Description: During the expedition "Arctic Ocean 96" cruise with the Swedish icebreaker ODEN (18.07.-21.09.96), sediments were collected from 20 basin and ridge stations in the abyssal regions of the central Arctic Ocean north of 85°N at water-depth between 864m an 4187m to investigate the question how the extreme scarceness of food in the perennial ice covered deep mediterranean effects the meiobenthic community. Meiofauna densities (including foraminiferans) ranged between 68-247 ind.·10cm-2 and were very low compared to values from temperate, central oceanic regions. Nevertheless, a decrease in abundance with increasing water depth as well as regional differences in abundance and community structure were detectable. Foraminiferans were by far the predominant taxon (58-86%), followed by nematodes (10-27%). Except for harpacticoids all other meiofauna taxa occurred just in low densities and very patchy. Very low meiofaunal abundances and a visible trend towards miniaturisation of organisms may be an outcome of the extremely limited food supply to the benthos under perennial ice-coverage of the central Arctic Ocean.

Description: The size distribution of benthic nematodes was investigated along different gradients of food availability in various regions of the NE Atlantic: I. across the continental margin and II. with increasing distance from the continental rise. An overall trend for miniaturization with increasing distance from the food source was found. However, a series of physical, chemical and biological factors clearly lead to variations in nematode size structure. Moreover, our results indicate that seasonally varying food supply or a periodically pulsed input of organic matter to the sea floor affects nematode size spectra. The hypothesis is proposed that the life cycle of deep-sea nematode species and hence the size structure of their populations are related to seasonal energy availability. This dependence might result in one-year life spans of deep-sea nematodes and probably other meiofauna.

Description: To test to what extent sea surface productivity governs distribution pattern of benthic organisms, meiobenthic standing stocks were investigated on the shelf, continental margin and the adjacent abyssal plains off the Western African Coast between Guinea (10°N) and Angola (18°S). The area of investigations is characterized by gradients in surface productivity due to spatial and seasonally varying coastal upwelling. Reflecting the dependency of deep-sea organisms on organic matter input from the euphotic zone, similar gradients ought to be expected within the benthos.Meiofaunal abundances and biomasses (including foraminifera) from a total of 57 stations along 13 transects across the continental margin showed a fairly close correlation with sediment-bound chloroplastic pigment concentrations, indicating the sedimentation of particulate organic matter from phytoplankton production. However, certain discrepancies in faunal and pigment distribution patterns were found in regions apart from the centres of enhanced primary productivity, i.e. apart from the upwelling centres: whereas pigment concentrations in the sediments were still comparably high, meiofaunal numbers in those peripheral areas were generally lower.It is suggested that smaller/lighter phytodetritial matter, transported over long distances by subsurface currents and exposed to ongoing microbial degradation during its passage, does probably not have the same energy content than relatively fast sinking larger phytodetritus aggregates ("marine snow") in the centres of enhanced primary productivity, which subsequently allow higher benthic stocks. Thus, meiobenthic abundances in relation to sediment-bound pigment concentrations on the Western African Continental Margin may indicate a fractionated sedimentation of organic matter to the sea floor.

Description: Temporal variations in activity and biomass of the smaller benthic biota (size range: bacteria up to small meiofaunal organisms) were investigated on the Goban Spur continental margin (NE Atlantic) within the framework of the multidisciplinary research programme OMEX ("Ocean Margin EXchange") sponsored by the European Union. Activities and biomasses were estimated analyzing a series of biogenic sediment compounds (enzymes, adenylates, DNA, phospho-lipids, particulate proteins). In contrast to the very time-consuming sorting, enumeration and weighing of organisms, the determination of biochemical sediment parameters represents a useful method to obtain rapid information on ecological dynamics within benthic systems.Measurements of activity and biomass parameters on the Goban Spur continental margin showed a strong seasonal cycle with two peaks in spring (May) and fall (September/October) and a rapid response within days and/or a few weeks of the most reactive part 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 activities and biomasses decrease with increasing water depth and distance from the shelf, and the seasonal signal fades with increasing depth. However, still high and sometimes even increasing values were found on a terrace in about 3600m water depth (Pendragon Escarpment) and also on the continental rise, indicating the presence of deposition centres for a down-slope transport of organic material.