The most common mollusk at Boundary Bay is the Asian snail, Batillaria attramentosa. There are vast acreages of intertidal mud flat where you cannot walk without stepping on them. They are believed to have hitch-hiked with oysters brought from Japan to resurrect that industry on this coast.
The second most commonly seen, from a mud’s surface point of view (for who knows what really goes on below?), is another import, the Purple Varnish Clam, Nuttallia obscurata. Its empty valves are scattered in great numbers atop the mud, high and dry, or strewn on the bottoms of the shallow, water-filled troughs between the low ridges that are exposed at low tide.
This species is thought to have arrived in the 1980s in dumped ballast water, and Boundary Bay is close to the epicentre of that introduction. Planktonic larvae are not in the least patrophilic, and over years and generations, in the right habitat, can spread a species far and wide. Nuttallia has spread up the Strait of Georgia, throughout the San Juan Archipelago and has reached the Olympic Peninsula of Washington and the west coast of Vancouver Island.
I have even, this past winter, found it among noodles in a Szechuan restaurant in Richmond.
Mills, C.E. 1999-present. Nuttallia obscurata, the purple varnish clam or the purple mahogany-clam. Electronic internet document available at http://faculty.washington.edu/cemills/Nuttallia.html. Published by the author, web page established March 1998, last updated 7 june 2004.