Ischadium recurvum - Hooked mussel

The species is native to the Northwest Atlantic Ocean. Its natural range extends from Cape Cod (Massachusetts, United States) in the north to the Gulf of Mexico in the south ^[2,3].

First observation in Belgium

In the spring (April and June) of 2021, 10 live juvenile specimens of the Hooked mussel were first found in Belgium, in the Doeldok in the Port of Antwerp. The organisms were attached to the concrete quay walls in a macroinvertebrate community dominated by the also non-native Australian tubeworm Ficopomatus enigmaticus ^[4].
 

Distribution in Belgium

To date, Belgian in situ observations are limited to the Waaslandhaven (including the Doeldok) in the Port of Antwerp ^[4-6].
 

Distribution in neighbouring countries

In 2018, the Hooked mussel was first observed in the Netherlands, in the North Sea Canal ^[7]. Based on growth lines, it is suspected that the species likely established itself in the area before 2012 ^[7,8]. To date, Belgium and the Netherlands are the only European countries where the species has been found.

The method of introduction for the Hooked mussel is unknown, but there is a strong suspicion that it occurred via ballast water or through fouling on ship hulls ^[4,7,8]. The introduction to the Port of Antwerp may have occurred directly from its origin area or indirectly through secondary transport (e.g., by drifting with sea currents) from the Dutch North Sea Canal ^[4].

The Hooked mussel is an epibenthic brackish water mussel found in salinities between 4.5 and 36 psu, but it requires a salinity above 8 psu to reproduce ^[3,9,10]. Although the species tolerates a wide range of water temperatures, from around freezing to 37°C, it is most successful in warm temperate and tropical waters ^[3]. The mussel is found in shallow water – from the intertidal zone to a depth of approximately 9 meters – in environments with moderate to low wave energy, where it attaches with byssal threads to hard substrates such as rocks, oyster reefs, and concrete quay walls ^[2,11].

Belgian ports provide suitable substrates for these organisms to attach to. Whether the species will establish itself permanently in the Port of Antwerp (as it has in the North Sea Canal, which has similar environmental and habitat characteristics) remains unclear. At the time of sampling, the salinity was 6.4 psu ^[12], which is too low for reproduction. However, a salinity of 11 psu was previously recorded at the same location during the summer ^[13], which could theoretically support reproduction. Additionally, brackish waters are typically low in species diversity and thus represent a relatively empty niche, making these areas susceptible to invasion and establishment by exotics ^[14]. It is therefore plausible that a population of the Hooked mussel will establish itself (or is already established) in the Port of Antwerp.

The species undergoes a planktonic larval stage ^[9,15], which allows the larvae to drift with sea currents, potentially facilitating further secondary spread. However, it is unlikely that the species will form large populations outside the Port of Antwerp. The Scheldt is a highly dynamic river with a substrate predominantly composed of soft sediments ^[16], whereas the species prefers environments with moderate to low wave energy and hard surfaces ^[2,11]. Consequently, potential spread is likely to be limited to other docks and canals with brackish water.

The potential impact of an established population of the Hooked mussel on the native fauna in the Port of Antwerp is not well understood ^[4]. The Hooked mussel is an efficient filter feeder primarily consuming phytoplankton ^[17-19], which could potentially lead to competition with other native or non-native filter feeders ^[4]. Conversely, the mussel itself is an important prey species for crustaceans and waterfowl ^[20,21].

Wherever the species is found, density typically ranges between 50 and 1,900 individuals per square meter, depending on salinity and substrate suitability, but densities of up to 8,450 individuals per square meter have been recorded on artificial oyster reefs ^[22-25]. Given that the Hooked mussel forms dense clusters ^[11] and can rapidly colonise artificial substrates, the species has potential for biofouling in sheltered areas with low wave energy (e.g., cooling water installations), as previously reported in the Port of Antwerp and elsewhere in Europe for another non-native species: Mytilopsis leucophaeata (Conrad’s false mussel) ^[26]. Further monitoring in the region is needed to track its spread and possible ecological effects ^[4].

The Hooked mussel is characterised by a somewhat sturdy, triangular shell that is slightly convex and angled. The surface is decorated with a pattern of fine, raised lines that often radiate towards the posterior end. The exterior of the shell is blue-black, while the interior is polished, purplish with a white edge. The species can reach a maximum length of 63.5 mm ^[2,3].

This mussel has separate sexes ^[27], reaches maturity at a shell length of approximately 25 mm ^[3], and has one annual spawning cycle ^[28]. Reproduction begins in the spring at a water temperature of 17.7°C and can continue until the temperature drops to 11.6°C in the autumn ^[27].

