30 Routes from the Sea 



Corophmm rohulator (Pallas) 1-9 5.90 



Leptocheurus hirsutimanus Zadd. 9 5.90 



Orchestia gamarellus (Pallas) 1-4,9 5.90 



Gammarus locusta (L.) 1-6 13.15 



Gammaru? marinus Leach 1-5 13.50 



Taliturus saltdtor (Mont.) 1,5 13.50 



Asellus aquaticus (L.) 17,21-26 0-0.5 



Sphaeromd rugicauda Leach 5-9 5.90 



Idothea viridis G. O. Sars 1-6 13.15 



Jaerd mdrina (Fa'rricius) 1-4 13.97 



Idothed bdlticd (Pallas) 1-3 15.36 



Ligyda ccednid (L.) 1-3 15.36 



Clearly these crustaceans also fall into three groups in their rela- 

 tions to salinity. 



Goodhart (1941) divides the amphipods in an estuary on the 

 coast of Hampshire into four groups that include: (1) two fresh- 

 water species that can endure no salt, (2) six brackish-water species 

 that cannot live permanently in either salt water or fresh water, (3) 

 eight marine species that can endure some dilution of sea water, and 

 (4) many marine species that do not occur in fresh water. Gunter 

 (1942) gives a list of 141 species of fishes that live in salt water or 

 fresh water. He points out (1947) that many primitive fishes are 

 euryhaline. He also states that marine fishes are found nine times 

 as often in fresh water as rice versa. So, most estuarine animals are 

 marine. Marine animals tend to grow smaller in fresh water. 



Prenant (1929) has called attention to the fact that the distribu- 

 tion of marine species in estuaries is correlated with respiratory 

 requirements. As water becomes less saline, respiration becomes 

 more difficult. The circulation of water by currents may in part 

 compensate for the difficulties associated with lowered salinity. Of 

 course variations in salinity have other effects on organisms besides 

 those connected with respiration. These will be considered more 

 fully in Chapter III, under Salinity. 



