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1.
Net sampling and continuous acoustic measurements within the Antarctic Polar Frontal Zone (APFZ) and in the vicinity of the
Prince Edward Islands were conducted during austral autumn (April/May) 1997 to describe the composition and distribution of
macrozooplankton and micronekton, and to investigate their relations to the prevailing oceanographic regime in the area. Two
major circulation patterns associated with the Subantarctic (SAF) and Antarctic Polar (APF) Fronts existed in the oceanic
environment surrounding the Prince Edward Islands, promoting high cross-frontal mixing both upstream and downstream of the
islands. Average abundance and biomass of macroplankton/micronekton in the top 300-m layer were 21 ind. 1000 m−3 and 467 mg DW 1000 m−3, respectively. Pelagic crustaceans (euphausiids and amphipods), fish, chaetognaths and gelatinous zooplankton dominated numerically
and by biomass. Continuous acoustic measurements displayed elevated pelagic biomass at the SAF and APF. Although four groupings
of stations were identified using cluster analysis, a single macroplankton/micronekton community was recognized in the top
300-m layer throughout the offshore area of the APFZ. A modification of the APFZ community was observed within the inter-island
region. Subantarctic species dominated zooplankton samples throughout the APFZ, although subtropical species were also well
represented at stations occupied in the northern region of the APFZ. A biological response reflected in macroplankton community
composition, resulting from an extensive cross-frontal mixing, was observed within the APFZ around the Prince Edward Islands.
Accepted: 27 November 1999 相似文献
2.
Relatively little is known about the distribution of fish in deep water (>200 m) in the Beaufort Sea. Data collected by an
Acoustic Doppler Current Profiler operated in the Chukchi and Beaufort seas in summer were examined for evidence of fish biomass
detections between 18 and 400 m. The presence of fish in waters between 1 and 30 m was explored opportunistically with a non-scientific
echo sounder. Evaluation of findings was enhanced by measurements of water column properties (temperature, salinity, fluorescence
and transmissivity). Relatively small shoals of fish were detected on the Chukchi shelf and eastern Chukchi shelf break, and
also on the Alaskan and Canadian Beaufort shelves in the upper 20 m (T = 2–5°C). Much larger shoals (putative polar cod) were detected within Atlantic Water along the Beaufort continental slope
(250–350 m) and near the bottom of Barrow and Mackenzie canyons, where temperatures were above 0°C. A warm-water plume of
Alaska Coastal Current water with high concentrations of phytoplankton, zooplankton, and fish was found extending along the
shelf 300 km eastward of Barrow Canyon. In contrast to the warm surface and Atlantic Water layers, very few fish were found
in colder, intermediate depth Pacific-origin water between them. The large biomass of fish in the Atlantic Water along the
continental slope of the Chukchi and Beaufort seas represents previously undescribed polar cod habitat. It has important implications
with regard to considerations of resource development in this area as well as understanding impacts of climate change. 相似文献
3.
The study of the pelagic ostracod fauna of the Arctic Ocean based on materials collected by numerous Russian expeditions (1929–1993)
and data from the literature showed the extreme poorness of the Arctic pelagic ostracod fauna, its mainly North Atlantic genesis
and complete isolation from the Pacific fauna. Maximum ostracod abundance was observed in the epipelagic zone, and the greatest
species diversity occurred in the relatively warm deep Atlantic layer throughout the year. To the north, east, and west of
Franz Josef Land and Spitsbergen, the number of species and abundance indices of pelagic ostracods were decreased. In superficial
water layers of the Central Arctic, maximum ostracod density and biomass were recorded in June and September. The best bioindicator
of warm Atlantic water in the Arctic basin is Obtusoecia obtusata; and of cold polar water in the North Atlantic, Boroecia maxima. 相似文献
4.
