FACTORS INFLUENCING AUTOTROPHIC AND HETEROTROPHIC NANOFLAGELLATE ABUNDANCE IN 5 WATER MASSES SURROUNDING NEW-ZEALAND

The aim of this study was to measure nanoflagellate abundance in New Z ealand waters, and identify the key factors which both influence, and are influenced by, nanoflagellate abundance. Nanoflagellate population s were sampled in winter and spring 1993 from a series of sites repres enting different water masses around the South Island of New Zealand. Both numbers and biomass of heterotrophic (HNF) and autotrophic nanofl agellate (ANF) populations were larger in spring by a factor of four. ANF were about three times as abundant as HNF in both seasons. The phy siochemical variables, temperature, NH4-N, and urea combined with bact eria and picophytoplankton numbers explained between 67 and 94% of the variation in nanoflagellate abundance. In addition, there was evidenc e that variation in abundances between seasons and water masses was in fluenced by food availability, predation, and changes in species compo sition represented by large differences in cell biovolume.