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Binyon, Edward John (1958) Studies on the permeability and ionic composition of the starfish Asterias rubens L. Doctoral thesis, Sir John Cass College.
Examination of the literature and some personal observations suggest that Asterias rubens L. is not to be found in water of reduced salinity in Great Britain. The lower limit of acclimatisation of Thames Estuary animals, taken as representative of the southern North Sea population, is about 23%. It is suggested that the Baltic Sea population occurring in water down to 8% constitutes a separate physiological race.
Previous work had suggested that a form of weight regulation existed in the North Sea Asterias rubens. This has been shown to be invalid, no evidence being obtained from large or small animals over a range of salinities and temperatures. Permeability measurements show the integument, tube feet, stomach and gut caeca to be freely permeable to water. Over a range of salinities the perivisceral and ambulacral fluids have been shown to be isotonic with the medium, and of similar composition. Potassium, however, is accumulated in the tube feet up to about twice the external concentration irrespective of temperature, and season or size of the animal. It is suggested that a form of active transport may be responsible for this condition. Calcium and carbon dioxide are present in slight excess in the perivisceral fluid. Both the tube feet and the aboral integument are freely permeable to most ions. The presence of a high sodium/potassium ratio in the stone canal suggests that if water passes through the madreporite at all, it does so only very slowly.
A table illustrating the distribution of sodium and potassium in the cells and tissues of A. rubens has been drawn up and the changes in the concentrations of these elements in both the male and female gonads have been followed for a year. A cyclical change in the sodium content was noted, this being inversely parallelled by changes in the potassium content.
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