56 
PACIFIC SCIENCE, Vol. XX, January 1966 
fortunately, insufficient data are available for 
comparing properties at different seasons, from 
this part of the eastern tropical Pacific or most 
other parts. The four cruises which yielded ob- 
servations of the desired kind in the region be- 
tween 5° and 12 °N and between 95 °W and 
the coast, were Eastropic, Scope, Scot, and Costa 
Rica Dome. On Scope and Costa Rica Dome 
the effort was concentrated in particular locali- 
ties like the Costa Rica Dome, but on Eastropic 
and Scot it was spread rather evenly over large 
parts of the area. The Eastropic observations 
were made in November, 1955 and the Scot ob- 
servations in May, 1958, and these two sets of 
data provide a little information about possible 
seasonal changes in surface chlorophyll a and in 
zooplankton at 0-300 m (Holmes et al., 1957; 
Holmes and Blackburn, I960). Surface chloro- 
phyll a averaged 0.28 mg/m 3 for 14 Eastropic 
stations and 0.29 mg/m 3 for 11 Scot stations. 
Zooplankton (small organisms) averaged 175 
ml/ l0 3 m 3 for 35 Eastropic stations and 128 ml/ 
10 3 m 3 for 24 Scot stations (both day and night 
observations included ) . Surface PO4-P, which is 
also of interest, averaged 0.53 gg-atm/1. for 18 
Eastropic stations and 0.34 /xg-atm/1. for 11 
Scot stations (Scripps Institution of Oceanog- 
raphy, 1962; Holmes and Blackburn, I960). 
This meager information suggests that no 
great change occurs in standing crops of biota 
or nutrients between one of the calmer and one 
of the windier months, and therefore does not 
deny the possibility of a steady state existing all 
year round. It was noted previously that the 
chlorophyll a and zooplankton standing crops for 
5 Northern Hemisphere autumn stations con- 
formed to the relationship indicated for the 
AB-ll-Z series; all these were in the above- 
mentioned region of apparent steady-state, as 
shown in Figure 1, although several other sta- 
tions from the same series in the same region 
did not conform in the same way. C and Z were 
correlated ( + 0.760, significant at the 1% level) 
for the 1 1 stations of the Northern Hemisphere 
autumn series (Table 2) which were in the 
steady-state region but not adjacent to the Costa 
Rica Dome. 
No explanation is offered for the fact that all 
standing crops at a few scattered stations, west 
and northwest of the apparent steady-state re- 
gion, conform with the relationships of the 
AB-ll-Z or the AB-8-H series or both; these 
are A7, B6, and B9, among the northern spring 
station-pairs (Fig. 2), and D5, D10, and Dll 
among the northern winter pairs (Table 1, D 
and Fig. 1). It is worth noting that no such 
conformity, or any indication of steady-state con- 
ditions, was found on any cruise in Baja Cali- 
fornia (west coast) or the Gulf of Tehuantepec; 
physical, chemical, and biological conditions are 
known to vary seasonally in these regions, partly 
as a result of upwelling and similar processes 
(Reid, Roden, and Wyllie, 1958; Blackburn, 
1962). No steady state was evident off the coast 
of Peru, an upwelling region (Wyrtki, 1963), 
although the useful biological data are scanty. 
It is concluded that standing crops of phyto- 
plankton, herbivores, and primary carnivores can 
occur off the Pacific coast of southern Central 
America in ways that are consistent with steady- 
state conditions, despite the moderately high 
levels of these crops. Such indications of pos- 
sible steady-state conditions are lacking for other 
areas of the eastern tropical Pacific, which does 
not deny the existence of such conditions in 
some of these areas. More information is needed 
about spatial changes and especially about tem- 
poral changes in such standing crops in the 
eastern tropical Pacific. 
Since the region off Central America has sup- 
ported a successful year-round tuna fishery for 
many years (Martin, 1962), there are grounds 
for doubting the generalization of Menzel and 
Ryther (1961), "It is only in the inefficient 
eutrophic environments which irregularly pro- 
duce large surpluses of basic food that large and 
dense populations of fishes can assemble and 
subsist.” Eutrophic regions, including this one, 
probably are inefficient in the way herbivores 
utilize phytoplankton, but this and other features 
of the productive cycle may be regular and stable 
in some of the regions. 
APPENDIX I 
A station list by Klawe (1961, Table 1) en- 
ables making a comparison between volumes of 
zooplankton (small organisms, ml/ 10 3 m 3 ) taken 
in an oblique haul to about 300 m and in a 
similar haul made immediately afterwards to 
