Environmental Research 211 (2025) 107397 Available online 24 July 2025 0141-1136/© 2025 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/bync-nd/4.0/ ). vertical, submerged and partially submerged habitats of different composition, including plastic polymers, metals or processed wood among others), and more available surface for the occurrence of fouling species in comparison to commercial ports (Minchin et al., 2006). Although a clear understanding of the influence of these artificial structures in the colonization of non-indigenous species would be significant for implementing management measures and economize sampling efforts, formal comparisons across different substrates in marinas are scarce (Sempere-Valverde et al., 2024). Most studies have explored the influence of substrate type in the recruitment patterns of fouling communities, using empty artificial passive collectors (e.g. fouling panels) as recruitment units (Satheesh and Wesley, 2010; Siddik et al., 2019; Xavier et al., 2023). This has shown that floating artificial structures, especially those made of plastic polymers, are particularly prone to non-indigenous species colonization due to their derived biofilm characteristics and chemical cues (Li et al., 2016; Pinochet et al., 2020). Indeed, the settlement in plastic surfaces implies a shorter exploring time and lower energy expenditure by the larvae in some bryozoan species, resulting in a higher fitness on the colonies settled on plastic (Pinochet et al., 2020). However, post-settlement processes can modulate the structure and composition of these communities over time and therefore, their habitat use patterns. Thus, it is also important to explore which communities inhabit the artificial structures in marinas. In this sense, most studies have focused on floating pontoons communities (Connell, 2000; Ros et al., 2013; Saenz-Arias et al., 2022), with a poor understanding of communities on other floating substrates, such as buoys (Sempere-Valverde et al., 2024) and ropes (Tempesti et al., 2023). Bryozoans constitute a very diverse taxonomic group (WoRMS Editorial Board, 2025) that play important ecological roles as filter feeders (Ryland and Hayward, 1991), preys (Lidgard, 2008), and as ecosystem engineers, providing available habitat for colonization of other organisms (Ros et al., 2013; Gavira-O’Neill et al., 2016; Guerra-- García et al., 2024). Components of this group are usually ubiquitous, small sized organisms with complex taxonomy, characterized by a versatile fouling capacity that, in many cases, includes colonizing artificial hard substrates. Some species of bryozoans show specific biological and ecological traits that make them exceptionally good colonizers, facilitating their growth on artificial hard substrates and crossing natural oceanographic barriers (Micael et al., 2017). Therefore, several non-indigenous bryozoans (NIB) have been recorded across the globe (Fofonoff et al., 2018). Indeed, NIB have been considered as models for marine bioinvasions due to: (1) their high occurrence in fouling communities (Farrapeira et al., 2011; Koçak et al., 2019), (2) their fast growth and reproduction, (3) their sessile lifestyle, (4) their tolerance to fluctuating and polluted environments, (5) their ability to colonize a wide range of substrates (Xavier et al., 2021) (even with preference for plastic structures (Pinochet et al., 2020), and (6) their role as early colonizers (Pinochet et al., 2020). And yet, the habitat use patterns of fouling bryozoans at multiple spatial scales are poorly understood. The Canarian archipelago constitutes a key point for the introduction and further spread of non-indigenous species of marine invertebrates (Pajuelo et al., 2016; Castro et al., 2023), including bryozoans (Arístegui, 1984; Moro et al., 2018; Ruiz-Velasco et al., 2025). As in other Macaronesia archipelagos (Souto et al., 2023), marinas in the Canary Islands may act as bridge between the Atlantic Ocean and the Mediterranean Sea for potentially invasive species (Souto et al., 2023; Ruiz-Velasco et al., 2025). Therefore, this area should be highlighted as an interesting location for early detection of these species. Although bryozoan diversity has been recently addressed in marinas from the Canary Islands (Ruiz-Velasco et al., 2025), habitat use and ecological preferences of these fouling species are not well understood yet (Kenworthy et al., 2018; Sempere-Valverde et al., 2024). This lack of knowledge hinders the possibility of a time-effective monitoring and early detection of NIB in this area. Additionally, like other volcanic islands, the Canarian archipelago is considered a natural laboratory for studying