Naturally seeded clams along Puget Sound often suffer extremely high mortality, which can affect the size of adult populations and harvests. Surprisingly little is known about causes of mortality and about early life stages of clams in general. This study will assess the key factors affecting the survival and growth of two common naturalized species: thick-shelled Manilla clams and thin-shelled Eastern softshell clams. Field experiments at eight highly diverse sites, from Willapa Bay to southern Puget Sound, will compare settlement and growth rates and first-year mortality as salinity, temperature and acidity vary. Lab experiments will help determine how rising temperatures will impact clams and which suspected predators—worms, small snails or young crabs—already affect them.