MARINE ORGANISMS AND ENVIRONMENTAL INFLUENCES 



277 



Turning now to the third important group in the marine phyto- 

 plankton, the coccolithophorids, there are only two species whose 

 salinity-growth relationship has been studied: Hymenonionas 

 carterae, originally referred to Syracosphaera (Braarud, 1951), and 

 Coccolithus huxleyi (IMjaaland, 1956). Hymenonionas carterae is, as 

 far as we know, an inshore species. The clone used in the experi- 

 ments was isolated from an artificial oyster pond where the salinity 

 during its occurrence varied between \1 %o and 30 %o. In culture it 

 showed very good growth between 15 %o and 45 %o, but even at 

 5%o> growth was fair (Fig. 4). Obviously salinity is not an im- 

 portant environmental factor for this species, which has only been 

 observed in abundance in littoral pools (Carter, 1938; Braarud 

 and Fagerland, 1946) where salinity is apt to show great variation. 



The other coccolithophorid, Coccolithus huxleyi, showed good, 

 growth between 20%q and 45 %o, while it was also able to grow at 

 15 %o (Fig. 5). This is in accordance with its worldwide distribu- 

 tion in oceanic waters of salinities around 35 %o and in coastal 

 waters of northern Europe as well, where it may occur in ex- 

 tremely dense populations at lower salinities of between 15 %o and 

 2()%o (Lohmann, 1908; Birkenes and Braarud, 1952). The experi- 

 mental results indicate that it requires too high a salinity to be 

 able to populate truly brackish waters. 



A 



Curve 



PLYMOUTH P3 



Pe 



WEATHER SHIPM STRAIN 



--100% 



-■ 50%- 



PLYMOUTH STRAIN P3 

 WEATHER SHIP M STRAIN 



10 20 30 A0%o 10 20 30 A0%o 



Fig. 5. Growth of Coccolithus liuxleyi at different temperatures (A) and salinities 

 (B) as percentage of maximal growth rate (Mjaaland, 1956). 



