Varnish Clams

Walking on the beach at Goose Spit in Comox this weekend got me thinking about clams. I always enjoy sorting through seaweed in the strand line and taking a closer look at shells that have washed up on the shore before returning them back to the beach where I found them. On this walk I found several “old-friends,” including the striking varnish clam.

Back in the mid-90s I was working my first job as an heritage interpreter at Rathtrevor Beach Provincial Park in Parksville, British Columbia. I immersed myself in learning as much as I could about the ecology of coastal Douglas fir forests and often spent a great deal of time out on the endless sandy beach poking around in tide pools and examining clam shells.

It was at Rathtrevor that I was introduced to the Varnish Clam (Nuttallia obscurata). The varnish clam is a distinctive clam. Its inner shell is a rich, royal purple and the outer shell is covered with a thick, brownish, peeling layer (periostracum) from which it gets its common name. It is also know as the Dark Mahogany-clam and the Purple Mahogany-Clam for the same reason.

Varnish Clam | Nuttalia obscurata
Varnish Clam | Nuttalia obscurata

The clam was a bit of a mystery to us – it wasn’t described in in Gloria Snively’s Exploring the Seashore or other reference books that we were using at the time. We couldn’t turn to a quick internet search on the subject because, as hard as it is to believe, conducting a Google search wasn’t possible in 1995.

The story of this clam is an interesting one. Bill Merrilees, then regional supervisor with BC Parks, identified the clam and its origin. An introduced species, it appeared in Boundary Bay in the late 1980s to early 1990s, probably as larvae in the ballast of ships from Korea and Japan. From that location it spread fairly rapidly and in less than 10 years was well established in the Georgia Strait between Vancouver Island and mainland British Columbia. I moved up island to work at Miracle Beach Provincial Park in the late 1990s and witnessed its arrival – by 1997 it was common there.

Varnish Clam | Nuttalia obscurata
Varnish Clam | Nuttalia obscurata

While the varnish clam appears to be a highly successful invasive species it is unclear if it is impacting the local native populations of clams. The varnish clam prefers sand-gravel habitat in the mid- to high-tidal zone, and is often found in areas of freshwater seepage. It grows to 7cm (2.8″) in length and buries itself 20 to 38cm deep in the substrate.

I have no interest in eating varnish clams but the BC Ministry of Agriculture and Lands has approved commercial harvesting of this “Savoury Clam.” Not a bad thing considering it looks like it is here to stay.

Those looking for good resources on marine life in British Columbia should consider: