TEMPORAL VARIABILITIES IN BENTHIC ACTIVITY AND BIOMASS ON THE WESTERN-EUROPEAN CONTINENTAL-MARGIN

Temporal variations in activity and biomass of the smaller benthic bio ta (size range: bacteria up to small meiofaunal organisms) were invest igated on the Goban Spur continental margin (NE Atlantic) within the f ramework of the multidisciplinary research programme OMEX (''Ocean Mar gin Exchange'') sponsored by the European Union. Activities and biomas ses were estimated analysing a series of biogenic sediment compounds ( enzymes, adenylates, DNA, phospho-lipids, particulate proteins). In co ntrast to the very time-consuming sorting, enumeration and weighing of organisms, the determination of biochemical sediment parameters repre sents a useful method to obtain rapid information on ecological dynami cs within benthic systems. Measurements of activity and biomass parame ters on the Goban Spur continental margin showed a strong seasonal cyc le with two peaks in spring (May) and autumn (September/October), and a rapid response within days and/or a few weeks of the most reactive p art of the benthic community, i.e. bacteria and protozoans (flagellata , ciliata, amoeba, foraminifera), following episodic inputs of organic matter via phytodetritus sedimentation. In general, benthic activitie s and biomasses decrease with increasing water depth and distance from the shelf, and the seasonal signal fades with increasing depth. Howev er, still high and sometimes even increasing values were found on a te rrace in about 3600 m water depth (Pendragon Escarpment) and also on t he continental rise, indicating the presence of deposition centres for a down-slope transport of organic material.