Yoldia limatula - File yoldia

The species is originally from the cold-temperate waters of the eastern coast of North America, ranging from Nova Scotia to North Carolina ^[1,2].

First observation in Belgium

The first observation of the File yoldia on Belgian territory occurred on September 30, 2020, on the beach between Oostduinkerke and Koksijde, following storm Odette. Four days later, a third specimen was found on the beach at Koksijde. The limited wear on the shells indicates that they were transported over a short distance and likely lived near the site of discovery ^[4].
  

Distribution in Belgium

Since the first observations in 2020, the species has been regularly reported at the beach of Knokke-Heist ^[5] and Bredene ^[6], as well as approximately 5 to 10 km off the coast of Zeebrugge and Knokke-Heist ^[5,6].
 

Distribution in neighbouring countries

On September 26, 2019, the File yoldia was found in a sediment sample in the Western Scheldt near Vlissingen (the Netherlands), marking the first observation of the species in Europe ^[7]. Two years later, in June 2021, both juvenile and adult specimens were found in the Voordelta ^[8].

In 2021, the species was observed for the first time in French waters, near the port of Le Havre (Normandy). Given that the Dutch and Belgian specimens from 2019 and 2020 were mature individuals over four years old, it is possible that the species was introduced to this region around five years earlier, and the population in Le Havre could be a result of secondary spread ^[9]. However, direct introduction from North America cannot be ruled out ^[9], as the Le Havre marina serves as a hotspot for the introduction of marine non-native species via ballast water ^[10].

A potential introduction vector is the transport of larvae in ship ballast water, which could also explain the initial occurrence in the Western Scheldt, an area characterised by intense shipping activity ^[4,9].

Given the limited number of observations in Belgian waters, it is premature to assert that the species has a successful presence in Belgian waters. In its natural range, the File yoldia primarily inhabits subtidal shallow waters (5 to 100 meters depth, occasionally up to 500 meters ^[3]), especially in bays and estuaries ^[2,12]. The species prefers silty substrates ^[13]. Areas with silt and muddy sand are primarily found along the Belgian coast between Ostend and Zeebrugge, but there are also silty zones on the West Coast that could be suitable for this species ^[4]. The increasing amount of silt in coastal waters may favor silt-loving species such as the File yoldia ^[4].

The larvae of the File yoldia undergo a short planktonic stage (4 to 7.5 days). This allows the larvae to disperse somewhat naturally by drifting with surface currents before settling on the seabed ^[9].

Based on public OBIS data, the optimal water temperature for the File yoldia is between 10 and 15°C, although the species has been found in waters ranging from 5 to 20°C ^[11]. The optimal salinity appears to be between 30 and 35 psu, but the species has also been recorded in waters with a salinity of 25 psu ^[11]. These conditions, combined with the presence of suitable substrate (as detailed further), suggest that the North Sea area provides an ideal habitat for the File yoldia to establish itself.

As a rapid burrower ^[13], the File yoldia disturbs the sediment, which can significantly impact the sediment structure (through bioturbation) and the native benthic community when present in large numbers ^[4]. Additionally, the sediment structure can be affected by the expulsion of indigestible remains and 'subsurface' sediment (from about 2-3 cm below the sediment-water interface ^[15]) into the water column through their siphons, with quantities exceeding 10 to 200 times their body weight on a daily basis ^[16,17]. Although bioturbation can positively influence ecosystem function by improving oxygen penetration and processing organic material, it can also have negative effects on other benthic organisms ^[8].

No management measures for this species are currently known.

The File yoldia is characterised by an elongated and flattened shell that is gaping on both sides, with the posterior end tapering to a beak-like point. The umbos are small and centrally located. The outer surface of the shell is covered with a shiny brown-green periostracum (outer skin), but when worn away, the shells appear smooth and glossy white. The hinge is also distinctive, with a row of 20 to 25 small, uniform teeth (taxodont) on either side of the ligament groove. Additionally, the foot, which extends outside the shell, is marked by a transverse ribbed longitudinal groove ^[4]. This foot primarily serves to burrow the shell into the sediment, with the File yoldia living approximately two-thirds buried in the sediment ^[13]. Using its two palps, the animal collects food mainly consisting of detritus ^[4].

In its natural range, the species can grow up to 64 mm in length ^[2,12]. In our regions, however, the specimens found were considerably smaller, ranging between 45 and 48 mm in length ^[4,7].

[1]          World Register of Marine Species (WoRMS) (2024). Yoldia limatula (Say, 1831). https://www.marinespecies.org/aphia.php?p=taxdetails&id=157005 (2024-10-18). 

