Bispira polyomma - Purple fan-worm

The origin area of this species is unknown ^[2].

First observation in Belgium

The occurrence of the Purple fan-worm was first confirmed in 2018 in the marina of Zeebrugge ^[3]. This confirmed occurrence suggested that the species had already been present at this location in 2015, but was not recognised as such at that time ^[4].

Distribution in Belgium

The Purple fan-worm has not been observed in Belgium outside of the marina of Zeebrugge so far.
 

Distribution in neighbouring countries

The Purple fan-worm was first observed on 18 September 2010 in the Eastern Scheldt near Yerseke, Netherlands ^[2]. This observation marked the first ever sighting of the species. The organism could not be assigned to any known species, necessitating a new description. Since the location had been thoroughly screened previously for non-native species without finding this one, it was assumed that its presence indicated a new species introduction ^[2].

The location in Yerseke is known for frequent introductions of non-native species ^[5]. It hosts a marina and serves as a major center for shellfish trade, with inland storage basins for oysters ('oyster ponds'). The species was initially found near the water outlet of an oyster pond (over 100 individuals in less than 1 m²). A week later, on 25 September 2010 (as well as on 2 October 2010), a population of hundreds of individuals was observed in the Yerseke marina, with the majority attached to floating pontoons at water depths between 30 and 70 cm. The presence of small individuals at this location during the summer of 2011 suggested successful reproduction ^[2]. The species was first found outside Yerseke in 2014, on floating piers in the Wemeldinge marina ^[6], 5 km east of Yerseke, indicating potential further spread through recreational boating ^[7]. A year later, in 2015, the species was observed about 20 km westward in the Roompot marina in Kamperland ^[7]. Meanwhile, specimens have also been found at various locations in the Grevelingenmeer ^[8].

Given the international nature of the marina in Yerseke, where pleasure craft from Belgium, France, the United Kingdom, and the Netherlands dock, it is possible that the species was initially introduced via recreational boating ^[8]. However, this hypothesis has not yet been confirmed, so the primary introduction vector must currently be classified as 'unknown' ^[9]. The further documented secondary spread towards other marinas ^[6,7] (including Zeebrugge) suggests that the species is further dispersed via recreational boating, which means that the Purple fan-worm may soon establish itself in other western European marinas ^[7].

Besides the aforementioned introduction vector, shellfish transport also poses a potential risk for the spread of the Purple fan-worm ^[8,9]. A risk analysis indicated that this vector presents a potential risk for the spread of this species towards the Wadden Sea (in addition to recreational boating ^[9]). However, the same study categorised the likelihood of population establishment in the Wadden Sea for most habitat types as rather unlikely, based on the habitat requirements of the Purple fan-worm. For further colonization in marinas or on dikes, peat, clay banks, stones, and gravel in the region, it was stated that the habitat requirements of the species are insufficiently known, making it unclear whether the species could establish itself ^[9,10].

The species appears to be unaffected by the water temperature variations in the Eastern Scheldt, fluctuating between 0°C (winter) and 19°C (summer), indicating that temperature tolerance is not a limiting factor for further colonisation of northwestern European seas ^[2]. The tolerance to salinity variations is currently unknown, as are any potential limitations regarding water depth ^[10]. Furthermore, the species seems to occur in both areas with nearly stagnant water and places with strong currents ^[2,10]. Unlike many other species that thrive in marinas, the Purple fan-worm does not seem to have a specific preference for sheltered spots ^[7].

Observations of the Purple fan-worm are limited to habitats characterised by hard substrates (stones, wood, oyster shells, piers, etc.), to which they can attach themselves ^[7,9,10]. It is likely that this is the only substrate on which the species can establish itself ^[10]. These substrates are usually found in harbors.

Little is known about the biology of the species. However, the sexual reproduction of other Sabellidae (fan worms) results in pelagic larval stages that can be transported to new areas by currents. In some species, this stage lasts several months, while in others it is much shorter ^[11]. This variable significantly determines the natural dispersal potential of the species. However, currently, there is no information available about the larval stage of the Purple fan-worm.

The ecological effects of this species are currently difficult to assess, as little is known about it. For instance, it is not known whether the species is a strong competitor for space and/or food ^[2]. However, it is not expected that the Purple fan-worm will cause significant ecological or economic damage in the short term. Currently, these animals are still present in modest numbers within the communities on hard substrates ^[8].