Zubkov Mikhail V.; Sleigh Michael A.; Burkill Peter H.; Leakey Raymond J.G. 《Journal of plankton research》2000,22(4):685-711
Samples were collected from the top 200 m of the water columnat 50 stations during two cruises in different, near equinoctialseasons on an Atlantic transect near the 20°W meridian between50°N and 50°S. These samples were analysed to determinecharacteristics of the heterotrophic bacterial populations.Flow cytometry was used to enumerate these bacteria and determinetheir average size so as to calculate their biomass. Heterotrophicbacterial production, and the rate of grazing of these bacteriaby heterotrophic nanoplankton in the main depth layers, weredetermined using 3H thymidine and 14C leucine techniques. Thebiomass of heterotrophic nanoplankton in these layers was determinedusing a glucosaminidase assay. Five provinces were distinguishedalong the transect and characterized by average values of allmeasured parameters. The relative composition and activity ofthe microbial community in the water columns within each provincechanged little between the two cruises. Lowest heterotrophicbacterial biomass of 12 mg C m3 and productionof 0.10.2 mg C m3 day1 were found in thenorthern and southern Atlantic gyres, and were relatively similarin both seasons. Biomass and production were 24 timeshigher in the northern and southern temperate waters, and inequatorial waters, than in the gyres and tended to show moreseasonal variation. Production and biomass in the layer belowthe pycnocline were lower by 1030% and about 50%, respectively,than values determined in the surface mixed layer, and variedless with latitude. Depth-integrated values of these two parameterswere generally of similar size in the mixed water layer andthe layer of the chlorophyll maximum and pycnocline, and tendedto vary with season. The specific growth rate of heterotrophicbacteria was in the range 0.05 to 0.12 day1 in the topmixed layer at all latitudes. In spite of the elevated temperatures,bacterial growth appears to be restricted by a shortage of nutrientsso that the microbial community cycles very slowly, with a turnovertime of the order of 1 week or more. The depth-integrated biomassof heterotrophic nanoplankton was generally about 100% of theheterotrophic bacterial biomass in the same water. Grazing bythese nanoplankton at the rate measured could consume all ofthe new production of heterotrophic bacteria in all waters,and they probably control the populations of both heterotrophicand phototrophic bacteria. 相似文献
5.
Fieldwork was carried out at Kerguelen Islands. Two groups of stations in a coastal area, the Morbihan gulf, were surveyed.
At both stations, macroplankton biomass ranged from 2.3 mg dry weight m−3 to 89 mg dry weight m−3 and consisted mostly of Themisto gaudichaudii with values ranging from 1.9 mg dry weight m−3 to 50.6 mg dry weight m−3. Biomass was high for sub-Antarctic waters with marked seasonal and inter-zone differences. Biomass minima were observed
at the end of the winter, from September to November, while maxima were recorded in summer and in early fall at the beginning
of the year between January and April. T. gaudichaudii showed a recruitment of new size classes, mainly from November to January, followed by a rapid growth phase in summer, which
slowed down during the southern winter period. Individuals breed after 1 year. Large individuals, older than 1 year, were
not a significant presence in the gulf of Morbihan. The main pattern of the population dynamics were characterised by an univoltine
life cycle with a very high biomass marked by a strong seasonal signal linked with the hydrological and trophic parameters
of the Gulf. 相似文献
6.
Enhanced zooplankton biomass was found in shallow (<900 m)and deep (>900 m) net samples collected over the EndeavourRidge hydrothermal plume in 1991 and 1992. This enhanced biomasswas manifest in considerably higher abundance values for mostspecies in proximity to the vent field compared with abundancevalues from net samples collected 1050 km off-axis. Thespecies most enriched in abundance by the hydrothermal plumewere those normally found in the mid-depth scattering layerat 400900 m depth. These mid-depth animals were alsothe dominant fauna in the deep scattering layers that overliethe hydrothermal plume at depths of 12001900 m near themain vent field. The abundance and biomass dominants were specieswith pronounced ontogenetic migration patterns, and their associatedpredators. The abundance of many typically deep species wasalso enhanced over the main vent field. Faimal compositionsof net samples were compared using a similarity measure andaverage linkage rule. Deep fauna in proximity to the vent fieldbut not associated with scattering layers (Group 1), were similarto deep fauna 1050 km off axis. The fauna of the deepscattering layer over the vent field (Group 2) was most similarto surface and mid- depth scattering layer fauna found withina 50km radius of the vent field. Statistical tests of linkagesobtained using a bootstrap method indicate that the abundanceand taxonomic composition of the two faunal groups were significantlydistinct in 1992, but not in 1991. We conclude that there wasconsiderable infiltration of shallow fauna into the deep scatteringlayers within 23 km of the main vent field, less extensiveinfiltration 1015 km to the noilh and south of the ventfield in 1991, and insignificant infiltration at stations 50kmto the west of the vent field in 1992. A bootstrap analysiscomparing the faunal composition of nets towed above 900 m depthshowed that shallow fauna were not significantly distinct betweenthe two sampling years or up to 50 km away from the vent field. 相似文献
7.
