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1.
The amino acid composition of the gut content of two species of deposit-feeding holothurians (Deima validum validum and Pseudostichopus villosus) is compared with that of the sediment trap particles and the surrounding sediment collected from the Demerara abyssal plain in the equatorial Atlantic Ocean at a depth of 4800 m.Amino acid concentrations are 10, 50 and 100 μmol g−1 in superficial sediment, sediment trap particles and ingested sediments, respectively. Compositions of the latter two are nearly identical and differ slightly from that of the former.No selective absorption of amino acids is noticed through the digestive tract. The acid-soluble (cold 2 N HCl) hydrolysed category, nearly absent in sediment trap particles from that depth as well as in superficial sediment, increases in gut contents for both species as a result of digestive system action on particulate matter. Glutamic acid which is largely predominant in this fraction may be partly secreted by the organisms or may result from bacterial activity. Similarly diaminopimelic acid (DAP) is important in gut contents only, but entirely in the free form. The bacterial cell numbers calculated from DAP concentrations are 100-fold that of direct epifluorescent microscopy counts but cannot be considered as the numbers of visible cells because the cell-wall mureid complex containing DAP is normally insoluble in water. Nevertheless, DAP concentrations lead pointedly to the fact that remains of larger bacterial populations or more intense bacterial activity exist in gut content compared to that of sinking particles and superficial sediment.In the superficial sediment, β-alanine and γ-aminobutyric acid account for about 8 mol%, almost entirely in the residual hydrolysed category. In sinking particles and gut contents they account for 1.5 mol% only, but their total amounts are similar to that of the superficial sediment. In gut contents about 40% of β-alanine and γ-aminobutyric acid are found in acid- and alkali-soluble hydrolysed categories, maybe as a result of the general decomposition of ingested organic matter. Absolute concentrations do not appear to change through the digestive tract. The inefficiency of organism assimilation systems and the intimate contact between mineral particles and digested organic compounds which occur in the digestive tract of deposit-feeders may be partly responsible for their increased relative abundance in pelagic sediments.

Résumé

La comparaison entre la composition en acides aminés des particules en voie de sédimentation et celles du sédiment superficiel et des contenus intestinaux d'holothuries abyssales permet de caractériser les échanges entre ces organismes et leur milieu.L'absorption lors du transit intestinal d'une partie du stock ingéré d'acides aminés, de composition identique à celle des particules récoltées par le piège à sédiment, s'effectue d'une manière non sélective.Les contenus intestinaux sont riches en composés protidiques solubles dans l'eau dont une partie non absorbée est rejetée avec les excréments et enrichit le sédiment environnant. Cette fraction soluble est caractérisée par sa richesse en acide glutamique qui peut être due à des sécrétions digestives des organismes, mais également être liée à des phénomènes bactériens mis en évidence par la richesse particulière des contenus intestinaux en acide diaminopimélique.La β-alanine et l'acide γ-aminobutyrique ne semblent pas être absorbés lors du transit, l'éventualité de leur association avec les phases minérales du sédiment sous une forme organique résiduelle pendant le transit intestinal est discutée.  相似文献   

