Description: The pore-densities (PD) in the tests of 232 specimens of the shallow infaunal foraminiferal species Bolivina spissa from eight locations off the Peruvian continental margin were investigated and compared to different environmental factors as water-depth, temperature, bottom-water oxygen ([O2]BW) and nitrate concentrations ([NO3–]BW). There is a negative exponential PD-[O2]BW correlation, but at oxygen-concentrations 〉10 µmol/l PD approaches a constant value without any further correlation to [O2]BW. The PD-[NO3–]BW relationship is better constrained than that for PD-[O2]BW. We hypothesize that the pores in the tests of B. spissa largely reflect the intracellular nitrate, and to a smaller extent the oxygen respiration. We also compared PD and porosity (P) of two single B.spissa and B.seminuda specimens from the same habitat. The comparison showed that P is significantly higher in B.seminuda than in B. spissa indicating that B.seminuda is much better adapted to strong oxygen-depleted habitats than B.spissa.

Description: Due to the scarcity of information concerning the role that large foraminifera play in deep-sea carbon cycling, the response of a foraminiferal community (>250 pm) to a simulated phytodetritus sedimentation event was assessed over two weeks using sediment cores collected from a deep-fjord environment. Sediment cores were collected from similar to 700 in water depth in the Korsfjorden, western Norway, and incubated ex situ with 1 9 C-org m(2) of labile C-13-labeled Skeletonema costatum for 2, 7, and 14 days. We selectively picked (without prior staining) cytoplasm-containing foraminifera and found the foraminiferal community to be largely dominated (91%) by the deep-dwelling species Globobulimina turgida and Melonis barleeanum, as well as the shallow infaunal species 1 Hyalinea balthica. None of the >250 mu m, cytoplasm-containing fraction was involved in carbon uptake during the first 7 days. After 14 days, 3% of the foraminiferal samples possessed delta C-13 signatures indicative of carbon uptake, but the uptake was confined to the surface-living (0-2 cm) G. turgida. Foraminifera contributed 2.4% to faunal carbon uptake (foraminifera plus macrofauna) after 14 days, despite making up 24% of the combined biomass. Both the dominance of deep-infaunal species, such as G. turgida and M. barleeanum (68%), which are known to prefer degraded over more labile material, together with their large size, which often makes foraminifera respond slower to phytodetritus deposition than the more abundant, smaller-size foraminifera, are possible reasons for the retarded response observed. Overall, results from this investigation highlight that the response of large-size foraminifera to phytodetritus deposition is very slow. In addition, the results presented provide evidence that the foraminiferal response is most likely driven by differences in foraminiferal community composition and structure, with large, deep-infaunal species showing slower reactions to phytodetritus deposition compared to smaller foraminifera, metazoan meiofauna, and macrofauna.

Description: As part of the large-scale, interdisciplinary deep-sea study “BIGSET”, the relationship between the monsoon-induced regional and temporal variability of POC deposition and the small-sized benthic community was investigated at several sites 2316–4420 m deep in the Arabian Sea during four cruises between 1995 and 1998. Vertical and horizontal distribution patterns of chloroplastic pigments (a measure of phytodetritus deposition), readily soluble protein and activity, and biomass parameters of the small-sized benthic community (Electron Transport System Activity (ETSA); bacterial ectoenzymatic activity (FDA turnover) and DNA concentrations) were measured concurrently with the vertical fluxes of POC and chloroplastic pigments. Sediment chlorophyll a (chl. a) profiles were used to calculate chl. a flux rates and to estimate POC flux across the sediment water interface using two different transport reaction models. These estimates were compared with corresponding flux rates determined in sediment traps. Regional variability of primary productivity and POC deposition at the deep-sea floor creates a trophic gradient in the Arabian Basin from the NW to the SE, which is primarily related to the activity of monsoon winds and processes associated with the topography of the Arabian Basin and the vicinity of land masses. Inventories of sediment chloroplastic pigments closely corresponded to this trophic gradient. For ETSA, FDA and DNA, however, no clear coupling was found, although stations WAST (western Arabian Sea) and NAST (northern Arabian Sea) were characterised by high concentrations and activities. These parameters exhibited high spatial and temporal variability, making it impossible to recognise clear mechanisms controlling temporal and spatial community patterns of the small-sized benthic biota. Nevertheless, the entire Arabian Basin was recognised as being affected by monsoonal activity. Comparison of two different transport reaction models indicates that labile chl. a buried in deeper sediment layers may escape rapid degradation in Arabian deep-sea sediments.

Description: Effects of monsoon-induced enhanced depositional regimes of particulate organic carbon (POC) on regional variability and distribution patterns and size spectra of metazoan meiofauna, particularly of nematodes, were investigated at five sites 3158–4414 m deep in the Arabian Sea. The sampling sites were subjected to different flux rates of POC. Total meiofaunal abundance ranged from 109 to 320 ind./10 cm2. Nematodes were the numerically most abundant taxon, with a relative abundance of 82.5–88.7%, followed by copepods and ostracods. Mean individual nematode biomass ranged from 0.0272 to 0.1033 μgC, and Mean nematode population biomass varied between 0.0026 and 0.0133 mgC/10 cm2. Mean nematode lengths ranged from 614.2 to 832.6 μm. The length distributions of nematodes at the different sites were typically skewed with the distributions extending into the longer size classes. At the sites with higher POC deposition rates, nematodes displayed deeper distributions in the sediment column (47.4–58.5% of nematodes in the top 1 cm layer of the sediment) in contrast to very shallow distributions at a site of low POC flux (75.1% of nematodes in the top 1 cm of the sediment). Regional variability of nematode biomass, size and vertical distribution was related to monsoon-driven gradients of POC- and chlorophyll a (chl. a) flux rates and bacterial biomass i.e. bioavailable organic carbon. This was in contrast to nematode abundance which did not correlate significantly with any of these environmental parameters. The differential pattern between biomass and abundance, distribution might be related to POC-dependent alterations in the species composition of the nematode assemblages at the different sites. The hypothesis of increased meiobenthic stocks due to monsoon-induced enhanced sedimentation could not be confirmed compared to data from other less productive oceanic regions. Nematode abundance and biomass in the Arabian Sea were similar to values obtained from the abyssal temperate NE-Atlantic.