Materials for plankton modelling: Vertical distribution of Atlantic zooplankton in summer 总被引:1,自引:0,他引:1
Current versions of plankton production models which allow variabilityin the vertical plane are based on very slender assumptionsabout vertical distributions of zooplankton. A late summer LHPRsection across the N.E. Atlantic and some spring and early summerLHPR hauls at 59°N indicate some of the details of verticaldistribution which seem to be important for model-formulation.It is suggested that a model which is designed to simulate verticalplankton structure in the North Atlantic should cause zooplanktonto be distributed during the production period so as to satisfythe following criteria: 6070% of the biomass must beof carnivores, and 2575% of all biomass should come tobe located within a discrete epiplankton layer within 40 d ofthe start of the seasonal production: this epiplankton shouldextend down to 34 times the depth of the mixed layer,with its lower limit near the base of the seasonal tbermocline;the epiplankton must extend deeper than the depth of negligiblechlorophyll, and 34 times deeper than the chorophyllmnTimnm; maximum concentrations of filter-feeders should belocated at aboout half the depth of the chlorophyll maximum,and the mmimnm of predators rather deeper; below the epiplankton,biomass should be rather constant down to 1,000 m, be about1530 times less abundant than the epiplankton, and shouldcontain discrete layers of interzonal migrants. It is suggested,by reference to FLEX LHPR profiles, that there are importantdifferences between the oceanic plankton and the copepod-dominatedspring plankton in the North Sea, which will have importantconsequences for plankton modelling.
*present address, Marine Ecology Laboratory, Bedford Instituteof Oceanography, Dartmouth, Canada 相似文献
8.
Zooplankton Abundance and Community Structure Over a 4000 km Transect in the North-east Atlantic 总被引:3,自引:0,他引:3
Zooplankton samples were collected by a high speed sampler,the U-Tow, in the north-east Atlantic between 61.6 and 36.7°Nduring June and July 1996, and were used to examine the causalityof spatial distributions along a 4000 km transect. Peak zooplanktonabundance and biovolume estimations were associated with a frontalsystem at 4852°N, which separated hydrographicallydistinct water masses. The zooplankton assemblage was dominatedby herbivorous/omnivorous taxa in the northern regions, andby carnivorous taxa in the southern regions. Arguments are developedto suggest that the switch in both the zooplankton size structureand trophic status, centred within the frontal region, are consistentwith bottom-up control of zooplankton size structurein this region of the Atlantic. 相似文献
9.
The Barents Sea is an important area with respect to fisheriesresources (i.e. capelin and cod). In May, June and August 1981zooplankton biomass was measured along a transect at 30°E,from the ice border southwards. A maximum was recorded in Atlanticwater by the end of June (>100 g wet weight m2 InAugust the biomass values were relatively low south of the Polarfront and increased northwards into Arctic water (50g m2 The species composition was influenced by the distributionof cold Arctic water and warmer Atlantic water. The zooplanktonwas dominated by the copepods Calanus finmarchicus and C. glacialis;the former is regarded as an Atlantic species and C. glacialisas an Arctic species. 相似文献
10.
