Introduction
During recent years, the astonishing increase of marine species invasions and its ecological impact around the world have aroused much attention (Molnar et al. Reference Molnar, Gamboa, Revenga and Spalding2008; Ben Rais Lasram and Mouillot Reference Rais Lasram and Mouillot2009; Sardain et al. Reference Sardain, Sardain and Leung2019; Hulme Reference Hulme2021). This is due to the introduction and spread of non-native or exotic species (NNS), which are considered one of the main threats to biodiversity in the marine realm (Diagne et al. Reference Diagne, Leroy, Vaissière, Gozlan, Roiz, Jarić, Salles, Bradshaw and Courchamp2021; Lockett and Gomon Reference Lockett and Gomon2001; Mack et al. Reference Mack, Simberloff, Mark Lonsdale, Evans, Clout and Bazzaz2000; Peyton et al. Reference Peyton, Martinou, Pescott, Demetriou, Adriaens and Arianoutsou2019; Simberloff Reference Simberloff2005). Although not all NNS will have such direct negative impacts in their recipient systems (Goodenough Reference Goodenough2010), some fishes are considered as one of the most important invasive species worldwide (Albins and Hixon Reference Albins and Hixon2013; Sala et al. Reference Sala, Kizilkaya, Yildirim and Ballesteros2011). For instance, along the Central American Atlantic coast, species such as the lionfish (Pterois volitans) have been observed to disrupt and negatively impact native fish communities (Albins and Hixon Reference Albins and Hixon2008). Therefore, every case of NNS first records deserves further attention.
The checklist of littoral fish species registered for the Canary Islands has increased in recent decades due to the large number of new arrivals. Most of these benthic or benthopelagic species are from nearby tropical regions. Several of these new fishes have entered the Canaries from the more meridional islands, which have warmer waters, and can be interpreted as an extent of their distribution range related with natural dispersion processes, such as current larvae drag, adult movement or rafting. However, important number of them have been found for the first time inhabiting the main harbours of Santa Cruz de Tenerife (SCT) and Las Palmas de Gran Canaria (LPG) (Brito et al. Reference Brito, Clemente and Herrera2011; González et al. Reference González, Espino and González-Lorenzo2025; Triay-Portella et al. Reference Triay-Portella, Pajuelo, Manent, Espino, Ruiz-Díaz, Lorenzo and González2015). A recent study by Falcón et al. (Reference Falcón, Brito, Herrera, Ayza, Moro and Caro2023) has analysed each of the NNS arrival cases, and they have concluded that there are two clearly distinguished invasion periods. From 1980 to 2010, most of the arrivals, 46 species in total, are due to natural geographic expansion, with just 11 species related to ballast water or to releases from aquaria. Since then to 2023, 13 species have presumably arrived by their own natural ways; however, the number of introduced species of tropical origin have increased to 26. This boom coincides in time with an increase of oil platform arrivals to SCT and LPG main harbours, which have been recently pointed out as the main transport vector of marine non-native fish species (Falcón et al. Reference Falcón, Herrera, Ayza and Hernández2015; González et al. Reference González, Espino and González-Lorenzo2025: Pajuelo et al. Reference Pajuelo, González, Triay-Portella, Martín, Ruiz-Díaz, Lorenzo and Luque2016).
We present here the results of a population study of a new colonizer of SCT harbour, the fish Tigrigobius zebrellus (Robins Reference Robins1958). The genus Tigrigobius (Fowler, Reference Fowler1931) encompasses various small-sized gobies, with vibrant colours and native to the warmer regions of the eastern Pacific and western Atlantic, including the Gulf of California and the Caribbean (Taylor and Hellberg Reference Taylor and Hellberg2005). This species has a compressed body, with the largest specimens reaching a length of 2.1 cm and distinctive colouration pattern characterized by narrow dark stripes along its body (Robertson et al. Reference Robertson, Peña, Posada and Claro2019). Unlike other species in the Tigrigobius genus, T. zebrellus displays 13 prominent vertical dark stripes extending from its pectoral fin to the caudal fin, which can sometimes be wider than the pale intermediate spaces (Robins Reference Robins1958; Taylor and Akins Reference Taylor and Akins2007). The native distribution of this species is restricted to the Caribbean Sea, specifically the area from the Gulf of Venezuela to Trinidad, where it typically inhabits shallow coastal areas associated with reefs, macroalgae, and rocky formations (Pezold et al. Reference Pezold, Van-Tassell, Tornabene and Aiken2015). The present study reports the presence of T. zebrellus in an area distant from its natural distribution range and in a relatively different environment than usual. Within this study, the species distribution, the population characteristics, as well as possible introduction mechanisms and management of this exotic fish are discussed.
