The more general distribution of G. flavum was attrib- 

 utable to the absence of pronounced thermal stratification 

 and the stage of the bloom cycle. The operation came near 

 the end of the bloom with the probability of a higher incidence 

 of dead or inactive cells which were affected to a greater 

 degree by variation in water movement and density. 



The contribution of macroplankton, present in 

 relatively low numbers, to light attenuation was not apparent 

 in either operation. 



Data taken during the presence of red water in 

 July 1964 supported the conclusions that single-celled 

 organisms in bloom quantities seriously affect light trans- 

 mission, and the distribution of these organisms is affected 

 by thermal gradients. 



An extensive literature documents the complexity of 

 causal factors on transparency in the sea. These works 

 clearly demonstrate the difficulties of attempting to gener- 

 alize from a limited study. The wide range of organisms, 

 materials, and other factors which are cited as reducing 

 light transmission includes not only concentrations of 

 organisms but their size, morphological variation, optical 

 density, pigmentation, metabolic products, and decomposi- 

 tion products, including released pigment. Further, a 

 vast spectrum of other light-intercepting debris, both 

 organic and inorganic, must be considered. To this im- 

 posing array of entities are added the vagaries of physical 

 factors such as tide, temperature, current, and salinity. 

 For example, it has recently been shown that the formation 

 of organic aggregates (Sutcliffe et al, 1963)"''^ is associated 

 with the adsorption of material on bubbles. Presumably, 

 air churned into the water by breaking waves would produce 

 bubbles in the sea. Oxygen-saturated water, such as exists 

 at times of bloom, would tend to create bubbles more 

 readily. Thus, such factors as the state of the sea and 

 oxygen content of the water must also be considered. 



The development of the ability to predict turbidity 

 will demand an understanding of all the aforementioned, 

 and is beyond the scope of this study. 



66 



