10 



COPEPODS OF LAST CRUISE OF CARNEGIE 



tical differences in temperature, however, is apparent on 

 examination of the station Hsts. At station 121, for ex- 

 ample, the three tows yielded 18 species of copepods. 

 Two species only were found at the surface, one of which 

 was represented by development stages only, with no 

 adults. Eleven species were present in the 50-meter tow, 

 and 16 in the 100-meter tow. Two of the former and 6 of 

 the latter were not present in either of the other two 

 tows. The temperature at the surface was only 7^4 C; at 

 50 meters it dropped 4°, and at 100 meters i?5 more. If 

 the variation in temperature were the reason for the 

 copepods' choice of depth, the 16 species should have been 

 found at the surface and not at the lOO-meter level. More- 

 over, a difference of only i?5 would hardly be sufficient 

 to cause a third of the entire number of species to locate 

 at the lOO-meter level to the exclusion of the 50-meter 

 level. 



At station 127, 14 species were obtained; 6 species were 

 present in the surface tow, 6 in the 50-meter tow, and 10 

 in the 100-meter tow. Three species were confined to the 

 surface, i to the 50-meter level, and 5 to the loo-meter 

 level. The temperature at the surface was i3?3 C; it 

 dropped 3° at 50 meters and 2° more at 100 meters. The 

 same considerations as before preclude the assumption 

 that the variation in temperature was the cause of the 

 differences in depth of the copepod species. Any copepod 

 that has become inured to living and breeding in water 

 as cold as is found in these northern latitudes will not be 

 much affected by changes of 2° or 3° in temperature. 



In the tropics, on the other hand, the water at the sur- 

 face is much warmer and the differences in temperature 

 between the three tow depths are sometimes large enough 

 to appear like important factors in copepod zoning. At 

 station 35, for instance, the temperature at the 100-meter 

 level was 13° lower than at the surface. At station 39, on 

 the equator, it was nearly 11° lower; at stations 71 and 

 72, latitude 10° south, it was about 10° lower. At station 

 109, over the Fleming Deep, there was a drop of 8°, at 

 several of the stations north of the Hawaiian Islands the 

 drop was 7° to 9°, and at a few stations southeast of the 

 Hawaiian Islands there was a difference of 8° to 16°. 

 These variations are all of sufficient magnitude to suggest 

 an appreciable influence of temperature on stratification. 

 An examination of the species lists at these stations re- 

 veals exceptionally well marked stratification, but in 

 every instance it is the exact opposite of what it should 

 be, on the hypothesis that higher temperature induces 

 greater concentration of copepods. The species were 

 bunched at the two lower levels instead of at the two 

 upper ones, and the loo-meter tow contained sometimes 

 two or even three times as many species as were found 

 at the surface. At station 152, the water at 50 meters was 

 13° colder than at the surface, and at the lOO-meter level 



it fell 3° more, a total drop of 60 per cent. Yet the 100- 

 meter tow contained almost three times as many species 

 as the surface tow, and the 50-meter tow nearly twice as 

 many. 



Frequently, however, the tropical stations showed but 

 little temperature change at the three tow depths. At 

 station 46, for example, the difference in temperature 

 between the surface and the loo-meter depth was less 

 than 1°. Yet 4 species were restricted to the surface tow, 

 5 to the 50-meter tow, and 13 to the loo-meter tow. At 

 stations 91 and 9:; the difference in temperature between 

 the two tow depths (0 and 50 meters) was o?2, but 80 

 per cent of the copepod species were present in one tow 

 and absent from the other. At station 80 the difference 

 in temperature between the two depths was only o?i, 

 but 1 1 species were confined to the surface tow and 23 to 

 the 50-meter tow. A difference of o?i in temperature 

 would hardly constitute a sufficient incentive for the 

 exclusive stratification of 63 per cent of the 54 species 

 captured at this station. At station 81 exclusive stratifica- 

 tion was shown by 70 per cent of the 47 species, with only 

 0?! difference in the temperature of the two tows. At 

 station 82 there was absolutely no difference in tempera- 

 ture at the two tow depths, and still 70 per cent of the 52 

 species showed a definite choice of one of the depths to 

 the exclusion of the other. At station 160 the temperature 

 was exactly the same at all three depths, but 50 per cent 

 of the species were confined to a single level, and 25 per 

 cent more were present in two of the tows but absent 

 from the third. Three-fourths of the species thus showed 

 definite zoning without any temperature incentive. We 

 are forced to conclude, therefore, that in most cases the 

 temperature variation is not large enough to produce the 

 amount of stratification shown; and when it does appear 

 to be of sufficient size, it seems to have the opposite effect 

 from what would be expected. 



In this connection it must be noted that some copepod 

 species are not influenced by even considerable changes 

 in temperature, and that many of them appear immune 

 to low temperatures. Expeditions into both the Arctic 

 and Antarctic regions have revealed species of copepods, 

 accustomed to warmer regions, living in the icy waters of 

 those regions, and apparently breeding freely. The same 

 is true of the copepods that live at considerable depths in 

 the temperate and tropical regions. A tow was taken July 

 20, 1953 in a closed net south of Georges Bank about 39 

 north latitude at a depth of 2000 meters. The net worked 

 perfectly, going down closed, opening at the desired 

 depth, and closing again before being drawn up. An 

 examination of this tow revealed hundreds of Metridia 

 belonging to four different species, and also specimens of 

 Rhincalaniis, Eiicalanns. Pareuchaeta, Centropages, Het- 

 erorhabdiis, Luciciitia, HaloptiUis, Gaiditts, Pseitdochi- 



