The effect of salinity and recruitment on the distribution of Tetraclita squamosa and Tetraclita japonica (Cirripedia ; Balanomorpha) in Hong Hong

The barnacles, Tetraclita squamosa and Tetraclita japonica, exhibit differe nt vertical and horizontal distributions along the salinity gradient from t he east to west coast of Hong Kong. On the oceanic east coast, T. japonica was common higher on the shore [1.25-2 m above chart datum (C.D.)] than T. squamosa (1-1.25 m above C.D.), whereas on the estuarine west coast, only T . squaumosa was found. Annual recruitment of both species occurred on the e ast coast but no recruitment was recorded on the west coast for 2 years, su ggesting that west coast populations of T. squamosa are relies of stochasti c, past recruitment, and may decline without further recruitment. Under lab oratory conditions, the two species do not vary in their salinity tolerance or osmoregulation. Adults of both species ceased activity when salinity dr opped to 10 parts per thousand, (= mean summer salinity on west coast). The LC50 of larvae was between 14-16 parts per thousand, and 100% of naupliar larvae died when salinity was 9 parts per thousand,, showing that the low s ummer salinities on the west coast may have an impact on some stages of the barnacles' life histories. The east-west distribution and population struc ture of these two species appear, therefore, to be dependent on the intensi ty and frequency of past settlement which may be affected by salinity stres s.