268 DISCOVERY REPORTS 



PLANKTON AND ROUGH WEATHER 



The force of the sea was recorded at every station in terms of Beaufort's scale. It has 

 often been supposed that plankton organisms tend to sink from the surface layers 

 during stormy weather. Our results do not confirm this supposition. In Table L the 

 results of all the surface hauls made with N ioo H nets have been collected in two series 

 for day and night under headings of Force of Sea, 0-2, 3-4 and 5-7. The actual numbers 

 of the more important organisms taken in the individual nets are recorded, together 

 with the average number per net according to each state of sea. These average figures 

 really mean little or nothing on account of the tendency of masses of the organisms to 

 occur in swarms. A general view should be taken of the actual numbers recorded, and 

 allowance made for the number of nets taken in each state of sea. 



The inequality in the number of stations in each state of sea must be kept in mind. 

 For the three states of sea employed in the table there are respectively 27, 18 and 12 

 stations in daylight and 8, 11 and 12 stations at night. Since the organisms occur in 

 swarms, the larger the number of stations considered the greater are the chances of 

 meeting with a big swarm. Parathemisto gaudichaudi illustrates this. The actual number 

 of hauls in which it was captured in the daytime in the three states of sea were 16, 11 

 and 6, which are approximately proportional to the number of stations: 27, 18 and 12. 

 Only one really big swarm was taken, 464, and this falls in the first category where 27 

 hauls were made. 



It will be seen that whilst there is a slight tendency for lesser numbers of some organ- 

 isms to be taken in the rougher seas during the daytime this is not so at night, and we 

 must come to the conclusion that the state of the sea has little or no bearing on the 

 number of organisms in the surface layers. 



We have already remarked (p. 11) upon the violence of the sudden storms which 

 are of frequent occurrence in these regions. It might be thought that the water 

 over the continental shelf would in consequence be churned up to such an extent 

 that the vertical distribution of the plankton would be so disturbed as often to 

 render an account of it of little value. We have, however, ample evidence to show 

 that this is not so. At St. 41 we have observed the vertical distribution of a number 

 of species at more or less two-hourly intervals; for example, we have seen the 

 marked migration of Colanus simillitnus and Drepanopus pectinatus, Figs. 101 and 102, 

 and lack of migration in Colanus acutus and Rhincalanus gigas, Figs. 111 and 112. 

 Now in the charts illustrating vertical distribution combining the N70H results 

 for all stations, whether taken in fair weather or rough, or after rough weather, we 

 see that these species show equally well the types of vertical distribution they 

 showed at St. 41, see Figs. 99, 100, 108 and 109. Had rough weather been an 

 important factor influencing the vertical distribution these charts would not have 

 revealed these clear-cut differences in behaviour. Nor can the instances of apparently 

 less regular behaviour, such as that of Colanus propinquus, Fig. 103, be due to such 

 a cause, for the stations and net hauls are the same as those in the other figures just 



