Manila Clam

Type Description

Ruditapes philippinarum has a large, solid, equivalve shell that is inequilateral. Its outline is almost rectangular, being longer than it is high, with beaks located at the anterior 1/3 and pointing towards the front. The shell exhibits coarse sculpture with numerous radial and concentric striae, which become nodulose at the point of intersection, with radial ribs slightly more prominent than concentric ones. The lunule is narrowly heart-shaped, and the pallial sinus is heel-shaped. The internal margin is smooth. Ruditapes philippinarum displays extreme variability in color and pattern. The exterior is typically cream-colored, with varying degrees of rayed, banded, or blotched brown markings. The interior ranges from white to pinkish-white, with a pale yellow flush within the pallial line. The common size of the shell ranges from 25 to 57 mm in length, with a commercial size of approximately 40 mm.

Habitat

"Ruditapes philippinarum inhabits brackish waters and burrows in sand or muddy-gravel bottoms below the mid-tide level to a few meters deep, typically in calm waters. Its habitat ranges from the intertidal zone to depths of 4 meters.
Ruditapes philippinarum's original distribution is in Japan. It was introduced for marine farming on the Atlantic coast of France, where it has become established in the wild since the 1980s. In the Mediterranean, it was first introduced in France in 1980 (Bodoy et al., 1981), and in 1983 in the Venice lagoons for experimental aquaculture (Cesari and Pellizzato, 1985; Breber, 1985 as Tapes semidecussatus). It is now found on the coasts of Romagna and Sardinia. A recent record in the Turkish North Aegean Sea, which is difficult to explain, is considered accidental until further evidence is provided (Albayrak et al., 2001)."

Reproductive Information

Studies carried out in Thau/France and Venice (Italy) lagoons revealed that the best growth period is during phytoplankton bloom (spring and autumn) at temperatures between 10 and 20°C and the reproduction period extends from May to October (Maitre-Alain, 1983, 1985).

Lifecycle

Broadcast spawners. Embryos develop into free-swimming trocophore larvae, succeeded by the bivalve veliger (with ciliated vellum to assist mobility and feeding), resembling a miniature clam. After 2-4 weeks, it develops into a peliveliger with a formed foot to assist further with swimming, as well as byssal threads to help the clam secure itself onto the seafloor once it finds a suitable substrate to settle on. Burrowing into the ground allows the animal to find food and be protected from predators. Once settled, it will stay in the substrate and continue to grow into a mature clam.

Nutrition Information

Ruditapes philippinarum feeds on phytoplankton.

General Impact Information

"Ruditapes philippinarum has a wide native range, from the southern Kuril and Sakhalin Islands, Russia (Golikov et al. 1976) to India, Sri Lanka, and the Philippines (Huang 2001; Academy of Natural Sciences of Philadelphia 2006; Mao et al. 2011). It was introduced to Hawaii as a food animal in 1918 (Carlton and Eldredge 2009), but reached the West Coast of North America (Samish Bay, Washington) with plantings of Pacific Oysters (Crassostrea gigas) (Carlton 1979), and was then widely introduced from British Columbia to California as a popular seafood item (Carl and Giguet 1972; Cohen and Carlton 1995). It was introduced to northern France in 1974, and is established from Ireland and the Netherlands, to Spain, Greece, and Turkey (Cigarria et al. 1997; Goulletquer et al. 2002; Zenetos et al. 2002; Drummond et al. 2006). It is now widely and often intensively farmed, as well as being recreationally harvested, in its native and introduced range (Food and Agricultural Organization 2013).

Competition - The extent to which R. philippinarum displaces native bivalves by competition for food or space is unclear. On British Columbia intertidal shores, the density of other bivalves was not affected in beds of farmed Manila Clams, compared with reference sites (Whiteley and Bendell-Young 2007). However, a later survey in British Columbia indicates that R. philippinarum is replacing the native Pacific Littleneck (Leukona staminea) in farmed and non-farmed areas, despite the introduced clam's greater vulnerability to predation (Bendell 2014). In lagoons of the northern Adriatic, where R. philippinarum is intensively farmed, the native V. decussata (Grooved Carpet Shell) has become rare, but is still present. However, the sites where R. philippinarum is now most abundant, had relatively low densities of native species (Breber 2002).

Hybridization: A few hybrids between R. philippinarum and the native V. decussata (9 of 222 putative V. decussata - 4%) have been found in the Ria de Vigo, Spain. However, the extent and significance of genetic exchange between the two species is not known (Hurtado et al. 2011).
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General Management Information

General Pathway Information

Notes

R. philippinarum is one of the most commercially exploited bivalve molluscs in the world, and its production comes from both fishing of natural stocks and cultivated grounds. The total catch of this species was reported to be approximately 40.000 tonnes in 2010 (FAO 2012). However, in Turkey, natural stocks are the only source of Ruditapes sp., and the annual catch was reported to be 14.9 tonnes in 2011 (Türkstat 2012).

References