CH. IX] THE PRODUCTIVITY OF THE SEA 205 



catches made here were no more abundant than in the Sargasso 

 Sea. Compare this with the Bay of Kiel in the cold Baltic. 

 Though Hensen and Brandt made 70 quantitative hauls during 

 the years 1889 — 1893, they found on only one occasion (February, 

 1894) so small a catch as was obtained from the sub-tropical 

 Sargasso Sea^. 



One would naturally expect that the pellucid and warm seas 

 of the tropics would afford the richest fauna and flora ; and that 

 the cold and turbid seas of the north would be relatively poor in 

 life. "The yellow Baltic," says Schiitt^ "even in full daylight, 

 only allows us to see the white net at a few metres beneath the 

 surface ; the green North Sea transmits light from a much greater 

 depth ; and what visitor to the Mediterranean does not know the 

 great transparency of that blue sea ? Yet investigations of colour, 

 transparency, and plankton contents give parallel results, and all 

 these shew that the pure blue is the colour of desolation of the 

 high seas." 



Thus the colder seas are richer in life than the warmer ones ; 

 or at the very least the amount of life in polar seas is not less 

 than in the tropics. We know that intense sunlight and high 

 temperature are favourable to plant life and so these results are at 

 first sight astonishing ones. The density of plant life on the land 

 is apparently a function of these two factors ; why then is not 

 this the case also in the sea ? One would expect that there 

 would not be such a difference between equatorial and polar seas 

 as between equatorial and polar lands. The range of temperature 

 in the sea is only 33-8' C. (- 2*8° to 31° C.) but on the land the 

 extreme difference is 131-5° C. (65° to - 66*5° C). But even with 

 this variation in the temperature of the seas one would expect 

 a corresponding difference in the density of life. Why is the 

 opposite the case ? " One stands," says Kjellmann, " as before an 

 insoluble problem when he makes a haul with a tow-net in the 

 Arctic and obtains abundant and strong vegetation, and this at 

 a time when the sea is covered with ice, the temperature is 

 extremely low, and nocturnal gloom predominates even at noon." 



1 " Die Fauna der Ostsee," Verhandl. deutschen zool. Gesell. Leipzig, 1897. 

 - " Das Pflanzenleben der Hochsee," Reisebeschreibung Plankt. Exped. Kiel u. 

 Leipzig, 1892, p. 314. 



