276 



Marine Microbiology 



A EX.(RG I ) S%o35.0 35.2 35.4 35.6 



0.1 0.2 0.3 0.4 0.5 0.6 T«C 22 24 26 28 



Fig. 1. Relations of extinction coefficient (EK) (at left) to particle and 

 phytoplankton numbers (at right). 



In one instance, a bloom of Prorocentrum micans was de- 

 tected by a sharp increase in turbidity at 4 m and confirmed by 

 a microscopic count of an intermediate sample taken at that 

 depth. 



Turbidity appears to depend on the number of particles 

 irrespective of «ize, so it would appear that interesting relation- 

 ships between turbidity, particle numbers and phytoplankton 

 numbers may be determined by attempts to correlate these. 



SORPTION AS A FACTOR 



Fluorescence microscopy is used in our laboratory and at 

 sea for the routine counting of phytoplankton, taking advantage 

 of the autofluorescence of chlorophyll ( 5 ) . This fluorescence can 

 be observed through the transparent particles, and frequently 

 several organisms can be observed as sorbed on one of the 

 larger particles. Small phytoplankters sorbed on the smaller 

 opaque particles emit a red halo. The relative number of sorbed 

 organisms is greater when the catch consists largely of nanno- 

 plankton, and therefore differs widely in different catches. The 

 presence of large numbers of particles also allows for the ad- 

 sorption of nutrients and metabolites, and so may affect the 

 population of microorganisms in several ways (4). 



VERTICAL DISTRIBUTION 



Samples taken at fixed stations on the continental shelf 

 outside Port Hacking (Cronulla) over several years have shown 

 that the greatest concentration of phytoplankton rarely occiu's 



