inoculum to allow at least 2 days' growth. 

 This suggests that requirements are low and 

 probably comparable to those of Gymnodinium. 



Results with Chaetoceros .--Two isolates of 

 the diatom, Chaetoceros, have been obtained, one 

 from the Dome, another from off Tehuantepec. 

 They grow as single cells rather than in the 

 chains of cells generally characteristic ofthis 

 genus. Their taxonomy and morphology have 

 not been studied. 



The Dome isolate grows well in ASP- 2 even 

 when vitannins are omitted. The saturation 

 light intensity for growth is about 500 ft.-c. 

 and the maximum generation tinne is about 

 12 hours. Studies of the temperature re- 

 quirements of both isolates are underway, 

 and further nutritional work is planned. 



Results with Other Cultures. --A culture of 

 a green alga from near Guadalupe Island has 

 been nnaintained since 1957, but no experi- 

 ments have yet been made with it. A culture 

 of a flagellate from San Diego Bay is likewise 

 available. Several algae are present in trans- 

 fers from the original cultures taken from 

 the Donne and Tehuantepec, but they have so 

 far defied isolation from contan-iinatmg micro- 

 flagellates. 



Resul ts with Natural Populations . - - Dur ing 

 Expedition SCOT (TO-58-1) cultures were 

 established aboard ship of the nnixed natural 

 populations available at the oligotrophic station 

 4 (west of Baja California) and the eutrophic 

 station 49 (Costa Rica Dome), and experiments 

 were made by offering suspected nutrients 

 in various combinations (a total of 14 treat- 

 ments) to culture aliquots (three per treatment) 

 which were then incubated at 25° C. and 600- 

 900 ft.-c. The nutrients were N, P, Si, trace 

 elements, soil extract, purines and pyrimi- 

 dines, and amino acids. The results were 

 broadly as follows: most components of the 

 phytoplankton at station 4 did not grow under 

 any treatment; and most components at station 

 49 behaved under the various treatnnents in a 

 way that suggested that N and P were not 

 growth-limiting and that Si, trace elements, 

 and the components of soil extract were 

 linniting. 



A paper entitled "The culture of tropical 

 oceanic phytoplankton" was published in ab- 

 stract form in the Preprints of the Inter- 

 national Oceanographic Congress, New York, 

 1959. 



Experimental Evaluation of the C^^ Method 

 of Measuring Productivity (w. H. Thomas) 



The carbon-isotope method of measuring 

 productivity (phytoplankton production rate) 

 has become widespread in oceanography since 



its introduction by Steeman Nielsen (1952). It 

 has had considerable use in the eastern 

 tropical Pacific (Holmes et al., 1957; Holmes, 

 1958; and later sections of this paper). The 

 question of what actually is measured (e.g., 

 gross or net production or neither) is con- 

 stantly raised and has been investigated by 

 several workers. It has been investigated in 

 the STOR laboratory by experinnents with 

 cultures of Dunaliella primolecta Butcher. 



The Steeman Nielsen C^'* nnethod for the 

 measurement of synthesis of organic matter 

 (production) by phytoplankton has been com- 

 pared with the increase in organic matter 

 and generation rates in Dunaliella cultures. 

 The C^'* measurements were also compared 

 with contemporaneous measurements of photo- 

 synthesis inade by the oxygen and pH methods. 

 Satisfactory agreement between all these 

 measurements was observed during the lo- 

 garithmic growth phase of well-nourished 

 cultures. At n-ioderately high light intensities 

 (200-1,500 ft.-c), production as measured 

 by the c''* nnethod accounted for 60- 80 percent 

 of the net production as measured by the oxygen 

 method. Measurable C^"* assimilation (cor- 

 rected for dark assimilation) persisted at 

 light intensities below the compensation point 

 for oxygen production. The ratio of dark- to 

 light-saturated C^'* assinnilation increased 

 under nitrogen-deficient, but not under phos- 

 phorus-deficient conditions. Under severely 

 nitrogen-deficient conditions, production 

 measured by the C^^^ method exceeded the 

 net oxygen production, but approximated oxygen 

 production corrected for respiration. In an 

 extremely phosphorus-deficient bacterized 

 mass culture, production measured by the 

 C method approxinnated the gross oxygen 



production rate; in a bacteria-free phospho- 

 rus-deficient culture, production by the C^"* 

 nnethod was less than the net oxygen produc- 

 tion rate. 



It is concluded that the Steeman Nielsen 

 C'* method provides adequate measurements 

 of organic matter synthesis by actively grow- 

 ing Dunaliella primolecta. Under conditions of ex- 

 treme deficiency of nutrients or at low 

 light intensities, the C^"* method provides 

 data which agree more closely with O2 pro- 

 duction uncorrected for respiration than with 

 net O2 production. These results are dis- 

 cussed in relation to the findings of other 

 workers and in relation to applications of the 

 method in the field. 



Measurements were considered to be accu- 

 rate to within 15 percent. Modifications of 

 the method to increase precision included 

 the preparation of uniform BaC O3 precipi- 

 tates for standardization and the addition of 

 a nnylar window to the counting chamber. 



28 



