28 



CERATIUM IN THE PACIFIC AND NORTH ATLANTIC OCEANS 



contamination of the open nets this tendency would be 

 more pronounced. 



Table 23. Records of occurrence of C. breve 

 at three levels 



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

 samples collected at that depth. 



The species is often found in comparatively large 

 numbers. There were 258 records of occurrence, of 

 which 112 were rare, 108 occasional, and 38 common. 

 Since it is a large species, it was found more often in the 

 net samples. There were 181 net samples and 77 pump 

 samples. Seventy -five of the records were in water con- 

 taining less than 10 mg P04/m3. 



27. Ceratium compressimi Gran 

 Figure 15A 



This is a very rare species previously known only 

 from the temperate waters of the North Atlantic. In the 

 Carnegie collection a single specimen was found. This 

 occurred in the 100-meter net sample from station 61 in 

 the southeastern Pacific, latitude 38.°5 south. Probably 

 this is a bipolar species occurring in the cooler waters 

 of both hemispheres. The surface temperature at station 

 61 was 16.°9 C. The environmental conditions at 100 me- 

 ters were: temperature, 10.°8 C; salinity, 34.0permille; 

 pH, 8.03; phosphate, 80 mg P04/m3. 



28. Ceratiimi euarcuatum Jorgensen 

 Figures 15N-M, chart 22, appendix table 26 



This is a distinct and easily recognized species 

 which varies comparatively little. It is an intolerant 

 tropical species, although found almost continuously in 

 the warm regions of the oceans (chart 22). It was found 

 at eighty-five stations- -fourteen in the Atlantic, and 

 seventy-one in the Pacific. In the Atlantic it was con- 

 fined to the warm Atlantic region and in the Pacific to 

 the warm Pacific region except for two stations in the 

 western part of the southeast Pacific region. The sur- 

 face temperatures at the stations where it occurred in 

 the Atlantic varied from 24.°0 to 28.°0 C and in the Pacif- 

 ic from 19.°0 to 29.°5 C. It was absent from the entire 

 southeastern Pacific east of 100° west longitude except 

 for one station west of the Galapagos Islands. Nielsen 

 (1934), however, foimd a single specimen in the Panama 

 region. 



Ceratiimi euarcuatum probably is one of the best in- 

 dicators of warm tropical water. It apparently is of no 

 value as an indicator of intrusions of water of tropical 

 origin, however, since it does not seem to extend beyond 

 the tropical boundaries in such currents as the Kuroshio 

 and Gulf Stream. Apparently it does not endure a lowering 



of the temperature. On the other hand, it is found within 

 the tropics in regions where cooler water has been 

 brought in from other regions or from vertical disturb- 

 ances. Thus, it was found west of the Galapagos where 

 the surface temperature was 19.°6 and south of Easter 

 Island where it was 19.°0 C. Nielsen (1934) found that it 

 was restricted to water where the surface temperatures 

 were above 22.° 5 C. During the cruise of the Dana the 

 temperatures in the region of the Galapagos were some- 

 what higher than when the Carnegie visited there but the 

 species was not found in this area by Nielsen. It is 

 probable that this region is in the line of distributional 

 limit for the species, that normally it does not occur 

 southeast of there, and that its occurrence in the region 

 of the Galapagos depends on the amount of mixing of the 

 waters in that region and on the amount of extrusion of 

 the water of the Humboldt Current. Peters (1934) con- 

 sidered C. euarcuatum an indicator of warm oligotrophlc 

 water in the South Atlantic. Nielsen (1934), on the other 

 hand, found it in water rich in nutrients and plankton as 

 well as in oligotrophlc water. 



One might conclude from the Carnegie distribution 

 of C. euarcuatum in the Atlantic and North Pacific that 

 the species preferred oligotrophlc water because its dis- 

 tributional limits in these oceans parallel quite closely 

 the line of 10 mg P04/m3 (cf . charts 22 and 50). This 

 correlation, however, does not hold in the South Pacific 

 where the species was frequently found in water rich in 

 nutrients. Thus, we must conclude that it is not high 

 concentration of nutrients which is limiting the distribu- 

 tion of the species in the northern waters but some other 

 factor associated with it. Only 86 of the 185 records of 

 occurrence were in water containing less than 10 mg 

 P04/m3. 



Within the tropics the species is fairly common so 

 there were many records of occurrence, namely, 185; of 

 which 97 were rare, 75 occasional, and 13 common. It 

 was found more often in net samples, with 128 net rec- 

 ords ana 57 pump records. 



The environmental conditions in situ were: temper- 

 ature, 13.°6 to 29.°3 C; salinity, 33.9 to 37.1 per mille; 

 pH, 7.17 to 8.47; phosphate, 3 to 123 mg P04/m3. 



Nielsen (1934) classified C. euarcuatum as a shade 

 species and the Carnegie data substantiate this classifi- 

 cation. As shown in table 24, it was fovind more frequent- 

 ly at the lower levels than at the surface. 



Table 24. 



Records of occurrence of C. 

 at three levels 



euarcuatum 



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

 samples collected at that depth. 



29. Ceratium fllicorne Nielsen 

 Figures 15B-C, chart 23, appendix table 27 



This species was described by Nielsen from the 

 Dana collection in the South Pacific. He stated that it is 

 closely related to both C. euarcuatum and C. svmmetricum 



