Bacterioplankton biomass and heterotrophic activity off Westland, New Zealand, June 1979

Abstract

Estimations of bacterioplankton biomass (total counts, ATP) and heterotrophic activity (¹⁴C‐glucose assimilation) were made from samples collected along 3 transects across the Westland shelf in June 1979. No statistically significant correlations were found between bacterioplankton and phytoplankton parameters (Chlorophyll a, biomass, productivity). A significant positive correlation between zooplankton and bacterioplankton biomass was found. The data is indicative of water masses of diiferent biological histories. Bacterioplankton biomass, ATP concentrations, and glucose assimilation rates reveal a general trend of near shore, near surface maxima attributable to freshwater inputs and upwelling, a minimum mid shelf, and an offshore maximum, around a warm centred hydrographic feature. Bacterioplankton standing stocks represent, on average, less than 0.2% of the total organic carbon pool in the euphotic zone, 9.4% of the phytoplankton biomass, and are close to the rate of mean daily integrated primary production. The light stimulation of ¹⁴C‐glucose uptake (photoheterotrophy) appears to be a real and commonly occurring phenomenon, amounting to an increase in the rate of uptake of 46–68% of that in the dark. The majority of this light enhancement effect occurs in the size fraction below 1 μm.

Key words:

• oceanography
• Westland
• Tasman Sea
• bacterioplankton
• ATP
• heterotrophic ¹⁴C‐glucose assimilation
• planktonic microbial biomass