environmental and ecological gradients, offering a unique geographic setting to explore patterns of faunal assemblages across multiple spatial scales (Whittaker et al., 2017). Therefore, our aim was to explore the habitat use of bryozoans in marinas of the Canary Islands across multiple spatial scales, with special focus on substrate use patterns. Specifically, we compare the species richness of bryozoans and its community structure between different types of floating artificial structures (i.e. floating pontoons, buoys and ropes) within different zones (i.e. interior and exterior) in marinas located in four islands of the Canarian archipelago. Special emphasis was given to the habitat use of NIB to inform on priority strategies for their early detection and monitoring. 2. Material and methods 2.1. Study sites The field survey was conducted in June 2023 in marinas on four different islands of the Canarian archipelago (Spain, North-Eastern Atlantic): Tenerife, Gran Canaria, Fuerteventura and Lanzarote. Three marinas were sampled per island: Garachico (GC) (28◦22 ′ 24.949 ″ N, 16◦45 ′ 20.863 ″ W), Las Galletas (LG) (28◦0 ′ 25.745 ″ N, 16◦39 ′ 39.876 ″ W) and Marina Tenerife (MT) (28◦29 ′ 35.953 ″ N, 16◦12 ′ 37.41 ″ W) in Tenerife; Big Canary Sports Dock (BC) (28◦7 ′ 39.842 ″ N, 15◦25 ′ 28.664 ″ W), Pasito Blanco (PB) (27◦44 ′ 49.821 ″ N, 15◦37 ′ 24.297 ″ W) and Taliarte (TA) in Gran Canaria (27◦59 ′ 25.072 ″ N, 15◦22 ′ 6.541 ″ W); Corralejo (CO) (28◦44 ′ 27.015 ″ N, 13◦51 ′ 47.135 ″ W), Gran Tarajal (GT) (28◦21 ′ 22.192 ″ N, 14◦1 ′ 34.93 ″ W) and Morro Jable (MJ) (28◦3 ′ 2.465 ″ N, 14◦21 ′ 29.262 ″ W) in Fuerteventura, and Marina Lanzarote (ML) (28◦57 ′ 53.058 ″ N, 13◦32 ′ 12.345 ″ W), Playa Blanca (PL) (28◦51 ′ 34.694 ″ N, 13◦50 ′ 5.548 ″ W) and Puerto Calero (PC) (28◦55 ′ 1.9 ″ N, 13◦42 ′ 13.114 ″ W) in Lanzarote (Fig. 1). 2.2. Sampling survey In each marina, we differentiated between the exterior zone (more exposed, closer to boat entrance) and interior zone (less exposed to hydrodynamics, farther from boat entrance). In each zone, we distinguished three different artificial floating substrates: buoys, ropes and lateral surface of floating pontoons. Ten different units of each substrate (i.e. floating pontoon sections, buoys and ropes) were examined in both exterior and interior zones of the marina using a 20 ×20 cm quadrat randomly placed on each substrate surface. In the case of the ropes, each one was folded and arranged in a doubled-up manner, covering the surface defined by the quadrant. All substrates were situated in approximately equal depths, near the surface, and were made of plastic polymers. Then, we registered the occurrence of bryozoan species in the area limited by the quadrat to establish their frequency of occurrence per substrate and per zone. In cases in which in situ identifications were not possible, bryozoan samples were preserved in 96 % ethanol and taken to the laboratory for their later identification using a stereomicroscope Motic SM7TR-TLED APO1X and a light microscope Leica DME, and using bibliography of reference of fouling bryozoans in Macaronesia (e.g. Fofonoff et al., 2018; Koçak et al., 2019; Xavier et al., 2021; Pajuelo et al., 2016). Material of the species found was deposited in the National Museum of Natural Sciences of Madrid (Museo Nacional de Ciencias Naturales, MNCN) (Ruiz-Velasco et al., 2025). Once identified, the biogeographical status of each species (i.e. native, non-indigenous, cryptogenic and unassigned) was assigned according to Carlton and Schwindt, 2024 criteria (see Ruiz-Velasco et al., 2025 for further information of the status of these bryozoans in the Canary Islands). 2.3. Statistical analyses The habitat use of fouling bryozoans at multiple spatial scales was explored through univariate and multivariate permutational analyses of variance. Our experimental design considered four different spatial S. Ruiz-Velasco et al. Marine Environmental Research 211 (2025) 107397 2 factors: (1) Substrate (fixed factor with three levels, “Floating pontoon”, “Buoy” and “Rope”), (2) Zone (fixed factor with two levels, “Exterior” and “Interior”), (3) Marina (random factor with 12 levels, each one corresponding to each sampled marina, nested within Island) and (4) Island (random factor with four levels, each one corresponding to each studied island). Following this four-way design, we examined the total number of bryozoan species, the number of NIB and the percentage of NIB (number of NIB/total number x 100) occurring in the artificial floating substrates using univariate PERMANOVAs with 9999 permutations on a Euclidean distance matrix transformed using the square root (Clarke and Warwick, 