o 



THE DISTRIBUTION AND LIFE HISTORY 



OF EUPHAUSIA TRIACANTHA . ^ 



HOLT AND TATTERSALL /^- '" ^ ,; 



T. . J r. T. , I WOODS 



By A. de C. Baker \ HOLE 



.^ ;; A^ V MASS.' 



(Text-figs. 1-16) 



INTRODUCTION 



NE approach to the problem of reveahng the basic principles governing the distribution of 

 _ planktonic organisms is to make special studies of selected representative species. Detailed 

 examination and comparison of species with different distributional, reproductive and feeding habits 

 should help to elucidate the factors controlling these habits. 



David (1955) has already made such a study of the carnivore, Sagitta gazellae Ritter-Zahony, 1909, 

 from the Discovery collections and Mr J. W. S. Marr, who is working on Euphausia superba Dana, 

 1852, has published a preliminary account of the broad features of its distribution (1956). The present 

 paper on E. triacantha Holt and Tattersall, 1906, is intended as a further contribution to this 



work. 



There are several reasons for selecting E. triacantha as a species for detailed exammation. John 

 (1936) has shown that the distribution of the southern members of the genus Euphmisia is such that 

 they occur in more or less overlapping concentric zones round the Antarctic continent. E. superba 

 occurs in the East Wind drift and Weddell Sea regions of the Southern Ocean (Marr, 1956) and 

 E triacantha is found to the north of this in the West Wind drift (John, 1 936) ; thus a useful comparison 

 can be drawn between the two species. Also E. triacantha displays little or none of the shoaling habit 

 found in E superba. That E. triacantha performs a marked diurnal vertical migration, a character 

 not found in Sagitta gazellae (David, 1955) nor in E. superba (Mr Marr, personal communication), 

 is of additional interest for purposes of comparison. It is also easily identified m the samples, a point 

 of some considerable importance where much material has to be examined. 



ACKNOWLEDGEMENTS 



This study was undertaken at the suggestion of Dr N. A. Mackintosh, C.B.E., who has given me 

 much helpful advice and criticism. 



I would also like to express my thanks to those of my colleagues who have given me help and advice 

 from time to time, particularly to Mr J. W. S. Marr for allowing me to use his data for the section 

 concerning E. superba and also for reading and criticizing the draft of that section; to Dr H. E 

 Bargmann for her assistance during the study of the reproductive system; to Mr P. M. David for 

 reading and criticizing the typescript and to Mr P. Foxton for allowing me to make use of the data 

 he collected during the sixth Antarctic commission (1950-1) of R.R-S. 'Discovery II . 



I would also like to thank Mr A. E. Fisher who helped me in the early stages of this work by sorting 

 many samples, and Mr A. Style who prepared several of the figures for publication. 



