Introduction
Cassiopea Péron & Lesueur, 1810, a distinct Scyphozoa genus, has been receiving growing interest attributed to its role as a model system for bioindicators (Epstein et al., Reference Epstein, Templeman and Kingsford2016; Harris et al., Reference Harris, Bouldin, Ili, Wilczek, Harris and Bouldin2020) and symbiotic associations (Ohdera et al., Reference Ohdera, Abrams, Ames, Baker, Suescún-Bolívar, Collins, Freeman, Gamero-Mora, Goulet, Hofmann, Jaimes-Becerra, Long, Marques, Miller, Mydlarz, Morandini, Newkirk, Putri, Samson, Stampar, Steinworth, Templeman, Thomé, Vlok, Woodley, Wong, Martindale, Fitt and Medina2018), its geographical extension, and its proliferation/invasive events (Stampar et al., Reference Stampar, Gamero-Mora, Maronna, Fritscher, Oliveira, Sampaio and Morandini2020; Mammone et al., Reference Mammone, Ferrier-Pages, Lavorano, Rizzo, Piraino and Rossi2021). Often, the introduction and the invasive events of Cassiopea have been attributed to Cassiopea andromeda disregarding the outdated taxonomic knowledge and the high phenotypic variability observed in this genus. Molecular analyses are thus needed for reliable taxonomic identifications (Holland et al., Reference Holland, Dawson, Crow and Hofmann2004; Morandini et al., Reference Morandini, Stampar, Moronna and da Silveira2017; Maggio et al., Reference Maggio, Allegra, Bosch-Belmar, Cillari, Cuttitta, Falautano, Milisenda, Nicosia, Perzia, Sinopoli and Castriota2019). To date, C. andromeda (sensu lato) has been recorded in the tropical and subtropical Atlantic (e.g. Brazil, Mexico, California, Cabo Verde) (Daglio and Dawson, Reference Daglio and Dawson2017; Moro et al., Reference Moro, Herrera, Ayza, Ocaña, Monterroso, Freitas, León, Cozzi, Iglesias, Marrero, Martín, Carballo, Rabeling, Bacallado and Ortea2020; Stampar et al., Reference Stampar, Gamero-Mora, Maronna, Fritscher, Oliveira, Sampaio and Morandini2020), in the Mediterranean Sea (Schembri et al., Reference Schembri, Deidun and Vella2010), and in the Indo-Pacific (e.g. French Polynesia, India, Sri Lanka) (Kayal et al., Reference Kayal, Roure, Philippe, Collins and Lavrov2013; Prasade et al., Reference Prasade, Nagale and Apte2016; Karunarathne et al., Reference Karunarathne, Liyanaarachchi and De Croos2020), and is often considered invasive due to its high proliferation rate and potential impact on tourism (stinging) and ecosystem (Bayha and Graham, Reference Bayha, Graham, Pitt Kylie and Lucas Cathy2014).
We present here the first report, supported by molecular analysis, of C. andromeda (Forskål, 1775) in the eastern Atlantic.
Materials and methods
Several Cassiopea cf. andromeda specimens with different umbrella sizes were sighted at the aquaculture facilities of the Oceanographic Center of the Canary Islands (Tenerife, 28°29′58.758″N, 16°11′46.8276″W) in April 2023. Specimens were observed in two types of inland culture tanks with an open system water supply: a 500 m3 raceway tank used as a reserve tank and a shallow tank (16 m2 and 0.5 m height) used for maintenance of the echinoderm Coscinasterias tenuispina and the anemone Exaiptasia diaphana, which are used for a test of Integrated Multi-Trophic Aquaculture. In September 2023, four specimens were randomly collected from the latter tank. Two specimens were preserved in formaldehyde (5%) for morphological analysis using identification keys provided by Jarms and Morandini (Reference Jarms and Morandini2019). The remaining two specimens were preserved in 98% ethanol.
