REPORT OF THE DIRECTOR 1920-21 1 53 



THE CHAMPLAIN SEA 



EVIDENCE OF ITS DECREASING SALINITY SOUTHWARD AS SHOWN BY 

 THE CHARACTER OF THE FAUNA 



BY WINIFRED GOLDRING 



Introduction 



Recent collecting in the postglacial banks of the Champlain 

 and St Lawrence valleys has brought out the fact that going south- 

 ward there is evidence of a marked change in the Pleistocene fauna, 

 similar to that seen in the living fauna of the Baltic sea today. 

 Study of this fauna and comparison with the conditions found in the 

 Baltic and elsewhere has led to the conclusion that the character 

 of this postglacial marine fauna is due in large part at least to decreas- 

 ing salinity in this direction in the waters of that time. 



The normal salt composition of sea water permits the develop- 

 ment of a fauna rich in species and genera. A reduction in the salt 

 content of the water produces an impoverished fauna, poor in species, 

 poor in lime, dwarfed in size but often rich in individuals (Shimer, 

 p. 473; Walther, 1919, p. 60). 



Marine animals are divided into three groups according to their 

 ability to live in water of various degrees of salinity: (1) stenohaline 

 types can not live in water with less than 30 or 35 permille 1 of salt 

 (normal open sea) ; (2) euryhaline types can endure without injury 

 a considerable freshening of the water; they need the salt but not 

 a definite percentage, and will live as long as any salt remains; 

 (3) brackish-water types are adapted to a small amount of salt and 

 an increase of the salt content is just as harmful as a reduction of 

 it. The brackish state of water has never been definitely delimited, 

 but probably the upper limit would be a salinity of 2 or 3 permille. 

 The stenohaline forms outnumber the euryhaline and brackish- 

 water forms in all groups (Walther, 1894, p. 6263; Grabau, p. 1044). 



Experiments have been undertaken with sea animals (by Beudant; 

 Walther, 1894, p. 63) to determine whether they can be induced to 

 live in gradually freshened water. It was found that if marine 

 mollusks are brought suddenly into fresh water, almost all the species 

 die; but many species can endure the gradual addition of fresh 

 to salt water until eventually the water has become quite fresh. 



1 That is, parts in a thousand. 



