Fenestrulina delicia -

In 1994, Fenestrulina delicia was observed for the first time in Maine (United States). Later, the species was sighted along the west coast of the United States, more specifically in Alaska and San Francisco ^[2]. Whether or not the species originates from the U.S. remains unknown.

First observation in Belgium

In 2009, Fenestrulina delicia was observed for the first time in Belgium, in Lombardsijde ^[3].

Spreading in Belgium

Since 2009, Fenestrulina delicia has only been observed along the Belgian coastline ^[3]. Afterwards, a determination key was published for bryozoans in Belgium and the Netherlands ^[4]. Naturalists have been able to find the species in multiple colonies, including some on washed-up plastic ^[5]. In 2020, Fenestrulina delicia was also found in the subtidal zone of the offshore wind farms ^[6].

Spreading in neighbouring countries

In the Netherlands, Fenestrulina delicia was observed in 2005. The species was found near Goesse Sas, attached to empty mussel shells at a depth of 5-10 metres. In 2011, it was present in the ‘Anna Frisopolder’ (a polder near the Scheldt). One year later (2012), Fenestrulina delicia was found in Zierikzee and Sint-Annaland. Nowadays, it is assumed that this species is widespread in the Eastern Scheldt ^[2].

Since 2002, the species has been present in Great Britain ^[7]. Five years later, it could be found in Normandy ^[2]. In May 2008, the species was found along the French coast: from the north to Pléneuf-Val-André (north Brittany) ^[5]. To the north, Fenestrulina delicia can be found as far as Helgoland (Germany), where it lives attached to brown algae. These algae are said to originate from the English Channel ^[5]. The most northern observation of the species comes from the Shetland Islands (Scotland) and between Bergen and Trondheim (Norway) ^[8].

Fenestrulina delicia often grows attached to mussel shells. Therefore, the import of bivalves for aquaculture might be an important transport vector for this bryozoan. The Japanese oyster Crassostrea/Magallana gigas and many species of mussels are still being imported from other countries, allowing foreign epifauna to travel along ^[9]. Secondary vectors could be hitchhiking on shipwrecks, algae, and plastic waste carried along by the currents ^[5].

Colonies of Fenestrulina delicia have been found on both natural (such as algae) and artificial (such as dams) substrates. After an introduction, the species can easily establish itself through the many artificial substrates in the North Sea, such as the concrete foundations of wind farms. These structures are used by many alien species, including Fenestrulina delicia, as ‘stepping stones’ to disperse towards new areas   ^{[5, 10]}.

In addition to travelling as part of the biofouling community on ship hulls, these bryozoans can adhere themselves to plastic or seaweed ^{[5, 9, 10]}.

The species' sensitivity to environmental conditions, such as salinity and temperature, has not yet been studied. Whether or not Fenestrulina delicia can establish itself in regions with a colder or tropical climate is unknown.

Attachment of biofouling species (like Fenestrulina delicia) to the hulls of ships can increase resistance when sailing. In turn, this increases fuel consumption, resulting in high economic costs. The removal of biofouling species is intensive work ^[11]. For this species, in comparison to other biofouling species (such as mussels and oysters), the effect of biofouling is smaller due to its limited size. However, intensive studies on the impact of this bryozoan as a biofouling species have yet to be conducted ^[5].

An individual bryozoan within a colony is called a zooid and consists of a cystid and a polypide. The cystid is the hard outer layer. The polypide consists of the lophophore and the organs. The lophophore can retract, and in some species, it is covered by an operculum. The cilia on the tentacles create a current that brings food towards the mouth ^[12].

Bryozoans are hermaphrodites (androgynous). The larvae exhibit positive phototaxis and swim towards the light. Later in life, they exhibit negative phototaxis and swim to the bottom, where they attach themselves to a suitable substrate. Once attached at the bottom, chemical substances in the water determine whether it is a suitable spot to remain. If so, an adhesive material gets excreted, and the larva becomes an ancestrula that founds a new colony. The ancestrula originates from sexual reproduction, but the resulting colony is formed by asexual reproduction ^{[12, 13]}.

[1]          World Register of Marine Species (WoRMS) (2024). Fenestrulina delicia Winston, Hayward & Craig, 2000. [http://www.marinespecies.org/aphia.php?p=taxdetails&id=408266] (2024-10-18).