[1]          World Register of Marine Species (WoRMS) (2024). Ischadium recurvum (Rafinesque, 1820). https://www.marinespecies.org/aphia.php?p=taxdetails&id=156861 (2024-10-18). 

[2]          Abbott, R.T.; Morris, P.A. (2001). A field guide to shells: Atlantic and Gulf coasts and the West Indies. 4th Edition. Peterson Field Guide Series, 3. Houghton Mifflin: Houghton [Boston]. ISBN 9780618164394. xxxiii, 350 pages : illustrations pp. [https://www.vliz.be/en/imis?module=ref&refid=394258] 

[3]          Nemesis (2022). Ischadium recurvum. https://invasions.si.edu/nemesis/species_summary/79561 (2024-02-26)

[4]          Boito, L.; Van den Neucker, T.; Van Damme, S.; Schoelynck, J. (2022). First record of the alien hooked mussel Ischadium recurvum (Rafinesque, 1820) (Bivalvia: Mytilidae) in Belgium. Belg. J. Zool. 152: 157-162. [https://www.vliz.be/nl/imis?module=ref&refid=383009]

[5]          waarnemingen.be. Ischadium recurvum (Rafinesque, 1820). https://waarnemingen.be/species/911155/ (2024-02-26) 

[6]          Bauwens, F.; Van den Neucker, T. (2023). Een speurtocht naar niet-inheemse soorten in het Galgeschoor en het Doeldok te Antwerpen. De Strandvlo 43(2): 39-50. [https://www.vliz.be/nl/imis?module=ref&refid=380571] 

[7]          Goud, J.; de Bruyne, R.; Offermans, R.; Melchers, M.; Nijland, R. (2019). Gebogen traliemossel Ischadium recurvum (Rafinesque, 1820) leeft mogelijk al sinds 2012 in het Noordzeekanaal. Spirula Newsletter = Spirula Mededelingenblad 418: 17-21. [https://www.vliz.be/en/imis?module=ref&refid=394059]  

[8]          Gmelig Meyling, A.; de Bruyne, R. (2020). De gebogen traliemossel lijkt zich nog niet uit te breiden. Kijk op Exoten 33: 2-3. [https://www.vliz.be/en/imis?module=ref&refid=394058]

[9]          Allen, J.F. (1960). Effect of low salinity on survival of the curved mussel, Brachidontes recurvus. The Nautilus 74(1): 1-8. [https://www.vliz.be/en/imis?module=ref&refid=394057] 

[10]        Montagna, P.A.; Estevez, E.D.; Palmer, T.A.; Flannery, M.S. (2008). Meta-analysis of the relationship between salinity and molluscs in tidal river estuaries of southwest Florida, U.S.A. Am. Malacol. Bull. 24(1): 101-115. [https://www.vliz.be/nl/imis?module=ref&refid=288319] 

[11]        Kennedy, V.S. (2011). Biology of the uncommon dreissenid bivalve Mytilopsis leucophaeata (Conrad, 1831) in central Chesapeake Bay. J. Moll. Stud. 77(2): 154-164. [https://www.vliz.be/en/imis?module=ref&refid=394055] 

[12]        Boito, L.; Van den Neucker, T.; Van Pelt, D.; Maris, T.; Van Damme, S.; Schoelynck, J. (2022). Ecologisch potentieel in de dokken van de Antwerpse haven . Report Ecosystem Management Research Group ECOBE, 021-R279. Universiteit Antwerpen: Antwerpen. 46 pp. [https://www.vliz.be/en/imis?module=ref&refid=394012] 

[13]        Gittenberger, A.; Rensing, M.; Wesdorp, K.H.; D’Hont, A. (2018). Monitoring non-native species in the port of Antwerp in 2017 conform the joint HELCOM/OSPAR port survey protocol. Commissioned by Antwerp Port Authority. GiMaRIS Rapport, 2018_01. GiMaRIS: Sassenheim. 46 pp. [https://www.vliz.be/en/imis?module=ref&refid=394011] 

[14]        Wolff, W.J. (1999). Exotic invaders of the meso-oligohaline zone of estuaries in the Netherlands: why are there so many? Helgol. Meeresunters. 52: 393-400. [https://www.vliz.be/nl/imis?module=ref&refid=40219] 

[15]        Chanley, P. (1970). Larval development of the hooked mussel, Brachidontes recurvus Rafinesque (Bivalvia: Mytilidae) including a literature review of the larval characteristcs of the Mytilidae (1970). Proceedings of the National Shellfisheries Association 60: 86-94. [https://www.vliz.be/en/imis?module=ref&refid=394014] 

