Mya arenaria currently occupies a wide geographical range in the northern hemisphere, on both coasts of the Atlantic as well as on the Pacific east coast. Some authors claim it also occurs on the Pacific west coast. The species originated in the Pacific during the Miocene and was already present on both Atlantic coasts in the Pliocene. However, it died out on the edst coasts of the Pacific and the Atlantic during glaciation of the Pleistocene. With the aid of man it was reintroduced to the North Sea some 400-700 years ago and to the East Pacific last century. In the 1960s it was also introduced to the Black Sea. M. arenaria invaded new habitats by different modes:(1) natural range expansion (2) intentional as plantings, (3) unintentional as a ballast species and (4) unintentional as a byproduct of oyster transplants. Properties that may fdvor its wide range of distribution and invading success are: high fecundity; planktonic dispersal stages and life stages that lend itself to unintentional transport by humans; a broad spectrum of habitat and food preference; tolerance of a wide range of environmental conditions such as salinity and temperature; longevity, and perhaps relatively large size.
I N T R O D U C T I O NT h e soft s e d i m e n t b i v a l v e Mya arenaria is u n i q u e b e c a u s e it is by far the e a r l i e s t int r o d u c e d s p e c i e s to t h e N o r t h Sea s h o r e t h a t s c i e n t i s t s are a w a r e of .
/Mya is p r e s e n t l y w i d e l y d i s t r i b u t e d at l e a s t o v e r b o t h n o r t h e r n coasts of the Atlantic as w e l l as o v e r t h e N o r t h Pacific e a s t coast. H o w e v e r , it not only occurs o v e r a w i d e g e og r a p h i c a l r a n g e , but also o f t e n plays a d o m i n a t i n g role in local b e n t h i c c o m m u n i t i e s . In E u r o p e a n w a t e r s Mya w a s f o u n d to b e t h e s p e c i e s w i t h t h e h i g h e s t b i o m a s s in a s t u d y on the s o u t h -w e s t c o a s t of E n g l a n d ( W a r w i c k & Price, 1975). It is also o n e of t h e t h r e e m o s t i m p o r t a n t p r o d u c e r s of b e n t h i c b i o m a s s a n d c a l c i m a s s in t h e W a d d e n Sea( B e u k e m a , 1982, 1992) a n d a m o n g t h e d o m i n a t i n g s p e c i e s on the w e s t c o a s t of S w e d e n (Evans & Tallmark, 1977) a n d in the Baltic S e a (Brey, 1991;Powilleit et al., 1995). During t h e last f e w c e n t u r i e s t h e c l a m w a s s u c h a typical c o m p o n e n t in t h e Baltic S e a t h a t the last s t a g e of t h e Baltic d e v e l o p m e n t h a s b e e n c a l l e d t h e [VIya Sea ( H e s s l a n d , 1946).After its i n t r o d u c t i o n in the 1960s, it b e c a m e a m a s s e l e m e n t in the R o m a n i a n p a r t of t h e Black S e a (Gomoiu, 1981).O n t h e Atlantic c o a s t of N o r t h A m e r i c a it is r e p o r t e d as a d o m i n a t i n g s p e c i e s in N o v a Scotia ( E m e r s o n et al., 1988) a n d f r o m m a n y e s t u a r i e s in N e w E n g ...