2.
As a contribution to the EC-OMEX-II program, sediment carbon and nitrogen budgets are presented for the Iberian Margin (northeastern Atlantic). The budgets for degradable organic carbon and associated nitrogen were calculated from sediment and pore water properties, using a steady-state version of a numerical coupled diagenetic model, OMEXDIA. Data were collected throughout the major upwelling period along five transects, four of which were located on the open margin and one positioned in a major submarine canyon, the Nazaré Canyon.A comparison of in situ oxygen profiles measured with monocathodic microelectrodes and with Clark type microelectrodes showed that monocathodic electrodes overestimate the oxygen concentration gradient near the sediment–water interface. This artifact probably results from the loss in sensitivity of the monocathodic microelectrode during profiling. Shipboard time course measurements with Clark type electrodes demonstrated transient conditions upon sediment retrieval on deck and indicated enhanced rates of oxygen consumption in the surface sediment, presumably as a result of lysis or exudation of oxidisable substrates by infauna. As a result, oxygen fluxes calculated from shipboard oxygen profiles overestimated in situ fluxes by up to a factor of 5 for water depths >1000 m.The sediments from the canyon and from a depositional area on the shelf were enriched in organic carbon (3–4.5 wt%) relative to the open margin stations (0.5–2 wt%) and showed C/N ratios exceeding Redfield stoichiometry for marine organic matter, indicating there was deposition of organic carbon of terrestrial origin in these areas. The oxidation of organic carbon on the open margin declined from ˜11 gCm−2y−1 on the shelf to 2 gCm−2y−1 at 5000 m water depth, and was dominated by aerobic oxidation. The reactivity of the degradable organic carbon at the time of deposition was <2.5 y−1 on the shelf, and declined to <0.5 y−1 offshore. The burial of refractory organic carbon at the stations along the open margin transects also declined with increasing water depth from ˜5 gCm−2y−1 on the shelf to <1 gCm−2y−1 at 2000 m depth, whereas the burial of particulate inorganic carbon declined from ˜20 gCm−2y−1 to <5 gCm−2y−1. A comparison of the estimated total organic carbon deposition and predicted delivery for the shelf suggest that 58 to 165 gCm−2y−1 is oxidized in the water column, laterally advected, or focused into one of the canyons.Anaerobic oxidation, denitrification and, therefore, total oxidation of organic carbon was enhanced within the canyon relative to the open margin. Total organic carbon oxidation decreased with water depth from 22 gCm−2y−1 at the head of the canyon to 3 gCm−2y−1 over its fan. The reactivity of the organic carbon deposited in the canyon was lower than those of the shelf stations, suggesting that the canyon is being enriched in older, laterally advected organic matter. The burial of refractory organic carbon in sediments from the Nazaré Canyon was considerably higher than in the sediments from the open margin; it also decreased with depth from 20 gCm−2y−1 at 343 m to ˜2.5 gCm−2y−1 at 4298 m water depth. The burial of particulate inorganic carbon was slightly lower than that of refractory organic carbon.The burial of refractory organic carbon and the deposition of degradable organic carbon were both positively correlated with the sedimentation rates for the Iberian Margin, and indicated burial efficiencies were 0.6 to 48%. A single trend for burial efficiency versus sedimentation rate for both the canyon and the open margin indicates that the sedimentation rate was the master variable for the geographical distribution of organic carbon oxidation and carbon preservation on the NW Iberian Margin.  相似文献   

3.
The Porcupine Abyssal Plain (NE Atlantic) time-series has shown large, wide-scale, changes in the composition of the benthic community at 4800 m depth (48°50′N, 16°30′W). The abundance of holothurians has increased significantly since 1996 and one species in particular, Amperima rosea, has increased in abundance by three orders of magnitude. Environmental forcing in the form of phytodetrital food supply to the benthos is believed to be driving these changes. Chlorophyll and carotenoid pigments were determined from the gut sediments of seven species of abyssal holothurian, sampled from the Porcupine Abyssal Plain during Autumn 2000 and Spring 2002. These two samples fell either side of the main phytoplankton bloom in the NE Atlantic, providing an opportunity for seasonal comparisons. Significant inter-species differences in pigment profiles were observed among the seven species. Seasonal differences were noted among four species sampled in both time periods. All seven species were collected from the same geographical area and depth. As algal pigments cannot be synthesised by the holothurians, they provide good biomarkers for the composition of the phytodetritus. Differences in pigments from gut sediment profiles are indicative of selective feeding among the holothurians. A. rosea had a gut profile dominated by the pigments zeaxanthin, chlorophyll a/echineone and β-carotene; these pigments were all present in significantly smaller quantities in the other species. The high quantities of these pigments are indicative of a diet rich in cyanobacteria. The gut sediments of A. rosea also lacked many chloropigments characteristic of other phytoplankton groups, which were observed in the guts of other holothurian species. Ovarian tissue for the five species taken in the pre-spring bloom 2002 sample were examined. All species showed similar carotenoid profiles, dominated by zeaxanthin, echinenone and β-carotene, all of which are important compounds for reproductive success in echinoderms. The differences in gut pigment profiles highlight the potential for several species of deposit-feeding holothurians to partition the same phytodetrital food source, possibly providing a mechanism for maintaining the high diversity of deposit feeders at abyssal depths. The dominance of reproductively important carotenoids in the guts and gonads of A. rosea may highlight the ability of this species to rapidly utilise any change in the composition of the phytodetrital flux and translate that advantage into a successful reproductive and recruitment event. The results are discussed in relation to work on bathyal holothurians and the potential for food-driven regime shifts in both the abyssal and bathyal Northeast Atlantic.  相似文献   