2001). Undetermined and cryptogenic species were not included in the NIB statistical analyses. Monte Carlo P-values were used when the number of possible permutations was low (Anderson et al., 2008). If a tested variable was significant for a fixed factor, we conducted pairwise tests run by permutations to compare between each level of the factor (Anderson and Robinson, 2001). To explore community structure patterns, we conducted a multivariate PERMANOVA using Bray-Curtis similarity matrix based on presence-absence data. A SIMPER analysis for the total community was also carried out to identify discriminant species between the levels of significant factors. A Principal Coordinate Analysis (PCO) was also conducted to visually represent the influence of the discriminant species (Anderson et al., 2008; Clarke and Gorley, 2001), showing species with a Pearson correlation value higher than 0.7. These analyses were carried out using PRIMER v6 & PERMANOVA+ (Anderson, 2005). 3. Results A total of 23 bryozoan species were observed in marinas from the Canary Islands, including 12 NIB, eight cryptogenic and three undetermined species (Table 1). The most frequent species were the nonindigenous Amathia verticillata (delle Chiaje, 1822), Bugula neritina (Linnaeus, 1758), Schizoporella errata (Waters, 1878) and Watersipora subtorquata (d’Orbigny, 1852), which were present in all sampled marinas. The species with the highest frequency of occurrence between zones within marinas were A. verticillata in the interior zone (48.1 %) and S. errata in the exterior zone (50 %). Regarding substrates, the Fig. 1. Location of study sites in marinas of the Canary Islands. Each code corresponds to the marinas mentioned in the text, including sampling sites in Tenerife, Gran Canaria, Fuerteventura and Lanzarote islands. Each diagram shows the percentage of bryozoans recorded by status at each sampling site: yellow =percentage of NIB, blue =percentage of cryptogenic bryozoans, black =percentage of undetermined bryozoans. S. Ruiz-Velasco et al. Marine Environmental Research 211 (2025) 107397 3 highest relative abundance for a particular species was registered in floating pontoons (A. verticillata, 62.1 %), followed by buoys (S. errata, 55.8 %). Indeed, several species were only found on buoys (i.e. Beania serrata Souto, Nascimento, Reverter-Gil & Vieira, 2019, Bugulina simplex (Hincks, 1886), Celleporaria brunnea (Hincks, 1884), ?Trematooecia persica Baradari, Nasrolahi & Taylor, 2019, Celleporaria cf. inaudita Tilbrook, Hayward & Gordon, 2001 and Microporella browni Harmelin, Ostrovsky, C´ aceres-Chamizo & Sanner, 2011), sometimes with very scarce abundances (e.g. M. browni, 0.8 % frequency of occurrence) (Table 1). The highest frequency of occurrence registered by marina was of Tricellaria inopinata d’Hondt and Occhipinti Ambrogi, 1985 in Morro Jable marina (93.3 %) (Table 1). Total species richness of bryozoans was significantly higher on buoys than on the other two substrates (Fig. 2A–D). This pattern was influenced by the marina but not by the zone within the marina or the island sampled (Table 2A). Total species richness on ropes only surpassed that observed on buoys in one case (exterior area in Marina Lanzarote). The highest average richness of bryozoans was registered on buoys from the interior area of Taliarte marina, and the lowest was recorded on ropes from the interior area of Marina Tenerife (Fig. 2A and B). In the case of NIB richness, we found a similar substrate use pattern, with higher NIB richness on buoys than in the other substrates. This pattern was influenced by both the zone within the marina and the marina itself but not by the island (Table 2B, Fig. 2E–H). As recorded for the total species richness, only the NIB richness on ropes of the exterior zone of Marina Lanzarote surpassed the ones observed on buoys in average. The highest average NIB richness was observed on buoys from the interior zone of Taliarte marina (followed by the interior of Marina Lanzarote and the exterior of Puerto Calero) (Fig. 2F–H), and the lowest values were recorded on ropes from Big Canary Sports Dock marina (both interior and exterior zones) (Fig. 2F). The percentage of NIB showed a similar pattern as the number of NIB, but with a higher significance. The percentage of NIB differed significantly between ropes and the other substrates (Table 2C), with ropes showing a lower percentage than buoys and floating pontoons. The bryozoan community composition was significantly different in the three substrates considered. Community composition also varied between marinas and zones, but not between islands. However, the substrate use pattern was influenced by the