With the potential further spread of the species through the transport of shellfish, rinsing with freshwater could be an effective measure to avoid contamination with living Purple fan-worms ^[9].

It appears that the species prefers vertical hard substrates (forming colonies), although there have also been observations of the species in lower densities on horizontal substrates ^[9]. The formation of colonies is most likely the result of asexual reproduction through fragmentation ^[9], where a fragment splits off from the parent organism and develops into a new individual that is genetically and morphologically identical to the parent organism. Additionally, sexual reproduction likely occurs with the formation of a larval stage, similar to other Sabellidae, but little is currently known about this as well ^[9].

The organism has a colorful appearance, especially when the animals are grouped together and their fan crowns, which reach a diameter of about 4 cm, are fully extended. The crowns have a purple-brown to gray-blue color with a characteristic spotted pattern. The crown is located at the head end of the worm's tube, which protrudes from the substrate and is used to catch plankton. The tube and the worm inside it are about 20 mm long, and the worm itself can reach a maximum thickness of 6 mm. Each fan arm has a large number of simple eyes that can detect potential danger, causing the organism to retract into its tube ^[2,8]. A detailed taxonomic and morphological description of the species is provided in the literature ^[2].

[1]          World Register of Marine Species (WoRMS) (2024). Bispira polyoma Giangrande & Faasse, 2012. https://marinespecies.org/aphia.php?p=taxdetails&id=740848 (2024-10-18)

[2]          Faasse, M.A.; Giangrande, A. (2012). Description of Bispira polyomma n. sp. (Annelida: Sabellidae): a probableintroduction to the Netherlands. Aquat. Invasions 7(4): 591-598. [https://www.vliz.be/en/catalogue?module=ref&refid=282174]

[3]          waarnemingen.be. Bispira polyoma Giangrande & Faasse, 2012. https://waarnemingen.be/observation/158504161/ (2024-05-22)

[4]          waarnemingen.be. Sabella pavonina (Savigny, 1820). https://waarnemingen.be/observation/103106656/ (2024-05-22)

[5]          Faasse, M.; Ligthart, M. (2009). American (Urosalpinx cinerea) and Japanese oyster drill (Ocinebrellus inornatus) (Gastropoda: Muricidae) flourish near shellfish culture plots in The Netherlands. Aquat. Invasions 4(2): 321-326. [https://www.vliz.be/en/imis?module=ref&refid=381265] 

[6]          Karremans, M. (2015). Bispira polyomma en Trailliella intricata in de jachthaven van Wemeldinge. Het Zeepaard 75(1): 29-31. [https://www.vliz.be/nl/imis?module=ref&refid=245449] 

[7]          Gittenberger, A.; Olthof, G.; van Os, V.; Van der Plas, M.; Schop, S.; De Vries, A.; Van der Windt, N. (2015). Bispira polyomma in Roompot Marina . Het Zeepaard 75(6): 194-196.  [https://www.vliz.be/en/catalogue?module=ref&refid=252229]

[8]          Meyling, A.G. (2021). Paarse kokerwormen geven onze wateren nog meer kleur. Kijk op Exoten 37: 2-3. [https://www.vliz.be/en/catalogue?module=ref&refid=353694]

[9]          Foekema, E.M.; Cuperus, J.; van der Weide, B. (2014). Risk assessment of alien species found in and around the oyster basins of Yerseke. IMARES Wageningen Report, C014.14. IMARES Wageningen UR: IJmuiden. 38 pp. [https://www.vliz.be/en/catalogue?module=ref&refid=353692]

[10]        Tamis, J.E.; Sneekes, A.C.; Jak, R.G. (2015). Invasieve soorten Waddenzee: introductiekansen van probleemsoorten via schelpdiertransport. IMARES Wageningen Report, C173/15. IMARES Wageningen UR: IJmuiden. 49 pp. [https://www.vliz.be/en/catalogue?module=ref&refid=353691]

[11]        Hartmann-Schröder, G. (1996). Annelida, Borstenwürmer, Polychaeta. 2nd revised ed. Die Tierwelt Deutschlands und der angrenzenden Meeresteile nach ihren Merkmalen und nach ihrer Lebensweise, 58. Gustav Fischer: Jena. ISBN 3-437-35038-2. 648 pp. [https://www.vliz.be/en/imis?module=ref&refid=23383]

VLIZ Alien Species Consortium (2024). Bispira polyomma – Purple fan-worm. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 5 pp.