4.
The selective feeding behaviour and assimilation efficiencies of deep-sea holothurians were investigated in order to assess their impact on carbon and nitrogen remineralisation on the Porcupine Abyssal Plain (PAP; 49°N 16°W, 4850 m water depth). Unfortunately, reliable determination of organic matter in the gut contents of the organisms proved to be difficult, because of the lysis of cells associated with the death of the animals on recovery. This was expressed in high levels of free fatty acids in the gut contents of Oneirophanta mutabilis, which we ascribe to unregulated lipolysis of phospholipids and triacylglycerides. It was not possible to estimate accurately the contribution that such material made to the gut contents, but based on the distributions of sterols in the gut sediments, it is likely to have been substantial. Therefore, all assimilation efficiencies calculated for holothurians in the deep sea should be treated with caution.Fortuitously, a bloom of holothurians that feed on the sediment surface (namely Amperima rosea and Ellipinion molle) during the period of study provided an opportunity indirectly to assess the impact of megafauna on organic matter cycling at the PAP. Observations suggest that the depletion of phytosterols from the surficial sediments between July and October 1997 resulted from the selective uptake of fresh phytodetritus by the blooming species. Deep-sea holothurians do not biosynthesise sterols de novo and an estimate of the sterol required by the increased population of A. rosea and E. molle is equivalent to the sterol flux to the seafloor during the spring/summer of 1997. The implications are dramatic. Firstly, these and other megafauna apparently turned over and selectively removed phytosterols from the freshly arrived phytodetritus and the surficial sediment (0–5 mm) at the PAP in less than four months. Secondly, their action impacted the food resource available to other organisms. Finally, as phytosterols are expensive to biosynthesise and are apparently an important resource for holothurians, we speculate that the supply of these compounds to the sedimentary community may be one important control on their population in the abyssal ocean.  相似文献   

5.
The Nazaré Canyon on the Portuguese Margin (NE Atlantic) was sampled during spring-summer for three consecutive years (2005–2007), permitting the first inter-annual study of the meiofaunal communities at the Iberian Margin at two abyssal depths (~3500 m and ~4400 m). Using new and already published data, the meiofauna standing stocks (abundance and biomass) and nematode structural and functional diversity were investigated in relation to the sediment biogeochemistry (e.g. organic carbon, nitrogen, chlorophyll a, phaeopigments) and grain size. A conspicuous increase in sand content from 2005 to 2006 and decrease of phytodetritus at both sites, suggested the occurrence of one or more physical disturbance events. Nematode standing stocks and trophic diversity decreased after these events, seemingly followed by a recovery/recolonisation period in 2007, which was strongly correlated with an increase in the quantity and bioavailability of phytodetrital organic matter supplied. Changes in meiofauna assemblages, however, also differed between stations, likely because of the contrasting hydrodynamic and food supply conditions. Higher meiofauna and nematode abundances, biomass and trophic complexity were found at the shallowest canyon station, where the quantity, quality and bioavailability of food material were higher than at the deeper site. The present results suggest that even though inter-annual variations in the sedimentary environment can regulate the meiofauna in the abyssal Nazaré Canyon, heterogeneity between sampling locations in the canyon were more pronounced.  相似文献   

6.
Holothurians dominate the abyssal megabenthos. They are key consumers and bioturbators of surficial sediment. Compounds essential for holothurian reproduction, such as carotenoids, are in short supply in the deep ocean. Holothurians cannot synthesise carotenoids de novo; the compounds are supplied with the flux of phytodetritus. Therefore, the supply of these compounds may play an important role in regulating processes on the seafloor. This study examines the link between the diet of abyssal holothurians and their ovarian carotenoid biochemistry. Phytodetritus, surficial sediment, holothurian gut content and ovaries were sampled in June 2004 and in July 2005 at the Porcupine Abyssal Plain (PAP), NE Atlantic. Gut content chlorophyll a concentration showed that Amperima rosea, Peniagone diaphana and Oneirophanta mutabilis fed selectively on fresh organic matter, although when this was scarce, O. mutabilis was outcompeted and fed on more refractory material. All three species display consistent ovarian carotenoid profiles and have relatively high carotenoid concentrations in their ovaries. Psychropotes longicauda, Paroriza prouhoi, Pseudostichopus aemulatus, P. villosus and Molpadia blakei fed less selectively and exhibited low ovarian carotenoid concentrations with inconsistent profiles. The results suggest that abyssal holothurian ovarian biochemistry is a complex function of OM supply, holothurian feeding guild and reproductive adaptation. Changes in upper ocean biogeochemistry, altering the composition of organic matter reaching the deep-sea floor, may favour certain holothurian species, as suggested by the interspecific differences in holothurian ovarian biochemistry. This may lead to large community changes as seen at the PAP, which can alter the reworking rates of sediment, probably affecting carbon burial. The study also demonstrated that using the presence of biomarkers in gut contents to infer feeding selectivity should be used with caution. Only biomarkers in gut contents that are not present in the tissues of the holothurians (e.g., chlorophyll a) should be used to determine their feeding selectivity.  相似文献   