island, as well as by the zone and the marina. These four factors interacted shaping both the total Table 1 Frequency of occurrence of bryozoan species at studied marinas of the Canary Islands. Species status and their occurrence at contrasting zones and types of substrates are given. Non-indigenous species are marked in bolds, according to Ruiz-Velasco et al. (2025) criteria. I =Introduced, C =Cryptogenic, U =Unassigned. FO =frequency of occurrence, I =Interior, E =Exterior, FP =Floating pontoon, B =Buoy, R =Rope, MT =Marina Tenerife, LG =Las Galletas, GC =Garachico, PB =Pasito Blanco, TA =Taliarte, BC =Big Canary Sports Dock, MJ =Morro Jable, GT =Gran Tarajal, CO =Corralejo, PL =Playa Blanca, PC =Puerto Calero, ML = Marina Lanzarote. The blue scale indicates species frequency of occurrence: Blank =Absence, light blue =>0–20 %, medium blue =>20–40 %, dark blue=>40 %. S. Ruiz-Velasco et al. Marine Environmental Research 211 (2025) 107397 4 Fig. 2. Average number (±standard deviation) of total bryozoan species (A–D) and NIB (E–H) observed in floating pontoons (light blue), buoys (dark blue) and ropes (yellow) in marinas of Tenerife (A, E), Gran Canaria (B, F), Fuerteventura (C, G) and Lanzarote (D, H). Marinas at each studied island of the Canary Islands correspond to the different sites listed in Table 1. Abundances are given for the interior (-I) and exterior (-E) zones of each marina. S. Ruiz-Velasco et al. Marine Environmental Research 211 (2025) 107397 5 community and the NIB community (Table 3A). The NIB community composition varied in a similar way, but the influence of the island in the substrate use pattern was lower (see IsxSu interaction in Table 3B). SIMPER analysis using the total community structure showed that the discriminant species between zones within marinas were S. errata (more prevalent on the exterior zone) and A. verticillata (prevailing on the interior zone) (Table 4A). The prevalence of A. verticillata in the interior zones can be observed in the PCO analysis, but not of S. errata in the exterior ones (Fig. 3A). Regarding substrates, the species that mostly marked the differences between floating pontoons and buoys were A. verticillata in the first substrate and T. inopinata in addition to S. errata in the second (Table 4B). These same species were the discriminant ones between floating pontoons and ropes, with a higher abundance of A. verticillata and S. errata in floating pontoons and of T. inopinata in ropes (Table 4C). Lastly, the comparison between buoys and ropes were characterized by S. errata, T. inopinata and W. subtorquata, all of them with a higher occurrence in buoys. In contrast, species of genus Crisia were more common in ropes in comparison to buoys (Table 4D). This clear characterisation of bryozoan species was observed in the PCO analysis, with A. verticillata characterizing floating pontoons and T. inopinata mostly buoys and ropes (Fig. 3B). Nevertheless, PCO analysis showed a low percentage of explained total variation. 4. Discussion Ecological features of non-indigenous bryozoans in recipient environments, such as marinas, have been scarcely explored (but see for instance Xavier et al., 2023). Although invasibility could be exacerbated in floating artificial substrates, especially in those bryozoans introduced by buoyant vectors (e.g. ship hulls), the importance of this effect at different spatial scales is not well understood. This lack of knowledge hinders the possibility to effectively manage NIB in marinas, which include some impactful ones, such as A. verticillata. This study highlights the key role of the type of floating substrate and the singularity of the marinas, with only a minor contribution from the island, in determining the richness and composition of total and non-indigenous fouling bryozoan assemblages in the Canary Islands. For management purposes, buoys (which harboured the highest richness of total and NIB species) emerge as a priority substrate for detecting and monitoring NIB in marinas. Understanding the role of artificial substrates for the recruitment and settlement in marinas can be very useful for non-indigenous species management, constituting interesting targets for monitoring programmes (Lehtiniemi et al., 2015; Ramalhosa et al., 2016; Ferrario et al., 2017; Martínez-Laiz et al., 2019). In addition to buoys recording the highest number of NIB in the present study, some recorded NIB only Table 2 Results of permutational ANOVAs for number of total (A), number of NIB (B) and percentage of NIB (C) in marinas from the Canary Islands. A 4-way model analysing the effects of the island, marina, zone within the marina and type of artificial substrate is