AMPHIPOD CRUSTACEA OF THE GENUS GAMMAKUS 



71 



TABLE 4 

 Phj'sical and Chemical Conditions of the Waters In North India 



b. Chemical factors. 



i. Dissolved oxygen content. Gammarus pulcx is a mesoxybiont (after Steinniann and 

 Siirbeck, quoted in Wundsch) which demands water rather rich in dissolved oxygen. Though 

 I have at hand no data of the dissolved oxygen in the waters of Kashmir and Ladak, it is 

 difficult to suppose that the dissolved oxygen may play a great part as a limiting factor. 

 According to Dr. Hutchinson's information, Lake Khyagar Tso in Ladak had an absolute 

 oxygen deficiency on the bottom. The gammarids in that lake seemed to l)e living as a free- 

 swimming form in open water, since immense numbers of them were found settling on the 

 anchor rope while one was making limnological observations. 



ii. Salt content of water, especially calcium. The correlation between the distribution 

 of Gaviniarus and some chemical environmental factors, especially calcium dissolved in water, 

 is discussed by several authors (cf. also Pia 1933). Thienemann (1912) found that the 

 gammarids in the torrents of Baumberg districts, rich in calcium, are larger in size than those 

 found in the torrents of Sauerland, where the water is very poor in calcium. Wundsch 

 ( 1915) observed in the Sieg, a branch of the Rhein, that Gai)imarus pulex entirely disappears 

 from a biocoenosis when the calcium content of the water Ijecomes less than 9-10 mg. per litre. 

 Schumann (1930) writes that at least 13 mg. per litre of CaCOg is necessary for the forma- 

 tion of the shell of Gammarus, because newly ecdysized gammarids with soft bodies take up 

 the lime for building up their shells in the state of bicarbonate from the water and then make 

 it monocarbonate in their bodies. Since COo-free water can dissolve only 13 mg. per litre of 

 CaCOg, below this lime content gammarids cannot use the lime for the formation of their 

 shells, being obliged to live as soft-bodied animals which have no external protection against 

 osmotic action. On the contrary, Pentland (1930) concluded that the chemical composition 

 of the water does not appear to control the distribution of Gammarus, the temperature of 

 water, vegetation, and the presence of enemies alone limiting the distribution. .Schlagintweit 

 (cited by Hesse 1924) reported an interesting fact that in Ladak the Puga torrent, rich in 

 borax, is favourable for crustaceans and fishes. 



A study of the physico-chemical data relating to North Indian waters, presented above 

 in Table 4, makes it very difficult to correlate the non-occurrence of Gammarus with the 

 alkaline reserve and the |)H-values of the waters in the zone between 1600 m. in Kashmir and 

 3800 m. in Ladak. The waters containing gammarids at high altitudes often have a 

 lower alkaline reserve and lower pH-values than those in intermediate region where 

 Gammarus does not occur. According to Schumann (op. cit.), the optimum pH of the water 



