OBSERVATIONS ON THE UNEVEN 

 DISTRIBUTION OF OCEANIC PLANKTON 



By A. C. Hardy, m.a. 



(Text-figs. 1-18) 

 INTRODUCTION 



IT has long been recognized that the marine plankton of coastal regions may be very 

 patchy in its distribution. It is not difficult to understand why this should be so ; near 

 the land the sea is frequently and abruptly disturbed over quite small areas by the 

 mixing of oceanic and coastal waters, tidal streams, and the upwelling of lower water 

 layers against coastal banks. The coastal plankton community is further upset by 

 receiving the sporadic outbursts of larval forms from the littoral fauna and the shallow- 

 water benthos. In the open ocean, however, where conditions are more uniform, it has 

 often been assumed that the plankton may remain comparatively constant in quality and 

 quantity over wide areas. Observations on the plankton made on oceanic voyages have 

 usually had to be taken at stations placed at considerable distances apart, so that little 

 evidence has been available as to the evenness or otherwise of the plankton distribution 

 between them. 



The supposition that the oceanic plankton is relatively evenly distributed has been 

 widely held under the influence of the theories of Victor Hensen and the Kiel plank- 

 tologists in spite of the early and vigorous attack by Haeckel (1890) in his Plankton 

 Studien. Since the present paper concerns so closely the opposing views of Hensen and 

 Haeckel it may be appropriate to quote the following passage from G. W. Field's 

 translation of the Plankton Studien (see literature references) : 



The composition of the plankton is in qualitative as well as quantitative relations very irregular, and 

 the distribution of the same in place and time in the ocean also very unequal. These two axioms apply to 

 the oceanic as well as to the neritic plankton. In both these important axioms, which in my opinion 

 must form the starting point and the foundation for the oecology and chorology of the plankton, are 

 embodied the concordant fundamental conceptions of all those naturalists who have hitherto studied 

 carefully for a long time the natural history of the pelagic fauna and flora. 



The surprise was general when Professor Hensen this year advanced an entirely opposite opinion, 

 "that in the ocean the plankton was distributed so equally that from a few hauls a correct estimate 

 could be made of the condition in a very much greater area of the sea". 1 He says himself that the 

 plankton expedition of Kiel, directed by him, started on this "purely theoretical view" , and that 

 it had "full results" because this hypothesis was proven far more completely than could have been 

 hoped. 2 



These highly remarkable opinions of Hensen, contradictory to all previous conceptions, demand 



1 Victor Hensen, 1890. Einige Ergebnisse der Plankton-Expedition der Humboldt- Stiftung. Sitzungs- 

 berichte der Berliner Akademie der Wissenschaften vom 13. Marz, 1890, p. 243. 



2 luc. cit. p. 244. 



1-2 