7.
We describe the quantitative and compositional (phytopigment, protein, carbohydrate and lipid) patterns of sedimentary organic matter along bathymetric gradients in seven submarine canyons and adjacent open slopes located at four European regions: one along the NE Atlantic and three along the Mediterranean continental margins. The investigated areas are distributed along a putative longitudinal gradient of decreasing primary production from the Portuguese (northeastern Atlantic Ocean), to the Catalan (western Mediterranean Sea), Southern Adriatic (central Mediterranean Sea) and Southern Cretan (eastern Mediterranean Sea) margins. Sediment concentrations of organic matter differed significantly between the Portuguese margin and the Mediterranean regions and also from one study area to the other within the Mediterranean Sea. Differences in quantity and composition of sediment organic matter between canyons and open slopes were limited and significant only in the eutrophic Portuguese margin, where the differences were as large as those observed between regions (i.e. at the mesoscale). These results suggest that the overall trophic status of deep margin sediments is controlled mostly by the primary productivity of the overlying waters rather than by the local topography. Moreover, we also report that the quantity and nutritional quality of sediment organic matter in canyons and adjacent open slopes do not show any consistent depth-related pattern. Only the Nazaré and Cascais canyons in the Portuguese margin, at depths deeper than 500 m, displayed a significant accumulation of labile organic matter. The results of our study underline the need of further investigations of deep margins through sampling strategies accounting for adequate temporal and spatial scales of variability.  相似文献   

8.
Five transects across the NW Iberian margin were studied in the framework of the EU-funded Ocean Margin EXchange II (OMEX II) project, to determine and establish recent sediment and organic carbon transport and accumulation processes and fluxes.On the Galician shelf and shelf edge, resuspension of sediments resulting in well-developed bottom nepheloid layers was observed at all stations, but transport of suspended sediment appears largely confined to the shelf. On the continental slope, only very dilute bottom nepheloid layers were present, and intermediate nepheloid layers were only occasionally seen. This suggests that cross-slope transfer of particles is limited by the prevailing northerly directed shelf and slope currents.Optical backscatter and ADCP current measurements by the BOBO lander, deployed at 2152 m depth on the Galician slope, indicated that particles in the bottom boundary layer were kept in suspension by tidal currents with highest speeds between 15–25 cm s−1. Net currents during the recording period August 6th–September 10th 1998, were initially directed along-slope toward the NNW, but later turned off-slope toward the SW.The separation of the water masses on the slope from the sediment-laden shelf water by the along-slope current regime is reflected in the recent sedimentary deposits of the Galician shelf and slope. Apart from compositional differences, shelf deposits differ from those on the slope by their higher flux of excess 210Pb (0.57–5.37 dpm cm−2y−1 versus 0.11–3.00 dpm cm−2y−1), a much higher sediment accumulation rate (315.6–2295.9 g m−2y−1 versus 10.9–124.7 g m−2y−1) and organic carbon burial rate (1.01–34.30 g m−2y−1 versus 0.01–0.69 g m−2y−1).In contrast to the observations on the Galician margin, pronounced nepheloid layers occurred in the Nazaré Canyon, which extended to considerably greater water depths. This indicates that significantly greater transport of fine-grained particles in both the INL and the BNL was occurring within the canyon, as reflected in the exceptionally high 210Pb excess flux (up to 34.09 dpm cm−2y−1), mass accumulation rates (maximum 9623.1 g m−2y−1) and carbon burial fluxes (up to 180.91 g m−2y−1) in the sediment. However, radioisotope fluxes in the lower canyon were only slightly higher than at comparable depths on the Galician margin. This suggests that transport and rapid accumulation is focused on the upper and middle part of the canyon, from where it is episodically released to the deep sea. Compared to the Galician margin, the Nazaré Canyon may be considered as an important organic carbon depocenter on short time-scales, and a major conduit for particulate matter transport to the deep sea on >100 y time-scales.  相似文献   

