SIMULATED DEGRADATION OF PHYTODETRITUS IN DEEP-SEA SEDIMENTS OF THE NE ATLANTIC (47-DEGREES-N, 19-DEGREES-W)

The degradation of phytodetritus in the deep sea was studied in sedime nt samples of the NE Atlantic in spring and summer 1992 using C-14-lab elled algal cells (Anacystis sp., Cyanophyceae) fed to the benthic pop ulation in ship-board experiments and measuring the liberation of labe lled (CO2)-C-14 over time. The mineralization process showed a 2-step behaviour with an initial rapid rate which later slowed down, indicati ng the initial attack of easily degradable material of the complex foo d and the later utilization of less labile matter. The profile of degr adation activity with sediment depth showed no clear vertical gradient in March, but in August the activity in the top horizon increased by a factor of 6.1 to 7.8, which was coherent with increased bacterial nu mbers or biomass (factor of 1.3 to 1.7), respectively, and might be ca used by the seasonal input of phytodetritus to the deep-sea bottom. Th e degradation measured was positively influenced by elevated incubatio n pressure mostly in summer, indicating that the summer stimulation of microbial activity in 1992 was based on the metabolic activation of t he indigenous benthic community, while surface-derived organisms attac hed to sedimented particles were of lesser importance with respect to consumption of phytodetritus. Several aspects on quality of phytodetri tus for nutrition of the deep-sea benthos, seasonality of detritus deg radation, and influence of pressure on microbial activity are discusse d.