SECT. 2] 



ORGANIC REGULATION OF 1'HYTOPLANKTON FERTILITY 



195 



Table VIII— (co?it.) 



Species 



B12 Thiamine Biotin 



Cyanophyceae 



Phormidium persicinum 



Rhodophyceae 



Qoniotrickum elegans, Bangia fusco-purpurea 



It 



() 



() 



() 



a R = required; = not required. Most of the data were contributed by Droop; J. C, 

 and R. A. Lewin ; Provasoli ; Pintner; McLaughlin; and Gold; other contributors are 

 A. Gibor, Ryther, and B. Sweeney (the author's references, up to 1958, are given in 

 Provasoli, 1958). 



b Species represented by strains with different vitamin requirements. 



c Grows slightly but indefinitely without the thiamine ; the addition of the thiamine 

 results in a 100 or more-fold increase in growth. 



The only perceptible trend is that algal groups differ in the incidence of 

 species requiring vitamins : the Cyanophyceae, Chlorophyceae and Bacillario- 

 phyceae are algal groups in which about half or less of the species require 

 vitamins (perhaps the non-requirers predominate) ; in the other algal groups 

 the vitamin requirers predominate. The latter algal groups are the richest in 

 animal tendencies (i.e. many species have lost the photosynthetic pigments 

 and phagotrophy is widespread even in species with photosynthetic pigments, 

 i.e. many chrysomonads). It has been postulated that incidence of auxotrophy 

 may correlate with developed animal tendencies (Provasoli, 1956). For practical 

 purposes the vitamin B^-like cobalamins and thiamine can be considered the 

 two most important vitamins for the phytoplankton and they may be relevant 

 ecological factors. We have mentioned that assessing the ecological importance 

 of B12 is difficult because several cobalamins are present in waters and the 

 vitamin Bi 2 -requiring organisms have themselves different patterns of specifi- 

 city. Tables X and XI summarize the situation for algae. Table XI lumps fresh- 

 water and marine algae because, as mentioned, they apparently behave 

 similarly ; unpublished data of our laboratory as well as data in collaboration 

 with Droop are included (Droop et al., 1959). Of the three algal groups most 

 important ecologically in the sea, the diatoms (Bacillariophyceae) seem to have 

 the widest specificity. This may be fortuitous ; still, they are apparently both 

 the most abundant producers of organic matter in the temperate and cold seas 

 and utilize all the known cobalamins in the environment. Therefore, although 

 dependent on B^-like compounds, they hold the advantage over the other 

 Bi2-requirers of narrower specificity. However, some cryptomonads — a group 

 not abundant in the sea — have wide specificity. Because of this complex 

 situation, assays on sea-water to be meaningful should be done with at least 

 two bioassay organisms in order to measure "total cobalamins" (E. coli assay) 

 and "true B12" [Ochromonas or Thraustochytrium assay (see Adair and Vishniac, 

 1958)]. Furthermore, the data of J. C. and R. A. Lewin (1960) indicate that 



