Boccardiella hamata -

B. hamata is native to the east coast of the United States ^[2] and in the North Pacific Ocean, along the coast of North America ^[3] and Japan ^{[2, 4]}.

First observation in Belgium

In 2013, twelve-year-old soil samples (2001), taken in between Japanese oysters (Crassostrea gigas) at a sheltered location in the outer port of Zeebrugge, were re-examined. B. hamata was observed for the first time in these samples. Initially, the bristle worm was misidentified as Boccardiella ligerica ^{[5, 6]}.

Spreading in Belgium

It remains unclear whether the species also occurs in Belgium outside of Zeebrugge.

Spreading in neighbouring countries

The first observation of B. hamata in Europe dates back to 2013. That year, the species was seen at several locations in the southwestern part of the Dutch Delta region (Vlissingen, Yerseke, Zierikzee) ^[7]. In each case, only a few individuals were found. In the Netherlands, this bristle worm is an established species ^[8].

Today, the species has a universal distribution in temperate waters throughout the northern hemisphere ^[7].

B. hamata occurs near shipping routes and shellfish aquaculture zones. In Belgium and the Netherlands, the species got probably introduced together with crustaceans for aquaculture purposes. However, transport on ship hulls (biofouling) or in ballast water (larvae) cannot be ruled out ^[7]. The presence of large international seaports, such as Antwerp and Rotterdam, makes shipping a major introduction vector for non-indigenous species ^{[9, 10]}. After the initial introduction, the bristle worm spreads naturally, facilitated by the increase in anthropogenic structures. This has allowed the development of permanent populations in the southern North Sea ^[7].

Reproduction of B. hamata occurs via the release of planktotrophic larvae that feed on phytoplankton during their free-swimming life stage ^[2]. This allows the species to spread over large distances ^[7]. In Boccardia proboscidea, larval development can also occur differently, in which adelphophagic offspring incubate advanced eggs. These larvae grow more rapidly in a capsule and hatch at a later stage ^[11]. Depending on the populations and area of distribution, females within this species either produce only planktotrophic or adelphophagic broods. Another possibility is the production of mixed broods. Unlike Boccardiella hamata, local populations of Boccardia proboscidea may therefore increase rapidly.

The larval development of the species depends on the type of habitat ^[2].

The presence of bristle worms belonging to the genus Polydora (i.e. mud worms) is causing concern among oyster farmers. Some of these species can 'drill' holes in calcareous substrates, such as the shells of molluscs ^[12-15]. This 'drilling' causes blistering and can lead to a significant reduction in growth and survival ^[16]. B. hamata is a ‘driller’, making monitoring of the habitats where the species has established essential ^[7].

B. hamata settles among Japanese oysters in Belgium and the Netherlands ^[7]. However, the species can colonise other habitats, such as shallow estuarine tidal flats ^{[3, 4]}, mudflats between rock crevices ^[2], in between tubes of fine sediment on rocks and oysters ^[2-4], between or on shells used by hermit crabs  ^{[2, 3]}, on the brackish water bay barnacle Amphibalanus improvisus ^[2], and in accumulated sand near the attachment of algae ^[3].

[1]          World Register of Marine Species (WoRMS) (2020). Boccardiella hamata (Webster, 1879). [http://www.marinespecies.org/aphia.php?p=taxdetails&id=333121] (2020-11-17).

[2]          Dean, D.; Blake, J.A. (1966). Life-history of Boccardia hamata (Webster) on the east and west coasts of North America. Biol. Bull. 130(3): 316-330. [http://www.vliz.be/nl/catalogus?module=ref&refid=299226]

[3]          Blake, J.A. (1966). On Boccardia hamata (Webster), new combination (Polychaeta: Spionidae). Bull. South. Calif. Acad. Sci. 65(3): 176-184. [http://www.vliz.be/nl/catalogus?module=ref&refid=299229]

[4]          Radashevsky, V.I. (1993). Revision of the genus Polydora and related genera from the North West Pacific (Polychaeta: Spionidae). Publ. Seto Mar. Biol. Lab. 36(1-2): 1-60. [http://www.vliz.be/nl/catalogus?module=ref&refid=299227]

[5]          Volckaert, A.; Engledow, H.; Spanoghe, G.; Degraer, S.; Vincx, M.; Coppejans, E.; Hoffmann, M. (2003). Onderzoek van de seizoenale variatie van macroalgen, macrofauna en vogels geassocieerd met interti- dale harde substraten langsheen de Vlaamse kust. Eindrapport in opdracht van het Min. Vlaamse Gemeenschap, Dept. Leefmilieu en Infrastructuur, Afd. Waterwegen en Zeewezen. Ministerie van de Vlaamse Gemeenschap: Brussel. 107 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=299243]

