INCORPORATION RATES AND BIOMASS CONTENT OF C AND P IN PHYTOPLANKTON AND BACTERIA IN THE BAY-OF-AARHUS (DENMARK) JUNE 1992

Biomass content and incorporation rates for carbon (C) and phosphorus (P) in microbial plankton in the Bay of Aarhus were investigated durin g a 1 week period. Samples taken daily at a fixed station, as well as during a diel cycle, allowed comparison of the water masses above, in and below the pycnocline, and in influxes of different water masses. T he coupling between the activity of phytoplankton and bacteria was exa mined by the stoichiometric composition in pools and fluxes. From micr oscope-based estimates of bacterial C and chemical determination of ph osphate in the size fraction 1-0.2 mu m, the mean C:P ratio (molar) fo r bacterial biomass was 78, while the mean C:P ratio for incorporation was 96 or 63 from thymidine- and leucine-based estimates of bacterial C production. Thymidine-based estimates of mean bacterial generation time varied from 2.5 to 4.1 days with a minimum in the interface betwe en water of Baltic and Skagerrak origin. These values are in good agre ement with P-based generation time estimates. C-14 measurements of pri mary production and orthophosphate incorporation into the size fractio n >1 mu m gave a mean C:P ratio of 118, similar to the Redfield ratio (106), but about twice the estimated mean C:P of 52 in protist biomass . The combined methodological concept can be used to examine the simul taneous role of microorganisms in the C and P budgets.