Ruditapes philippinarum - Manila clam
SCIENTIFIC NAME
Ruditapes philippinarum (A. Adams & Reeve, 1850)
2011 - 2020
NW Pacific
Aquaculture - importing live animals
Intentional introduction
The Manila clam is native to the northwestern Pacific Ocean, near Japan, China, and the Philippines [2].
First observation in Belgium
On July 4, 2014, one live specimen and around thirty fresh paired shells of the Manila clam were found among the stones and reef-forming Japanese oysters (Crassostrea/Magallana gigas) near the outer dike of the Zeebrugge harbor. Based on the growth rings on the empty paired shells, it was estimated that the oldest specimen was likely about three years old, suggesting that the species may have already established itself at this location by 2011 [3]. Additionally, in 2013, fresh paired shells were reported several times on the beaches of the Western Coast, though it could not be definitively concluded whether these were washed ashore or discarded food remains [3].
Since 1980, the species has been occasionally introduced into the Sluice Dock in Ostend for cultivation and research purposes [3,4], but this has not yet resulted in a widespread presence of the Manila clam in the Spuikom [3]. Over the past decade, about four live specimens have been reported from the Spuikom [5].
Distribution in Belgium
A year after the first discovery of a live specimen in Zeebrugge, several live specimens were found on the beach of Ostend (2015) [6]. In recent years, the Manila clam has been regularly observed along the entire Belgian coastline. Although live specimens are occasionally found, the majority of records consist of shell fragments or paired shells [5].
Distribution in neighbouring countries
In 1972 and 1975, the Manila clam was intentionally introduced into the Bay of Arcachon (France) for aquaculture purposes [7]. It was later introduced into various bays and estuaries in Spain (1980) [8-11], Italy (1983) [12-14], the United Kingdom (1984-2010) [15], and Portugal (late 1980s) [8]. Shortly after its intentional introduction into Poole Harbour (southern England) in 1988 [16,17], the species was already widespread in the region [16,18,19], sparking a new type of commercial fishery targeting the Manila clam [16,20]. By 2010, at least 11 estuaries in southern England hosted established populations of this clam, including estuaries without a history of officially sanctioned introductions [15].
In 2008, the first live specimen of the Manila clam was observed in the Netherlands, in the Eastern Scheldt [21]. The species subsequently spread rapidly across the entire Eastern Scheldt and Veerse Meer [22]. In 2011 and 2012, fresh specimens with tissue remnants were found in the Western Scheldt near Kaloot (Borssele) [23]. In recent years, the species has also established itself in the Wadden Sea [24].
Given its economic importance, the Manila clam has been intentionally introduced to numerous locations worldwide for aquaculture purposes, including in Europe [7]. In addition, unintentional introductions have also occurred [3], such as in the Dutch Eastern Scheldt, where clams were carried along with mussels imported between 2005 and 2007 from areas including Poole Harbour in southern England [21,25], a site where the Manila clam had already been introduced two decades earlier [16,17].
Its presence in Belgium is likely the result of a secondary introduction. For instance, larvae from French or Dutch populations could drift with ocean currents and reach Belgium. Another possibility for secondary transport is via ballast water from ships or through sediment carried by dredging vessels operating in various Western European ports [3].
The Manila clam demonstrates great adaptability, tolerating wide variations in environmental parameters such as temperature (0–35°C), salinity (optimal between 24–35 psu), and dissolved oxygen levels [24,26]. Similar to the Japanese oyster (Crassostrea/Magallana gigas), it was previously incorrectly assumed that the low winter water temperatures along the Atlantic and North Sea coasts would prevent successful reproduction [3,16]. Reproduction typically occurs at water temperatures between 14 and 26°C (optimum 20–22°C), one or two times per year [24,26].
The Manila clam lives shallowly buried in the substrate, ranging from the intertidal zone to shallow waters, but is sometimes simply found lying loose on the surface [3]. Usually, it is buried only 2 to 4 cm deep in sandy to muddy substrates [27,28]. Occasionally, the clam attaches itself to stones or shells (e.g., oysters or mussels) using byssal threads [29].
In both its native range and colonised regions, the species seems to prefer sheltered areas with minimal wave action and relatively clear water [18]. However, occurrences along the Belgian coast (e.g., the outer dike of the Zeebrugge harbor) indicate that the species is not strictly confined to sheltered locations [3].
