Size Distribution of Photosynthesizing Phytoplankton in the Indian Ocean

The size distribution of photosynthesizing phytoplankton was estimated at 7 stations in the Indian Ocean for the waters at the surface as well as at 50m depth. Four light bottles filled with the same sample water were incubated under light source after adding 14C solution, and then filtered through XX13 net, Millipore HA, AA, SM filter respectively. The photosynthetic activities of each fraction were evaluated from the results of counting for each filter. The activity of organisms retained by net is only a small part of total activity whereas the phytoplankton with the size between 0.8 and 110μ play the most part of the activity. The smallest size fraction with the size smaller than 0.8μ has a considerable activity for the surface water, but is almost negligible for the water from 50m depth.