[2]          Abbott, R.T. (1974). American Seashells: the marine Mollusca of the Atlantic and Pacific coasts of North America. Second edition. Van Nostrand Reinhold: New York. ISBN 0-442-20228-8. 663 pp. [https://www.vliz.be/nl/imis?module=ref&refid=16563] 

[3]          Ockelmann, K.W. (1954). On the interrelationship and the zoogeography of northern species of Yoldia Möller, s. str. (Mollusca, Fam. Ledidae). Meddelelser om Grønland, 107(7). C.A. Reitzel: Copenhagen. 32 pp. [https://www.vliz.be/en/imis?module=ref&refid=393271] 

[4]          Fabrice, A.; Kerckhof, F. (2020). De Gladde snavelneut Yoldia limatula (Say, 1831), een nieuwe geïntroduceerde soort in de Belgische mariene fauna. De Strandvlo 40(3): 88-93. [https://www.vliz.be/en/imis?module=ref&refid=331657] 

[5]          GBIF. Yoldia limatula (Say, 1831). https://www.gbif.org/occurrence/map?taxon_key=2285504 (2024-01-30)

[6]          waarnemingen.be. Yoldia limatula (Say, 1831). https://waarnemingen.be/species/946539/ (2024-01-30)

[7]          Driessen, F., van Looijengoed, W., de Bruyne, R. (2020). De Gladde snavelneut, een nieuwe tweekleppige in Nederland. In: Nature Today. Stichting ANEMOON. https://www.naturetoday.com/intl/nl/nature-reports/message/?msg=26297 

[8]           Craeymeersch, J., Leuverink, C. (2021). Wanneer bereikt de Gladde snavelneut de Waddenzee? In: Nature Today. Stichting ANEMOON. https://www.naturetoday.com/intl/nl/nature-reports/message/?msg=27889 

[9]           Dauvin, J.-C.; Gofas, S.; Raoux, A.; Bouchet, V.; Pavard, J.-C.; Pezy, J.-P. (2022). The American protobranch bivalve Yoldia limatula (Say, 1831) in European waters. Bioinvasions Records 11(2): 473-481 [https://www.vliz.be//en/imis?refid=353499]

[10]        Pezy, J.-P.; Baffreau, A.; Raoux, A.; Rusig, A.-M.; Mussio, I.; Dauvin, J.C. (2021). Non-indigenous species in marine and brackish waters along the Normandy coast. Bioinvasions Records 10(4): 755-774. [https://www.vliz.be/en/imis?module=ref&refid=393272] 

[11]        OBIS. Yoldia limatula (Say, 1831). https://obis.org/taxon/157005 (2024-01-30)   

[12]        Rehder, H.A. (1981). The Audubon Society field guide to North American seashells. Alfred A. Knopf: New York. 894 pp. [https://www.vliz.be/en/imis?module=ref&refid=393273] 

[13]        Drew, G.A. (1899). Some observations on the habits anatomy and embryology of members of the Protobranchia. Anat. Anz. XV(24): 493-519. [https://www.vliz.be/en/imis?module=ref&refid=393274] 

[14]        Fettweis, M.; Du Four, I.; Zeelmaekers, E.; Baeteman, C.; Francken, F.; Houziaux, J.-S.; Mathys, M.; Nechad, B.; Pison, V.; Vandenberghe, N.; Van den Eynde, D.; Van Lancker, V.R.M.; Wartel, S. (2007). Mud Origin, Characterisation and Human Activities (MOCHA): Final report. Belgian Science Policy: Brussel. 59 pp. [https://www.vliz.be/nl/imis?module=ref&refid=115401] 

[15]        Rhoads, D.C.; Young, D.K. (2020). The influence of deposit-feeding organisms on sediment stability and community trophic structure. J. Mar. Res. 78(3): 169-195. [https://www.vliz.be/en/imis?module=ref&refid=393275] 

[16]        Bender, K.; Davis, W.R. (1984). The effect of feeding by Yoldia limatula on bioturbation. Ophelia 23(1): 91-100. [https://www.vliz.be//en/imis?refid=353498]

[17]        Rhoads, D.C. (1963). Rates of sediment reworking by Yoldia limatula In Buzzards Bay, Massachusetts, and Long Island Sound. J. Sediment. Petrol. 33: 723-727. [https://www.vliz.be/en/imis?module=ref&refid=393277]

VLIZ Alien Species Consortium (2024). Yoldia limatula – File yoldia. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 5 pp.