30 Marine Microbiology 



iopsis antarctica, Biddulphia weissflogii and Synedra pelagica are 

 restiicted to waters south of the subti'opical or of the sub-antarctic 

 convergence. Upwelhngs of sub-Antarctic and Antarctic waters 

 can sometimes be clearly indicated by the presence of certain 

 diatom species outside tlieir expected range. Antarctic species 

 have been collected in upwelling water off the east Australian 

 coast, and current movements are such that tliese must have sur- 

 vived ( presumably as spores ) for at least a year at high pressures 

 in darkness. 



A group of organisms which has rarely been recorded from 

 the oceanic phytoplankton, but which is generally present is the 

 Euglenidae, particularly Eutreptia viridis, and Euglena spp. 



Wood recorded the frequency of occurrence of large numbers 

 of colorless flagellates amongst the phytoplankton, and that in 

 fact they may be tlie dominant microorganisms in the plankton. 

 As such organisms are obligate heterotrophs, and as chloroplasts 

 are difficult to see in the smaller photosynthetic forms, it is easy 

 to draw false conclusions regarding tlie numbers of photo-syn- 

 thonts from samples studied by the Utermohl technique of phy- 

 toplankton counting. They may also assist in giving the negative 

 results sometimes found in the C^* assimilation techniques used 

 for productivity studies. 



EVIDENCE OF HETEROTROPHY IN PHYTOPLANKTON 



Bernard has found Coccolithophores and blue-green algae 

 at depths of more than 1,000 m, i.e., far below the photic zone, 

 let alone the compensation depth. I have found diatoms (6) 

 which are believed to be functional in bottom deposits at depths 

 to 10,000 m, and one can usually find pennate and discoid 

 species (Navicula, Diploneis, Synedra, Frusttdia, Coscinodiscus 

 particularly C. mavginatus, C. lineatus & C. centralis, and Melosira 

 polymorpha subsp. granuJata) at or near the surface of bottom 

 deposits. They do not contain chlorophyll and are brown in color. 

 On the continental shelf, below the photic zone ( 1% surface light), 

 I have frequently found naviculoid species (Pleurosigma spp., 

 Navicula spp., Diploneis, Cocconeis, Mastogloia, Frustulia) with 

 green chloroplasts and exhibiting active motility and phototro- 

 pism. Bursa (Chapter 58) has found diatoms growing in the 