9.
Results are presented from particle flux studies using sediment trap and current meter moorings along a transect at the European continental margin at 49°N within the EU-funded Ocean Margin Exchange (OMEX) project. Two moorings were placed, at the mid- and outer slope in water depths of 1500 and 3660 m, with traps at 600 and 1050 m and at 580, 1440 and 3220 m, respectively. Residual currents at the mid-slope follow the slope contour, whereas seasonal off-slope flow was registered at the outer slope. At 600 m on the slope fluxes are similar to those in the abyssal North Atlantic. The flux of all components (bulk dry weight, particulate organic and inorganic carbon, lithogenic matter and opal) increased with water depth. Highest fluxes were recorded at 1440 m at the outer slope, where off-slope residual currents mediate particle export. The injection of biogenic and lithogenic particles below the depth of winter mixing results in the export of particles from shallower waters. Calculated lateral fluxes of particulate organic carbon exceed the primary flux by over a factor of 2 at 1440 m on the outer slope. Estimated lateral fluxes of suspended particulate matter in the water column and intermediate nepheloid layers at the outer slope are potentially large compared to sinking fluxes measured by sediment traps. A comparison is made of particle flux at three continental margin sites and two sites in the adjacent open North Atlantic, from which it is seen that bulk and organic matter flux increases exponentially with proximity to the shelf break. The percentage contribution of particulate organic carbon to biogenic fluxes increases from a mean of 5.7% in the abyssal N. Atlantic to 13.9% at the continental margins.  相似文献   

10.
Living (Rose Bengal stained) benthic foraminifera were investigated at 18 deep-sea stations sampled in the Whittard Canyon area (NE Atlantic). The stations were positioned along 4 bathymetric transects ranging from 300 to 3000 m depth: two along the main canyon axes (Western and Eastern branches) and two along adjacent open slopes (Western and Eastern slopes). The aim of this study was to assess changes of foraminiferal standing stock, composition and microhabitat in relation to the physico-chemical conditions prevailing at and below the sediment-water interface in various canyon and open-slope environments. Minimal oxygen penetration depths and maximal diffusive oxygen uptakes were recorded at upper canyon stations, suggesting a high mineralisation rate. This is confirmed by the high phytopigment concentrations measured in the sediment of the upper canyon axes. Foraminiferal abundance was positively correlated with diffusive oxygen uptake and phytopigment concentration in the sediment. This suggests a control of organic matter fluxes on the foraminiferal communities. Foraminiferal abundance was generally higher along the canyon axis compared to open-slope sites at comparable water depths. The species composition varied with water depth along all four transects, but was also different between canyon branches and adjacent slopes. The silty/sandy intercalations at many of the deeper canyon stations may have been rapidly deposited by fairly recent gravity flows. At station 51WB (3002 m), the faunal characteristics (strong dominance, shallow infaunal microhabitats) suggest that the foraminiferal community is in an early state of ecosystem colonisation after these recent sedimentation events, which would have supplied the important amounts of phytopigments.  相似文献   

11.
The biochemical response of three species of deep-sea holothurian (Oneirophanta mutabilis, Pseudostichopus villosus, and Psychropotes longicauda) to temporal variation in food supply at the Porcupine Abyssal Plain (PAP; ∼4850 m water depth in the NE Atlantic) was studied over a period of 22 months. Lipid contents of P. longicauda showed a strong positive correlation with the contents of lipids in the surficial sediments (0–5 mm; Spearman rank correlation, Rs=1.0, P<0.001). O. mutabilis did not show the same trend in total lipid, but there was an apparent enrichment of sterol in both particulate organic matter (POM) arriving at the sea floor in September–October 1997 and the tissues of O. mutabilis, suggesting that this species can respond to changing availability of food resources. Lipid contents of P. villosus did not vary temporally, probably because this species feeds on deeper layers of sediment, which show little or no temporal variation in lipid composition or concentration. The biochemical response of holothurians to variations in food supply appears to depend on their feeding mode. Changes in the quantity and quality of organic matter have the potential to change deep-sea benthic community structure.  相似文献   