One 16S rDNA sequence, available in GenBank (accession number PP496631), was determined for one of the Cassiopea preserved in ethanol. Its genomic DNA was extracted with the ‘QuickExtract™ DNA Extraction Solution’. Polymerase chain reaction (PCR) included a mixture of 0.25 μl of DNA template, 0.4 μl of each primer (primers SHA and SHB designed by Cunningham and Buss, Reference Cunningham and Buss1993), 6.5 μl of ‘Supreme NZYTaq II 2x Green Master Mix’ (Nzytech, Lisbon, Portugal), and 5.25 μl of H2O, subjected to the following conditions: 95°C for 5 min (one cycle), followed by 34 cycles consisting of 94°C for 30 s, 46.5°C for 40 s, and 72°C for 45 s, and a final extension at 72°C for 5 min. After checking the success of the PCR through an electrophoresis run in agarose gel, the PCR product was purified using ‘AMPure XP’ (Beckman Coulter, Inc.) and later subjected to Sanger sequencing. The taxonomic identity of the 16S barcode generated was then confirmed through a ‘Nucleotide Blast’ search in GenBank (https://blast.ncbi.nlm.nih.gov/). Finally, we then retrieved all the 16S barcodes of C. andromeda available in GenBank, aligned these with two sequences of Cassiopea xamachana (sister species, used as outgroup) and the new 16S barcode of C. andromeda from the Canary Islands, and generated a maximum-likelihood phylogenetic tree through the PHYML server (http://atgc.lirmm.fr/phyml/).
Results
Cassiopea specimens showed an exumbrella disc-shaped with a bell diameter varying from 10 to 5.4 cm for the preserved specimens and 2 cm for the specimens used for molecular analysis; 16 rhopalia; five short and blunt marginal lappets between each rhopalium (Figure 1C); eight dichotomous oral arms that were longer (10 cm specimen) or shorter (5.4 cm specimen) than the bell radius; colour of the club-shaped vesicle was variable from white (Figure 1A, B) to dark brown and blue, mainly with a brown umbrella.
Figure 1. Cassiopea andromeda specimens observed and sampled on Tenerife Island: (A) live specimen in the tank; (B) preserved specimen, (C) marginal lappet. Credit: (A) Alejandro Escánez; (B, C) Sonia K.M. Gueroun.
The 16S sequence determined for one of the Cassiopea from the Canary Islands revealed 100% identical to 16S sequences of Cassiopea andromeda collected in Florida (Daglio and Dawson, Reference Daglio and Dawson2017; Muffett and Miglietta, Reference Muffett and Miglietta2023) and sister to one 16S haplotype known from the Pacific Ocean and the Red Sea (Figure 2).
Figure 2. Maximum-likelihood phylogenetic tree, with 1000 repeats of standard bootstrap analysis, including all the available 16S sequences of Cassiopea.
Discussion
The present study constitutes the first confirmed record of Cassiopea andromeda in the eastern Atlantic, supported by DNA barcoding with the 16S rDNA marker. While the specimens in the aquaculture tank were sighted in April 2023, reaching a density peak in September 2023, Citizen Science (https://redpromar.org) reported the presence of Cassiopea specimens in August 2023 on a beach (8 m depth) less than 2 km to the east of the current study location. Another recent sighting occurred in February 2024 (same location, 5 m depth), suggesting the persistence of C. andromeda during winter and a potential population establishment in the Canary Islands. Although C. andromeda has recently been documented in Cabo Verde based on morphological analysis (Moro et al., Reference Moro, Herrera, Ayza, Ocaña, Monterroso, Freitas, León, Cozzi, Iglesias, Marrero, Martín, Carballo, Rabeling, Bacallado and Ortea2020), the identification of the Cassiopea species solely based on morphological traits cannot be reliable (Gamero-Mora et al., Reference Gamero-Mora, Collins, Boco, Geson and Morandini2022), as is often the case with several scyphozoan species (Bayha et al., Reference Bayha, Collins and Gaffney2017; Lawley et al., Reference Lawley, Gamero-Mora, Maronna, Chiaverano, Stampar, Hopcroft, Collins and Morandini2021; Moura et al., Reference Moura, Ropa, Magalhães and Gonçalves2022). Among the ten valid species in the Cassiopea genus, only Cassiopea frondosa presents unique traits and can be precisely identified. For the remaining species, morphological traits are too plastic and occur in more than one nominal species, rendering morphology-based identifications unreliable (Jarms and Morandini, Reference Jarms and Morandini2019; Gamero-Mora et al., Reference Gamero-Mora, Collins, Boco, Geson and Morandini2022; Muffett and Miglietta, Reference Muffett and Miglietta2023). Despite this, around half of the scientific literature records of C. andromeda worldwide have been determined based on morphological analyses, either from anatomical laboratory approaches or from specimens photographed during dives/snorkelling, decreasing the resolution of the morphological analysis (Figure 3).
