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. 2026 Oct 6;107(10):e70540. doi: 10.1002/ecy.70540

First discovery of a barnacle (Balanus crenatus) on the critically endangered flapper skate (Dipturus intermedius)

Adnan Shahdadi 1, Danielle L Orrell 2,3, Alfonso Cohuo 2,3, Min‐Hsien Lee 1, Benny K K Chan 1,✉
PMCID: PMC13640494  PMID: 42836568

Charles Darwin, who devoted many years to the study of barnacles, once remarked that “Cirripedes now abound so under every zone, all over the world, that the present period will hereafter apparently have as good a claim to be called the age of Cirripedes as the Palaeozoic period has to be called the age of Trilobites” (Darwin, 1851). Thoracican barnacles are among the most versatile colonizers in the marine realm, occupying a niche breadth that spans from high‐intertidal rocks to deep‐sea hydrothermal vents. Their success is rooted in an extraordinary plasticity for substrate selection (e.g., Figure 1); they encrust everything from driftwood and ship hulls to the living tissue of crustaceans, sea turtles, and cetaceans (Chan et al., 2009; Pilsbry, 1916).

FIGURE 1.

FIGURE 1

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(a) Capture location of the flapper skate Dipturus intermedius off the south coast of Ireland (51.604, −8.616) denoted by a red box. (b) Dorsal view of a female flapper skate, D. intermedius, under evaluation during the 1‐min health screening window. The indicative location of the abnormal thorn is depicted by a black arrow. (c and d) Tail of the flapper skate, captured off the south coast of Ireland on June 14, 2023 showing the positions of the abnormal median dorsal thorn with the attached barnacles Balanus crenatus (denoted by a white circle) in between the first and second dorsal fin; (e) Magnified view of the inflamed thorn with attached barnacles, B. crenatus individuals (highlighted by black arrows) attached to the enlarged median thorn, note the other three barnacles on the left side of the three barnacles were already dissected for molecular and morphological analysis showing the calcareous bases left on the thorn's surface. Scale bar = 2 mm. Figures (b)–(d) created by Danielle L. Orrell (CETUS project); Figure E created by Benny K. K. Chan.

While marine mammals, namely, whales and dolphins, are described as “moving islands” commonly colonized by epibionts including barnacles (Geraci & Aubin, 1987). Fishes, however, are among the few animal groups on which barnacles do not commonly occur, possibly due to the protective mucus layer of fish skin (Balakrishnan, 1969). Species of Conchoderma, the stalked barnacle typically associated with floating substrates and crustaceans (including parasitic copepods and isopods), have nonetheless been recorded from several fish species, where it reportedly attaches to spines, areas of damaged skin, or in the mouth of fishes (Anislado‐Tolentino et al., 2021; Hastings, 1972). Similarly, Lepas anatifera has been documented on the damaged skin of a stranded sunfish, Mola mola (Barreiros & Teves, 2005). The occurrence of Platylepas decorata on the scales of a garpike remains the only documented case of a sessile barnacle recorded from a fish host (Ryder, 1879). Seilacher (2005) postulated that the acorn barnacle species evolved specialized anchoring mechanisms and host‐specific adaptations that allow them to settle and colonize living hosts. Similarly, Anelasma squalicola, a naked stalked barnacle, represents a highly specialized parasitic form that attaches to deep‐sea sharks that predominantly attach to the dorsal or pectoral fins in an area where the skin is thinner, or turbulence may facilitate attachment (Eliassen, 2016; Ste‐Marie et al., 2023). While ectoparasites are commonly recorded as occurring on the skin of skates in the Atlantic (superorder: Batoidea) (Boxshall, 1974), to our knowledge, there is no documented observation of any barnacle species colonizing skates (Family: Rajidae) to date.

