igS THE DENSITY OF ANIMALS ON THE OCEAN FLOOR 



means of a series of samplings in tropical waters and the southern hemi- 

 sphere, we would obtain a basis of comparison between the animal com- 

 munities of the North Atlantic and those of other waters. 



It need hardly be said that the greatest interest attached to working 

 the Petersen grab at the extreme depths, where it had never been worked 

 before, and where therefore nothing could be known about the quantity 

 of the fauna. It was to be expected that the number of animals there 

 would be very small. Food production takes place in the uppermost 

 layers, and the further we get from the source of production the poorer 

 must we expect food conditions to be. It would not have been surprising 

 if the fauna on the deep ocean floor had been so scattered that most of 

 the samples contained no living animals at all. 



So it was with great excitement that we awaited the result of our first 

 sampling of the deep ocean bed, which took place on December 19, 1950, 

 off Angola. Would the grab bring up anything at all? Was the gear of 

 any use at the great depths? The first attempt was a failure; the grab had 

 not closed. But then it came up from 3,660 metres full of deep-sea ooze; 

 and on sorting the material out we found that it contained three different 

 species of polychaete worms, one of them a species common in Danish 

 waters (Ammolrypane aulogaster) , together with three small bivalves closely 

 related to our common Leda. Thus in one-fifth of a square metre no 

 fewer than four species were represented by six individuals weighing 0.3 

 grams, which corresponds to more than one gram and about 30 animals 

 per square metre. Hence, this sample showed, first, that the gear can 

 be operated at great depths, and, secondly, that there appears to be an 

 astonishingly great wealth of species and density of individuals even on 

 the deep ocean floor. 



Confirmation of this was forthcoming. Altogether, we made 28 success- 

 ful samplings of the deep ocean floor beyond 2,000 metres, seven of 

 which were in the oceanic trenches deeper than 6,000 metres. The first 

 fact to emerge was that few of the samples contained no animals at all. 

 In the Philippine Trench we succeeded in getting a sample up from 

 10,120 metres; it contained a small sea-cucumber weighing just under 

 o.i gram, which corresponds to about five individuals and about half 

 a gram per square metre. A couple of astonishingly rich samples were 

 taken in the Weber Deep in the Banda Sea, at 7,280 and 6,580 metres 

 respectively. The first yielded three species of animals and 6 individuals 

 weighing 2.5 grams, and the second eight species and 1 1 individuals 

 weighing 2.1 grams. This gives a weight of no less than 10 — 12 grams 

 and a density of about 60 — ^70 individuals per square metre. 