Figure 3. Worldwide records of C. andromeda and its identification method in the literature and in OBIS (2024) (black spots) (Holland et al., Reference Holland, Dawson, Crow and Hofmann2004; Çevik et al., Reference Çevik, Erkol and Toklu2006; Özgür and Öztürk, Reference Özgür and Öztürk2008; Schembri et al., Reference Schembri, Deidun and Vella2010; Gülşahin and Tarkan, Reference Gülşahin and Tarkan2012; Armani et al., Reference Armani, Tinacci, Giusti, Castigliego, Gianfaldoni and Guidi2013; Kayal et al., Reference Kayal, Roure, Philippe, Collins and Lavrov2013; Prasade et al., Reference Prasade, Nagale and Apte2016; Gómez Daglio and Dawson, 2017; Maggio et al., Reference Maggio, Allegra, Bosch-Belmar, Cillari, Cuttitta, Falautano, Milisenda, Nicosia, Perzia, Sinopoli and Castriota2019; Karunarathne et al., Reference Karunarathne, Liyanaarachchi and De Croos2020; Moro et al., Reference Moro, Herrera, Ayza, Ocaña, Monterroso, Freitas, León, Cozzi, Iglesias, Marrero, Martín, Carballo, Rabeling, Bacallado and Ortea2020; Stampar et al., Reference Stampar, Gamero-Mora, Maronna, Fritscher, Oliveira, Sampaio and Morandini2020; Thé et al., Reference Thé, Gamero-Mora, Chagas da Silva, Morandini, Rossi and Soares2021; Muffett and Miglietta, Reference Muffett and Miglietta2023).
The presence of C. andromeda in the eastern Atlantic is still unclear. This nominal species, originally described from the Red Sea, was so far DNA barcoded from the Red Sea (only one specimen), the Mediterranean, Brazil, the Caribbean, Florida, and the Pacific Ocean in French Polynesia, Baja California, and Hawaii (Maggio et al., Reference Maggio, Allegra, Bosch-Belmar, Cillari, Cuttitta, Falautano, Milisenda, Nicosia, Perzia, Sinopoli and Castriota2019; Muffett and Miglietta, Reference Muffett and Miglietta2023). The 16S haplotype of C. andromeda we detected in the Canary Islands is only known to occur in Florida (Figure 2) and eventually in Hawaii (cf. Muffett and Miglietta, Reference Muffett and Miglietta2023), but is still unknown to occur in the natural biogeographic range of the nominal species, preventing further explanation on the species introduction into the Atlantic based on molecular methods.
An introduction of the pelagic stage (which, in the Cassiopea's case, would most likely be the ephyrae rather than the medusae, which typically reside on shallow substrates) via oceanic currents is less likely plausible as the main current systems in Macaronesia follow a southward direction and then turn west in the south of the Canary Islands after joining the North Equatorial Current towards the Tropical West Atlantic. A hull fouling-mediated introduction of the polyps is a more probable scenario, especially in the Canary Islands, where the number of ports/marinas and the total marina area have a strong effect on the non-native species richness, alongside the distance from the mainland (Castro et al., Reference Castro, Carlton, Costa, Marques, Hewitt, Cacabelos, Lopes, Gizzi, Gestoso, Monteiro, Costa, Parente, Ramalhosa, Fofonoff, Chainho, Haroun, Santos, Herrera, Marques, Ruiz and Canning-Clode2022). In the case at hand, the presence of a nearby harbour next to the aquaculture facility where C. andromeda was sighted (<800 m distance), strongly points to the boat-mediated introduction hypothesis.