The flapper skate, Dipturus intermedius (Parnell, 1837) is the largest skate recorded in the North Atlantic, reaching over approximately 2.5 m in total length (Last et al., 2016). Flapper skate is a conservation‐listed demersal species that exhibits K‐selected life history traits that make it vulnerable to extinction. While it has a constrained distribution (Garbett et al., 2023), mark‐recapture data suggest individuals are capable of dispersal across the North Sea (Little, 1995) and the North Channel (between Northern Ireland and southwestern Scotland; Orrell et al., 2025). Although there are published records of ectoparasites, including copepods, isopods, and marine leeches on the common skate complex (Boxshall, 1974; Isler et al., 2022), no barnacle has been reported to be attached to D. intermedius. Flapper skates possess a median row of 12–18 predorsal thorns that extends along the median disc and tail (Last et al., 2016). In the present study, we report for the first time a case where a barnacle has colonized a flapper skate (D. intermedius), which was captured in shallow water off the southwest coast of Ireland. Several specimens of boreo‐Arctic barnacle Balanus crenatus were collected from an enlarged and abnormal median thorn on the skate's tail (Figure 1).

We identified the barnacle as B. crenatus based on morphological examination. BLAST analyses showed that the newly generated cytochrome c oxidase subunit I (COI) sequence clustered within available sequences of B. crenatus, exhibiting a maximum similarity of 99.51% to a B. crenatus sequence from the North Sea (GenBank accession number PQ739635.1), supporting the results from morphological identification. In the haplotype network (Figure 2), the new sequence (H2) stays close to a common haplotype (H1), with two mutation steps between them. The COI network shows that the most common haplotype (H1) is shared between Atlantic and Pacific populations.

FIGURE 2.

FIGURE 2

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TCS haplotype network based on COI sequences of Balanus crenatus across its distribution range. Each hatch mark represents a single mutational step. Colored circles represent individual haplotypes, with colors indicating geographic regions and circle sizes proportional to haplotype frequency. Black circles denote unsampled (hypothetical) haplotypes. H1 represents the most common haplotype, and H2 represents the haplotype obtained in this study. Skate illustration created by Danielle L. Orrell using Magma (https://magma.com/).

B. crenatus was originally described from the coast of England and the North Sea and is widely distributed in the northern Atlantic, northern Pacific, and Arctic seas (Darwin, 1854; Pilsbry, 1916), as well as within the study area in the Celtic Sea (GBIF, 2023). This species occupies a variety of substrates, and while it is not considered parasitic, it has been found to occupy crustacean carapaces and molluscan shells, from the subtidal zone to deeper waters of approximately 70 m (Darwin, 1854; Pilsbry, 1916). It has also occasionally been reported from floating objects and pebbles on the seafloor, but notably not from rocky substrates (Darwin, 1854). B. crenatus is an obligate cross‐fertilizing hermaphrodite with high fecundity (over 10,000 embryos in large individuals) and peak settlement in spring and summer. It exhibits rapid juvenile growth, with basal diameter increasing by several millimeters per month (Barnes & Powell, 1953; Rainbow, 1984).

Considering the high abundance of larvae during the peak season, and the short period of planktonic naupliar stages (10 days, Weiss, 1948), B. crenatus can settle wherever suitable surfaces are encountered. Flapper skates occupy a range of depths, overlapping with that of B. crenatus, from shallow water coastal areas with a core depth range of 20–200 m but also recorded at depths of up to 600 m (Ellis et al., 2024). Flapper skates have been observed to rest for extended periods of time on the seabed, which could enable colonization by epibionts (Wearmouth & Sims, 2009). The lack of documented batoid–barnacle interactions to date is likely due to the abrasive microtopography of placoid scales, which are highly effective deterrents under normal physiological conditions (Damodaran & Murthy, 2016), reducing larval attachment success and preventing secure cementation. In this case, host pathology likely created a suitable surface for attachment, enabling colonization by opportunistic barnacle cyprids. The settlement of B. crenatus on D. intermedius represents a significant departure from known cirripede–elasmobranch interactions. In this skate specimen, settlement was localized to a site where the median thorn was enlarged and diffusely hard (mineralized) relative to the other thorns. Rajidae caudal thorns have been identified as long‐standing structures and have therefore proven useful in aging studies (Gallagher et al., 2005). The surface in this case could provide a longitudinal attachment point for opportunistic settlement. Hitchhiking events on rafting flotsam or mobile megafauna could provide a stepping stone to maintain genetic connectivity across large spatial scales (Schiffer & Herbig, 2016; Shahdadi, 2023). We posit the host‐size and predictability hypothesis, whereby large, long‐lived, mobile hosts provide a sufficiently stable substratum for epibionts, with movement facilitating reliable water flow for continuous filter feeding. While B. crenatus has been documented as being attached to floating debris that moves passively in ocean currents, flapper skates have the potential to actively disperse over large distances. For example, two skates tagged in Scotland traveled 240 km (581 days at liberty) and 900 km (~1949 days at liberty), respectively. Our finding underscores the importance of rare and opportunistic behavior in the evolutionary success of sessile invertebrates in factors including biogeographic dispersal and population connectivity and highlights the potential for elasmobranchs to act as potential vectors for epibiotic dispersal, which may be more significant than currently recognized. While current efforts to study large‐scale movements of rare skates include employing mark‐recapture and electronic tagging (i.e., satellite tags), epibionts such as barnacles offer a unique biological “passport” that can help piece together regional movements, space use, and connectivity (Detjen et al., 2015). Future work should include monitoring for epibiotic and parasitic life on flapper skates to determine their frequency of occurrence and assess potential factors that drive host‐associations. Additionally, investigation of epibiont tolerances, that is, thermal preferences, is important in the context of climate change and connectivity across remaining hot spots for critically endangered host species, like the flapper skate.