Materials and methods
The study was carried out in the Marina SCT (28°27ʹ59.9″ 16°14ʹ37.3″ W), located in the northeastern part of the Tenerife Island, situated in the subtropical region of the central-eastern Atlantic Ocean, and belonging to the Spanish autonomous community of the Canary Islands (Figure 1).
(a) Satellite image showing harbour Marina Santa Cruz and the different sampled docks: interior dock 1 (InD1), interior dock 2 (InD2), exterior dock 1 (ExD1), and exterior dock 2 (ExD2). Source: Google Earth (2022). (b) Interior section of the harbour docks considered during the study. (c) Satellite image showing the area of Castillo de San Juan Bautista (black circle) and the Auditorium Adán Martín (white triangle). The white line indicates the sampled path. Source: Google Earth (2022).
In order to investigate the presence of the goby T. zebrellus in the harbour environment, a sampling methodology focused on the submerged portion of the floating docks used for the mooring and unmooring of vessels has been designed. The sampling was carried out during August 2022. For this purpose, four docks within the harbours have been selected: two docks adjacent to the wall considered ‘interior’ docks (InD1 and InD2), and two protruding docks considered ‘exterior’ docks (ExD1 and ExD2) (Figure 1).
In each of the docks, a linear transect was conducted along its inner part (Figure 1), covering a distance of 60 m within a time span of 45 min. The sampling was carried out using snorkelling equipment and consisted of a visual census to obtain direct observations of the individuals. In addition to tallying the number of observed individuals, a preliminary classification based on their size was performed: small (<1 cm), medium (between 1 and 2 cm), and large (≥2 cmr). This classification was conducted through direct visual measurement by calibrated observers using photo quadrats with scales to ensure accuracy. A statistical descriptive analysis was carried out by calculating the mean and standard deviation of the number and sizes of individuals recorded in the different studied zones.
Due to the high number of individuals recorded during the study, subsequently, an additional sampling was carried out in the area closest to the mouth of the marina, specifically in the zone of Castillo de San Juan Bautista, also known as ‘Castillo Negro’ (Figure 1). In this additional sampling, a 90-min survey was conducted using the same methodology described earlier, covering an approximate distance of 240 meters, but considering a broader range of observation in terms of depth, spanning from the intertidal zone (0–1 m) to 10 m. Various habitat types were considered, encompassing both natural and artificial hard substrates as well as the nearest sandy bottoms.
In addition to visual sampling, photographs of some of the observed specimens were taken during the sampling and afterwards in the laboratory. These images were examined based on morphological characteristics, such as the number of pectoral fin rays and the number of scales at the base of the caudal peduncle, and compared with existing scientific descriptions to confirm the identification of T. zebrellus.
Results
A total of 232 individuals of the goby Tigrigobius zebrellus (Table 1) were counted during four transects conducted within Marina SCT in August 2022. Among these, 202 were found in the inner docks (InD1 and InD2), while 30 were found in the outer docks (ExD1 and ExD2). Specimens of T. zebrellus in all three sizes – small (<1 cm), medium (between 1 and 2 cm), and large (≥2 cm) – were observed in all docks (Table 1). In the three sizes considered, the mean number of observed individuals was higher in the interior docks than in the exterior ones (Table 2). In relation to size, approximately 38% of the individuals were small (<1 cm), around 42% were medium-sized (between 1 and 2 cm), and only 20% were larger (≥2 cm). One of the ‘large’ sized individuals observed exhibited the first ray of the dorsal fin clearly elongated, a characteristic of males during the breeding period. Photographs of some observed specimens were taken during sampling and later in the laboratory (Figure 2), providing morphological data such as 13 vertical stripes extending from behind the pectoral fin to the caudal fin, 18 rays in the pectoral fins, and 4 large scales at the base of the caudal peduncle, among others. Other fish species observed during the sampling at the docks included the goby Gobius xanthocephalus and the blennies Hypleurochilus pseudoaequipinnis and Microlipophrys velifer.