presented. Pairwise analyses of significant fixed factors are included. Is = Island, Zo =Zone, Su =Substrate, Ma =Marina, Res =Residual. *** =p <0.001, ** =p <0.01, * =p <0.05. FP =Floating pontoon, B =Buoy, R =Rope. Source of variation df (A) Total richness (B) NIB richness (C) NIB percentage MS Pseudo-F P(MC) MS Pseudo-F P(MC) MS Pseudo-F P(MC) Is 3 1.014 0.657 0.597 n.s. 0.663 0.281 0.833 n.s. 1962.9 0.213 0.8861 n.s. Zo 1 0.365 0.298 0.604 n.s. 0.51 1.348 0.329 n.s. 1778.4 0.288 0.6281 n.s. Su 2 19.317 18.762 0.002** 23.637 18.553 0.004** 87490 30.581 0.001** Ma(Is) 8 1.543 10.669 0.001** 2.357 13.019 0.001** 9206.2 12.818 0.0001*** IsxZo 3 1.225 2.231 0.181 n.s. 0.379 0.425 0.75 n.s. 6170.6 1.636 0.261 n.s. IsxSu 6 1.03 2.383 0.079 n.s. 1.274 1.569 0.25 n.s. 2860.9 0.703 0.653 n.s. ZoxSu 2 0.48 2.379 0.181 n.s. 0.212 2.031 0.226 n.s. 1439.6 1.182 0.363 n.s. Ma(Is)xZo 8 0.549 3.795 0.001** 0.889 4.915 0.001** 3771.3 5.251 0.0001*** Ma(Is)xSu 16 0.432 2.987 0.001** 0.812 4.485 0.001** 4072.4 5.67 0.0001*** IsxZoxSu 6 0.202 1.849 0.153 n.s. 0.104 0.321 0.916 n.s. 1217.8 0.826 0.5709 n.s. Ma(Is)xZoxSu 16 0.109 0.755 0.721 n.s. 0.324 1.79 0.022* 1475.1 2.053 0.01* Res 648 0.145   0.181   718.24   Total 719          Pair-wise analysis: Su B ∕= (FP =R)   B ∕= (FP =R)   R ∕= (FP =B)   Table 3 Results of PERMANOVAs for community structure of the total species (A) and non-indigenous bryozoans (NIB) (B) in marinas of the Canary Islands. A 4-way model analysing the effects of the island, marina, zone within the marina and type of artificial substrate. Pairwise analyses of significant fixed factors are included. Is =Island, Zo =Zone, Su =Substrate, Ma =Marina, Res =Residual. ** =p <0.01, * =p <0.05. FP =Floating pontoon, B =Buoy, R =Rope. Source of variation df (A) Total community (B) NIB community MS Pseudo-F P(MC) MS Pseudo-F P(MC) Is 3 51839 1.436 0.219 n.s. 31244 1.127 0.392 n.s. Zo 1 59373 4.461 0.041* 60661 9.827 0.011* Su 2 1.25 ×10 5 9.765 0.001** 1.31 ×10 5 13.07 0.002** Ma(Is) 8 36086 23.716 0.001** 27723 17.896 0.001** IsxZo 3 13309 1.253 0.298 n.s. 6172.7 0.847 0.597 n.s. IsxSu 6 12858 1.774 0.045* 10026 1.489 0.148 n.s. ZoxSu 2 10030 1.121 0.379 n.s. 7693.9 1.245 0.351 n.s. Ma(Is)xZo 8 10625 6.983 0.001** 7268.5 4.704 0.001** Ma(Is)xSu 16 7246.9 4.763 0.001** 6733.7 4.347 0.001** IsxZoxSu 6 8945 2.542 0.005** 6180.2 1.951 0.042* Ma(Is)xZoxSu 16 3518.8 2.313 0.001** 3168.3 2.045 0.001** Res 648 1521.6   1549.1   Total 719       Pair-wise analysis: Su FP ∕= B ∕= R  FP ∕= B ∕= R  S. Ruiz-Velasco et al. Marine Environmental Research 211 (2025) 107397 6 occurred on this type of substrate (i.e. B. simplex, C. brunnea, ?T. persica and M. browni). Considering the importance of early detection of potential invaders for a proper management of these species (Lehtiniemi et al., 2015; O’Shaughnessy et al., 2023), our results highlight the role of buoys as hotspots for NIB, that should be useful to focus on during monitoring efforts in case of logistic or economic limitations (Sempere-Valverde et al., 2024). Furthermore, the presence and number of buoys should also be considered as a risk factor for the dispersal of NIB acting as (1) reservoir for the further spread of NIB via hull fouling and, (2) potential marine debris, affecting not only other port environments, but also nearby natural areas. Indeed, in contrast to fixed substrates such as floating pontoons, buoys and ropes can be easily detached and become drifting marine debris, enhancing the dispersion of NIB to natural areas, as discussed in Pinochet et al. (2020) and Xavier et al. (2023). Therefore, buoys should be prioritized for monitoring and management programmes of potential invader species in marinas (Sempere-Valverde et al., 2024), and their use in port environments should be carefully controlled. Substrate type, through its composition, structure, and orientation, acts as a filter shaping early colonization and succession in fouling assemblages (Xavier et al., 2023). Indeed, both total and NIB richness and community structure differed according to the types of substrates considered in our study (seeTable 3). We found a higher number of total and NIB species in buoys in comparison to floating pontoons and ropes. This agrees with Sempere-Valverde et al. (2024), who demonstrated that buoys facilitate the establishment of NIB more effectively than the lateral surfaces of floating pontoons, likely due to differences in inclination, submersion time, and resulting microhabitats and ecological interactions (Glasby, 2001; Chebaane et al., 2022). Buoys tend to generate shaded, sloped environments favourable to animal recruitment, whereas pontoons, being more vertical and exposed, promote