32 



CERATIUM IN THE PACIFIC AND NORTH ATLANTIC OCEANS 



station 15) but the temperatures were quite high (2i°8 C). 

 In the Pacific this particular form does not occur. Its 

 representative, however, (fig. 16F) is a warm-water 

 form, although not markedly so because the form in the 

 Pacific is not so distinct. 



Bucephalum is truly of temperate- and cold-water 

 origin. Figures 16D and E show the form from the North 

 Pacific region, figure 16A from the Humboldt Current, 

 and figure 16C from the southeast Pacific region. It is 

 absent from the tropics and thus is bizonal as Peters 

 (1934) first demonstrated. 



Since bucephalum showsthis geographic distribution, 

 and since it Intergrades with C. arietinum . it should be 

 considered a subspecies of C- firiptinnm- Jorgensen's f. 

 gracilentum is also a subspecies since it is limited to 

 quite warm water. It is useless, however, to name the 

 many variations and intergrades which occur among the 

 subspecies as they are innumerable and apparently of no 

 ecologic significance. 



The species as a whole is a fairly common one. In 

 the Carnegie collection it occurred at sijrty-two stations 

 --ten in the Atlantic and fifty-two in the Pacific. The 

 total number of records was 123, of which 87 were rare, 

 30 occasional, 4 common, and 2 abundant. There were 

 67 net records and 56 pump records. 



Nielsen reported C. arietinum as an outstanding 

 deep-water species. This is substantiated by the Car- 

 negie observations, which show the species much more 

 frequent at the 100-meter level than at 50 meters or the 

 surface (table 29). It was least frequent at the surface. 



Table 29. 



Records of occurrence of C. 

 at three levels 



arietinum 



A=Number of records. B=Per cent of total number of 

 samples collected at that depth. 



As indicated by the wide range of the species, it is a 

 rather eurythermal form. In the Atlantic it occurred at 

 surface temperatures ranging from 11° to 27.°5 C. In the 

 Pacific the range was greater; from 6.°9 (northeast of 

 Japan) to 29.°5 C (in the central tropics). The total ranges 

 of environmental conditions in situ were: temperature, 

 l.°6 to 29f5 C; salinity, 32.7 to 36.5 per mille, pH, 7.85 

 to 8.39; phosphate, 3 to 193 mg P04/m3. 



The species was found more frequently in the richer 

 waters. Only 17 of the 123 records of occurrence were 

 from water containing less than 10 mg P04/m3. 



36. Ceratium decluiatimi Karsten 

 Figures 16Q-T, 17A-C, chart 28, appendix table 33 



This is a very variable, slightly tolerant tropical 

 species. Jorgensen (1911, 1920) made several varieties 

 among the variants of the species. Peters (1934) desig- 

 nated three subspecies in his South Atlantic material; 

 C. declinatum declinatum . C. declinatum angusticornum . 



and C. declinatum laticornum. Melsen (1934) stated that 

 he could not distinguish between Peters' angusticornum 

 and laticornum . and in his South Pacific material he rec- 

 ognized only two "subspecies" — declinatum and angusti - 

 cornum. These two forms occurred in the same regions 

 so they are not subspecies in the sense used by Peters, 

 who foimd a certain geographic segregation of the vari- 

 ants. When a world collection is studied, such as that of 

 the Carnegie , it becomes evident that the species con- 

 sists of a large number of intergrading units. The nam- 

 ing of these serves no useful purpose. They are not 

 subspecies so far as can be determined, since they oc- 

 cur indiscriminately throughout the entire range of the 

 species. 



Seven of these variants are shown in figures 16Q-T 

 and 17A-C. Some of these can be identified with named 

 forms of other authors. Thus, figure 16S is similar to 

 Jorgensen's var. maius: figure 16T to Peters' laticornum: 

 figure 16Q to declinatimi : figures 17A to C to angusti- 

 cornum: whereas figure 16R, with outturned right antap- 

 ical, has not been named. 



In the Carnegie collection the species as a whole was 

 found rather continuously throughout the warm Atlantic, 

 warm Pacific, and southeast Pacific regions. It occurred 

 at a total of ninety-eight stations- -fourteen in the Atlan- 

 tic and eighty-fovir in the Pacific. In the Atlantic it oc- 

 curred at twelve stations in the warm Atlantic region and 

 at one in the cold Atlantic region, where it doubtless was 

 displaced by the Gulf Stream (station 3). In the Pacific 

 it did not occur in the cold North Pacific region but was 

 found off California at temperatures of 19.°1 and 16°2 C 

 at the northern part of the warm Pacific region. It oc- 

 curred in the southern part of the southeast Pacific re- 

 gion at stations where the surface temperatures were as 

 low as 16.°9 C. In the warm Pacific region it occurred 

 where the surface temperatures were as high as 29.° 5 C. 



The environmental conditions in situ were as follows: 

 temperature, 13.°6 to 29.°4 C; salinity, 31.7 to 37.1 per 

 mille; pH, 7.17 to 8.42; phosphate, 3 to 123 mg P04/m3. 



The ubiquity of this species (within the tropics) is 

 shown by the number of records, which was 204, of which 

 133 were rare, 67 occasional, and 4 common. Since it is 

 a very small species, it was found more commonly in the 

 pump samples. It occurred in 87 (16 per cent) net sam- 

 ples and 117 (32 per cent) pimip samples. 



It seemed to show no preference for oligatrophic 

 water. Seventy-six of the 204 recordsof occurrence were 

 from water containing less than 10 mg P04/m3. 



Nielsen (1934) stated that C. declinatum is definitely 

 a surface form. The Carnegie records show a decrease 

 in frequency with increase in depth (see table 30), but by 

 no means do they indicate that the species is exclusively 



Table 30. 



Records of occurrence of C. declinatum 

 at three levels 



A=Number of records. B=Fer cent of total number of 

 samples collected at that depth. 



