FISHERY BULLETIN: VOL. 73, NO. 1 



Table 2. — The mean, non-setose population (cells/liter and Mg C/liter) in the >20- /um size class in the upper 50 m. Lower value in cell 



abundance (i.e. nin) represents number of dead cells. 



(54%). The latter was also important at Station 34 

 (23%); the maximum, mean abundance of 

 Schroederella delicatula (1,318 cells/liter) was 

 also found here. Coscinodiscus spp. were usually 

 next to Lauderia in numerical importance, and 

 composed a maximum of 10 to 15% of the mean 

 population. Table 3 lists the species of 

 Coscinodiscus found. (Coscinodiscus "large 

 species" may represent several species difficult to 

 identify properly in the counting chamber.) 

 Planktoniella sol contributed from about 2 to 25% 

 of the mean population, and Lithodesmium un- 

 dulatum usually around 7 to 12%. 



The absolute abundance of the unique colonial 

 aggregate, Planktoniella muriformis, which can 

 have up to at least 530 cells/colony (Loeblich et al. 

 1968), is unknown; individual cells in the colonies 

 were not counted. The mean number of colonies 

 per liter in the upper 50 m ranged from 6 to 92, 

 with the low levels (6 to 10) persistent at stations 

 made after Station 25 (Table 2). The mean vertical 



distribution of this species shows a similar abun- 

 dance (22 to 30 colonies/liter) in the upper 40 m 

 (Table 4; Figure 2), contrary to expectations, and 

 will be reconsidered later. 



Species ofRhizosolenia >20 ^^m were not abun- 

 dant, and included: bergoni ,calcar avis ,imbricata 

 var. shrubsolei , stolterfothii . Diatoms which are 

 included in OTHERS in Table 2, and their max- 

 imum abundance (cells per liter) are: 



Asteromphalus heptactis (12) 

 Corethron pelagicum (19) 

 Dactyliosolen sp. (72) 

 Hemidiscus cuneiformis (84) 

 Leptocylindrus danicus (228) 

 Paralia sulcata (79) 

 Skeletonema costatum (152) 

 Stephanopyxis cf turris (192) 

 Thalassionema nitzschioides (126) 

 Thalassiothrix cf. mediterranea var. 

 pacifica (16) 



42 



