Contribution of microplankton and nannoplankton in the waters of a tropical estuary

Four different size groups of algae were sampled from Cochin Backwater by passing sea water through different grades of bolting nylon. C assimilation, chlorophyll (chl.) a concentration and cell numbers of each size group were determined throughout the year along with those of non-fractionated material. The contribution of nannoplankton, largely composed of diatoms, was found to be much greater than that of microplankton throughout the year. Pooled values of fractionated material agreed closely with those of non-fractionated material, but no regular seasonal trend was found in photosynthesis, chl. a and cell numbers of any size group. A greater dominance of nannoplankton as primary producers over microplankton seems relevant to food chain considerations, as filter-feeding larval stages are probably able to utilize nannoplankton more efficiently than microplankton