Nuttallia obscurata, or the purple varnish clam, is a non-native species that has spread recently and rapidly in the coastal Northeastern Pacific. Attempts at commercial marketing have largely failed. This is in contrast to Venerupis philippinarum, the Manila clam, which was accidentally introduced to the region in the 1930s but is now very important to commercial shellfish industry. Finally, Leukoma staminea is the local littleneck clam, another popular edible bivalve. These three ecologically important species were studied and their physiological tolerances were compared to help determine why N. obscurata is succeeding as an invasive species. To study physiological tolerances, specimens collected from multiple field sites were used in controlled experiments with altered seawater temperature and salinity levels. Gill tissue tolerance was used as a correlate for whole organism tolerance; thus, time to tissue death was evaluated for each species under different conditions. Regressions were used to interpolate specific temperatures at which each species survived for 60 minutes: 41.1 °C for N. obscurata, 40.6 °C for V. philippinarum and 36.1 °C for L. staminea, with N. obscurata having the highest overall tolerance to high temperatures. Nuttallia obscurata also tolerated significantly lower salinities than the other two clams, with the native L. staminea having the least tolerance to decreased salinities. In addition, excised gill tissue of N. obscurata survived in a wide range of salinities far longer than did V. philippinarum and L. staminea. Tissue of V. philippinarum and L. staminea did not survive for more than 48 hours, while all N. obscurata tissue survived for 2+ weeks, even at extremely low salinities. The higher abiotic tolerances of N. obscurata may well contribute to its success as an invasive species