The Manila clam has a prolonged planktonic larval stage lasting up to 40 days [30], allowing juveniles to disperse over long distances by drifting with ocean currents [3]. Its high adaptability, combined with high fertility and an extended planktonic larval stage, enables the species to spread rapidly and establish itself in new regions.
Introduced Manila clams are capable of rapidly becoming wild. The species exhibits an invasive character in certain regions [3], partly due to its high fertility and prolonged pelagic larval stage [26]. The clams compete for food and space with other bivalves that have similar biology [26]. Along the French Atlantic and Normandy coasts, wild populations have displaced native clams (e.g., Ruditapes decussatus, Venerupis corrugata) [3]. The Manila clam can also impact the plankton community, though this effect is only expected at densities above 2,000–2,500 individuals per m², which occurs mainly in aquaculture settings [18].
In southern England, the species is not considered aggressively invasive, as it does not appear to pose a significant risk to native species diversity or ecosystem functioning in the region [15]. However, high densities of Manila clams have led to the development of new types of fisheries targeting this bivalve [16,20], a situation also seen in Portugal, among other places [31].
The shell of the Manila clam is oval-rectangular and can reach up to 75 by 35 mm, though it is typically smaller [29]. The apex is positioned far from the center. The shell resembles that of the native carpet clam Venerupis corrugata, but it features a distinct lunule (crescent-shaped area) and a characteristic rough surface texture made up of intersecting longitudinal ribs and concentric grooves, which together create a prominent lattice-like pattern [3,23,29]. Additionally, the species is not always easily distinguishable from other carpet clam species found elsewhere in Europe, such as the Grooved carpet shell (Ruditapes decussatus) [3]. The Grooved carpet shell has a more elongated and angular shell, while the Manila clam is generally rounder, less angular, and more colorful [29].
The outer shell is yellowish-white, yellow-brown, or brown, often displaying striking color patterns, such as elegant zigzag and vibrant speckled designs. The inner surface of the shell can also be vividly colored (lilac, dark purple, or ochre yellow). The shell has a strong external hinge ligament [23,29].
The Manila clam is an efficient filter feeder [32,33], consuming phytoplankton, cyanobacteria, and small organic matter [28].
[1] World Register of Marine Species (WoRMS) (2024). Ruditapes philippinarum (A. Adams & Reeve, 1850). https://www.marinespecies.org/aphia.php?p=taxdetails&id=231750 (2024-10-18).
[2] Ponurovsky, S.K.; Yakovlev, Y.M. (1992). The reproductive biology of the Japanese Littleneck, Tapes philippinarum (A. Adams and Reeve, 1850) (Bivalvia: Veneridae). J. Shellfish Res. 11(2): 265-277. [https://www.vliz.be/nl/imis?module=ref&refid=289112]
[3] Kerckhof, F. (2014). Een populatie van de Aziatische tapijtschelp Ruditapes philippinarum (Adams & Reeve, 1850) in de Zeebrugse haven. De Strandvlo 34(2): 57-61. [https://www.vliz.be/nl/imis?module=ref&refid=240737]
[4] Claus, C.; Maeckelberghe, H.; De Pauw, N. (1983). Onshore nursery rearing of bivalve molluscs in Belgium. Aquacult. Eng. 2: 13-26. [https://www.vliz.be/nl/imis?module=ref&refid=3369]
[5] waarnemingen.be. Ruditapes philippinarum (A. Adams & Reeve, 1850). https://waarnemingen.be/species/235068/ (2024-10-02)
[6] Kerckhof, F. (2016). Nieuwe natuur: de bivalven fauna van het Klein Strand in Oostende en een tweede populatie van de Filipijnse tapijtschelp Ruditapes philippinarum. De Strandvlo 36(1): 6-11. [https://www.vliz.be/nl/imis?module=ref&refid=255285]
