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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 302 (1983), S. 520-522 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Since 1979, routine photo-transects obtained with the Institute of Ocanographie Sciences' epibenthic sledge7"9, and time-lapse photography using the Bathysnap system10, have revealed a patchy, detrital layer on the sea floor in the Porcupine Seabight in the north-east Atlantic (50 N, 13 W), at ...
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  • 2
  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 362 (1993), S. 737-739 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A camera system was deployed on a mooring above the Porcupine abyssal plain in the mesotrophic Northeast Atlantic (47° 45' N, 19° 28' W) on 20 April 1990 and recovered 154 days later after taking images of a 20-litre volume every 512 minutes. The apparatus was at an average depth of 270 m. ...
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 345 (1990), S. 805-807 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 5
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dependency of in situ weight-specific fecundity of adult females (as egg production) and growth of juveniles (as somatic production) upon individual body weight in marine planktonic copepods was examined. A compilation was made of results where wild-caught individuals were incubated in natural seawater (often pre-screened to remove large organisms), at near in situ temperatures, over short periods of the order of 24 h. The results demonstrate that for the adult broadcast-spawning group weight-specific fecundity rates are dependent upon body weight, but independent of temperature. We postulate this may be the result of global patterns in available phytoplankton. Weight-specific growth rates are dependent upon individual temperature and body weight in juvenile broadcast-spawners, with rates declining as body weight increases. Sac-spawners have growth/fecundity rates that are independent of body weight in adults, juveniles, and both combined, but which are temperature-dependent. Globally applicable equations are derived which may be used to predict growth and production of marine copepods using easily quantifiable parameters, namely size-distributed biomass and temperature. Some of the variability in growth which remained unaccounted for is the result of variations in food quantity and quality in the natural environment. Comparisons of the rates compiled here over the temperature range 10 to 20 °C with previously compiled food-saturated rates over the same temperature interval, revealed that in situ rates are typically sub-optimal. Adults appear to be more food-limited than juveniles, adult rates in situ being 32 and 40% of those under food saturation in broadcasters and sac-spawners, respectively, while juvenile in situ rates are on average ∼70% of those at food saturation in both broadcasters and sac-spawners.
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  • 6
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract   Ophiocten gracilis is an ophiuroid found at bathyal depths in the North Atlantic Ocean. The adults show strong seasonal reproduction, with an ophiopluteus in the surface plankton. Settling postlarvae were collected in sediment traps moored at 1000 and 1400 m depth in the NE Atlantic during Julian Days 142 to 212 (May to July) in 1996. During this period, growth of postlarvae in the traps was linear and the diet consisted of phytodetritus and foraminifera. Experiments suggest that postlarvae sink at rates of up to 500 m d−1, although this may well be slower in the natural environment. The high fecundity, seasonality and high population density resulted in high fertilization success, and many of the offspring were advected outside the normal adult range, where they were able to settle but did not survive to adulthood.
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  • 7
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Data are presented on the biomass of the invertebrate megafauna at 22 stations on the continental slope in the Porcupine Seabight (PSB) (northeast Atlantic Ocean). Samples were collected between 1980 and 1982. Several units of biomass are used, all of which illustrate a decrease by a factor of about 30 from 500 to 4100 m. Lognormal curves were fitted to the data, the gradients of which were very similar for all biomass units and similar to the value for a transect down the continental slope in the western Atlantic. Biomass levels in the PSB are compared with those from other deep-sea environments. Some published values are more than ten times higher than the values reported here, while others are less than a tenth. The reasons for these differences and trends are discussed in terms of food supply. Sampling variability was examined at two stations, but by chance one (at 1300 m) appeared to encompass a sharp faunal discontinuity of the dominant fauna and the other (at 4000 m) contained very small numbers of large animals. For these reasons, sample variability was high at the repeat stations. Suspension-feeders and crustaceans dominated the biomass at upper-slope depths, while echinoderms were dominant on the middle and lower slope. As a result of this phyletic change, there was a small but insignificant decrease in mean body weight with increasing depth. Within phyla there was also a small but insignificant decrease with depth. If large species are excluded from the biomass/depth regression, the gradient changes considerably, demonstrating the increasing importance of small species at greater depths. The size distribution of megafaunal biomass was examined at several stations. This indicated that the megafauna form a functional group distinct from the macrofauna, just as the macrofauna are distinct from the meiofauna.
