200 



THE DENSITY OF ANIMALS ON THE OCEAN FLOOR 



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The contents of a bottom sample, one-fifth of a square metre, from the Banda Deep at 

 6, §80 metres. 



and in the Gulf of Panama. This is the first series of samples made with 

 the same gear and technique in a series of tropical and subtropical waters 

 and in the southern hemisphere. It shows that quantitatively the condi- 

 tions of animal life on the level sea bed of these waters are similar to 

 those in sampled European coastal waters. It is possible to establish a 

 clear division into zones, characterized by one or a very few predominant 

 species, which may often occur in very large amounts. However, in tro- 

 pical and subtropical coastal waters the weights per square metre arc 

 considerably lower than in such waters in North-west Europe, sometimes 

 from 50 to 100 times lower. The general rule is for the density of bottom- 

 dwelling animals to diminish with increasing distance from the coast. 

 But in some tropical waters, for example near East Africa, the maximum 

 density was not found near the coast but between 100 and 150 metres out. 

 A series of samples taken off South-west Africa near Walvis Bay is of 

 special interest. In the first place, these samples showed very high values, 

 fully up to those found in Northern European waters. For example, there 

 was the sample taken at 22 metres which contained 66.8 grams of living 

 animals made up of about 2,500 specimens, including no fewer than 

 327 of the bristle-worm Pterampharete, 220 of the small razor-shell Cul- 



