COMPARISONS OF PLANKTON 



Tlie largest number of species at a single station in the 

 Atlantic was 60, at station 23, and half the stations had 

 each a total of less than 25 species. Pacific station 56 

 yielded 108 species; 14 stations yielded iSo to 96 species 

 each, and 17 stations from 71 to 78 species each. At only 

 15 (12 per cent) of the 124 Pacific stations did the species 

 total fall below 25. The entire number of different species 

 obtained from all the Pacific stations was 265, whereas 

 the Atlantic stations yielded only 132. Thus in the Car- 

 negie towings the Pacific yielded, on the whole, 100 per 

 cent more copepod species than the Atlantic. 



But there are some excellent reasons why this ratio, 

 although it is entirely correct for the Carnegie material, 

 should not be too hastily adopted as true for the entire 

 plankton of the two oceans. In the first place, only a part 

 of the North Atlantic was covered by the Carnegie tow- 

 ings. If the North and South Atlantic had been as com- 

 pletely towed as were the North and South Pacific, the 

 result would certainly have been different. In other 

 words, the comparison is only a partial one. In the second 

 place, the cruise of the Carnegie covered those parts of 

 the Pacific which have been found by other investigators 

 to be most prolific in copepod species. On the contrary, 

 the parts of the North Atlantic that were included are 

 regarded as the least prolific by all who have investigated 

 the Atlantic plankton. The comparison, therefore, not 

 only is incomplete, but also favors the Pacific to a con- 

 siderable degree. Jespersen (1926), in discussing the 

 tjuantity of macroplankton obtained in the Atlantic by 

 Danish investigators, concluded that the minimum 

 volume in the upper 100 meters was to be found in the 

 western Atlantic between 20° and 30° north latitude, in 

 the Caribbean Sea, and in the Sargasso Sea. The last two 

 are the parts traversed by the Carnegie, which did not 

 touch the regions of maximum volume. Jespersen stated 

 that around the Azores the volume of plankton was 20 

 to :;o times as large as in the Sargasso Sea. If the region 

 of the Azores, therefore, and other more prolific regions 

 of the Atlantic had been included in the cruise of the 

 Carnegie, the comparison of the plankton of the two 

 oceans would have been much less favorable to the 

 Pacific. In the third place, as has already been shown, 

 more than half the Pacific stations came within the in- 

 fluence of surface currents, whereas only a few of those 

 in the Atlantic were so situated. If these currents are 

 really as conducive to copepod plankton as they appear 

 to be, this is another advantage for the Pacific. 



All these reasons are well worthy of consideration, but 

 in spite of them it does not seem as if the inclusion of 

 the more prolific parts of the Atlantic would produce 

 enough additional species to take away the supremacy 

 established by the Carnegie material for the Pacific. In 

 looking for an explanation of the small number of species 



found in the Sargasso Sea and in the Caribbean Sea, we 

 may note that at the stations which are compared above 

 we find in the Atlantic a comparatively high temperature 

 combined with an exceptionally high salinity. A high 

 salinity is known to be adverse to ordinary pelagic 

 copepods, and it is possible that when combined with a 

 fairly high temperature it may become a deterrent to 

 copepod life in the epiplankton. 



It is worthy of comment that there was not found in 

 the Pacific any trace of such countless swarms of a single 

 copepod species as are often seen of Calaniis finmarchiciis 

 at certain seasons in the North Atlantic. They may exist 

 in the Bering Sea north of the Aleutian Islands, but this 

 region was not visited by the Carnegie. 



Comparison ov Different Regions of the Pacific 



Although the Carnegie towings thus are inadet^uate 

 for a satisfactory comparison of the plankton of the two 

 oceans, they do furnish an ideal basis for comparing the 

 copepod faunas of the different regions of each ocean, 

 especially of the Pacific. They are extensive enough to 

 include adequate samples from practically all the im- 

 portant regions of the ocean, and at the same time they 

 furnish enough data with reference to the environment 

 in each of the regions to explain the differences that 

 appear. 



As has been found by all other investigators, the trop- 

 ical parts of the ocean are richer in species than the tem- 

 perate regions, but the tow is often inferior in volume. 

 The plankton of the South Pacific contained a greater 

 number of species than were found in the North Pacific, 

 but the volume of the tow reached its maximum in the 

 northernmost part of the ocean. In the South Pacific the 

 stations yielding the most species were located in the 

 eastern part alongside the Humboldt Current and in the 

 western part north of the Samoan Islands. In the North 

 Pacific the richest stations were found off the coast of 

 Japan in the western part, and halfway between San 

 Francisco and the Hawaiian Islands in the eastern part. 

 Station 56, situated in latitude 31° 49' south and longi- 

 tude 109° 04' west, yielded 108 species and becomes 

 thereby the banner station of the entire cruise. Station 55, 

 outside the Pacific end of the Panama Canal, was second 

 with 96 species, and station 113, close to the eastern coast 

 of Japan, was third with 93 species. Stations 40 and 109 

 were fourth, each with 90 species. The last of these, num- 

 ber 109, was the station above the newly discovered 

 Fleming Deep, the depth of the bottoiTi being 5252 

 meters. There were 9 stations each yielding from 80 to 88 

 species, 18 stations each with 71 to 78 species, 16 stations 

 each with 60 to 69 species, and 26 stations each with 50 to 

 59 species. This makes a total of 75 stations, or 59 per cent 



