The effect of salinity and recruitment on the distribution of Tetraclita squamosa and Tetraclita japonica (Cirripedia; Balanomorpha) in Hong Kong
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The barnacles, Tetraclita squamosa and Tetraclita japonica, exhibit different vertical and horizontal distributions along the salinity gradient from the 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. squamosa was found. Annual recruitment of both species occurred on the east coast but no recruitment was recorded on the west coast for 2 years, suggesting that west coast populations of T. squamosa are relics of stochastic, past recruitment, and may decline without further recruitment. Under laboratory conditions, the two species do not vary in their salinity tolerance or osmoregulation. Adults of both species ceased activity when salinity dropped to 10‰ (=mean summer salinity on west coast). The LC50 of larvae was between 14–16‰ and 100% of naupliar larvae died when salinity was 9‰, showing that the low summer salinities on the west coast may have an impact on some stages of the barnacles' life histories. The east-west distribution and population structure of these two species appear, therefore, to be dependent on the intensity and frequency of past settlement which may be affected by salinity stress.
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