AUTHOR CONTRIBUTIONS

Adnan Shahdadi: Writing—review and editing; investigation; data analysis. Benny K. K. Chan: Conceptualization; data analysis; writing—review and editing. Danielle L. Orrell: Conceptualization; investigation; project administration; visualization; resources; writing—review and editing. Alfonso Cohuo: Investigation; review and editing. Min‐Hsien Lee: Data analysis.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

ETHICS STATEMENT

The Health Products Regulatory Authority of Ireland approved experimental procedures under project license AE19130/P189. Animal handling followed best practice guidelines for the focal species.

Supporting information

Appendix S1.

ECY-107-e70540-s001.pdf (292.3KB, pdf)

ACKNOWLEDGMENTS

Fieldwork was possible thanks to the support of the Courtmacsherry community and operators, including West Cork Charters and the Courtmacsherry Sea Angling Centre in County Cork, Ireland. We extend our sincere thanks to the fieldwork support offered by the CETUS elasmobranch research team including Dr. Damien Haberlin, Luke Harman, and Dr. Tom Doyle, as well as the broader Marine Ecology Group. Thank you also to Dr. Harley Newton and Dr. Georgina Cole for providing pathological insights. Danielle L. Orrell is funded by the Sustainable Energy Authority of Ireland under the SEAI Research, Development & Demonstration Funding Programme 2021, grant number 21/RDD/670. This is publication no. 8 of the SEAI‐funded CETUS Project. Benny K.K. Chan is supported by a grant from the National Science and Technology Council, Taiwan (NSTC‐115‐2621‐B‐001 ‐002 ‐MY3). Adnan Shahdadi is supported by the Post‐doctoral Fellowship of the National Science and Technology Council, Taiwan (NSTC‐115‐2811‐B‐001 ‐013).

Shahdadi, Adnan , Orrell Danielle L., Cohuo Alfonso, Lee Min‐Hsien, and Chan Benny K. K.. 2026. “First Discovery of a Barnacle (Balanus Crenatus) on the Critically Endangered Flapper Skate (Dipturus Intermedius).” Ecology 107(10): e70540. 10.1002/ecy.70540

Handling Editor: John Pastor

DATA AVAILABILITY STATEMENT

Details of the material examined and the methods used in this study are provided in Appendix S1: Section S1. All DNA sequences analyzed in this study are available in the National Center for Biotechnology Information (NCBI) GenBank database, with accession numbers and corresponding links provided in Appendix S1: Section S2. The sequence generated in this study is available in GenBank under accession number PX988570 at https://www.ncbi.nlm.nih.gov/nuccore/PX988570.

