Simulated degradation of phytodetritus in deep-sea sediments of the NE Atlantic (47° N, 19° W)

Abstract

The degradatlon of phytodetntus In the deep sea was studled in sediment samples of the NE Atlantlc In spnng and summer 1992 uslng I4C-labelled algal cells (Anacystls sp , Cyanophyceae) fed to the b e n t h ~c population in sh~p-board expenments and measuring the hberat~on of labelled I4CO2 over tune The rmnerahzation process showed a 2-step behaviour with a n ~n i t ~a l r a p ~d rate w h ~c h later slowed down, indicat~ng the init~al attack of easily degradable matenal of the complex food and the later uthzatlon of less labile matter The prof~le of degradation act~vlty with s e d ~m e n t depth showed no clear vertlcal gradlent in March, but in August the activity in the top honzon increased by a factor of 6 1 to 7 8, w h ~~h was coherent with Increased bacterial numbers or biomass (factor of 1 3 to 1 7 ) , respectively, and might be caused by the seasonal Input of phytodetntus to the deep-sea bottom The degrad a t ~o n measured was pos~tively influenced by elevated incubation pressure mostly in summer, indicat-Ing that the summer stimulation of mlcroblal activity in 1992 was based on the metabolic activation of the indigenous benthic community while surface-denved organisms attached to sedlmented part~cles were of lesser importance w ~t h respect to consumption of phytodetntus Several aspects on quality of phytodetrltus for nutrition of the deep-sea benthos, seasonality of detntus degradat~on, and influence of pressure on microbial activ~ty are discussed