The base of the photic zone, as defined by the 1-percent light depth
and discontinuance of photosynthetic carbon fixation, was determined to be at 130140
meters on stations off the Hawaiian Islands. Measurements, including radiant
energy transmission, plant nutrients, and chlorophylls, were made in the depth
interval 0-250 meters. The numerical vertical abundance, biomass, and the identity
of phytoplankton, microzooplankton, bacteria, and fungi were determined. A
discussion of the biological dynamics within this photic zone is based on these
observations and on measurements of photosynthetic production, nitrogen
fixation, and other microbial activities