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  • 8
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During a 25 d Lagrangian study in May and June 1990 in the Northeast Atlantic Ocean, marine snow aggregates were collected using a novel water bottle, and the composition was determined microscopically. The aggregates contained a characteristic signature of a matrix of bacteria, cyanobacteria and autotrophic picoplankton with inter alia inclusions of the tintiniid Dictyocysta elegans and large pennate diatoms. The concentration of bacteria and cyanobacteria was much greater on the aggregates than when free-living by factors of 100 to 6000 and 3000 to 2 500 000, respectively, depending on depth. Various species of crustacean plankton and micronekton were collected, and the faecal pellets produced after capture were examined. These often contained the marine snow signature, indicating that these organisms had been consuming marine snow. In some cases, marine snow material appeared to dominate the diet. This implies a food-chain short cut wherby material, normally too small to be consumed by the mesozooplankton, and considered to constitute the diet of the microplankton can become part of the diet of organisms higher in the food-chain. The micronekton was dominated by the amphipod Themisto compressa, whose pellets also contained the marine snow signature. Shipboard incubation experiments with this species indicated that (1) it does consume marine snow, and (2) its gut-passage time is sufficiently long for material it has eaten in the upper water to be defecated at its day-time depth of several hundred meters. Plankton and micronekton were collected with nets to examine their vertical distribution and diel migration and to put into context the significance of the flux of material in the guts of migrants. “Gut flux” for the T. compressa population was calculated to be up to 2% of the flux measured simultaneously by drifting sediment traps and 〈5% when all migrants are considered. The in situ abundance and distribution of marine snow aggregates (〉0.6 mm) was examined photographically. A sharp concentration peak was usually encountered in the depth range 40 to 80 m which was not associated with peaks of in situ fluorescence or attenuation but was just below or at the base of the upper mixed layer. The feeding behaviour of zooplankton and nekton may influence these concentration gradients to a considerable extent, and hence affect the flux due to passive settling of marine snow aggregates.
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  • 9
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Copepod faecal pellets have often been considered as rapid transporters of material out of the euphotic zone. Laboratory experiments on their degradation and sinking rates support this view, but field data on the distribution and flux of pellets through the water colomn present contradictory evidence. We suggest that due to the exclusion of metazoans from previously published degradation experiments, such studies may have little relevance to the natural environments. In 1987/1988 we carried out experiments using adult copepods of mixed species but dominated byCentropages hamatus collected in Kiel Bight (FRG). We have demonstrated that copepods can be highly adept at breaking up their own pellets while ingesting only a small proportion, a behaviour we define as “coprorhexy”. The microbiota is probably unable to cause significant modification to faecal pellets before they are fragmented within a few hours of their production. Thereafter, microbial remineralisation will become important. Many of the “difficult” field data can be readily explained if the process of coprorhexy is taken into account and, indeed, breakage of large particles by crustacean zooplankton may be an important process in modifying material transport in the ocean. Copepods appear to perform coprorhexy by removing the peritrophic membrane with its attached bacterial flora and this may then be ingested. We speculate on the nutritional value of such a behaviour and the possible significance of “ghost” pellets, consisting of a membrane with little or no apparent solid content.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 66 (1982), S. 185-190 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The functional responses of Oithona nana (Giesbr.) to various phytoplankton and zooplankton food species are described. The food species were divided into three size categories, the seasonal abundances of which were measured in Loch Turnaig, a Scottish sea loch in 1977. The seasonal variations in feeding rates in the sea for each size class were derived. The seasonal variation in respiration rate of O. nana was measured, and metabolic requirements were claculated as between 6 and 40% of the food material estimated as being eaten. O. nana differs from other common copepods in having a wide food-particle size spectrum and a low metabolic rate. It is suggested that these adaptations constitute the strategy whereby O. nana maintains its population levels throughout the year.
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