REFERENCES

  1. Anislado‐Tolentino, V. , Del Moral‐Flores L. F., Wakida‐Kusunoki A. T., and Andrade‐Gonzalez Z. D. S.. 2021. “Presence of Conchoderma auritum and C. virgatum (Maxillopoda, Lepadidae) and Gloiopotes huttoni (Copepoda, Caligidae) on the Black Marlin, from the Gulf of Tehuantepec, Mexico.” Crustaceana 94: 1327–1334. [Google Scholar]
  2. Balakrishnan, K. P. 1969. “Observations on the Occurrence of Conchoderma virgatum (Spengler) (Cirripedia) on Diodon hystrix Linnaeus (Pisces).” Crustaceana 16: 101–103. [Google Scholar]
  3. Barnes, H. , and Powell H. T.. 1953. “The Growth of Balanus balanoides (L.) and Balanus crenatus Bruguière under Different Conditions of Submersion.” Journal of the Marine Biological Association of the United Kingdom 32: 107–128. [Google Scholar]
  4. Barreiros, J. P. , and Teves M.. 2005. “The Sunfish Mola mola as an Attachment Surface for the Lepadid Cirriped Lepas anatifera: A Previously Unreported Association.” Aqua – International Journal of Ichthyology 10: 1–4. [Google Scholar]
  5. Boxshall, G. A. 1974. “Infections with Parasitic Copepods in North Sea Marine Fishes.” Journal of the Marine Biological Association of the United Kingdom 54: 355–372. [Google Scholar]
  6. Chan, B. K. K. , Prabowo R. E., and Lee K. S.. 2009. Crustacean Fauna of Taiwan: Barnacles. Cirripedia: Thoracica Excluding the Pyrgomatidae and Acastinae 1–297. Taiwan: National Taiwan Ocean University. [Google Scholar]
  7. Damodaran, V. B. , and Murthy N. S.. 2016. “Bio‐Inspired Strategies for Designing Antifouling Biomaterials.” Biomaterials Research 20: 18. 10.1186/s40824-016-0064-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Darwin, C. 1851. A Monograph on the Fossil Lepadidae or, Pedunculated Cirripedes of Great Britain. London: The Palaeontographical Society in London. [Google Scholar]
  9. Darwin, C. 1854. A Monograph on the Sub‐Class Cirripedia, with Figures of All the Species. The Balanidae, the Verrucidae, etc , Vol. 2. London: Ray Society. [Google Scholar]
  10. Detjen, M. , Sterling E., and Gómez A.. 2015. “Stable Isotopes in Barnacles as a Tool to Understand Green Sea Turtle (Chelonia mydas) Regional Movement Patterns.” Biogeosciences Discussions 12: 4655–4669. 10.5194/bgd-12-4655-2015. [DOI] [Google Scholar]
  11. Eliassen, L. K. 2016. “An Investigation into the Parasitic Barnacle, Anelasma squalicola; Prevalence, Infection Behaviour and Effects on its Host, Etmopterus spinax, in Lusterfjord, Norway.” Master thesis, University of Bergen Open Research Archive. https://bora.uib.no/bora-xmlui/bitstream/handle/1956/15831/146895300.pdf?sequence=1.
  12. Ellis, J. R. , McCully‐Philips S. R., Sims D., Walls R. H. L., Cheok J., Derrick D., and Dulvy N. K.. 2024. “Dipturus intermedius (Amended Version of 2021 Assessment).” The IUCN Red List of Threatened Species 2024: e.T18903491A256581177. 10.2305/IUCN.UK.20241.RLTS.T18903491A256581177.en. [DOI]
  13. Gallagher, M. , Nolan C., and Jeal F.. 2005. “The Structure and Growth Processes of Caudal Thorns.” Journal of Northwest Atlantic Fishery Science 35: 125–129. [Google Scholar]
  14. Garbett, A. , Loca S. L., Barreau T., Biscoito M., Bradley C., Breen J., Clarke M., et al. 2023. “A Holistic and Comprehensive Data Approach Validates the Distribution of the Critically Endangered Flapper Skate (Dipturus intermedius).” Journal of Fish Biology 103: 516–528. [DOI] [PubMed] [Google Scholar]
  15. GBIF . 2023. “Balanus crenatus Bruguière, 1789.” GBIF Backbone Taxonomy. Checklist Dataset. 10.15468/39omei. [DOI]
  16. Geraci, J. R. , and Aubin D. J. S.. 1987. “Effects of Parasites on Marine Mammals.” International Journal for Parasitology 17(2): 407–414. [DOI] [PubMed] [Google Scholar]
