properties in amd on either side of a narrow 

 ocean front yielded some indications that 

 standing crops of chlorophyll a and zooplank- 

 ton were highest in the front itself. Charts of 

 distribution of standing crop of zooplankton 

 are available for many months and years off 

 the west coast of Baja California (Thrailkill, 

 1963, and references). Some broad features 

 of these distributions have been discussed by 

 Reid (1962) in relation to physical and chemical 

 oceanographic properties. 



TAXONOMIC COMPOSITION OF 

 STANDING CROPS 



Little emphasis has been placed on taxonomic 

 composition of standing c rops of phytoplankton, 

 zooplankton, and micronekton in the eastern 

 tropical Pacific, Some studies have been made 

 of major groups within the phytoplankton 

 (diatoms, dinoflagellates, coccolithophores: 

 Hasle, 1960, and references). Hasle was the 

 first worker to identify samples collected in 

 water bottles, rather than in nets or in bottom 

 samples, from the central or eastern Pacific. 

 Her material was collected on operation 13, 

 near the equator at long. 145° W., just outside 

 the eastern tropical Pacific as defined in this 

 paper. Coccolithophores were numerically 

 dominant in most sannples. Smayda (1963, 1965), 

 who studied a long series of water-bottle 

 samples from the Gulf of Panama, found that 

 diatoms made up about 97 and 99 percent of 

 phytoplankton biomass, and 86 and 71 percent 

 of phytoplankton cell numbers, during the up- 

 welling and nonupwelling seasons. 



Mais and Jow (1960) tabulated the main 

 constituents of net-caught zooplankton from 

 operations 10 and 11, mostly taken in areas 

 5, 6, 9, and 10. Volumetric ally, the main 

 constituents were: copepods (20 percent), 

 tunicates (15), chaetognaths (12), siphonophores 

 (8), euphausiids (5), medusae (3), decapods (2), 

 amphipods (1), aind ostracods (<1). Numeri- 

 cally, the nnain constitutents were copepods 

 (63 percent), chaetognaths ( 1 5), tunicates (6), 

 euphausiids (5), siphonophores (1), ostracods 

 ( 1 ), amphipods (<1), decapods (<1), and medusae 

 (<1). 



Blackburn (MS., see footnote 2) gave similar 

 information, volumetrically only, for mi- 

 cronekton. For a total of 131 night hauls 

 distributed over most of the eastern tropical 

 Pacific except areas 1, P_, and 14, the main 

 constituents were: galatheids (40 percent), 

 myctophids (15), leptocephali ( 1 0), euphausiids 

 (8), peneids (4), gonostomatids (3), enoploteu- 

 thids (3), portunids (3), larval squillids (2), 

 sergestids (2), cranchiids (2), and postlarval 

 and adult squillids ( 1) . The galatheids, peneids, 

 portunids, and squillids (postlarvae and 

 adults) occurred mainly in particular parts 

 of the region- -the galatheids in area 3, 

 peneids in 4, portunids in 5, and squillids 



in area 4- -whereas the other groups were 

 widely distributed. 



ECOLOGY OF SPECIAL GROUPS 

 OF ORGANISMS 



Some attention has been given in the eastern 

 tropical Pacific to the kind of biological 

 oceanography which attempts to describe and 

 explain the distribution and abundance of dif- 

 ferent taxonomic components of the biota. In 

 this region, as in others, the general pro- 

 cedure of such investigations has been to 

 compare the distributions of several species 

 of the same taxon with each other and with 

 various properties or features of the physical 

 environment in such a way as to show which 

 species are characteristic ("indicators") of 

 specific types of water, and sometimes to 

 explain why. 



Some of the best work of this kind deals 

 with the Chaetognatha; it was done by Bieri 

 (1959), Sund and__Renner (1959), Sund (1961, 

 1964), and Alvarino (1964a, b). The twopapers 

 by Sund are the most detailed. Horizontal and 

 vertical distributions of species were com- 

 pared with those of simple properties (tempera- 

 ture, salinity, dissolved-oxygen concentra- 

 tion) and with combinations of those properties, 

 including the well-known temperature-salinity 

 curves which are generally considered to 

 characterize water masses. The following 

 groups of species were distinguished: those 

 that inhabit only one water mass, even though 

 within it they tolerate such wide variations 

 in properties that one might expect them to 

 occur in other water masses also; those whose 

 distribution appears to be determined by 

 properties (including depth beneath the sea 

 surface), and which are not necessarily re- 

 stricted to a single water mass; and those 

 which occur almost anywhere in the eastern 

 tropical Pacific (Sund, 1961). The species 

 limited to a single water mass are potentially 

 useful, as a supplement to physico-chemical 

 properties, in identifying water masses in 

 regions where the boundaries change from time 

 to time, as in the region at the southern tip 

 of Baja California and the subequatorial region 

 off the coast of South America. Some of the 

 species that are related to definite properties, 

 but not to a single water mass, are potentially 

 useful, again as a supplement to other prop- 

 erties, in identifying situations where vertical 

 motion of water, such as upwelling, has oc- 

 curred. Distributions of species limited to a 

 single water mass in the Peru region were 

 used to confirm physical-oceanographic hy- 

 potheses about the way in which certain kinds 

 of advection produced a Nino condition in 1958, 

 and occurrences of species requiring only cer- 

 tain properties were used in the same region 

 to confirm the identification of areas and 

 periods of coastal upwelling (Sund, 1964). 



14 



