ABSTRACT
The salinity tolerances of Ophiocomina nigra Ophiura albida and Amphiura chiajei were assessed and are interpreted in terms of their relative euryhalinities. It was found that the failure of the mouth podia to respond to mechanical stimulation was a reliable indication of the point of death in these species. This criterion was employed in a series of LD50 experiments in which these three species were exposed to various concentrations of sea water ranging from 40% to 100% sea water. The aata were analysed by the methods of Wilcoxon and Litchfield (1949) producing mortality curves. The sampling stations E6, E11, E14 and E24 in Loch Etive represent areas of decreasing salinity in the order E6 > E11 > E14 > E24. It is shown that A. chiajei from station E24 frave a greater tolerance to reduced salinity than those from E11. Animals from E11 have a greater tolerance than those from E6. A similar situation exists for O. albida. At any given dilution O. albida had a greater tolerance than A.chiajei from the same sampling station. Though these two species occur at the same sampling station it is suggested that the different modes of life may result in them being subjected to different salinity regimes which may allow different tolerances to reduced salinity to develop, Field observations suggest that O.albida has a high degree of physiological flexibility.