the colonization of photophilic species such as macroalgae (Sempere-Valverde et al., 2024). Moreover, buoys are also subjected to more disturbances due to their possible temporal subtraction from the water and their rotating movement (on their vertical axis) (Sempere-Valverde et al., 2024). Nevertheless, it is important to note that comparisons between communities on floating pontoons and buoys have been limited to the vertical sides of the pontoons, which may differ from the horizontal submerged surfaces of these structures (Xavier et al., 2023). Ropes share with buoys high levels of disturbance (due to a more Table 4 Results of SIMPER analyses of bryozoan communities to address discriminant species between marina zones (interior and exterior) (A) and between substrates: floating pontoons and buoys (B), floating pontoons and ropes (C), and buoys and ropes (D). Av. Abund =Average abundance, Av. Diss =Average dissimilarity, Diss/SD = Dissimilarity/Standard deviation, Cumulative =Cumulative contribution. (A) Interior and exterior areas Average dissimilarity =73.59 I E Species Av. Abund Av. Abund Av. Diss Diss/SD Contribution (%) Cumulative (%) Schizoporella errata 0.26 0.49 13.32 0.77 18.10 18.10 Amathia verticillata 0.49 0.30 12.79 0.71 17.39 35.48 Tricellaria inopinata 0.33 0.32 10.47 0.68 14.23 49.71 Bugula neritina 0.21 0.24 8.11 0.62 11.02 60.74 Crisia sp. 0.14 0.13 5.52 0.44 7.50 68.24 Crisia denticulata 0.10 0.11 4.15 0.39 5.64 73.88 (B) Floating pontoons and buoys Average dissimilarity =77.73 FP B Species Av. Abund Av. Abund Av. Diss Diss/SD Contribution (%) Cumulative (%) Amathia verticillata 0.62 0.30 14.13 0.87 18.17 18.17 Tricellaria inopinata 0.15 0.47 11.97 0.81 15.41 35.58 Schizoporella errata 0.32 0.56 11.79 0.82 15.16 48.75 Watersipora subtorquata 0.00 0.43 9.38 0.74 12.7 60.81 Bugula neritina 0.16 0.31 7.89 0.69 10.15 70.97 (C) Floating pontoons and ropes Average dissimilarity =82.07 FP R Species Av. Abund Av. Abund Av. Diss Diss/SD Contribution (%) Cumulative (%) Amathia verticillata 0.62 0.24 19.39 0.88 23.62 23.62 Schizoporella errata 0.32 0.25 13.12 0.71 15.99 39.61 Tricellaria inopinata 0.15 0.35 11.94 0.71 14.55 54.16 Bugula neritina 0.16 0.21 8.68 0.60 10.57 64.73 Crisia sp. 0.01 0.23 7.90 0.50 9.63 74.36 (D) Buoys and ropes Average dissimilarity =80.21 B R Species Av. Abund Av. Abund Av. Diss Diss/SD Contribution (%) Cumulative (%) Schizoporella errata 0.56 0.25 11.94 0.87 14.89 14.89 Tricellaria inopinata 0.47 0.35 11.51 0.81 14.35 29.24 Watersipora subtorquata 0.43 0.01 8.67 0.71 10.81 40.05 Amathia verticillata 0.30 0.24 7.92 0.68 9.88 49.93 Bugula neritina 0.31 0.21 7.73 0.71 9.64 59.56 Crisia sp. 0.17 0.23 7.43 0.60 9.26 68.82 Crisia denticulata 0.11 0.21 5.68 0.54 7.08 75.90 S. Ruiz-Velasco et al. Marine Environmental Research 211 (2025) 107397 7 frequent removal from the water) and mobility, which may shape the richness of fouling assemblages (Tempesti et al., 2023) by favouring early successional species, such as many NIB (Glasby, 2001; Xavier et al., 2023), as observed in our study. Their smaller size can also determine post-settlement processes as discussed before. Additionally, in comparison to buoys and floating pontoons, ropes exhibit greater surface complexity and microscale roughness that could enhance species recruitment (Tempesti et al., 2023; Sedano et al., 2020). Different substrates may also influence the prevalence of different growth forms (Xavier et al., 2023). While floating pontoons, buoys and ropes hosted in our case both encrusting and erect species, some erect species were especially prevalent on ropes, like B. flabellata, and mainly, the cyclostomes C. denticulata and Crisia sp. (see Tables 1 and 4). This prevalence of C. denticulata on ropes could explain the lower percentage of NIB on ropes compared to the other substrates (see Table 2D). Although the PCO analysis shows a low percentage of explained total variation, T. inopinata appears to be more closely associated to ropes and buoys than to floating pontoons. Indeed, it seems that erect bryozoans may prefer ropes as substrate, since Xavier et al. (2023) detected only erect species on experimental ropes deployed for two months. Nevertheless, in longer periods of submersion, encrusting species may be observed as well (Fernandez-Gonzalez and Sanchez-Jerez, 2017). In conjunction with hosting a broad variety of available substrates, enclosed habitats with low water exchange like marinas (Floerl and Inglis, 2003) show higher water retention and concentration of pollutants in relation to the distance to the boat entrance (Schiff et al., 2007). This environmental gradient also influences species settlement, with the most