Mya arenaria currently occupies a wide geographical range in the northern h
emisphere, on both coasts of the Atlantic as well as on the Pacific east co
ast. Some authors claim it also occurs on the Pacific west coast. The speci
es originated in the Pacific during the Miocene and was already present on
both Atlantic coasts in the Pliocene. However, it died out on the east coas
ts of the Pacific and the Atlantic during glaciation of the Pleistocene. Wi
th the aid of man it was reintroduced to the North Sea some 400-700 years a
go and to the East Pacific last century. In the 1960s it was also introduce
d to the Black Sea. M. arenaria invaded new habitats by different modes: (1
) natural range expansion (2) intentional as plantings, (3) unintentional a
s a ballast species and (4) unintentional as a byproduct of oyster transpla
nts. Properties that may favor its wide range of distribution and invading
success are: high fecundity; planktonic dispersal stages and life stages th
at lend itself to unintentional transport by humans; a broad spectrum of ha
bitat and food preference; tolerance of a wide range of environmental condi
tions such as salinity and temperature; longevity, and perhaps relatively l
arge size.