Thé et al. (Reference Thé, Gamero-Mora, Chagas da Silva, Morandini, Rossi and Soares2021) were the first to identify C. andromeda in aquaculture settings, specifically semi-natural ponds for prawn farming on Brazilian mangroves and old salt flat ponds. The present record is the first in artificial marine aquaculture tanks located inland. Aquaculture facilities' nutrient-rich and stable environmental conditions support the development and reproduction of C. andromeda (Thé et al., Reference Thé, Barroso, Mammone, Viana, Batista Melo, Mies, Banha, Morandini, Rossi and Soares2020, Reference Thé, Gamero-Mora, Chagas da Silva, Morandini, Rossi and Soares2021, Reference Thé, Mammone, Piraino, Pennetta, De Benedetto, Garcia, de Oliveira Soares and Rossi2023). The establishment and blooms of jellyfish, including allochthones species, in areas associated with aquaculture activities have been described worldwide in several species (Lo et al., Reference Lo, Purcell, Hung, Su and Hsu2008; Dong et al., Reference Dong, Liu and Keesing2010, Reference Dong, Morandini, Schiariti, Wang and Sun2019).
An upside-down jellyfish, identified as C. andromeda was recorded in the Cabo Verde (Moro et al., Reference Moro, Herrera, Ayza, Ocaña, Monterroso, Freitas, León, Cozzi, Iglesias, Marrero, Martín, Carballo, Rabeling, Bacallado and Ortea2020) in 2019, but only based on general morphology. Assuming that the observed specimen was indeed C. andromeda, then its successive observation in Cabo Verde and then in the Canary Islands may constitute another example supporting the ‘stepping stone’ biogeographical concept along various species (Afonso et al., Reference Afonso, Porteiro, Fontes, Tempera, Morato, Cardigos and Santos2013; Schäfer et al., Reference Schäfer, Monteiro, Castro, Rilov and Canning-Clode2019; Schäfer, Reference Schäfer2023).
Various human activities may facilitate the potential spread of C. andromeda in Tenerife and other Canary Islands. The Canary Islands, being major tourist destinations in Europe, have experienced significant degradation of their coastal habitats due to tourism (Riera and Delgado, Reference Riera, Delgado and Charles2019). This degradation includes the modification of shorelines to create artificial beaches, marinas, and seaports, resulting in the proliferation of artificial structures such as rock walls, breakwaters, dykes, and groynes (Riera et al., Reference Riera, Becerro, Stuart-Smith, Delgado and Edgar2014; Riera and Delgado, Reference Riera, Delgado and Charles2019). These modified areas, characterized by shallow, sunlit waters, soft bottoms, and often high nutrient levels, provide ideal conditions for the establishment of C. andromeda colonies (Duarte et al., Reference Duarte, Pitt, Lucas, Purcell, Uye, Robinson, Brotz, Decker, Sutherland, Malej, Madin, Mianzan, Gili, Fuentes, Atienza, Pagés, Breitburg, Malek, Graham and Condon2013; Mammone et al., Reference Mammone, Ferrier-Pages, Lavorano, Rizzo, Piraino and Rossi2021; Cillari et al., Reference Cillari, Allegra, Berto, Bosch-Belmar, Falautano, Maggio, Milisenda, Perzia, Rampazzo, Sinopoli and Castriota2022). In addition, human-mediated introduction via the frequent ship traffic between the Canary Islands, other oceanic islands (Madeira, Azores), and the continental shores of Europe and Africa will more likely contribute to its long-distance spread in the eastern Atlantic, alongside the tropicalization of these waters.
Data
The data supporting this study's findings are available from the corresponding author, S. K. M. G., and the author, C. J. M., for molecular data, upon reasonable request.
Acknowledgements
We thank the anonymous reviewers for their valuable comments and suggestions for improving the manuscript.
Author contributions
Sampling and monitoring: A. E., E. A.; morphological analysis: S. K. M. G.; molecular analysis: C. J. M.; scientific writing: S. K. M. G., C. J. M., A. E., E. A.; manuscript editing: S. K. M. G., C. J. M.
Financial support
Sonia K. M. Gueroun is currently funded by the Madeira regional funds through ARDITI (CEECINST/00098/2018 Concurso Estímulo ao Emprego Científico Institucional 2018). Alejandro Escánez has been funded by the Action financed by the Ministry of Universities of the Spanish Government under the application 33.50.460A.752 and by the European Union NextGeneration EU/PRTR through a Margarita Salas contract of the University of Vigo. Eduardo Almansa's activities are funded by the European Maritime and Fisheries Fund (Project AMTI- Integrated Multi-Throphic Aquaculture). Carlos J. Moura was funded by FCT (Portuguese Foundation for Science and Technology) and Aga-Khan Foundation through project MARAFRICA (AGA-KHAN/540316524/2019).
Competing interests
None.
