Pacific littleneck clams are commonly found in the first 2 to 3 inches of substrate, and are found up to 2.5 inches in length. Spawning in the spring or summer depending on the region, pacific littleneck clam eggs and larvae are dispersed by the current throughout the water column. After developing a foot, larvae move to the bottom and search for a suitable surface to which they can attach. Young clams often attach in deeper water. As the clam grows, it moves toward shallower water.
Adults are sedentary.
This species gathers food by filtering water for phytoplankton and diatoms. Rock crabs, fish, birds, sea otters, and others feed on clams depending on the region. Because of their sedentary nature, clams are highly susceptible to human-induced changes in their environment. High coliform bacteria levels resulting from municipal sewage discharges have permanently closed some areas to harvest. High siltation caused by logging, upland development, dredging, and marina construction affect the abundance of Pacific littleneck clams.