Studies of the deep water fauna and related problems

Abstract

1. 1. Investigations on the Kuril Trench, carried out in 1953 by the Soviet expedition on the Research Ship Vitjaz allowed several general principles to be laid down in the change of the bottom and the pelagic faunas with increasing depth. 2. 2. The biomass of benthos and plankton in the ultra-abyssal zone (> 6,000 m) is 1,000 times less than in the surface zone. 3. 3. With the increase of depth the variety of species of benthos decreases ; its diversity increases at first and then decreases, for the most part within the ultra-abyssal zone. 4. 4. The colouring change of bottom and pelagic animals also takes place differently according to depth. Many pelagic animals are pigmented up to depths of 6–7,000 m. Only the plankton of the ultra-abyssal zone is totally devoid of pigment (except the amphipad Andaniexis subabyssi Birst. et M. Vin.). The bottom animals become pigmentless, at depths greater than about 2,000 m. Possibly this dissimilarity is due to vertical migrations of broad range peculiar to pelagic animals. 5. 5. The relative importance of predators of plankton increases with depth. This contracts with the bottom animals, for which there is an increase in relative importance of detritus eaters and a lesser importance of predators at increasing depths. 6. 6. One of the many sources of food supply for the abyssal and ultra-abyssal fauna is provided by the transportation of organic matter from the zone of photosynthesis down to the great depths by means of vertical migration of zooplankton, performed either within each fixed vertical zone, or having a still broader range. During their vertical migrations the upper layers of deep-sea animals become the prey of the lower dwellers and thus the organic matter produced in the zone of photosynthesis is brought to the greatest depths of the ocean. 7. 7. The body-size comparison of species of the same genus inhabiting different depths shows a tendancy to greater body-size with greater depth. This is true for both bottom and pelagic animals. It cannot be explained by temperature changes. 8. 8. The deep-sea fauna comprises a great quantity of ancient and primative forms. 9. 9. The zoogeographic regions of the ocean ought to be determined from separate vertical zones. In addition, the determination of zoogeographic regions of the abyssal zone will show not only the connections and the hydrological regime of the contemporary seas and oceans but also those of the seas and oceans of the remote past. 10. 10. The ultra-abyssal faunas of each trench must comprises endemic species or even units of a higher taxonomic grade. A set of these species was discovered in the extreme depths of the Kuril Trench.