Daase Malin; Vik Jon Olav; Bagoien Espen; Stenseth Nils Christian; Eiane Ketil 《Journal of plankton research》2007,29(10):903-911
We quantify statistical relationships between hydrography andabundance of Calanus spp. in the Arctic–Atlantic transitionzone around Svalbard (78–82°N) during early autumn.The Atlantic species C. finmarchicus was more abundant in warmerand more saline waters, as expected from its distributionalcore area. Conversely, the Arctic species C. hyperboreus wasmore abundant in colder and fresher waters. However, the Arcticspecies C. glacialis showed opposing relationships with hydrographyin shallow compared with deep regions. In shallow waters, thenumbers of C. glacialis decreased with temperature and salinityas expected, while somewhat surprisingly the opposite trendwas found in deep locations. Sub-surface hydrography between50–150 m was in most cases a better predictor for Calanusspp. abundance than near-surface conditions, the former generallyexplaining up to 50% of the variability in abundance of eachspecies. Despite finding significant relationships between hydrographicproperties and the abundance of each of the three Calanus species,we did not detect significant relationships between the totalCalanus biomass and temperature. 相似文献
11.
The relationship between marine fronts and fish diversity in the Patagonian Shelf Large Marine Ecosystem 总被引:1,自引:0,他引:1
Aim To evaluate the relationship between marine fronts and (1) fish diversity patterns, (2) fish biomass distribution, and (3) fish assemblage structure. Location Patagonian Shelf, Southwestern Atlantic Ocean. Methods Three main frontal systems and eight nearby zones (frontal vs. non‐frontal areas) were compared. An extensive fishery database, obtained during an a priori sampling scheme (spatial resolution 1 × 1) from 1978 to 1979, was employed. Analyses of 248 trawling stations were performed using a combination of diversity measures (species richness, Shannon diversity and evenness), biomass analyses and multivariate analyses [nonparametric analysis of similarity (ANOSIM), non‐metric multidimensional scaling ordination (NMDS) and similarity percentages (SIMPER)] to evaluate the effect of fronts on fish communities. Results In total, 46 fish taxa were identified. Demersal fish diversity increased at the tidal front of Península Valdés but decreased in the frontal zones of the Southern Shelf‐Break and Magellan frontal systems. The richness and biomass of pelagic fish were higher at the Península Valdés Tidal Front, while the biomass of demersal fish was higher at its non‐frontal counterpart. Fish diversity did not differ consistently along the Northern Shelf‐Break Front. However, a higher fish biomass was registered at the non‐frontal zone. Demersal and pelagic fish assemblages differed between frontal and non‐frontal zones. Main conclusions The Patagonian Shelf Large Marine Ecosystem has diverse frontal types that appear to have different effects on fish diversity and assemblage structure. Seasonal (tidal) or permanent fronts have different effects on the parameters analysed, which could be due to productivity–diversity relationships. The Península Valdés Tidal Front, a relatively short temporal scale system, demonstrates a stronger influence on fish diversity, biomass and assemblage structure than the other frontal areas studied. The seasonality of nutrient input owing to frontogenesis, which begins during the austral spring, may play an important role in determining local diversity. At permanent frontal features, diversity decreases when the nutrient availability is high. This is potentially because, when food resources increase, a few species become dominant. 相似文献
12.
Quality and status of fish stocks in lakes: gillnetting,seining, trawling and hydroacoustics as sampling methods 总被引:1,自引:0,他引:1
All sampling methods give selective or biased estimates of fish species abundance, distribution and size structure. This creates
problems, e.g. in regard to the Water Framework Directive of the European Union, which demands evaluation of the quality and
status of fish stocks in lakes. We compared fish sampling by means of Nordic multimesh gillnets, seining, trawling and hydroacoustics
in two Finnish lakes in summer 2007 and 2008. Sampling methods were used ‘as such’, i.e. no special design was implemented
for method comparison. In the shallow eutrophicated lake the species’ composition of gillnet sampling and seining were very
different. The biomass-% of percids dropped from gillnet (61%) to seining (9%) and that of cyprinids grew from 39 to 90%,
respectively. In the deep pelagic area of the oligotrophic lake, vendace and smelt predominated in trawl catches. The number
of fish caught by gillnetting in that area was too small to make any conclusions about the species composition. In the eutrophicated
lake, the combined length distribution for all fish species differed significantly between gillnetting and seining. In the
oligotrophic lake, the gillnet catches were too small for any comparison of fish size. The difference in the length distribution
of fish between trawl and echosounding was significant in most analysed depth layers. In upper depth layers acoustics sampled
larger fish than trawling, and in deeper layers smaller fish. Using a combined acoustic-trawl method, the pelagic fish biomass
was estimated to be approx. 17 kg ha−1 in the deep and oligotrophic lake. We conclude that in large and deep-water areas, the use of active gear is enough in fish
sampling to evaluate the quality and status of fish stocks. Gillnetting together with seining is an appropriate method to
work out the quality and status of fish stocks in shallow and littoral areas of large lakes. Variation in the catch selectivity
of fish sampling gear requires a discrete ecological classification for each type of gear. 相似文献
13.
