SIZE-FRACTIONATED PHYTOPLANKTON BIOMASS AND PHOTOSYNTHESIS IN MANUKAUHARBOR, NEW-ZEALAND

We measured the seasonal variation in phytoplankton biomass and photos ynthesis in three size classes at four contrasting sites in Manukau Ha rbour during 1993-94. Low levels occurred during winter, when the < 5 mu m class dominated (43-51% of chlorophyll a, 46-58% of photosynthesi s). The 5-22 mu m class dominated during early summer(47-66%, and 52-7 1%, respectively), whereas the > 22 mu m class dominated during a late summer bloom of Odontella sinensis and other large diatoms, particula rly at the inner harbour sites (41-57%, and 43-61%, respectively). Val ues of the photosynthetic parameter P-m(B) for the different size clas ses were similar. Values of I-k for the > 22 mu m class were 22-44% hi gher on average than those for both the smaller classes. The ratio of photosynthesis to biomass in the euphotic zone-a simple index of poten tial growth rate-varied seasonally; but at any given time values for a ll three size classes were similar. Despite this, during summer the bi omass of the smaller size classes increased much less than that of the > 22 mu m class, implying the smaller cells were lost at a greater ra te then.