12.
A 2800 m deep station was sampled on three occasions, in January 1999, June 1999 and April 2000, in the lower part of Cap-Ferret Canyon (Bay of Biscay). This area is characterised by a rapid accumulation of fine-grained sediments and by important inputs of reworked organic matter in an intermediate state of decay. Diagenetic reactions within the sediment follow the well-established depth sequence resulting from the oxidation of organic deposits by different electron acceptors. At our station, live benthic foraminiferal faunas differ strongly from faunas previously collected at nearby open slope sites at a comparable water depth. Spectacularly high densities of deep infaunal species are observed in the deeper parts of the sediment for all three sampling periods. In our opinion, these high deep infaunal densities are a direct response to the massive flux of partially degraded organic matter, which is slowly introduced into the deeper parts of the sediment, where it induces a rather stable succession of redox gradients. Melonis barleeanus lives in the dysoxic part of the sediment whereas Globobulimina affinis appears preferentially close to the zero oxygen boundary. Both taxa occupy niches where the highest content of Mn (III, IV)-oxides and -oxihydroxides and Fe (III)-oxides are recorded. The fact that most of the geochemical reactions within the sediment are directly or indirectly catalysed by heterotrophic and chemolithoautotrophic bacterial consortia could suggest that deep infaunal foraminifera may be highly specialised protozoans able to feed on, or live in symbiosis with these prokaryotic communities.  相似文献   

13.
Chlorophyll and carotenoid pigments were determined from the gut sediments of five species of bathyal holothurian in the NE Atlantic, sampled shortly after the spring/summer phytoplankton bloom in 2001 and prior to the spring bloom in 2002. Three species, Laetmogone violacea, Paroriza pallens and Bathyplotes natans, sampled within a similar depth range (900–1100 m) in the summer of 2001 showed significant differences in their chlorophyll and carotenoid pigment concentrations. This suggests they may select for slightly different components from the available food resource. Four species sampled in early spring 2002, Laetmogone violacea, Paroriza pallens, Benthogone rosea and Benthothuria funebris, also had significant differences in their pigment concentrations. These species were sampled over a wider depth range (1000–3100 m) showing a bathymetric trend in pigment concentrations. There was a distinct seasonal change in the composition and concentration of the pigments, linked to a reduction in the availability of fresh organic material during autumn and winter periods.Ovarian tissue was also examined. The carotenoid pigments found in the ovary also occurred in the OM ingested by the holothurians. The dominant gonadal carotenoid pigments were β-carotene, echinenone and zeaxanthin. The potential for using these carotenoids to gain a competitive advantage through selectivity of chlorophyll and carotenoid pigment biomarkers are discussed in relation to competition for food resources by deposit-feeders. The results were also compared with selectivity in abyssal species.  相似文献   

14.
Megafauna biomass and feeding guilds were studied on the NW Iberian upwelling Continental Margin in order to determine the presence of enriched zones pointing to enhanced particle input. We compare these findings with similar data obtained from a transect across the Celtic Continental Margin that represents a regime without coastal upwelling. Additionally sediment concentrations of phytopigments (chlorophyll-a, phaeophorbides) representing recent inputs of algal production and of nucleic acids (DNA, RNA) are used as proxies for microbial biomass, to assess if there was a relation between these parameters and the megafauna distribution. The sediment on the upper slope (<1600 m) of the Iberian Margin was found to be inhabited by filter-feeding megafauna (26–73% of total invertebrate density, and 1–35% of biomass), and contained relatively low levels of phytopigments (3–6 ng/cm3 chlorophyll-a) and nucleic acids (12–16 μg−1 DNA, 1.5–3.5 μg−1 RNA). In contrast, on the upper slope of the Celtic Margin the dominant component of the megafauna were deposit-feeders (57–92% of total invertebrate density, and 23–90% of biomass) and the sediments contained higher concentrations of phytopigments and nucleic acid. These observations, supplemented by video records revealing the presence of current ripples on the Iberian upper slope, show that these upper slope regions are non-depositional, high energy environments. Conditions at the lower slope and the abyssal plain on the Iberian transect were more quiescent with large deposit-feeding holothurians dominating the megafauna (72–94% of invertebrate biomass), and with relatively high sediment concentrations of phytopigments (7–9 ng/cm3 chlorophyll-a, 157–170 ng/cm3 phaeophorbides) and nucleic acids (21–38 μg−1 DNA, 2.4–5.5 μg−1 RNA). On the basis of our data we argue that the benthic food for the deepest stations on the Iberian transect does not consist of shelf derived organic matter. More likely, fast sinking offshore blooms, possibly associated with filaments of upwelling water, form the major contribution to the annual food supply of the deep living megafauna.  相似文献   