tolerant species colonizing the innermost zones of the marina (Simpson et al., 2017), and therefore, hosting a lower diversity in this area (Johnston and Roberts, 2009; Marchini et al., 2015; Kenworthy et al., 2018) and a higher abundance of non-indigenous species (Floerl and Inglis, 2003; Sempere-Valverde et al., 2024). Nevertheless, the zone did not have a major effect on the total and NIB richness. This could be related to the tolerant nature of bryozoan species recorded in this study, with most species being very common in fouling assemblages. Indeed, most species were recorded in both interior and exterior zones (except M. browni, a very scarce species that only occurred in interior zones), and mostly with similar frequency of occurrence (see Table 1). In this sense, marina design could determine the water exchange among the zones within the marinas (Toh et al., 2017), which could explain the interactive influence of marinas and zones in the substrate use patterns of total and NIB species composition in our study. The response to this gradient of pollutants and other abiotic characteristics (Kenworthy et al., 2018) may be driven by certain dominant species, such as A. verticillata (most common on interior zones) and S. errata (most prevalent on exterior zones). Regarding A. verticillata, this soft-bodied widespread species forms dense colonies that are prone to fragmentation via mechanical stress (Marchini et al., 2015), suggesting that low-hydrodynamic conditions may favour its growth and persistence. On the other hand, S. errata exhibits morphological plasticity in relation to different hydrodynamics conditions (Cocito et al., 2000; Hayward and McKinney, 2002). Moreover, Sokolover et al. (2018) observed a fast colony growth of this species under strong current conditions. Despite hydrodynamics in port environments are generally low in comparison to natural areas, exterior zones within marinas show a higher water renovation rate in contrast to interior ones, which could influence the growth rates in S. errata. Additionally, spatial and nutritional competition could be driving bryozoan community structure (L´ opez-Gappa, 1989; Turner and Todd, 1994). Although species from genus Schizoporella have been considered as “overgrowth dominants” (Turner and Todd, 1994), the prevalence of a strong competitor such as A. verticillata on interior zones could be hindering its establishment and growth. Ecological dynamics among these species should be further explored. In addition to the variability observed within marinas, archipelagos such as the Canary Islands offer a valuable opportunity to examine differences in community composition at a broader spatial scale. Oceanographic patterns at the Canarian Archipelago are mainly influenced by the Saharan upwelling, trade winds and the Canary Current (Barton et al., 1998; Barton and Arístegui, 2004). Therefore, islands from this archipelago show a longitudinal surface sea water temperature (SST) gradient, with the lowest values in the easternmost island (Lanzarote) and the highest in the westernmost islands (El Hierro and La Palma) (Barton et al., 1998). These environmental characteristics determine the prominent occurrence of species with temperate affinities in natural habitats on the eastern islands (i.e. Lanzarote and Fuerteventura) and species of tropical affinities on the western islands (i.e. El Hierro and La Palma) (Sangil et al., 2011). Moreover, SST also varies within islands due to a combination of the upwelling filaments from the Saharan coast and mesoscale variability (Barton et al., 1998; Arístegui et al., 2009). This results in lower values on the northern and north-eastern coasts in comparison to the western coast of each island (Barton et al., 1998; L´ opez et al., 2020). Despite these intricate Fig. 3. Principal Coordinate Analyses (PCO) assessing the structure of bryozoan communities studied at marinas of the Canary Islands. Data are presented showing differences by marina zones (interior and exterior) (A) and substrate types (pontoons, buoys and ropes) (B) considered. Islands are differentiated by shape, and the variables (zones and substrates) by colour. Species that better correlated with each axis are given (R 2 =0.70). S. Ruiz-Velasco et al. Marine Environmental Research 211 (2025) 107397 8 environmental conditions, the island only influenced the bryozoan communities interacting with other factors and had no effect on the richness of total and NIB, nor on the percentage of NIB. Although it must be noted that our study mostly included the central and eastern islands, substrate use patterns of bryozoan assemblages in marinas seemed mostly governed by the singularity