DEVELOPMENT OF MICROBIAL COMMUNITY DURING SKELETONEMA-COSTATUM DETRITUS DEGRADATION

Microbial degradation of algal detritus was studied experimentally usi ng the diatom Skeletonema costatum prekilled culture as a substrate fo r the marine microbial community. The qualitative and quantitative cha nges in the microbial community and the algal detritus structure were followed during 11 days of incubation at the water temperature of 20 d egrees C. Most of the bacterial parameters (epifluorescence microscopy counts of free-living and attached cells, mean cell volume, biomass a nd productivity) were the highest after 24 h from the algal detritus a ddition to the microbial community. The bacterial peak (3.6 x 10(6) ce lls ml(-1), biomass 3.1 mu gC ml(-1), net production 66 x 4 ngC ml(-1) h(-1)) was followed by a precipitous increase of homogenous nanoflagel late population with a maximum number of 2.6 x 10(5) cells ml(-1), whi ch in turn declined quickly after ciliates appeared in the community. The bacterial production, initiated by the supplement of algal detritu s, was totally ingested by microzoans within 3 days. Changes of the st ructure of marine bacterial assemblage and relative increase of the am ount of attached bacteria during the period of massive development of nanoflagellates emphasized the importance of small flagellates predati on on the free-living average size (cell volume 0.1-0.2 mu m(3)) pelag ic bacteria. After 11 days of incubation on algal detritus the initial bacterial assemblage was replaced by the mixed succession of bacteria , flagellates and ciliates at a proportion of 1000: 1.5 :0.2. The stab ilization of microbial community and changes in algal detritus structu re allow to expect that pelagic microbial utilization of Skeletonema c ostatum bloom (53 x 10(6) cells 1(-1)), could be finished within a per iod of 8-11 days at the summer water temperature.