126 DISCOVERY REPORTS 



THE SURVEY OF DECEMBER 1930 



During the 1930-1 season a plankton survey of seventeen stations was made in 

 Bransfield Strait by the ' Discovery II '. The first two lines of this survey were disposed 

 somewhat farther to the eastward than on those previously described, as can be seen 

 from Fig. 56. 



It will be seen that the first line, of five stations, was worked from the strait between 

 Elephant and Clarence Islands — south-westwards in the direction of Joinville Island. 

 The full analyses of the phytoplankton material collected on this line are given in 

 Table XXXIX. At all four stations to the north-east, Sts. 537-540 inclusive, it will be 

 seen that Corethron valdiviae was strongly dominant, with Rhizosolenia gracillima 

 present in moderate numbers at Sts. 538 and 539, and increasing numbers of small 

 forms such as Fragilaria antarctica and Chaetoceros fieglectus at Sts. 539 and 540. At 

 Sts. 537 and 540 the phytoplankton was moderate in quantity, and at the two middle 

 stations it was rich. The findings on the next line worked to the west served to make it 

 fairly clear that this flora represented the last of the dense Corethron plankton of the 

 spring increase within the Bransfield Strait drifting away to the north-east. A note- 

 worthy feature of these stations was the large number of Corethron cells in process of 

 forming auxospores, thereby more than doubling their size. The increased proportion 

 of small forms at the two more southerly stations in this case undoubtedly indicated 

 slight admixture with Weddell Sea surface water, as the rising salinities with falling 

 surface temperatures are sufficient to show. 



At the southernmost station on this line a phytoplankton of an entirely diff'erent 

 nature was encountered, as can be seen from the fact that though it occupied barely 

 half the volume of the catch at the preceding station, the total diatoms, exclusive of 

 minute, uncountable colonial forms, exceeded the estimated total at St. 540 by some eight 

 hundred thousand. This was primarily due to a great falling ofi^ in the proportion of 

 Corethron valdiviae, and to the presence of a much greater variety of small forms, 

 sixteen species being recorded against nine at the preceding station to the north-east. 

 That this station, St. 541, was worked well within the sphere of Weddell Sea influence 

 is clearly shown by the sharp rise in salinity and fall in temperature at the surface. The 

 dominant form here was Chaetoceros socialis in minute uncountable colonies, and other 

 leading species were Thalassiosira antarctica, Chaetoceros tortissimiis, Corethron valdiviae 

 and Chaetoceros neglectiis, in that order of importance. A precisely similar phytoplankton 

 was found at the two southernmost stations on the fine next to be described, which were 

 evidently worked within the eddy of Weddell Sea water round Joinville Island. In 

 examining the catch from St. 541 unusually large numbers of faecal pellets of Eu- 

 phausians were observed, many of large size being obviously attributable to Euphaiisia 

 superba. This may indicate that the feeding was good. 



The next line of this midsummer survey was worked very slightly to the east of the 

 lines south from Admiralty Bay of the previous surveys, from Cape Melville on King 

 George Island southwards. The full analyses of the phytoplankton hauls from the six 