15.
The impact of seasonal pulses of phytodetritus on the grazing behaviour of Oneirophanta mutabilis was assessed on the Porcupine Abyssal Plain (PAP) in the NE Atlantic. Sediment and sediment trap samples were analysed by HPLC to estimate the quantity and quality of the organic material in terms of phytopigments and nucleic acids. Food selection by Oneirophanta was estimated by analysing these constituents in the gut contents.The study area is characterised by large interannual variations in the deposition of fresh organic material. The mass fluxes at 10 m above bottom (mab) varied from 0.25 g DW m−2 d−1 in September 1996 to <0.1 g DW m−2 d−1 in March 1997. The material caught in the sediment trap in September 1996 had a relative fresh signature with a chlorophyll-a:phaeophorbide ratio of 1.33. During the other seasons (March 1997, July 1997 and October 1997) the chlorophyll-a:phaeophorbide ratio remained low. In sediment cores this ratio showed a similar seasonal and inter-annual pattern, and again September 1996 was the period of maximum abundance of fresh organic material in the surficial sediment. The analyses of the gut contents of Oneirophanta mirrored exactly the seasonal variation of the phytopigments in both the sediment and the sediment trap material. Concentrations of pigments in the fore-gut were 5 to 15 times higher than in the sediment and the nucleic acid concentrations were up to 80 times higher. This discrepancy between pigments and nucleic acids concentrations suggests that the latter are “indigenous” to the gut of Oneirophanta, either because the gut contains high numbers of actively-dividing bacteria or as a result of cell lysis of the gut epithelium. The seasonal differences in the pigment concentration factor suggest that Oneirophanta does not actively search for hotspots where pigment concentrations are enriched. By using the degradation rate of chlorophyll-a in the PAP sediments, the minimum residence time of chlorophyll in the sediment within the gut of Oneirophanta was calculated. In combination with gut volume and density data it was estimated that each year the Oneirophanta population skims a third of the sediment surface at the PAP site.  相似文献   

16.
The composition, density and community structure of the benthic macrofauna were investigated in sediments of the Campeche Canyon in the SW Gulf of Mexico. Total macrofaunal density ranged from 9466±2736 ind m−2 at the continental shelf station to 1550±195 ind m−2 in the canyon. Density values significantly diminished with distance from the coast and depth; only a few stations in the center of the canyon displayed larger density values (E-37 with 4666±1530 ind m−2, E-36 with 5791±642 ind m−2 and E-26 with 6925±2258 ind m−2). Densities were positively correlated to organic nitrogen in the sediment (r=0.82) and coarse silt (r=0.43), and negatively with depth (r=−0.74) and distance from the coast (r=−0.68). At all stations, the polychaete worms contributed most to the multi-species community structure. The nematodes and Foraminifera displayed their highest densities in the center of the canyon. The biomass values declined significantly with depth. We conclude that the macrofauna density and biomass changed in response to organic matter contents in the sediment, both with distance from the coast and with depth.  相似文献   

17.
In late 1980s, a dense network of deep capillary burrows was reported on the Vøring Plateau, Nordic Seas, and associated with a sipunculan belonging to the genus Nephasoma. This sipunculan was responsible for rapid transport of organic matter from the sediment surface down a deep burrow network. Over 460 specimens belonging to the genus Nephasoma were collected from the deep Nordic Seas during four cruises from 2000–2005 and four species identified: Nephasoma abyssorum abyssorum, N. diaphanes diaphanes, N. diaphanes corrugatum and N. lilljeborgi. The species responsible for the deep burrows and rapid subduction of organic matter can now be confirmed as Nephasoma lilljeborgi. Deep burrows associated with N. lilljeborgi were observed on the Vøring Plateau, Bear Island Fan, Svalbard Margin and Yermak Plateau and may be a seabed feature endemic to the Nordic Seas region. N. lilljeborgi could have a significant role in influencing the ecology and geochemistry of the Nordic Seas region. It is recommended that future benthic community studies in the Nordic Seas region confirm the species identity of sipunculan specimens in order to determine the ecological and geochemical importance of the specimens.  相似文献   

