Bugulina simplex -

In the early 20^th century, B. simplex already occurred on the east coast of North America, in the Mediterranean Sea and the Adriatic Sea. Its limited distribution in North America suggests that the species originated in the Mediterranean region ^[2]. This species was officially described by Hincks in 1886, based upon specimens from the Adriatic Sea ^[2].

First observation in Belgium

In September 2000, B. simplex was discovered for the first time in Belgium on a pontoon in the Port of Ostend ^[2]. The species is often found attached to colonies of other bryozoans, such as Cryptosula pallasiana. Other surfaces such as stone, wood, hulls, sea lettuce or ship hulls also appear to be substrates to attach to ^{[3, 4]}.

Spreading in Belgium

Initially, B. simplex was found in the marina of Ostend. In 2000 and 2001, the species occurred alongside B. stolonifera, another non-native species ^{[2, 5]}. In 2004, B. simplex was found attached to a washed-up plastic bucket at the level of the tidemark on the beach between Blankenberge and Zeebrugge ^[6]. Since June 2007, this bryozoan is a permanent resident of the marina of Zeebrugge ^{[5, 7, 8]}. In our study region, B. simplex is also found in the marinas along the Western Scheldt ^[5].

Spreading in neighbouring countries

The first detailed report of B. simplex in Great Britain dates back to 1957 when the species was sighted in Holyhead (Wales). However, there are indications that this bryozoan was already present in Britain in – maybe even before – 1893. Later, the species was observed in Lowestoft (Suffolk) ^[9]. This was immediately followed by observations a little further to the south, namely from Milford Haven (Wales). Each time, the individuals were found on test panels placed to study biofouling communities ^[10].

Recent observations along the West European coasts indicate an expansion of this species’ habitat ^{[2, 5]}. For instance, this is the case in the Netherlands. Similar to Belgium, the first observations of B. simplex occurred in September 2000, in the region of ‘Sas Van Goes’ along the Eastern Scheldt ^[3]. Due to the expansion to other marinas, this bryozoan regularly occurs locally in small concentrations in the Western and Eastern Scheldt of Zeeland ^{[5, 6]}. There are recent reports from Trébeurden Marina in France and a few locations along the south coast of England ^[5]. Furthermore, the species was recently observed in Ireland and Scotland ^[11].

Meanwhile, B. simplex is spreading to the north. In 2014, individuals were collected for the first time in a port on the Shetland Islands. Due to regular shipping traffic to Norway, it is assumed that the species will soon be introduced there as well ^[12]

Because B. simplex is often found in harbours and as a part of the biofouling community on ships and sailing yachts, this species was probably transported in this way from more southern regions ^[2].

This species’ success, especially in ports, can be explained by its attachment to solid substrates such as ship hulls or port infrastructure. Moreover, B. simplex can tolerate polluted conditions ^[2].

Due to the attachment and growth on ships and yachts, B. simplex can easily move between ports and over long distances ^[2]. Therefore, further dispersal is to be expected ^[3].

Just like other bryozoans – and many other species, including barnacles, tube worms, sea squirts etc. – B. simplex is part of the biofouling community in ports on hard substrates, like ship hulls. The removal of this fauna is extremely expensive. It requires lifting the boat out of the water, cleaning it with high pressure and treatment with antifouling paint ^[13].

In the early 21^st century, this species occurred locally and in small concentrations. Therefore, a strong expansion along the northeast Atlantic was not expected ^[3]. In the near future, scientists suspect that this species could have an effect – through competition for space – on the local fauna of ports and coasts, due to increased shipping and global warming. At the moment, B. simplex is on the rise in terms of the number of newly colonized marinas. Furthermore, the population size of this species keeps growing ^[14].

B. simplex belongs to the moss animals (Bryozoa). Bryozoans live in colonies consisting of a group of individuals – zooids – connected to each other. The colony size varies from a few tens to millions of individuals. Each zooid has a protective shell or cystid containing the body or polypide. Each individual consists of a bundle of nerves, a muscular system, a stomach with a supply channel and a “crown” of tentacles surrounding the mouth (Figure 1). The polypide can stretch out its tentacles through an opening in the cystid for feeding. The tentacles contain tiny vibrating cilia that create a water current, causing suspended particles to flow towards the mouth opening ^{[7, 15]}.

B. simplex has a bush-like appearance, similar to other Bugulina species. Although B. simplex is present throughout the year, the colonies are tallest (up to four centimetres) in August and September. During this period, larvae are released into the water column. They only have a couple of hours to settle on a suitable substrate, otherwise, they die. After the summer, the biggest part of the old colonies dies off. The newly settled colonies expand minimally at first, making them difficult to observe ^{[7, 14]}.

