Relative Importance of Groups of Protozoa and Algae 239 



Nostocaceae in the phytoplankton of the Indian Ocean, while 

 Oscillaioria erythmea (Tricliodesmium) , O. tJuebaultii, O. bon- 

 nemaisonii, O. Jiiklebrandtii, Katagmjmene spiralis and Halar- 

 acline lenticularis are frequently important members of the phy- 

 toplankton in the Coral Sea, Arafura Sea, Timor Sea, and North- 

 east Indian Ocean in spring and summer. O. en/thraea in particu- 

 lar may fomi vast sheets or windrows extending for many miles. 



THE RATIO OF DIATOMS TO DINOFLAGELLATES 



In the Indian Ocean and the Coral Sea, the highest ratio of 

 diatom to dinoflagellate species occurs in restricted waters such 

 as Macassar, Sunda, Lombok and Vitiaz Straits, and in the low 

 salinity waters off the southwest coast of New Guinea, where 

 the ratio is as high as 96 per cent diatoms in some instances. The 

 lowest ratios were found in the southern Coral and Tasman Seas 

 (0-5%) in late summer. In the Antarctic, and south of the sub- 

 tropical convergence, however, the ratio of diatoms to dinoflagel- 

 lates is high, even in oceanic waters. High diatom ratios have 

 also been found associated with upwelling of cold water of sub- 

 Antarctic origin north and east of North Cape, New Zealand. 



SIGNIFICANCE OF OTHER GROUPS OF ORGANISMS 



In the Coral and North Tasman Seas, the Coccolithophores 

 occur frequently but not in great numbers, while Chrysomonads 

 and Cryptomonads are relatively common. In the northeast Indian 

 Ocean, however, Coccolithophores are dominant on occasion. 

 Silicoflagellates are to be observed frequently but are never num- 

 erous. 



CONCLUSIONS 



The present stage in our investigations of phytoplankton in 

 Australian waters and the adjacent seas is still one of exploration 

 and speculation. One may conclude, however that the nanno- 

 plankton is of greater importance in warmer than in cool waters; 

 that colorless flagellates are sufficientlv numerous to make it 

 necessary to distinguish between these and the photosynthonts 

 when studying the catches of smaller plankton elements; that 

 the naked dinoflagellates, myxophyceae, and chrysomonads are 

 important members of the phytoplankton in the waters round 



