SMAYDA: NET PHYTOPLANKTON IN UPWELLING WATERS 



Table 3. — The mean population as cells/liter (a) and ng C/liter 

 (b) of the different Cosdnodiscus species >20 fjm in the upper 

 50 m. 



These species are listed only to indicate their pres- 

 ence; their actual abundance is probably greater, 

 since most of these would routinely pass through a 

 20-Mni mesh net depending on orientation of the 

 cells during filtration. 



Ceratium furca usually dominated the 

 dinoflagellates >20-)Um ; populations of Ceratium 

 fusus were persistent. Reproductive stages simi- 

 lar to those depicted by von Stosch (1964) for some 

 ceratians were frequent. Pyrocystis was present, 

 including an organism quite reminiscent oi Py- 

 rocystis lunula (vide Figure 559 in Schiller 1937) 

 in shape and stages found. Maximum abundance 

 was 60 cells/liter in the upper 10 m at Station 38 

 (13.96° to 14.31°C, otherwise similar to Station 27 

 (Table 1)). Various stages of the cf. Pyrocystis 

 lunula cycle were also found during growth exper- 

 iments carried out with mixed, natural popula- 

 tions. The dinoflagellate population was usually 

 sparse, however, with no indication of red tide in 

 the >20-/;m size fraction either visually or mi- 

 croscopically. However, several weeks later, fol- 

 lowing temporary subsidence of upwelling, a red- 



tide outbreak occurred in these waters (Walsh, 

 pers. commun.) similar to pre-upwelling blooms 

 encountered during MESCAL I in March 1972 

 (Walsh et al. 1974). 



A coccolithophorid similar to Syracosphaera 

 apsteini (15 cells/liter) was found occasionally. 



Noctiluca scintillans was frequently encoun- 

 tered in the samples, especially at Station 38, with 

 evidence of active predation of the phytoplankton 

 by Noctiluca. 



Carbon Abundance 



The mean carbon content in the upper 50 m for 

 the dominant non-setose diatom component 

 >20 jum, exclusive of Planktoniella muriformis, 

 Rhizosolenia spp., and OTHERS is given in Table 

 2. The reason for excluding Planktoniella 

 muriformis is because of the great difficulty to 

 enumerate the cells within the colonies, whose 

 size varied considerably. Insufficient specimens of 

 the rarer Rhizosolenia and "other" species pre- 

 vented reliable cell sizing to calculate cell volume. 



The mean carbon content in the upper 50 m 

 ranged from 6.12 to 20.44 /ug C/liter at the various 

 stations; the overall mean was 10.67 /U g C/liter 

 (Tables 2 to 4). Comparison of the percent of the 

 total population represented by a species on a 

 numerical and carbon basis shows an inherent 

 inadequacy of the numerical census as a popula- 

 tion monitor. For example, the Coscinodiscus spp. 

 as carbon contributed from 16.7 to 53.4% of that in 

 the >20-iJ.m size fraction (exclusive of the non- 

 setose species which were not monitored), while 

 numerically they composed only from 4.8 to 

 16.7%. The corresponding means for all stations 

 were about 36% and 11%, respectively. The six 

 most abundant species as carbon {x = 10.67 ug 

 C/liter) compared to their numerical (x = 4,732 

 cells/liter) importance in the upper 50 m are: 



For Coscinodiscus (Brenneckella) spp., the means 

 are 3.53 ug C/liter (33.1%) and 458 cells/liter 

 (9.7%). The Coscinodiscus (Brenneckella) spp. and 

 the four other species given above compose 9.13 



43 



