56 LIFE IN THE SEA [CH. 



everywhere in the seas of the world are conspicuously 

 more abundant the further north or south we go. 

 But some pelagic algae the small form Tricho- 

 desmium, and Sargassum, the gulf-weed, occur in 

 abundance only in tropical waters. The mangrove 

 swamps of the tropical sea-margins are also instances 

 of associations of brackish water plants which do not 

 occur in the temperate or polar seas. 



All experience shows that the polar and temperate 

 seas are, generally speaking, far richer in life than are 

 the tropical ones. There is a striking picture of the 

 relative density of life on land and sea in Darwin's 

 description of Tierra del Fuego. That desolate and 

 inhospitable land sustains with difficulty a sparse and 

 cannibalistic population, while the seas near the shore 

 contain such an abundance of life as Darwin could 

 only compare with that of a terrestrial forest in the 

 intertropical zone. Chun, in his account of the voyage 

 of the German exploring ship 'Valdivia,' speaks of 

 the teeming plant and animal life of the ice-covered 

 Antarctic sea. The naturalist Kroyer found an abun- 

 dance of invertebrate life in the sea off Spitzbergen 

 such as he had never seen surpassed elsewhere. The 

 greatest and most productive fisheries of the world 

 are those of the seas round Britain, off the coasts of 

 northern Norway, on the Banks of Newfoundland, in 

 the seas off Iceland, and off' north Europe close up to 

 the ice-packs. Nowhere else in the world has there 



