18 



CERATIUM IN THE PACIFIC AND NORTH ATLANTIC OCEANS 



Cpratiiim ranHplahniTn was found throughout the 



warm-water regions without respect to the nutrient con- 

 tent of the water. Thus, 117 of the 353 records of oc- 

 currence were in water containing less than 10 mg 

 P04/m3. The range of surface temperatures at the sta- 

 tions where it occurred was from 15.°9 to 29.°5 C. The 

 ranges of environmental conditions in situ were: tem- 

 perature, 8f8 to 29.°5 C; salinity, 30.0 to 37.1 per mille; 

 pH, 7.76 to 8.47; phosphate, 3 to 189 mg P04/m3. 



Variation. - -Several varieties of C. candelabrum 

 have been described, the most important of which are 

 var. depressum Jorgensen (1920) and f. commune Bohm 

 (1931). Nielsen (1934) distinguished these two Variations 

 and stated that both are found in the western part of the 

 Pacific investigated by him but only var. depressum was 

 found in the eastern Pacific. The writers are inclined 

 to agree with Peters (1934) that the variations in this 

 species are too continuous for any separation of varie- 

 ties, although it must be stated that most of the Carnegie 

 material resembled the var. depressum form. Figure 6 

 shows a series of specimens with variously bent horns, 

 both apical and antapical, and with various lengths of 

 horns. 



6. Ceratium furca (Ehrenberg) Dujardin 

 Figure 7, chart 6, appendix table 6 



Ceratium furca Is an interesting cosmopolitan spe- 

 cies probably composed of many subspecies or races. 

 Jorgensen (1911) designated two subspecies; a northern 

 form, subsp. a berghii and a tropical form, 6 eugram- 

 minn. Ceratium hircus Schroder, which Jffrgensen ac- 

 cepted as an independent species, is probably also a va- 

 riety of C. furca. In his study of Mediterranean Ceratla, 

 Jorgensen (1920) designated many more varieties. Bohm 

 (1931) attempted to show that in his material from the 

 western Pacific there were two genotypes, both belonging 

 to the tropical subspecies eugrammum . These were sep- 

 arated on the basis of total length; a short variety with 

 length from 130 to 168 microns, and a large varietyfrom 

 170 to 244 microns. Nielsen (1934) did not consider 

 Bohm's evidence conclusive, and made a statistical study 

 of length in his material from the South Pacific. In only 

 one sample did he find a separation into two groups on 

 this basis. Bi other samples long ones or short ones 

 were represented, and often medium-sized ones. Never- 

 theless Nielsen considered that two races were repre- 

 sented. 



As a result of the study of the Carnage material the 

 writers tend toward JOrgensen's (1920) opinion, that the 

 species is a complex of many varieties and races, not of 

 two. No separation could be made on the basis of size 

 alone. No attempt was made to separate the different 

 variants. The number is great and the intergradations 

 common, fii figure 6 several variants are shown. 



The distribution of C. furca is of particular interest. 

 Peters (1934), in his study of the Ceratia of the Meteor 

 expedition in the South Atlantic, concluded that C. furca 

 is a typically neritic species. It was found abundantly in 

 the mouths of great rivers and in regions of upwelling. It 

 seemed to avoid the middle regions of the oceans. Niel- 

 son (1934) accepted this classification of the species and 

 stated that it is distinctly a neritic form, although also 

 found at many oceanic stations. He found it at every sta- 

 tion but two between Panama and Tahiti, and at various 

 stations between that point and Australia. He stated that 



its occurrence at these oceanic stations can be explained 

 by the disturbed water about the islands in the western 

 Pacific and by the eutrophic water occurrence in the 

 eastern part of the South Equatorial Current. Such a 

 broad use of the term "neritic," however, leaves no 

 room for the term oceanic so such usage cannot be ac- 

 cepted. Nielsen's data show, on the other hand, that C^ 

 furca is oceanic as well as neritic. In the Carnegie col- 

 lection the species did show a tendency to occur more 

 frequently and more abundantly in richer water but, 

 nevertheless, was often found in oligotrophic water. 

 Only 40 of the 231 records of occurrence were in water 

 containing less than 10 mg P04/m^. 



In the Carnegie collection there is no indication of 

 an avoidance of oceanic water or of the middle regions 

 of the open oceans on the part of C. furca . Not only are 

 there many station records for the open North Atlantic 

 and the Pacific, but there are as many records of occa- 

 sional and common for stations remote from land as for 

 stations close to land (see chart 6). 



In the Atlantic there were two distributional areas, 

 probably representing the distributions of the two sub- 

 species; a northern one from stations 6 to 11a (from 

 southwest of Ireland around the North Sea and Iceland to 

 southeast of Greenland), and a tropical region from sta- 

 tions 14 to 24 (straight down through the middle of the 

 Atlantic). There was also one station in the Caribbean. 

 In the Pacific, also, the distribution was interrupted. 

 The species was found quite regularly in the southeast- 

 ern Pacific, but was scattered irregularly over the other 

 tropical regions of the Pacific. It was notably absent 

 from the northern line of stations from stations 118 to 

 128 inclusive. No northern form was found in this ocean. 



The surface temperatures in this " C. furca -free" 

 water in the northern Pacific varied from 7.° 2 to 16.°4C. 

 This should not have constituted a barrier to this species 

 as it was found In the Atlantic where the surface temper- 

 atures were as low as 8.°9. The tropical subspecies was 

 confined to warm water in the Atlantic (surface temper- 

 atures 21.°2 to 28.°0 C), but in the Pacific it extended into 

 somewhat cooler water (surface temperatures from 15.°0 

 to 29.°4 C). Obviously the northern subspecies of the 

 Atlantic was not found in the Pacific. 



Ceratium furca is frequently found in quantities. 

 Records of "abundant" were from the North Sea, south- 

 eastern Pacific, and southeast of Japan. The species was 

 found at 91 Carnegie stations--19 in the Atlantic and 72 

 in the Pacific. There were 232 records of occurrence, 

 with 140 rare, 65 occasional, 22 common, and 4 abundant. 



Nielsen (1934) classified C. furca as a surface form. 

 The Carnegie data show that it is truly not a shade form, 



Table 7. 



Records of occurrence of C. furca 

 at three levels 



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

 samples coUected at that depth. 



