THE ACCOMMODATION OF SOME MARINE INVERTEBRATES TO REDUCED OSMOTIC PRESSURES

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Abstract
1. The distribution of 14 species of invertebrates in the Narraguagus Bay and River was compared with the osmotic pressure (indirectly determined by means of freezing points) of the water at a series of stations ranging from the open sea to the head of the tide. 2. The osmotic pressure of the water confined in the mud flats was found to be almost constant at high and low tides in contrast with the marked tidal variations in surface water. 3. Typical marine animals were found in an environment having a freezing point of —.404° C., or the equivalent of 19 per cent sea water. 4. The survival of Nereis virens in fresh water was extended as the process of acclimatization was made more and more gradual. 5. Tests on 14 species showed that all but one were able to survive experimental exposure to reduced osmotic pressure below that found in their natural environment. 6. Members of a species collected from water of low salinity were more resistant to reduced osmotic pressure than individuals collected from the open sea. 7. Nereis virens was able to accommodate without marked change of weight down to a concentration of 16 per cent sea water. At this point a rapid increase in weight occurred. The dilution process above 16 per cent was accompanied by an increased oxygen consumption. Below 16 per cent sea water oxygen consumption decreased.