Photographs of different specimens of Tigrigobius zebrellus observed in the harbour Marina Santa Cruz. The first two images were taken in the laboratory, while the remaining images were captured in situ. Authors: Leopoldo Moro, Juan Carballo, María Belén Caro, and Marc Martín.
Number of observed individuals of Tigrigobius zebrellus in the different sampled docks, classified by size: small (<1 cm), medium (1–2 cm), and large (>2 cm)
Data were collected in August 2022 from four transects within Marina Santa Cruz de Tenerife, each 60 m long and surveyed for 45 min by two observers.
Mean and standard deviation of the number of Tigrigobius zebrellus observed in exterior and interior docks, categorized by size: small (<1 cm), medium (1–2 cm), and large (>2 cm)
Data were collected in August 2022 from four transects within Marina Santa Cruz de Tenerife, each 60 m long and surveyed for 45 min by two observers.
Regarding the additional sampling carried out in the Castillo de San Juan Bautista area, no individuals of T. zebrellus were recorded. However, species from the Blenniiformes order were observed, such as Parablennius goreensis, Tripterygion delaisi, and Ophioblennius atlanticus, as well as the cling fish Lepadogaster candolii.
Discussion
In the present study, we confirm the presence of Tigrigobius zebrellus in the Canary Islands and Eastern Atlantic waters, and it has also been reported a population of over 232 individuals in a relatively confined habitat, specifically concentrated in the inner sections of floating docks within the harbour. It has also been observed that there are differences in the abundance of T. zebrellus depending on the area of the port. The ‘interior’ docks show a higher quantity of individuals compared to the ‘exterior’ docks. This phenomenon could be attributed to the reduced exposure to light and wave action in the ‘interior’ docks, which promotes a greater development of their fouling community (Glasby Reference Glasby1999; Jessen et al. Reference Jessen, Voolstra and Wild2014), mainly invertebrates that serve as a refuge for the species. As noted in other studies, submerged artificial structures, including those located in ports, provide suitable habitats to be colonized by various organisms (Airoldi et al. Reference Airoldi, Turon, Perkol‐Finkel and Rius2015; Mineur et al. Reference Mineur, Cook, Minchin, Bohn, MacLeod and Maggs2012). However, it has been demonstrated that exotic species often outperform native species in colonizing these substrates, appearing in higher proportions in these artificial environments (Airoldi et al. Reference Airoldi, Turon, Perkol‐Finkel and Rius2015; Glasby et al. Reference Glasby, Connell, Holloway and Hewitt2007; Megina et al. Reference Megina, González-Duarte and López-González2016; Ruiz et al. Reference Ruiz, Freestone, Fofonoff and Simkanin2009). The described population of T. zebrellus in the Marina de Santa Cruz serves as a clear example of an exotic species that has found the optimal habitat for its development within a harbour environment in the Canary Islands.
In its natural region, the species tends to be associated with reef areas, where it can survive in different habitats such as those consisting of macroalgae, soft or hard corals, and large rocky formations. However, it has also been observed in areas of rocky or sandy rocky coastline with small loose rocks and algae (Pezold et al. Reference Pezold, Van-Tassell, Tornabene and Aiken2015). Regarding its natural biogeographical distribution, it is observed about 5000 km away from its native distribution and in such a restricted environment on the island suggests that it is an introduced species through maritime traffic. Maritime traffic is considered the primary pathway for the introduction of exotic species worldwide, acting as vectors for transporting organisms mainly through ballast water or hull fouling on ships (Carlton Reference Carlton1996; Hewitt et al. Reference Hewitt, Gollasch and Minchin2009). In the Canary Islands, a relevant vector linked to the introduction of exotic species is also the arrival of oil platforms at major ports, most of them coming from tropical regions of the Atlantic such as Brazil, the Caribbean, or the Gulf of Guinea (Falcón et al. Reference Falcón, Herrera, Ayza and Hernández2015; Pajuelo et al. Reference Pajuelo, González, Triay-Portella, Martín, Ruiz-Díaz, Lorenzo and Luque2016). These platforms, due to their slow movement, facilitate the survival of some of their associated organisms during the journeys (Creed et al. Reference Creed, Fenner, Sammarco, Cairns, Capel, Junqueira, Cruz, Miranda, Carlos-Junior, Mantelatto and Oigman-Pszczol2017; López et al. Reference López, Clemente, Moreno, Ocaña, Herrera and Moro2019). This implies that large ports, including those receiving oil platforms, are considered hotspots for exotic species and, at the same time, priority areas for the early detection and management prior to the spread of potential marine biological invasions (Lehtiniemi et al. Reference Lehtiniemi, Ojaveer, David, Galil, Gollasch and McKenzie2015; Romeo et al. Reference Romeo, D’Alessandro, Esposito, Scotti, Berto and Formalewicz2015; Tempesti et al. Reference Tempesti, Langeneck, Maltagliati and Castelli2020).