New data have been acquired on the biology, morphological features and distribution of Norwegian (Atlantic) pollock Theragra finnmarchica in the Barents Sea. Two individuals of this rare species gadoid (Gadidae) were caught in June and July 2012 in the south-eastern part of the Barents Sea, indicating a wider distribution area of this species than previously thought. It has been confirmed that a number of morphological features of Norwegian pollock is different from T. chalcogramma, and that it feeds on macroplankton (Euphausiidae, Hyperiidae). 相似文献
14.
Cristiana Callieri Beatriz Modenutti Claudia Queimaliños Roberto Bertoni Esteban Balseiro 《Aquatic Ecology》2007,41(4):511-523
We measured biomass and primary production of picophytoplankton (PicoPhy: 0.2–2 μm) and of autotrophic size fraction >2 μm
in six deep ultraoligotrophic lakes in the Andean-Patagonian region (around 41°S) during summer stratification. Surface Photosynthetically
Active Radiation (PAR) ranged from 1277 to 1849 μmol photons m−2 s−1, and the euphotic zone, generally deeper than the mixed layer, varied between 28 m and 49 m. We found a strong photoinhibiting
effect of high PAR and UV-A at surface levels, whereas UV-B radiation (<320 nm) had low extra contribution in the photosynthesis
inhibition. As a consequence, cell numbers, Chl a and primary production rates of both fractions increased towards deep layers in all lakes. The photosynthetic efficiency
(Chl-specific production per photon unit) of both fractions increased with depth, although this increase was higher in PicoPhy,
indicating a higher fitness to low-light. The per cent contribution of PicoPhy production to total production, showed an inverse
significant relation with total dissolved phosphorus (TDP). Moreover our data fitted the existing database showing a significant
trend towards a decrease of PicoPhy biomass and an increase of its relative contribution to total biomass with decreasing
trophic state. At very low-phosphorus concentration, typical of north Patagonian lakes, we found good evidence of the competitive
advantage of PicoPhy. Low-light and low TDP may interact to create the most favourable conditions for the smaller photosynthetic
organisms. In conclusion, we found that at low-light and very low nutrient regime PicoPhy achieves higher photosynthetic efficiency
than the larger autotrophic organisms. 相似文献
15.
Breaking the ice: large-scale distribution of mesozooplankton after a decade of Arctic and transpolar cruises 总被引:4,自引:4,他引:0
Mesozooplankton collected during five summer expeditions to the Arctic Ocean between 1987 and 1991 was analysed for regional
patterns in biomass and species distribution, distinguishing between an epipelagic (0–100 m) and a deeper (0–500 m) layer.
A total of 58 stations was sampled mainly in the Nansen, Amundsen and Makarov Basins of the central Arctic Ocean and in areas
of the Greenland Sea, West Spitsbergen Current and Barents Sea. Results from the different expeditions were combined to create
a transect extending from the Fram Strait across the Eurasian Basin into the Makarov Basin. Mesozooplankton dry mass in the
upper 500 m decreased from 8.4 g m−2 in the West Spitsbergen Current to less than 2 g m−2 in the high-Arctic deep-sea basins. In the central Arctic Ocean, biomass was concentrated in the upper 100 m and was dominated
by the large copepods Calanus hyperboreus and C. glacialis. In contrast, the mesozooplankton in the West Spitsbergen Current was more evenly distributed throughout the upper 500 m,
with C. finmarchicus as the prevailing species. The distribution of abundant mesopelagic species reflected the hydrographic regime: the calanoid
copepod Gaetanus tenuispinus and the hyperiid amphipod Themisto abyssorum were most abundant in the Atlantic inflow, while Scaphocalanus magnus was a typical component of the high-Arctic fauna. The relatively high mesozooplankton biomass and the occurrence of boreal-Atlantic
species in the central Arctic Ocean are indicators for the import of organic material from allochthonous sources, especially
from the northern North Atlantic. Hence, in spite of its enclosure by land masses, the Arctic Ocean is characterized by an
exchange of water masses and organisms with the North Atlantic, and advection processes strongly influence the distribution
of plankton species in this high-latitude ecosystem.