[6]          Engledow, H.; Spangoghe, G.; Volckaert, A.M.; Coppejans, E.; Degraer, S.; Vincx, M.; Hoffman, M. (2001). Onderzoek naar (1) de fysische karakterisatie en (2) de biodiversiteit van strandhoofden en andere harde constructies langs de Belgische kust: eindrapport van de onderhandse overeenkomst dd. 17.02.2000 i.o.v. de Afdeling Waterwegen Kust van het Ministerie van de Vlaamse Gemeenschap, Departement Leefmilieu en infrastructuur, Administratie Waterwegen en Zeewezen. Rapport Instituut voor Natuurbehoud, 2001.20. Instituut voor Natuurbehoud/Universiteit Gent: Gent. 110 + annexes pp. [http://www.vliz.be/en/imis?module=ref&refid=25266]

[7]          Kerckhof, F.; Faasse, M.A. (2014). Boccardia proboscidea and Boccardiella hamata (Polychaeta: Spionidae: Polydorinae), introduced mud worms new for the North Sea and Europe, respectively. Marine Biodiversity Records 7(76): 1-9. [http://www.vliz.be/en/imis?module=ref&refid=240728]

[8]          Nederlands Soortenregister. Overzicht van de Nederlandse biodiversiteit (2018). Boccardiella hamata. [https://www.nederlandsesoorten.nl/linnaeus_ng/app/views/species/nsr_taxon.php?id=174799] (2018-07-24).

[9]          Wolff, W.J. (2005). Non-indigenous marine and estuarine species in the Netherlands. Zool. Meded. 79(1): 3-116. [http://www.vliz.be/en/imis?module=ref&refid=101200]

[10]        Kerckhof, F.; Haelters, J.; Gollasch, S. (2007). Alien species in the marine and brackish ecosystem: the situation in Belgian waters. Aquat. Invasions 2(3): 243-257. [http://www.vliz.be/en/imis?module=ref&refid=114365]

[11]        Gibson, G.; Paterson, I.G.; Taylor, H.; Woolridge, B. (1999). Molecular and morphological evidence of a single species, Boccardia proboscidea (Polychaeta: Spionidae), with multiple development modes. Mar. Biol. (Berl.) 134(4): 743-751. [http://www.vliz.be/nl/catalogus?module=ref&refid=296697]

[12]        Hoeksema, B.W. (1983). Excavation patterns and spiculae dimensions of the boring sponge Cliona celata from the SW Netherlands. Senckenb. Marit. 15(1-3): 55-85. [http://www.vliz.be/nl/catalogus?module=ref&refid=296700]

[13]        Bailey-Brock, J.H. (2000). A new record of the polychaete Boccardia proboscidea (Family Spionidae), imported to Hawai’i with oysters. Pac. Sci. 54(1): 27-30. [http://www.vliz.be/nl/catalogus?module=ref&refid=296701]

[14]        Ruellet, T. (2004). Infestation des coquilles d’huîtres Crassostrea gigas par les polydores en Basse-Normandie: recommendations et mise au point d’un traitement pour réduire cette nuisance = Infestation of the oyster shells Crassostrea gigas by polydorid species in Normandy (France): recommendations and treatment to reduce this harmful effect. PhD Thesis. Université de Caen/Basse-Normandie: Caen. 537 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=296703]

[15]        Simon, C.A.; Thornhill, D.J.; Oyarzun, F.; Halanych, K.M. (2009). Genetic similarity between Boccardia proboscidea from Western North America and cultured abalone, Haliotis midae, in South Africa. Aquaculture 294(1-2): 18-24. [http://www.vliz.be/nl/catalogus?module=ref&refid=296704]

[16]        Sato-Okoshi, W.; Okoshi, K. (1997). Survey of the genera Polydora, Boccardiella and Boccardia (Polychaeta, Spionidae) in Barkley Sound (Vancouver Island, Canada), with special reference to boring activity. Bull. Mar. Sci. 60(2): 482-493. [http://www.vliz.be/nl/catalogus?module=ref&refid=296705]

VLIZ Alien Species Consortium (2020). Boccardiella hamata. Non-indigenous species in the Belgian part of the North Sea and adjacent estuaries anno 2020. Flanders Marine Institute (VLIZ). 4 pp.