Photographic records of some observed individuals during sampling, combined with a detailed examination of a specimen in the laboratory, revealed key morphological traits of the species, including 13 vertical stripes extending from behind the pectoral fin to the caudal fin, 18 rays in the pectoral fins, and 4 large scales at the base of the caudal peduncle. These characteristics align with the existing descriptions of the species (Robertson et al. Reference Robertson, Peña, Posada and Claro2019; Robins Reference Robins1958), further confirming its identification. Despite the large number of specimens recorded within the harbour, their presence was not detected in the shallow seabeds closest to the harbour environments. In the area around Castillo de San Juan several introduced fish species have been recorded, such as Pomacanthus maculosus (Brito et al. Reference Brito, Pascual, Falcón, Sancho and González2002), Abudefduf saxatilis, Acanthurus coeruleus (Falcón and Monterroso Reference Falcón and Monterroso2018), and Acanthurus monroviae (Falcón et al. Reference Falcón, Brito, Herrera, Ayza, Moro and Caro2023). Despite the absence of T. zebrellus during the sampling in the surroundings, this area remains important for their early detection in the event of potential expansion beyond the harbour. On the other hand, this suggests that, despite having successfully developed within the harbour environment, the species has not been able to thrive on its own in its immediate vicinity yet. Among other factors, this could be due to the limited dispersal capacity exhibited by certain goby species (Taylor and Hellberg Reference Taylor and Hellberg2003). There are similar cases of introduced fish species in the Canary Islands that have used port environments as their initial settlement sites. For instance, the case of the tropical blenny, Hypleurochilus pseudoaequipinnis, which was recorded in Gran Canaria in 2013 (Falcón et al. Reference Falcón, Herrera, Ayza and Hernández2015) and later in Tenerife in 2016 and El Hierro in 2019 (Falcón et al. Reference Falcón, Brito, Herrera, Ayza, Moro and Caro2023). In this case, despite not being considered a species with high invasive potential, it could be potentially competing with similar native species occupying the same ecological niches, such as Gobius niger, Vanneaugobius canariensis, or Parablennius pilicornis. However, the process of tropicalization could favour, in a future scenario, some of the marine species considered exotic (Brito et al. Reference Brito, Moreno-Borges, Escánez, Falcón and Herrera2017) that are currently classified as non-invasive or have insufficient data.
The success of the species in reproducing and dispersing depends on various factors. However, observations like these underscore the need to address the issue, especially in cases like the current study, where the population of the introduced species is geographically confined, making its management relatively straightforward. Since T. zebrellus is restricted to the harbour, targeted eradication measures could be considered. Chemical treatments such as clove oil or rotenone have been effective in removing non-native fish in controlled environments (Ling Reference Ling2003; Rytwinski et al. Reference Rytwinski, Taylor, Donaldson, Britton, Browne, Gresswell, Lintermans, Prior, Pellatt, Chantal and Cooke2019), though their potential impact on native species must be carefully assessed. Alternatively, non-chemical methods like manual removal with nets, selective traps, or habitat modification may offer viable solutions depending on logistical feasibility and ecological considerations. Furthermore, the present study highlights the importance of initiating long-term monitoring in the main harbour environments of the Canary Islands. This monitoring would allow for both, tracking of exotic species inhabiting these environments and the early detection of newly arrived species, such as the current case study of T. zebrellus.
Acknowledgements
We would like to express our gratitude to Juan Carballo for his contribution during the in situ sampling and the images provided for this publication, as well as to Dr. Jesús M. Falcón for his assistance to identify the species.
Author contributions
Formulating the research question(s): MMS, JCH; Designing the study: MMS, MBCT, LMA; Carrying out the study: MMS, MBCT, JCH; Analysing the data: MMS, JCH; Interpreting the findings: MMS, MBCT, LMA, JCH; Writing the article: MMS, MBCT, JCH.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Competing interests
The authors declare none.
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