Ecology of Algae, Protozoa, Fungi and Viruses 35 



than the change in population due to a change in physical, chem- 

 ical or other biological conditions produced by a change in water 

 mass or by mixing. 



Diurnal variation may be caused by grazing, diurnal repro- 

 ductive rhythms or in part by vertical movements of phytoplank- 

 ton. It is one of the immediate problems of marine microbiology. 



Horizontal distribution seems from Wood's results to be 

 surprisingly uniform to the extent that, in a uniform water mass, 

 stations up to 60 miles and at times up to 300 miles apart may 

 show a variation of surface phytoplankton numbers which is of 

 the order to be ascribed to diurnal variation. This would appear 

 to apply both in oceanic waters and in neritic regions. This means 

 that we can assess the significance of samples taken two or three 

 times a day from a ship steaming at say 12 knots. Qualitative 

 studies can also be invoked to extend our knowledge of the uni- 

 formity or heterogeniety of samples, and to increase the validity 

 of the quantitative results. 



In estuaries and close inshore, especially in areas of turbu- 

 lence, horizontal variation is greatly increased, and it becomes 

 more difficult to assess the validity of sampling programs. 



Motoda has shown that maximum photosynthesis did not al- 

 ways coincide with maximum light intensity, and suggests that, 

 in cooler waters, there is a compensating mechanism which per- 

 mits of a more efficient use of light energy. 



MARINE FUNGI AND YEASTS 



The importance of fungi and yeasts in the ocean has not really 

 been assessed, though work is now going on, particularly in the 

 United States and Germany to fill this gap in our knowledge. 

 Kolilmeyer (Chapter 30) has attempted with some success the 

 difficult task of assessing the criteria for a marine fungus. He 

 points out that, while marine Ascomycetes usually possess spore 

 appendages which assist in flotation or attachment, marine Deu- 

 teromycetes as a group do not. He therefore considers that the 

 latter are less truly marine. He shows also that the marine As- 

 comycetes have genera that are wholly marine, while the Deu- 

 teromycetes do not. Tlie physiological adaptation of fungi to the 



