EXPLORING THE SURVIVAL THRESHOLD: A STUDY OF SALINITY TOLERANCE OF THE NONNATIVE MUSSEL MYTELLA CHARRUANA

In this study, our objective was to understand life history attributes of Mytella charruana, a newly introduced species to the southeastern Atlantic coast of the United States, that would enable its survival in the introduced range. We therefore addressed the following questions regarding the range of salinities in which M. charruana can survive: First, in what range of salinities is survival possible for M. charruana if slowly adjusted to test salinities? Second, in what range of salinities can these mussels survive when experiencing rapid changes of salinity? Third, in what range of salinities can M. charruana survive with temporary, rapid changes of salinity (6-h duration)? We tested survival in salinities ranging from freshwater to hypersaline conditions (0-45 ppt) and determined whether mussel size affected experimental results. All experiments examined survivorship of mussels by increasing or decreasing the salinity from the field value under laboratory conditions. Mortality in each tank was recorded daily for 43 days for the gradual adjustment trials, and 12 days for permanent and 6-h shock trials. Large M. charruana (20-54 mm) survived best in salinities from 2-23 ppt, with 100% mortality at 0 ppt and 45 ppt with gradual adjustment. Small M. charruana (3-19 mm) survived in a wider range of salinities (2-40 ppt) with gradual adjustment to new salinities. However, survival of both large and small mussels was significantly lower in permanent shock trials at salinity extremes. Six-hour shock trials had no effect on survival at any of the test salinities (0-45 ppt) for both large and small M. charruana. Overall, the data indicate that these mussels could invade a wide variety of saline environments with significant freshwater or saltwater input