[7] Flassch, J.P.; Leborgne, Y. (1992). Introduction in Europe, from 1972 to 1980, of the Japanese Manila clam (Tapes philippinarum) and the effects on aquaculture production and natural settlement. ICES Mar. Sci. Symp. 194: 92-96. [https://www.vliz.be/nl/imis?module=ref&refid=297761]
[8] Cigarria, J.; Fernández, J.M. (2000). Management of Manila clam beds: I. Influence of seed size, type of substratum and protection on initial mortality. Aquaculture 182(1-2): 173-182. [https://www.vliz.be/nl/imis?module=ref&refid=396030]
[9] Campos, C.J.A.; Cachola, R.A. (2006). The introduction of the Japanese carpet shell in coastal lagoon systems of the Algarve (south Portugal): a food safety concern. Internet Journal of Food Safety 8: 1-2. [https://www.vliz.be/nl/imis?module=ref&refid=396032]
[10] Hurtado, N.S.; Pérez-García, C.; Móran, P.; Pasantes, J.J. (2011). Genetic and cytological evidence of hybridization between native Ruditapes decussatus and introduced Ruditapes philippinarum (Mollusca, Bivalvia, Veneridae) in NW Spain. Aquaculture 311(1-4): 123-128. [https://www.vliz.be/nl/imis?module=ref&refid=396035]
[11] Juanes, J.A.; Bidegain, G.; Echavarri-Erasun, B.; Puente, A.; García, A.; García, A.; Bárcena, J.F.; Álvarez, C.; García-Castillo, G. (2012). Differential distribution pattern of native Ruditapes decussatus and introduced Ruditapes philippinarum clam populations in the Bay of Santander (Gulf of Biscay): Considerations for fisheries management. Ocean Coast. Manag. 69: 316-326. [https://www.vliz.be/nl/imis?module=ref&refid=396043]
[12] Breber, P. (2002). Introduction and acclimatisation of the Pacific carpet clam, Tapes philippinarum, to Italian waters, in: Leppäkoski, E. et al. (Ed.) Invasive aquatic species of Europe: distribution, impacts and management. pp. 120-126. [https://www.vliz.be/nl/imis?module=ref&refid=40592]
[13] Sladonja, B.; Bettoso, N.; Zentilin, A.; Tamberlich, F.; Acquavita, A. (2011). Manila clam (Tapes philippinarum Adams & Reeve, 1852) in the Lagoon of Marano and Grado (Northern Adriatic Sea, Italy): Socio-economic and environmental pathway of a shell farm, in: Sladonja, B. (Ed.) Aquaculture and the environment - a shared destiny. pp. 51-78. [https://www.vliz.be/nl/imis?module=ref&refid=396053]
[14] Mura, L.; Cossu, P.; Cannas, A.; Scarpa, F.; Sanna, D.; Dedola, G.L.; Floris, R.; Lai, T.; Cristo, B.; Curini-Galletti, M.; Fois, N.; Casu, M. (2012). Genetic variability in the Sardinian population of the Manila clam, Ruditapes philippinarum. Biochem. Syst. Ecol. 41: 74-82. [https://www.vliz.be/nl/imis?module=ref&refid=396057]
[15] Humphreys, J.; Harris, M.R.C.; Herbert, R.J.H.; Farrell, P.; Cragg, S.M. (2015). Introduction, dispersal and naturalization of the Manila clam Ruditapes philippinarum in British estuaries, 1980–2010. J. Mar. Biol. Ass. U.K. 95(6): 1163-1172. [https://www.vliz.be/nl/imis?module=ref&refid=287870]
[16] Jensen, A.C.; Humphreys, J.; Caldow, R.W.G.; Grisley, C.; Dyrynda, E.A. (2004). Naturalization of the Manila clam (Tapes philippinarum), an alien species, and establishment of a clam fishery within Poole Harbour, Dorset. J. Mar. Biol. Ass. U.K. 84(5): 1069-1073. [https://www.vliz.be/nl/imis?module=ref&refid=67886]
[17] Utting, S.D.; Spencer, B.E. (1992). Introductions of marine bivalve molluscs into the United Kingdom for commercial culture - case histories, in: Sindermann, C. et al. Introductions and Transfers of Aquatic Species. Selected papers from a Symposium held in Halifax, Nova Scotia 12-13 June 1990. ICES Marine Science Symposia, 194: pp. 84-91. [https://www.vliz.be/nl/imis?module=ref&refid=396058]
[18] Humphreys, J.; Caldow, R.W.G.; McGrorty, S.; West, A.D.; Jensen, A.C. (2007). Population dynamics of naturalised Manila clams Ruditapes philippinarum in British coastal waters. Mar. Biol. (Berl.) 151(6): 2255-2270. [https://www.vliz.be/nl/imis?module=ref&refid=140607]
