April 15th, 2012 | by Dave Ingram | 1 Comment
Published in Intertidal Zone, Sea Shore, Shellfish
Tags: Bivalves, British Columbia, Clams, Horse Clam, Miracle Beach, Pacific Gaper, Tresus nutallii, Vancouver Island
It is not often that you see a living horse clam on the surface of the beach unless you have taken the effort to dig one out yourself. That’s why Jocie and I initially thought that the Pacific gaper (Tresus nuttallii) that we found at Miracle Beach was dead. We quickly realized otherwise after touching the extended siphon and watching it retract (as much as it was able) into the protection of the its two shells.
The Pacific gaper is a fascinating clam and this was a great opportunity to take a closer look at a living specimen. The body of the clam was so large that it seemed as if the two shells could not close completely and the opening where the foot protrudes was visible (hence the name “gaper”). The siphon had two openings: the clam takes in water containing oxygen and food in one opening and expels waste water through the other. The siphon was also too large to completely retract into the shell.
Clams usually live their lives under the sand, mud or cobble in which they are found. The siphon extends up through the substrate and is often the only sign of the bivalve below. When they are on the surface, clams are vulnerable to predators like sea gulls and small children (and adults) and to environmental threats like dessication and abrasion.
I took a few quick photographs of this Pacific gaper before attempting to bury it back down beneath the sand, using an old empty horse clam shell as a digging tool. These clams are generally found at a depth of 30 cms or more and it was challenging to dig down that far because of the wet sand and rocks. Clams begin life as tiny free floating larva after the hatch from eggs. When they settle to the bottom of the ocean they are small enough that they are able to work their way down to a safe depth. Mature clams the size of this horse clam would not be able to do this on their own.
I hope that this magnificent clam manages to survive its “replanting, but it probably would have been better if it hadn’t been dug up in the first place. Touching the exposed siphon tips of naturally buried horse clams is entertaining enough and you can get an idea of what the animal looks like by examining the shells you find on the beach. There really is no reason to dig these amazing bivalves up!