Abstract
Phototaxis appears to be a factor that influences the dispersal of zoospores of the marine fungus Rhizophydium littoreum. By using a quantitative method to study phototaxis, zoospores were found to be positively phototactic toward blue wavelengths of light. White light in the range of 20 to 6,000 microeinsteins m s and blue light in the range of 1 to 300 microeinsteins m s gave positive responses in the laboratory. Results of field studies confirmed the ability of zoospores to respond to light under natural conditions. Phototaxis may be an important adaptive mechanism which influences vertical migration of zoospores in the photic zone where plant products are available as nutrients.