Size fractionation of phytoplankton as an estimate of food available to herbivores

Eight species of phytoplankton with sizes and shapes common in temperate oceans were partitioned into categories with six or seven sizes of screens and filters. Analysis of chlorophyll a, particle numbers, and volume in succesive size fractions showed clear cell or colony breakage for only one species. The size fractionation technique thus seems to be an informative way to partition phytoplankton into size classes available to suspension-feeding zooplankton. The technique does not always separate elongate species on the basis of their longest axial dimension, as some species seem more likely than others to orient in the direction of the flow.