Received: 18 December 1997 / Accepted: 11 April 1998 相似文献
16.
Sediment samples collected during the expedition “Arctic Ocean `96” with the Swedish ice-breaker ODEN were investigated to
estimate for the first time heterotrophic activity and total microbial biomass (size range from bacteria to small metazoans)
from the perennially ice-covered central Arctic Ocean. Benthic activities and biomass were evaluated analysing a series of
biogenic sediment compounds (i.e. bacterial exoenzymes, total adenylates, DNA, phospholipids, particulate proteins). In contrast
to the very time-consuming sorting, enumeration and weight determination, analyses of biochemical sediment parameters may
represent a useful method for obtaining rapid information on the ecological situation in a given benthic system. Bacterial
cell numbers and biomass were estimated for comparison with biochemically determined biomass data, to evaluate the contribution
of the bacterial biomass to the total microbial biomass. It appeared that bacterial biomass made up only 8–31% (average of
all stations = 20%) of the total microbial biomass, suggesting a large fraction of other small infaunal organisms within the
sediment samples (most probably fungi, yeasts, protozoans such as flagellates, ciliates or amoebae, as well as a fraction
of small metazoans). Activity and biomass values determined within this study were generally extremely low, and often even
slightly lower than those given for other deep oceanic regions, thus characterizing the seafloor of the central Arctic Ocean
as a “benthic desert”. Nevertheless, some clear trends in the data could be found, e.g. generally sharply decreasing values
within the sediment column, a vague tendency for declining values with increasing water depth of sampling stations, and also
differences between various Arctic deep-sea regions.
Received: 16 May 1997 / Accepted: 28 August 1997 相似文献
17.
Alfred L. Rosenberger 《Journal of Mammalian Evolution》2006,13(2):139-146
As a derivative of the hypothesis that anthropoids evolved from omomyid-like primates, the enigmatic North American fossil Rooneyia viejaensis, from the latest Eocene of Texas, is placed in a new higher taxon, Protoanthropoidea, which is proposed as the sister-group of Anthropoidea. Rooneyia and anthropoids share synapomorphically a pattern of character states relating to the unique orbital morphology of higher primates, including; highly convergent and frontated orbits roofed above by an extended frontal bone; funnel-shaped orbital fossae; orbital apices that are recessed beneath the forebrain; a deep, large lateral process of the frontal bone (upper portion of the postorbital bar) that may presage closure of the orbit by an enlarged ascending process of the zygomatic. If the sister-group of anthropoids occupied North America as part of a Laurasian geographic distribution during the Paleogene, as some primate genera did, ancestral anthropoids may likewise have occurred across Laurasia, prestaging them to enter Africa and Central/South America in two independent episodes of dispersal—without having the ancestral platyrrhines crossing the daunting Atlantic Ocean. 相似文献
18.