  17. Hastings, R. W. 1972. “The Barnacle, Conchoderma virgatum (Spengler), in Association with the Isopod, Nerocila acuminata Schioedte & Meinert, and the Orange Filefish, Alutera schoepfi (Walbaum).” Crustaceana 22: 274–278. [Google Scholar]
  18. Isler, L. , Benjamins S., and Dodd J.. 2022. “Observations of the Ectoparasite Community of an Endangered Elasmobranch, the Flapper Skate (Dipturus intermedius).” In MASTS Annual Science Meeting 2022: Supporting Delivery of the Blue Economy Vision.
  19. Last, P. , White W., de Carvalho M., Séret B., Stehmann M., and Naylor G.. 2016. Rays of the World. Victoria: CSIRO Publishing. 832 p. [Google Scholar]
  20. Little, W. 1995. “Common Skate and Tope: First Results of Glasgow Museum's Tagging Study.” Glasnik Prirodnjackog Muzeja u Beogradu 22: 455–466. [Google Scholar]
  21. Orrell, D. L. , Wögerbauer C., O'Reilly S., Doyle T. K., and Roche W.. 2025. “Community Science Datasets Identify the Spatial Occurrence and Hotspots of Flapper Skate (Dipturus intermedius).” Journal of Fish Biology 103: e3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Pilsbry, H. A. 1916. “The Sessile Barnacles (Cirripedia) Contained in the Collections of the United States National Museum: Including a Monograph of the American Species.” Bulletin of the United States National Museum 93: 1–366. [Google Scholar]
  23. Rainbow, P. S. 1984. “An Introduction to the Biology of British Littoral Barnacles.” Field Studies 6: 1–51. [Google Scholar]
  24. Ryder, J. A. 1879. “Strange Habitat of a Barnacle on a Gar Pike.” The American Naturalist 13: 453. [Google Scholar]
  25. Schiffer, P. H. , and Herbig H. G.. 2016. “Endorsing Darwin: Global Biogeography of the Epipelagic Goose Barnacles Lepas spp. (Cirripedia, Lepadomorpha) Proves Cryptic Speciation.” Zoological Journal of the Linnean Society 177: 507–525. [Google Scholar]
  26. Seilacher, A. 2005. “Whale Barnacles: Exaptational Access to a Forbidden Paradise.” Paleobiology 31: 27–35. [Google Scholar]
  27. Shahdadi, A. 2023. “Gene Flow with the Help of Sea Turtles: Phylogeography of the Epibiont Barnacle Chelonibia testudinaria (Linnaeus, 1758) (Crustacea: Cirripedia: Chelonibiidae) from the Persian Gulf.” Journal of Crustacean Biology 43: ruad014. [Google Scholar]
  28. Ste‐Marie, E. , Glenner H., Rees D. J., and Hussey N. E.. 2023. “First Recorded Occurrence of the Parasitic Barnacle (Anelasma squalicola) on a Greenland Shark (Somniosus microcephalus) in the Canadian Arctic.” Journal of Fish Biology 103: 189–193. [DOI] [PubMed] [Google Scholar]
  29. Wearmouth, V. J. , and Sims D. W.. 2009. “Movement and Behaviour Patterns of the Critically Endangered Common Skate Dipturus batis Revealed by Electronic Tagging.” Journal of Experimental Marine Biology and Ecology 380(1): 77–87. [Google Scholar]
  30. Weiss, C. M. 1948. “Seasonal and Annual Variations in the Attachment and Survival of Barnacle Cyprids.” The Biological Bulletin 94(3): 236–243. [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Appendix S1.

ECY-107-e70540-s001.pdf (292.3KB, pdf)

Data Availability Statement

Details of the material examined and the methods used in this study are provided in Appendix S1: Section S1. All DNA sequences analyzed in this study are available in the National Center for Biotechnology Information (NCBI) GenBank database, with accession numbers and corresponding links provided in Appendix S1: Section S2. The sequence generated in this study is available in GenBank under accession number PX988570 at https://www.ncbi.nlm.nih.gov/nuccore/PX988570.

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