18.
Downward fluxes of microbial assemblages associated with sinking particles sampled in sediment traps deployed at nominal depths of 1000 m (trap A), 3000 m (trap B) and 4700 m (trap C) were measured between October 1995 and August 1998 on the Porcupine Abyssal Plain (PAP, NE Atlantic). The goal of the study was to provide detailed information on the microbial contributions to the particulate organic carbon and DNA fluxes. Bacterial fluxes associated with settling particles in the PAP area were generally low and significantly lower than bacterial fluxes reported from the same area during 1989–90. Marked seasonal pulses in the microbial assemblages were observed in all years that were associated with particle flux maxima in April–June. No significant differences were found in microbial fluxes between 1000 and 4700 m depth, but both the bacterial biomass flux and the frequency of dividing bacteria increased with depth, suggesting that organic matter turnover and conversion into bacterial biomass increased in the deeper traps. The structure of microbial assemblages displayed clear changes with increasing depth; the ratios of bacteria to both flagellates and cyanobacteria increased up to 4-fold between 1000 and 4700 m, showing a marked increase in bacterial dominance in the deeper layers of the water column. A parallel increase of the bacterial contribution to particulate organic carbon (POC) and DNA fluxes was observed. Total microbial contribution to the POC flux in the PAP area was about 2%, whereas the contribution of cyanobacteria was negligible. Fluxes of microbial assemblages were significantly correlated with DNA fluxes and on average the bacteria accounted for 5% of DNA fluxes. Data reported here confirm that the “rain” of particulate bacterial DNA may represent an important source of nucleotides for deep-sea bacteria, but also suggests that a much larger pool of detrital DNA is potentially available to deep-sea micro-organisms.  相似文献   

19.
In an extended deep-sea study the response of the benthic community to seasonally varying sedimentation rates of organic matter were investigated at a fixed abyssal site in the NE Atlantic (BIOTRANS station or JGOFS station L2 at 47°N–20°W, water depth >4500 m) on four legs of METEOR expedition 21 between March and August 1992. The vertical flux at 3500 m depth and temporal variations in the chloroplastic pigment concentration, a measure of phytodetritus deposition, and of total adenylates and total phospholipids, measures of benthic biomass, and of activity of hydrolytic enzymes were observed. The flux patterns in moored sediment traps of total chlorophyll, POC and total flux showed an early sedimentation peak in March/April 1992, followed by low fluxes in May and intermediate ones from June to August. Thus 1992 differed from other years, in which one large flux peak after the spring phytoplankton bloom was observed. Unusually high concentrations of chloroplastic pigments were consistently observed in March 1992, reflecting the early sedimentation input. At the same time biomass of small benthic organisms (bacteria to meiobenthos) and activity of hydrolytic enzymes were higher compared to values from March 1985 and from the following months in 1992. In May and August 1992 pigment concentrations and biomass and activity parameters in the sediment were lower than during previously observed depositions of phytodetrital matter in summer. The data imply that the deep ocean benthic community reacts to small sedimentation events with transient increases in metabolic activity and only small biomass production. The coupling between pelagic and benthic processes is so close that interannual variability in surface water production is “mirrored” by deep-sea benthic processes.  相似文献   

20.
Meiofauna and macrofauna communities and several sediment characteristics were compared between a slope situated far from the coast (Goban Spur) and two transects across the Iberian Margin with steep slopes and close to the shore. The northern Galician transect (off La Coruña) was situated in an area subjected to wind-induced upwelling events. The western Galician transect was also subjected to upwelling, was additionally influenced by outflows of water rich in organic matter from the Rías Bajas. This transect also included the Galicia Bank. Macrofauna density decreased exponentially from the shelf edge (154 m) to the abyssal plain (4951 m) and different communities occurred on the shelf, the upper- and lower slope and on the abyssal plain. Apart from two extremely low-density stations on the Iberian Margin, there were no significant differences in the meiofauna between the Goban Spur and the Iberian Margin. Along the La Coruña-transect a station where meiofaunal densities were low occurred at a depth of 1522 m, where the sediment was characterised by having a high median-grain size, ripple structures, a low Corg and total N content. There were relatively high numbers of macrofaunal filter-feeders but low numbers of crustaceans, indicating a high current velocity regime. On top of the Galicia Bank (˜770 m) the sediment consisted mainly of shells of pelagic foraminifers, and had low contents of Corg and N. The macrofauna was dominated by filter-feeding and carnivorous taxa. At both these stations meiofauna densities were low. Meiofauna densities and community structure differed between the Goban Spur and the Iberian Margin. Meiofauna densities on the Galician shelf were more than double those on the Goban Spur shelf. The two deep stations on the La Coruña transect and the deepest station on the Galicia Bank transect all contained meiofaunal densities that were higher than found at similar depths off the Goban Spur. The meiofaunal densities were inversely correlated with %CaCO3 content and, excluding the shelf stations, were positively correlated with both %Corg and total N at the Iberian Margin. Neither upwelling nor the enriched outflows from the rias affected the macrofauna, but meiofaunal densities were greatly enhanced.  相似文献   

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