The Dutch common name ‘Geel vogelkopmosdiertje’ (Literal English translation: ‘yellow bird head moss animal’) is inspired by the bird-like appearance of the avicularium typical of the Bugulina species. The avicularia are the zooids responsible for the protection of the colony. They are equipped with a lid or operculum with which they are able to perform a ‘bite movement’. In our regions, you can also find the non-natives species B. stolonifera. Both species are relatively easy distinguishable, but you do need a microscope or a good loupe. The straw yellow colonies of B. simplex stand out in comparison with the relative mat-coloured colonies of B. stolonifera. Additionally, B. simplex – with a height of two to three centimetres – is smaller, and does not have two rows of individuals on each branch. Instead, B. simplex has three to six rows of zooids per branch. The branches of B. simplex are fan-shaped, which is not the case with B. stolonifera. Finally, B. simplex contains only one spine – instead of two – on the outside of each individual ^{[2, 7]}.

Figure 1: Simplified diagram of two individuals (zooids). The retractor muscle ensures that the body can be retracted into the shell. (Source: VLIZ)

[1]          World Register of Marine Species (WoRMS) (2020). Bugulina simplex (Hincks, 1886). [http://www.marinespecies.org/aphia.php?p=taxdetails&id=834016] (2020-11-17).

[2]          Kerckhof, F. (2001). Het mosdiertje Bugula simplex Hincks, 1886 (Bryozoa, Cheilostomatidae) nieuw voor de Belgische fauna. De Strandvlo 21(1): 36-39. [http://www.vliz.be/en/imis?module=ref&refid=19339]

[3]          De Blauwe, H.; Faasse, M. (2001). Extension of the range of the Bryozoans Tricellaria inopinata and Bugula simplex in the north-east Atlantic ocean (Bryozoa: Cheilostomatida). Ned. Faunist. Meded. 14: 103-112. [http://www.vliz.be/imis/imis.php?module=ref&refid=19401]

[4]          WoRMS image (2020). Bugula simplex [http://www.marinespecies.org/aphia.php?p=image&tid=111162&pic=12798] (2020-11-17).

[5]          Ryland, J.S.; Bishop, J.D.D.; De Blauwe, H.; El Nagar, E.; Minchin, D.; Wood, C.A.; Yunnie, A.L.E. (2011). Alien species of Bugula (Bryozoa) along the Atlantic coasts of Europe. Aquat. Invasions 6(1): 17-31. [http://www.vliz.be/en/imis?module=ref&refid=206248]

[6]          De Blauwe, H. (2005). Bryoza op wieren en plastic uit de herfstvloedlijn van het najaar 2004. De Strandvlo 25(1): 14-16. [http://www.vliz.be/en/imis?module=ref&refid=72344]

[7]          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]

[8]          De Blauwe, H.; Dumoulin, E. (2009). De zeefauna en -flora uit de jachthaven van Zeebrugge, in het bijzonder de fouling-organismen van drijvende pontons. De Strandvlo 29(2): 41-63. [http://www.vliz.be/imis/imis.php?module=ref&refid=139489]

[9]          Ryland, J.S. (1958). Bugula simplex Hincks, a newly recognized polyzoan from British waters. Nature 181: 1146-1147. [http://www.vliz.be/en/imis?module=ref&refid=139167]

[10]        Ryland, J.S. (1960). The Britisch species of Bugula (Polyzoa). Proc. Zool. Soc. Lond. 134: 65-105. [http://www.vliz.be/en/imis?module=ref&refid=120943]

[11]        Minchin, D.; Nunn, J.D. (2013). Rapid assessment of marinas for invasive alien species in Northern Ireland. Northern Ireland Environment Agency Research and Development Series, 13/06. Northern Ireland Environment Agency: Belfast. 113 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=297207]

[12]        Porter, J.S.; Jones, M.E.S.; Kuklinski, P.; Rouse, S. (2015). First records of marine invasive non-native Bryozoa in Norwegian coastal waters from Bergen to Trondheim. Bioinvasions Records 4(3): 157-169. [http://www.vliz.be/nl/catalogus?module=ref&refid=297208]

[13]        Woods Hole Oceanographic Institution (1952). The effects of fouling, in: Hedgepeth, J.W. Marine fouling and its prevention. Contributions of the Woods Hole Oceanographic Institution, 580. Contributions of the Woods Hole Oceanographic Institution. U.S. Naval Institute: Annapolis, Maryland: pp. 3-19. [http://www.vliz.be/en/imis?module=ref&refid=140669]

[14]        De Blauwe, H. (2010). Persoonlijke mededeling

[15]        Ruppert, E.E.; Barnes, R.D. (1994). Invertebrate zoology. 6th edition. Saunders College Publishing: Orlando. ISBN 0-03-026668-8. 1056 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=9414]

VLIZ Alien Species Consortium (2020). Bugulina simplex. Non-indigenous species in the Belgian part of the North Sea and adjacent estuaries anno 2020. Flanders Marine Institute (VLIZ). 6 pp.