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Perna viridisThe Asian green mussel, Perna viridis, is a large (> 80 mm) bivalve, with a smooth, elongate shell typical of several mytilids (but see below). It has visible concentric growth rings and a ventral margin that is distinctly concave on one side. The characteristic green coloration comes from the periostrocum, the proteinaceous outer layer of the shell. It is uniformly bright green in juveniles, but dulls to brown with green margins in mature individuals. The inner surfaces of the valves are smooth and iridescent blue to bluish-green in color. A prominent, kidney-shaped retractor muscle scar is present, but the species lacks anterior adductor muscles. Close examination of the beak (i.e., where the two valves hinge together) reveals a pair of hinge teeth on the left valve that interlock with a single hinge tooth on the right valve (DeVictor and Knott undated, NIMPIS 2002, Rajagopal et al. 2005).
As is typical of most members of the family, P. viridis attaches to hard surfaces by means of proteinaceous byssal threads.
Green mussels are coastal bivalves, typically occurring at depths of less than 10 m, and shown to be tolerant of a wide range of turbidity and pollution (Power 2004).
The native range of the Asian green mussel broadly encompasses the Asia-Pacific and Indo-Pacific regions. The known introduced range of the species is extensive and includes portions of coastal Australia, Japan, the Caribbean, and North and South America (Benson et al. 2002; NIMPIS 2002).
Green mussels are large, with shells typically reaching 80-100 mm in length and occasionally growing larger than 160 mm (Rajagopal et al. 2005). They live for approximately three years (Power et al 2004).
In parts of their native range, rapid growth rates of up to 6-10 mm per month have been reported. In Tampa Bay where the species has been introduced, even more rapid growth rates of 4-5 mm per week have been reported (Power 2004).
Reproduction is sexual, sexes are separate, and fertilization is external. Onset of sexual maturity is rapid, occurring at 2-3 months of age in parts of the animal's native range and in as little as 1-2 months in parts of its non-native tange, e.g., Tampa Bay (Power 2004).
Green mussels occur in environments whose temperatures range from 10-35ºC and exhibit optimal response at temperatures between 26ºC and 32ºC (Power 2004). Although the reported native thermal range of the green mussel is broad, reduced temperatures have been demonstrated to significantly negatively impact growth rates (Chatterji et al. 1984).
The green mussel is euryhaline, able to tolerate both hypersaline conditions (80 ppt) and reduced salinities, e.g., 12 ppt (Sivalingam 1977, Chatterji et al. 1984, Morton, 1987). An optimal salinity range has been reported as 27-33 ppt (Power 2004).
Although economically important fisheries and aquaculture industries based green mussels exist within their native range, utilization as a food resource in areas into which they have been introduced is uncommon. Consumption of introduced green mussels taken from polluted waters is discouraged as they are known to accumulate some toxic substances.