These living mussels are from Ala Spit, Whidbey Island, WA. The barnacle is Balanus glandula. Photo by Dave Cowles, Sept 2005 Note here the two color phases, brown and black, seen in mussels. The black phase is usually much more common than the brown. Nagarajan et al. (2002) found that black oystercatchers optimized their long-term energy intake by preferentially eating the brown mussels of the related species Mytilus edulis. While shell thickness and tissue content was similar between the color phases, the brown phase had significantly lower moisture content so that the oystercatchers were able to pack more energy-yielding food into their crops by eating the brown phase mussels.
The inside of the shell shows the prominent scar of the posterior adductor muscle (at the right side of the top, left valve and the left side of the bottom, right valve), while the anterior adductor muscle scar is vary small and hard to find.
These mussel shells show some of the variety of colors possible with M. trossulus. Brown shells are usually small individuals. Photo by Dave Cowles, Sept 2005 at Ala Spit.
This individual is in the process of secreting a byssal thread with its foot, and attaching it to the glass floor of an aquarium. Photo by Dave Cowles, July 2005
