2?2 DISCOVERY REPORTS 



referred to; any disturbance of the water must affect them all alike. Again the 

 hydrological data, Figs. 7 and 8, do not support the conception of marked vertical 

 disturbances being brought about by violent gales. 



A CONSIDERATION OF THE POSSIBILITY OF A LUNAR 

 INFLUENCE UPON THE PLANKTON 



It is known that the moon has a marked influence on the breeding of certain marine 

 animals governing the period at which the dehiscence of eggs and sperm takes place, so 

 that the two are liberated at the same time. Worms of the genus Leodice and certain 

 Echinids are examples of organisms influenced in this way by phases of the moon. 1 It 

 occurred to us that the swarming of planktonic organisms might take place under the 

 same influence. We have not sufficient evidence from our present survey to come to any 

 conclusion in the matter, but we have thought it worth while to tabulate our results, so 

 that later workers can refer to them and combine our insufficient material with later 

 observations, and thus in time provide a body of evidence which will decide whether 

 or no any such influence is at work. In Table LI we have set out the age of the moon 

 in 2-day periods and below tabulated all the occurrences of the organisms which occur 

 in large numbers in the N 100 H nets. 2 Only those occurrences when their numbers 

 exceed 100 are shown. There are periods for which very little or no information is . 

 available. The samples are taken from all over the survey, and thus in one phase of the 

 moon more may be taken in one area than in another, so that any apparent correlation of 

 numbers zuith phases of the moon is likely to be due to differences in regional distribution rather 

 than to the effect of lunar periodicity. On the other hand, it is just possible that the reverse 

 is in fact the case, and that our idea of distribution is upset by the influence of the moon 

 upon swarming. We see in this particular set of observations that larger numbers of 

 Euphausia superba, Thysanoessa spp. and Salpa fusiformis are taken round about the 

 period of the full moon rather than at other times, and in the case of Parathemisto 

 gaudichaudi and Euphausia frigida more are taken at the first quarter than at other times, 

 with a slight indication that they are taken in larger numbers again at the last quarter. 

 Calamis propinquus shows no such apparent periodicity. 



These results are put forward with the utmost reserve and diffidence. It must be 

 understood that no significance is intended to be attached at present to the lunar corre- 

 lations here suggested : the figures are provided solely for the convenient reference of 

 future workers who may be able to add further data. 



1 Since this was written Savage and Hodgson (1934) have described the influence of the moon on 

 the shoaling of the East Anglian herring. 



2 All N 100 H nets, i.e. not only surface nets, are used for this, since presumably swarms, if any, 

 formed under lunar influence would not disperse in diurnal migration. 



