Some Relationships of PhytoplaJikton to Environment 279 



Table 4, which shows a continuous run of 100 miles (from 

 0845 to 1715 hours), the population would once again appear 

 uniform both as regards phytoplankters (fluorescent organisms) 

 and total microorganisms except for diurnal variation. The higher 

 counts on the second morning were probably influenced by prox- 

 imity to land as they were taken on the continental shelf. Once 

 again the species were uniform. 



Studies of the phytoplankton counts from cruises of the re- 

 search vessels referred to, show that, in general, in the Coral 

 Sea, Arafura Sea and North-east Indian Ocean, the greatest con- 

 centrations of phytoplankton occur near land masses ( see Cruise 

 Reports of Gascoyne 1 and 2/60, 1/61 and Diamantina 2/60). 

 Increases of population also occur in the vicinity of upwellings. 



TROPICAL RED TIDES 



An important featine of tropical waters in the South Pacific 

 and Indian Oceans is the "red tide" due to Oscillatoria ( Tricho- 

 desmiwn) erythroea. This blue-green alga occurs at times, especi- 

 ally in spring, in vast sheets on the surface. I have flown over such 

 a red tide with an area of the order of 20,000 sq. miles. The con- 

 centration of the alga was confined to 0.5 m from the surface, 

 with the greatest amount at the surface. It is usually in long 

 windrows in the direction of the prevailing wind, giving the 

 impression from the air of a series of sandbanks, shallow on one 

 side, steep on the other. Although Oscillatoria enjthraea normally 

 beha\'es like other members of the phytoplankton, in the red tide 

 stage it adheres to samplers and collecting bottles and cannot be 

 retained by centrifugation. These Oscillatoria blooms are not con- 

 fined to neritic areas, but occur in the open ocean. I have seen 

 one such occurrence about 500 miles northwest of Fremantle in 

 the Indian Ocean. In this case, the requisite concentration of 

 nutrients could have been brought about by a divergence which 

 exists west of Western Australia. 



SALINITY AND TEMPERATURE 



Determinative studies have now been made of phytoplankton 

 from a large number of stations in the Southwest Pacific and 

 northeast Indian Oceans, and the species have been recorded 



