242 THE CONDITIONS OF LIFE IN THE SEA [PART III 



frequented by these vessels \ Sometimes the abundance of fish 

 on a certain ground appears to be related to the temperature of 

 the water during the preceding season'-^. Many other instances of 

 this kind might be given. 



We have seen that the abundance of life in the sea is related 

 to temperature in such a way that the colder seas have a more 

 abundant fauna than the warmer ones. This is well shewn in 

 the case of the quantitative plankton catches made in the course 

 of the German " Plankton-Expedition." If the reader will refer 

 to the synoptical chart prepared by Schutt^ he will see that the 

 larger catches were made in the cold water to the south and east 

 of Greenland, and in the upwelling tongue of cold water which is 

 situated off the Gulf of Guinea; while the poorest catches were 

 made in the warm waters of the Sargasso Sea. These results 

 are apparently paradoxical, for the general effect of increased 

 temperature is the increased metabolism of marine animals. It 

 will be seen, however, that the effect is an indirect one, and 

 depends either on the greater activity of certain forms of bacteria 

 in reducing the amount of available nitrogen food-salts, at higher 

 temperatures ; or on the relations between what we may call a 

 general anabolic, as opposed to a general katabolic process in 

 the sea. 



Speaking quite generally we may say that the effect of increase 

 of temperature in the sea is to increase the metabolism of cold- 

 blooded animals. The cold winter months are the period of 

 ebb-tide in the life-processes of such creatures. Many fishes live, 

 during the winter, in a state of semi-hibernation, when they 

 are quite inactive, do not feed, do not respire so much as in the 

 summer, and lose weight. When the temperature rises in the 

 spring they become more active, begin to feed, and their meta- 

 bolism increases. Generally it is during the spring and summer 

 months that reproduction takes place in the sea. In the case of 

 the lower marine plants the enormous reproduction during the 



^ "Aberdeen Trawling Statistics," Fishery and hydrographical investigations 

 in the North Sea and adjacent waters (Cd. 2612), 1905, p. 344. 



2 As in the case of the abundance of anchovies in the river Scheldt. Journ. 

 Mar. Biol. Ass. vol. i. {N.S.), 1889-90, p. 340. 



2 Analytische Plankton- Studien, Kiel and Leipzig, 1892. 