of each marina and not by island-scale patterns. Similar results have been observed in areas which also show a coastal salinity and temperature gradient (see studies from southern Iberian Peninsula (Guerra-García et al., 2021; Saenz-Arias et al., 2022). Therefore, it seems that each marina constitutes a unique habitat due to the combination of different complex elements such as their spatial design, the type and quantity of surface susceptible to be colonized and the type and intensity of maritime traffic they host, among other factors (Guerra-García et al., 2021). In this sense, propagule pressure derived from the intensity of maritime traffic could determine the prevalence and dominance of non-indigenous species in marinas (Ferrario et al., 2024). This must be highlighted especially considering that most recent introductions in Macaronesia occurred by secondary transfer from other islands via shipping (Castro et al., 2022, 2023). The various uses and services provided by different ports may also influence these introductions (Anderson et al., 2015; Tempesti et al., 2022). Although large commercial ports with touristic harbours hosted the highest number of NIB in marinas from the Mediterranean Sea (Tempesti et al., 2022), we did not observe a clear pattern of higher number of NIB in the two marinas that were adjacent to large commercial ports in our study area. While Marina Lanzarote in Lanzarote hosted a higher number of NIB within the island, the number of NIB in Big Canary Sports Dock in Gran Canaria was the lowest within the island in average (see Fig. 2), reinforcing the singularity of the marinas and highlighting the challenges of effectively managing these introduced species. This complexity emphasizes the need for effective monitoring strategies for early detection, including the use of genetic reference libraries and metabarcoding that should be addressed in the future to improve the identification of non-indigenous species at the early stages of introduction (Aylagas et al., 2024; Lavrador et al., 2024). 5. Conclusions Fouling communities of bryozoans in marinas of the Canary Islands, both in terms of total number of species and number of NIB, are mainly shaped by the type of substrate where they settle and by the singularity of the marinas, rather than by the island where these marinas are located, which plays a comparatively minor role. Floating substrate types considered in this study (i.e. floating pontoons, buoys and ropes) showed a distinctive bryozoan community, with some discriminant species between substrates. Buoys showed the highest number of total and NIB, with some of them, such as Bugulina simplex, Celleporaria brunnea, ?Trematooecia persica and Microporella browni, being registered only on this substrate. These results highlight the importance of focusing on buoys for monitoring and implementing management programs for NIB in marinas. CRediT authorship contribution statement Sofía Ruiz-Velasco: Writing – original draft, Visualization, Investigation, Formal analysis, Conceptualization. Jos´ e M. Guerra-García: Writing – review & editing, Visualization, Supervision, Methodology, Investigation, Formal analysis, Conceptualization. Macarena Ros: Writing – review & editing, Supervision, Methodology, Investigation, Formal analysis, Conceptualization. Carlos M. L´ opez-F´ e: Writing – review & editing, Investigation, Conceptualization. ´ Angela Izquierdo: Writing – review & editing, Investigation. María Pastor-Montero: Writing – review & editing, Investigation. Sabrina Clemente: Writing – review & editing, Supervision, Methodology, Investigation, Formal analysis, Conceptualization. Funding sources This study was supported by a predoctoral grant provided by Ministerio de Universidades (Spanish Ministry of Universities) to S. RuizVelasco (Ref: FPU21/02406). Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements We sincerely thank three anonymous reviewers for their valuable comments, which helped to enhance the quality of this work. We gratefully acknowledge Puertos Canarios for granting their permission to conduct the samplings included in this study, and the staff from the marinas for their kind help when needed. We are very grateful to Elena García Martínez for letting us use her art for the graphical abstract. We are also indebted to the General Investigation Services of the University of Seville (CITIUS). Data availability Data will be made available on request. References Anderson, M.J., 2005. PERMANOVA: a FORTRAN Computer Program for Permutational Multivariate Analisis of Variance. Department of Statistics. University, of Auckland, New Zealand. 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