[19] Jensen, A.; Humphreys, J.; Caldow, R.; Cesar, C. (2005). The Manila clam in Poole Harbour, in: Humphreys, J. et al. The ecology of Poole Harbour. Proceedings in Marine Science, 7: pp. 163-173. [https://www.vliz.be/nl/imis?module=ref&refid=396060]
[20] Morgan, C.J. (2000). The ecology and fishery of the Manila clam Tapes philippinarum in Poole Harbour. Shellfish News 10: 10-11. [https://www.vliz.be/nl/imis?module=ref&refid=4913]
[21] Faasse, M.; Ligthart, M. (2008). De exotische tapijtschelp Ruditapes philippinarum (Adams & Reeve, 1850) vestigt zich in Nederland. Het Zeepaard 68(6): 175-179. [https://www.vliz.be/nl/imis?module=ref&refid=128489]
[22] van Bragt, P.H. (2013). Filippijnse tapijtschelp definitief gevestigd op onze kust. Nature Today 1 September: online. [https://www.vliz.be/nl/imis?module=ref&refid=396061]
[23] Goetheer, B. (2012). Heeft de Filippijnse tapijtschelp Ruditapes philippinarum (Adam & Reeve, 1850) zich in de Westerschelde gevestigd? Spirula 387: 107. [https://www.vliz.be/nl/imis?module=ref&refid=289113]
[24] Reise, K., Wegner, K.M., Borcherding, R., Brand, S., Buschbaum, C., Waser, A.M. (2024). Manila clams Ruditapes philippinarum spreading north and establishing in the European Wadden Sea. Estuarine, Coastal and Shelf Science, Volume 309, 1 December 2024, 108940.
[25] Wijsman, J.W.M.; Smaal, A.C. (2006). Risk analysis of mussels transfer. IMARES Wageningen Report, C044/06. Wageningen IMARES: Ijmuiden. 103 pp. [https://www.vliz.be/nl/imis?module=ref&refid=244138]
[26] Nederlands Soortenregister. Overzicht van de Nederlandse biodiversiteit. Filipijnse tapijtschelp Ruditapes philippinarum. https://www.nederlandsesoorten.nl/linnaeus_ng/app/views/species/nsr_taxon.php?id=174600 (2024-10-02)
[27] Uddin, M.J.; Jeung, H.-D.; Yang, H.S.; Kim, B.-K.; Ju, S.-J.; Choi, K.-S. (2013). Quantitative assessment of reproductive effort of the Manila clam Ruditapes philippinarum in a lagoon on Jeju Island (Korea) using enzyme-linked immunosorbent assay. Invertebr. Reprod. Dev. 57(4): 316-324. [https://www.vliz.be/nl/imis?module=ref&refid=396062]
[28] Nakamura, Y. (2001). Filtration rates of the Manila clam, Ruditapes philippinarum: dependence on prey items including bacteria and picocyanobacteria. J. Exp. Mar. Biol. Ecol. 266(2): 181-192. [https://www.vliz.be/nl/imis?module=ref&refid=396063]
[29] ANEMOON. Ruditapes philippinarum (A. Adams & Reeve, 1850). https://www.anemoon.org/beheer/website/bewaar/soorten/id/258/filipijnse-tapijtschelp (2024-10-02)
[30] Solidoro, C.; Melaku Canu, D.; Rossi, R. (2003). Ecological and economic considerations on fishing and rearing of Tapes phillipinarum in the lagoon of Venice. Ecol. Model. 170(2-3): 303-318. [https://www.vliz.be/nl/imis?module=ref&refid=297772]
[31] Coelho, P.; Carvalho, F.; Goulding, T.; Chainho, P.; Guerreiro, J. (2021). Management models of the Manila clam (Ruditapes philippinarum) fisheries in invaded European coastal systems. Front. Mar. Sci. 8: 685307. [https://www.vliz.be/nl/imis?module=ref&refid=396064]
[32] Magni, P.; Montani, S.; Takada, C.; Tsutsumi, H. (2000). Temporal scaling and relevance of bivalve nutrient excretion on a tidal flat of the Seto Inland Sea, Japan. Mar. Ecol. Prog. Ser. 198: 139-155. [https://www.vliz.be/nl/imis?module=ref&refid=65042]
[33] Harris, M.R. (2016). A study of the naturalisation and dispersal of a non-native bivalve, the Manila clam, Ruditapes philippinarum (Adams and Reeve 1850) in estuaries along the South coast of England. PhD Thesis. University of Portsmouth: Portsmouth. 262 pp. [https://www.vliz.be/nl/imis?module=ref&refid=396067]
VLIZ Alien Species Consortium (2024). Ruditapes philippinarum – Manila clam. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 7 pp.