[16]        Meire, P.; Ysebaert, T.J.; Van Damme, S.; Van den Bergh, E.; Maris, T.; Struyf, E. (2005). The Scheldt estuary: a description of a changing ecosystem. Hydrobiologia 540(1-3): 1-11. [https://www.vliz.be/nl/imis?module=ref&refid=75930] 

[17]        Gedan, K.B.; Kellogg, L.; Breitburg, D.L. (2014). Accounting for multiple foundation species in oyster reef restoration benefits. Restor. Ecol. 22(4): 517-524. [https://www.vliz.be/en/imis?module=ref&refid=394006] 

[18]        Galimany, E.; Lunt, J.; Domingos, A.; Paul, V.J. (2018). Feeding behavior of the native mussel Ischadium recurvum and the invasive mussels Mytella charruana and Perna viridis in FL, USA, across a salinity gradient. Est. Coast. 41(8): 2378-2388. [https://www.vliz.be/en/imis?module=ref&refid=394005] 

[19]        Galimany, E.; Lunt, J.; Freeman, C.J.; Segura-García, I.; Mossop, M.; Domingos, A.; Houk, J.; Paul, V.J. (2021). Bivalve feeding on the brown tide Aureoumbra lagunensis in a shallow coastal environment. Front. Mar. Sci. 8: 714816. [https://www.vliz.be/en/imis?module=ref&refid=394004] 

[20]        Ebersole, E.L.; Kennedy, V.S. (1995). Prey preferences of blue crabs Callinectes sapidus feeding on three bivalve species. Mar. Ecol. Prog. Ser. 118: 167-177. [https://www.vliz.be/en/imis?module=ref&refid=394003] 

[21]        Wells-Berlin, A.M.; Perry, M.C.; Kohn, R.A.; Paynter, K.T.; Ottinger, M.A. (2015). Composition, shell strength, and metabolizable energy of Mulinia lateralis and Ischadium recurvum as food for wintering surf scoters (Melanitta perspicillata). PLoS One 10(5): e0119839. [https://www.vliz.be/en/imis?module=ref&refid=394002] 

[22]        Bergquist, D.C.; Hale, J.A.; Baker, P.; Baker, S.M. (2006). Development of ecosystem indicators for the Suwannee River estuary: Oyster reef habitat quality along a salinity gradient. Est. Coast. 29(3): 353-360. [https://www.vliz.be/en/imis?module=ref&refid=394010] 

[23]        Rodney, W.S.; Paynter, K.T. (2006). Comparisons of macrofaunal assemblages on restored and non-restored oyster reefs in mesohaline regions of Chesapeake Bay in Maryland. J. Exp. Mar. Biol. Ecol. 355(1): 39-51. [https://www.vliz.be/en/imis?module=ref&refid=394009] 

[24]        Poirrier, M.A.; Caputo, C.E. (2015). Rangia cuneata clam decline in Lake Pontchartrain from 2001 to 2014 due to an El Niño Southern Oscillation shift coupled with a period of high hurricane intensity and frequency. Gulf and Caribbean Research 26(1): 9-20. [https://www.vliz.be/en/imis?module=ref&refid=394008] 

[25]        Lipcius, R.N.; Burke, R.P. (2018). Successful recruitment, survival and long-term persistence of eastern oyster and hooked mussel on a subtidal, artificial restoration reef system in Chesapeake Bay. PLoS One 13(10): e0204329. [https://www.vliz.be/en/imis?module=ref&refid=394007] 

[26]        Verween, A.; Vincx, M.; Degraer, S. (2010). Mytilopsis leucophaeata: the brackish water equivalent of Dreissena polymorpha? A review, in: van der Velde, G. et al. (Ed.) The Zebra mussel in Europe. pp. 29-43. [https://www.vliz.be/nl/imis?module=ref&refid=197919] 

[27]        Allen, J.F. (1962). Gonad development and spawning of Brachidontes recurvus in Chesapeake Bay. The Nautilus 76(1): 9-16. [https://www.vliz.be/en/imis?module=ref&refid=394000] 

[28]        Shaw, W.N. (1965). Seasonal setting patterns of five species of bivalves in the Tred Avon River, Maryland. Chesapeake Science 6(1): 33-37. [https://www.vliz.be/en/imis?module=ref&refid=393997]

VLIZ Alien Species Consortium (2024). Ischadium recurvum – Hooked mussel. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 6 pp.