PLANKTON AS AN INDICATOR OF WATERS OF DIFFERENT ORIGINS 



IN THE NORTH ATLANTIC SEAS 



V. D. Abramova 



INTRODUCTION 



During the last few years, the Polar Institute has been carrying out large-scale complex 

 investigations in the North Atlantic Seas, as a result of which it has now become possible for the 

 Soviet deep-sea herring fleet to operate throughout the year. 



If the resources of fish in the North Atlantic Seas are to be exploited further, the habitats 

 of the herring must be studied and, first and foremost, currents and plankton must be investigated. 



Plankton is the basic food of the herring, and on the distribution of the plankton organisms 

 depends the behavior of the herring at any given season and, consequently, the success of the 

 herring- fishing industry. 



In its turn, the distribution of the plankton depends on the hydrological conditions, which 

 means that plankton organisms can serve as indicators of the hydrological conditions in any given 

 area. 



The idea of using plankton as an indicator of the hydrological conditions of the sea has long 

 occupied the attention of research workers. It has been established that plankton organisms are 

 the most delicate indicators, reacting to the slightest changes in the hydrological conditions of the 

 environment. 



Plankton is particularly valuable as a biological indicator in those areas of the sea where 

 masses of water of different origins meet and intermingle and cannot be determined by hydrologica 

 methods . Only the presence of specific forms of plankton in the waters can give any idea of their 

 origins . 



A great deal of work has been carried out by Russian investigators in the polar seas with a 

 view to discovering whether or not it is possible to use plankton, and phytoplankton in particular, 

 in the preparation of ice forecasts and for determining the lengths of biological seasons in differ- 

 ent seas (3, 14, 18). 



Similar investigations were begun in other countries somewhat earlier. Cleve (20) and 

 Gran (21) did extensive work in the Norwegian Sea and in Icelandic waters, as a result of which the 

 ecology of individual species of phytoplankton and zooplankton and their zoogeograp)hical distribution 

 have been described. Gran identified certain groups of plankton organisms which are characteristic 

 of Atlantic and Arctic waters. This work is still valuable today. 



The work of the British investigators Hardy (22), and Russell (23, 24, 25) in the seas round 

 the south of Britain and in the North Sea date from a somewhat later period. However, we are still 

 far from having a perfect knowledge of the biology of plankton organisms . 



Our task was to explain the influence of the currents and temperature on the qualitative and 

 quantitative distribution of plankton, to identify the principal forms characteristic of certain con- 

 ditions and to use them as biological indicators of the hydrological conditions of the sea . 



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