[2]          Faasse, M.; van Moorsel, G.; Tempelman, D. (2013). Moss animals of the dutch part of the north sea and coastal waters of the Netherlands (Bryozoa). Ned. Faunist. Meded. 41: 1-14. [http://www.vliz.be/nl/catalogus?module=ref&refid=302003]

[3]          Verhaeghe, F. (2010). Het mosdiertje Fenestrulina delicia (Winston, Hayward & Craig, 2000) voor het eerst aangespoeld aan de Belgische kust, 29 december 2009, Lombardsijde. De Strandvlo 30(2): 36-38. [http://www.vliz.be/nl/catalogus?module=ref&refid=198512]

[4]          De Blauwe, H. (2009). Mosdiertjes van de Zuidelijke bocht van de Noordzee: Determinatiewerk voor België en Nederland. Vlaams Instituut voor de Zee (VLIZ): Oostende. ISBN 978-90-812-9003-6. 445 pp. [http://www.vliz.be/imis/imis.php?module=ref&refid=138282]

[5]          De Blauwe, H.; Kind, B.; Kuhlenkamp, R.; Cuperus, J.; van der Weide, B.; Kerckhof, F. (2014). Recent observations of the introduced Fenestrulina delicia Winston, Hayward & Craig, 2000 (Bryozoa) in Western Europe. Studi Trent. Sci. Nat. 94: 45-51. [http://www.vliz.be/en/imis?module=ref&refid=240414]

[6]          Degraer, S.; Brabant, R.; Rumes, B.; Vigin, L. (Ed.) (2022). Environmental impacts of offshore wind farms in the Belgian part of the North Sea: Getting ready for offshore wind farm expansion in the North Sea. Memoirs on the Marine Environment. Royal Belgian Institute of Natural Sciences, OD Natural Environment, Marine Ecology and Management: Brussels. ISBN 978-9-0732-4267-8. 106 pp. [https://www.vliz.be/nl/imis?module=ref&refid=362156] 

[7]          Wasson, B.; De Blauwe, H. (2014). Two new records of cheilostome Bryozoa from British waters. Marine Biodiversity Records 7: e123. [http://www.vliz.be/nl/catalogus?module=ref&refid=242784]

[8]          Collin, S.B.; Tweddle, J.F.; Shucksmith, R.J. (2015). Rapid assessment of marine non-native species in the Shetland Islands, Scotland. Bioinvasions Rec. 4(3): 147-155. [http://www.vliz.be/nl/catalogus?module=ref&refid=301873]

[9]          Wijsman, J.W.M.; Smaal, A.C. (2006). Risk analysis of mussels transfer. IMARES Wageningen Report, C044/06. Wageningen UR. IMARES: Ijmuiden. 103 pp. [http://www.vliz.be/en/imis?module=ref&refid=244138]

[10]          Kerckhof, F.; Norro, A.; Jacques, T.; Degraer, S. (2009). Early colonisation of a concrete offshore windmill foundation by marine biofouling on the Thornton Bank (southern North Sea), in: Degraer, S. et al. Offshore wind farms in the Belgian part of the North Sea: State of the art after two years of environmental monitoring. Management Unit of the North Sea Mathematical Models, Marine Ecosystem Management Unit/Royal Belgian Institute of Natural Sciences: Brussel: pp. 39-51. [http://www.vliz.be/en/imis?module=ref&refid=142997]

[11]        Fitridge, I.; Dempster, T.; Guenther, J.; de Nys, R. (2012). The impact and control of biofouling in marine aquaculture: a review. Biofouling 28(7): 649-669. [http://www.vliz.be/nl/catalogus?module=ref&refid=302004]

[12]        Brusca, R.C.; Brusca, G.J. (2003). Invertebrates. Second Edition. Sinauer Associates, Inc.: Sunderland, Massachusetts. ISBN 0–87893–097–3. xix, 936 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=301874]

[13]        Ramel, G. (2012). The Phylum Ectoprocta (Bryozoa). [https://www.earthlife.net/inverts/bryozoa.html] (2017-05-22).

VLIZ Alien Species Consortium (2024). Fenestrulina delicia. Introduced alien species in the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 5 pp.