Salinity tolerance in different life history stages of an invasive false mussel Mytilopsis sallei recluz, 1849: implications for its restricted distribution.
Although the false mussel Mytilopsis sallei Recluz, 1849 is recognised as an aggressive invasive species, its populations in several estuaries in Thailand are restricted to small areas. A salinity gradient is a major characteristic of its habitat, hence the effect of various salinity levels (0-40 ppt) on the mortality of larvae, juveniles and adults of M. sallei was investigated. Condition Indices of adults reared at different salinity levels for two months were measured. Spatial and temporal variations of salinity and false mussel abundance in a canal with a salinity gradient were also monitored. After an acute (48 h) test, survival of larvae was highest at salinity levels of 12.5 and 16.25 ppt and decreased at lower and higher levels. Juveniles survived at all salinity levels, but most adults died in the first 24 h at a salinity of 40 ppt, while condition indices were lowest at salinity levels of 30 and 35 ppt. In the field survey, highest false mussel abundance was consistently found at the middle part of the canal with mid-range salinity. The results suggested that salinity is a determinant of survival in M. sallei larvae and potentially regulates the dispersal success of false mussels. However, the importance of salinity was marginal in the later stages of its life history.