Isla Jose Alejandro; Llope Marcos; Anadon Ricardo 《Journal of plankton research》2004,26(11):1301-1313
Size-fractionated mesozooplankton grazing and metabolism wereinvestigated along the wide latitudinal range (50°N30°S)covered during the Atlantic Meridional Transect (AMT) 11 cruise.Five different oceanic provinces were traversed in this cruise:North Atlantic Drift (NADR), North Atlantic Subtropical Gyral(NAST), Canary Coastal (CNRY), Eastern Tropical Atlantic (ETRA),and South Atlantic Gyral (SATL). CNRY and ETRA were affectedby the upwelling Mauritanian and equatorial respectively andprimary production in these provinces was higher than in theoligotrophic subtropical gyres (NAST and SATL). Both mesozooplanktonand phytoplankton biomass were highest around the equator. Theamount of chlorophyll a ingested daily by copepods was noticeablyhigher in mesotrophic than in oligotrophic provinces as shownby the spatial distribution of gut content values and the highabundances of copepods recorded at the equator. Grazing impactalong the transect ranged from 0.2 to 5.6% of the phytoplanktonstanding stock and from 1.6 to 14.5% of primary production.If only phytoplankton >2 µm are considered, the rangesare 1.019.4% (stock) and 3.444.7% (primary production).Grazing impact upon both phytoplankton biomass and primary productionfollowed a spatial distribution similar to that of chlorophylla ingestion, with higher values in upwelling zones than in thegyres. Weight-specific rates of respiration and NH4+ and PO43excretion showed large variability both along the transect andwithin provinces, but did not differ between provinces. Therefore,zooplankton assemblages inhabiting the different provinces visitedin the AMT 11 seem to be adapted to the prevailing thermal conditions.Given the substantial proportion of nitrogen and phosphorusthat are supplied to primary producers through the excretoryactivity of mesozooplankton (the percentage of nitrogen andphosphorus requirements of phytoplankton accounted for by mesozooplanktonexcretion was >30% in all the provinces) it follows thatthey may play a crucial role as nutrient regenerators, especiallyin the oligotrophic gyres where regenerated production dominates. 相似文献
19.
Is Oithona the most important copepod in the world's oceans? 总被引:1,自引:0,他引:1
Oithona has been described as the most ubiquitous and abundantcopepod in the world's oceans. Most of our knowledge of zooplanktonabundance and distribution is derived from net samples whosemesh size is often 200 µm or greater, and researchershave commented on losses of smaller organisms such as Oithonaand Oncaea, as well as juvenile forms of larger copepods, fromthese nets. We review the literature on this subject over thelast 50 years, and note that such nets remain in common usefor estimating the abundance, biomass and productivity of mesozooplankton.We show that an important fraction of mesozooplankton between200 and 800 µm in length is significantly under-representedin many current and historical data sets. A 5 year study ofthe abundance and size distribution of zooplankton biomass onthe Atlantic Meridional Transect has produced a very large dataset covering a wide range of ecosystem types across the AtlanticOcean, from subtropical oligotrophic to areas of upwelling andvernal blooming. We use these data to derive estimates of meshselection effects for commonly used nets on measures of zooplanktonabundance, biomass and secondary production, and compare theseestimates to those derived from the literature. We estimatethat the conventionalWP-2 net with a 200 µm mesh may capture<10% of conventional mesozooplankton numbers, whilst underestimatingbiomass by one-third and leading to an underestimate of secondaryproduction by two-thirds. This has serious implications forestimates of zooplankton-mediated fluxes and for the modellingof ecosystem dynamics. 相似文献
20.
Abstract
Relationships between biofilm structural components (algal and bacterial biomass) and the activities of some extracellular
enzymes that contribute to the ability to degrade organic matter) were explored for six Atlantic and three Mediterranean streams
and rivers. The biofilms in these fluvial systems accounted for a wide range of bacterial and algal biomass and colonized
the most common benthic habitats. Ratio of bacteria/algae biomass was lower in Atlantic than in Mediterranean streams, but
enzymatic activities (β-glucosidase, β-xylosidase, phosphatase) were in general greater in the Mediterranean stream biofilms.
Climatic characteristics (especially temperature) may explain the differences in enzymatic activities between biofilms of
similar structure but different flow regime. The ratio β-xylosidase: β-glucosidase was similar (around 0.5) for all streams
and substrata considered, showing that there is a general higher utilization of cellobiosic than xylobiosic molecules in fluvial
systems. In general, highly heterotrophic biofilms showed lower extracellular enzymatic activities than more autotrophic biofilms.
Maximum enzymatic activity is achieved when the algal biomass is two- to threefold higher than the bacterial biomass. The
relevance of algal biomass on the heterotrophic ability of biofilms may be related to the physical proximity between the two,
but also to the high proportion of polymeric carbohydrates included in algal exudates and lysis products, whose use is enzyme-mediated.
Received: January 2000; Accepted: April 2000; Online Publication: 18 July 2000 相似文献