QUANTITATIVE INVESTIGATIONS AS TO PHVTOPLANKTON AND PELAGIC 

 PROTOZOA IN THE GULF OF ST. LAWRENCE AND OUTSIDE THE SAME. 



By II. H. Gran. 



The plankton investigations wliicli have been carried out in North European waters 

 since P. T. Cleve and Aurivillius, in the nineties of the past century, made their pioneer 

 researches on the phuikton of the Skagerak, and which from 1901 have been under 

 the guidance of the International Council for the Exploration of the Sea, have, as a 

 first general result, given us a very close knowledge of the distribution of the different 

 :,pecies and their relative frequency at the various seasons of the year. A survey of 

 die data thus acquired has been issued by the Council in a series of papers, edited by 

 Dr. C. II. Ostenfeld.i 



The next aim of the investigations is to enable us to determine the quantitative 

 occurrence of the plankton as a measure of the production in the different areas of sea. 

 The question was already raised by Hensen, and his methods of operation, by vertical 

 hauls made with " quantitative " nets and countings of individuals in certain fractions 

 of the catch — or simple determinations of volume for the whole — made the first steps 

 towards a solution of this great and many-sided problem. With the fundamental work 

 of Lohmann in this field, a great advance was made in regard to the methods employed, 

 and we are now able to determine the quantity of plankton in relatively small water 

 samples, by means of the centrifuge. In seeking to ascertain the relation of plankton 

 production to various external conditions, such as light, temperature, salinity and food, 

 it will not be enough to work merely with samples taken in vertical hauls, as the con- 

 ditions in question are by no means uniform throughout the entire column of water 

 filtered by the net. A series of water samples, on the other hand, taken at the same 

 locality, but at different depths, will show how the quantity of the plankton varies with 

 the depth, so that we can, with a suiRcient quantity of material, ascertain the depend- 

 ence of the production upon the different factors, which vary in a horizontal as well 

 as in a vertical direction, throughout the sea. 



A further improvement of the method, and adaptation of the same to particular 

 purposes, was made when I succeeded in finding a means of preserving water samples 

 by means of Flemming's liquid, added in the proportion of 1-25 ; this rendered it pos- 

 sible to collect a greater quantity of material in a short time, and store it for subse- 

 quent thorough investigation. The method was employed for research work through- 

 out the whole of the year in the Norwegian coastal waters, as also in extensive investi- 

 gations of the North sea and North Atlantic, carried out in ^lay-June, 1912, by the 

 North Sea countries acting in concert.- 



The large amount of material and observations collected in the course of these 

 investigations presents various points of difficulty in regard to judging the results, 

 as it is distinctly seen that the conditions in the sea are rarely, if ever, so stationary 

 that we can immediately presume the existence of causal relation between the quan- 

 tities of plankton found at any spc>t and the conditions of life there prevailing at the 

 time. The plankton moves, not only with the currents in a horizontal and a vertical 

 direction, but sinks to a great extent, and rises also, though in a lesser degree, 

 actively, within the water mass in which it has developed. We often find, for instance, 

 considerable quantities of pelagic algte at depths far beyond the level at which they 

 can have developed; so far down, indeed, that their assimilation of carbonic acid 



1 Bull. Trimestriel .... Resume des Observations sur le Plankton, Parts 1-3, 1910-19«13. 



3 H. H. Gran. The Plankton Production of the North European Waters in the spring of 

 1912. Bulletin Planktonique pour I'annee 1912, publie par le bureau du Conseil Permanent Inter- 

 national pour I'exploration de la mer. Copenhague 1915. 



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