MONSOONAL DIFFERENCES IN MICROBIAL BIOMASS, RESPIRATORY ACTIVITY AND BACTERIAL NUMBERS IN THE BANDA SEA

In August 1984 and in February 1985 biomass as ATP, respiration rate as ETS activity and bacterial numbers were estimated in the upper 300 m water column of the eastern part of the Banda Sea and the northern Arafura Sea (Indonesia). In August, during upwelling (southeast monsoon), maxima of activity and biomass were found in the upper 40 m, while in February, during downwelling (northwest monsoon), maxima were found at deeper levels, but never deeper than 80 m. The highest values were found during upwelling in the northeast of the study area, south of Irian Jaya. Integrated over 300 m and recalculated to carbon units, the biomass of organisms smaller than 50 μm did not differ much during the two seasons. In February it was 2.9 g C·m-2 and in August 2.6 g C·m-2. Per volume unit the ATP values were in the surface layers of the upwelling area sometimes 2.4 times higher. The respiration (0-300 m) activity was 1.7 g C·m-2·d-1 in February and 2.5 g C·m-2·d-1 in August. At drift stations diel rhythms were studied. During the light period ATP increased and there was a tendency for bacterial numbers to increase during the night. In February production calculations of the daily increase showed a net production of 385 mg C·m-2 during the light period and a gross production of 900 mg C·m-2·d-1. In August, these values were 607 and 1300 respectively. If we assume, a loss due to sedimentation and grazing of about 25% of the primary production for the upper 100 m, then these mentioned production values are 25% too low. © 1990.