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1.
The spring mesozooplankton community at South Georgia: a comparison of shelf and oceanic sites 总被引:3,自引:3,他引:0
Mesozooplankton (predominantly 200–2000 μm) were sampled at a shelf and an oceanic station close to South Georgia, South
Atlantic, during austral spring (October/November) 1997. Onshelf zooplankton biomass was extremely high at 10–16 g dry mass
m−2 (0–150 m), 70% comprising the small neritic clausocalaniid copepod Drepanopus forcipatus. Large calanoid species, principally Calanoides acutus and Rhincalanus gigas, contributed only 8–10%. At the oceanic station, biomass in the sampled water column (0–1000 m) was ∼6.5 g dry mass m−2 and 4–6 g dry mass m−2 in the top 200 m. Here, large calanoids composed 40–50% of the standing stock. Antarctic krill (Euphausia superba) occurred in low abundances at both stations. Vertical profiles obtained with a Longhurst Hardy Plankton Recorder indicated
that populations of C. acutus and R. gigas, which overwinter at depth, had completed their spring ascent and were resident in surface waters. Dry mass, carbon and lipid
values were lower than found in summer but were consistent with overwintered populations. Phytoplankton concentrations were
considerably higher at the oceanic station (2–3 mg chlorophyll a m−3) and increased over the time on station. In response to this, egg production of both large calanoid species and growth rates
of R. gigas approached those measured in summer. Onshelf phytoplankton concentrations were lower (<1 mg m−3), and low egg production rates suggested food limitation. Here phytoplankton rations equivalent to 6% zooplankton body C
would have been sufficient to clear primary production whereas at the oceanic station daily carbon fixation was broadly equivalent
to zooplankton carbon biomass.
Accepted: 25 April 1999 相似文献
2.
Abstract
Freshwater ecosystems derive organic carbon from both allochthonous and autochthonous sources. We studied the relative contributions
of different carbon sources to zooplankton in a small, polyhumic, steeply stratified lake, using six replicate surface-to-sediment
enclosures established during summer and autumn 2004. We added 13C-enriched bicarbonate to the epilimnion of half the enclosures for three weeks during each season and monitored carbon stable
isotope ratios of DIC, DOC, POC and Daphnia, along with physical, chemical and biological variables. During summer, 13C-enriched DIC (δ13C up to 44 ± 7.2‰) was soon taken up by phytoplankton (δ13C up to −5.1 ± 13.6‰) and was transmitted to Daphnia (δ13C up to −1.7 ± 7.2‰), demonstrating consumption of phytoplankton. In contrast, during autumn, 13C-enriched DIC (δ13C up to 56.3 ± 9.8‰) was not transmitted to Daphnia, whose δ13C became progressively lower (δ13C down to −45.6 ± 3.3‰) concomitant with decreasing methane concentration. Outputs from a model suggested phytoplankton contributed
64–84% of Daphnia diet during summer, whereas a calculated pelagic carbon mass balance indicated only 30–40% could have come from phytoplankton.
Although autumn primary production was negligible, zooplankton biomass persisted at the summer level. The model suggested
methanotrophic bacteria contributed 64–87% of Daphnia diet during autumn, although the calculated carbon mass balance indicated a contribution of 37–112%. Thus methanotrophic
bacteria could supply virtually all the carbon requirement of Daphnia during autumn in this lake. The strongly 13C-depleted Daphnia values, together with the outputs from the models and the calculated carbon mass balance showed that methanotrophic bacteria
can be a greater carbon source for Daphnia in lakes than previously suspected. 相似文献
3.
Dilution experiments were performed to examine the growth and grazing mortality rates of picophytoplankton (<2 μm), nanophytoplankton
(2–20 μm), and microphytoplankton (>20 μm) at stations in the Chesapeake Bay (CB), the Delaware Inland Bays (DIB) and the
Delaware Bay (DB), in early spring 2005. At station CB microphytoplankton, including chain-forming diatoms were dominant,
and the microzooplankton assemblage was mainly composed of the tintinnid Tintinnopsis beroidea. At station DIB, the dominant species were microphytoplanktonic dinoflagellates, while the microzooplankton community was
mainly composed of copepod nauplii and the oligotrich ciliate Strombidium sp. At station DB, nanophytoplankton were dominant components, and Strombidium and Tintinnopsis beroidea were the co-dominant microzooplankton. The growth rate and grazing mortality rate were 0.13–3.43 and 0.09–1.92 d−1 for the different size fractionated phytoplankton. The microzooplankton ingested 73, 171, and 49% of standing stocks, and
95, 70, and 48% of potential primary productivity for total phytoplankton at station CB, DIB, and DB respectively. The carbon
flux for total phytoplankton consumed by microzooplankton was 1224.11, 100.76, and 85.85 μg C l−1 d−1 at station CB, DIB, and DB, respectively. According to the grazing mortality rate, carbon consumption rate and carbon flux
turn over rates, microzooplankton in study area mostly preferred to graze on picophytoplankton, which was faster growing but
was lowest biomass component of the phytoplankton. The faster grazing on Fast-Growing-Low-Biomass (FGLB) phenomenon in coastal
regions is explained as a resource partitioning strategy. This quite likely argues that although microzooplankton grazes strongly
on phytoplankton in these regions, these microzooplankton grazers are passive.
Handling editor: K. Martens 相似文献
4.
Microcystis aeruginosa, a cosmopolitan form, is a colonial cyanobacterium, which is also common in many freshwater bodies in Mexico. In eutrophic
water bodies cyanobacteria are often the main phytoplankton that co-exist with cladocerans. We evaluated the effect of mixed
diets, comprising 0, 25, 50, 75, and 100% on dry weight basis of M. aeruginosa, and the rest of one of two green algal species (Chlorella vulgaris and Scenedesmus acutus), on the population growth of the cladocerans Ceriodaphnia dubia and Moina macrocopa. Regardless of the share of M. aeruginosa in the mixed diet, C. dubia fed Chlorella had a longer initial lag phase. However, in mixed diet with S. acutus, the lag phase of C. dubia increased with increasing proportion of M. aeruginosa. When raised on 100% M. aeruginosa, the population growth of C. dubia was lowered compared with 100% S. acutus or 100% C. vulgaris. Increased proportion of M. aeruginosa in the mixed diet also resulted in decreased abundance of M. macrocopa. Irrespective of diet type, M. macrocopa had a shorter lag phase than C. dubia. Depending on the diet type, the rate of population increase (r) of C. dubia varied from 0.07 to 0.26 d−1 while that of M. macrocopa was higher (0.14–0.61 d−1). For both cladoceran species, the lower r values were obtained when fed Microcystis. Our study showed that the strain of M. aeruginosa was not highly toxic to cause total elimination of either C. dubia or M. macrocopa. Addition of a green algal component to the diet improved the population growth rates of both cladoceran species. 相似文献
5.
In order to provide a better understanding of the dynamics of phytoplankton in the coastal regions of high latitudes, a study
was carried out to estimate the dynamics of carbon biomass of autotrophic and heterotrophic algal groups over the austral
spring-summer 1997/1998 period. At a fixed station located in the central basin (Paso Ancho) of the Straits of Magellan (53°S),
surface water samples were collected at least once a week from September 1997 (early spring) to March 1998 (late summer).
Quantitative analysis of biomass of phytoplankton was estimated from geometric volumes, using non-linear equations, and converted
to biomass. The pattern of chlorophyll a showed a strong temporal variability, with maximum values (mean 2.8 mg m−3) at the austral spring phytoplankton increase or bloom (October/November) and minimum values during early spring (September:
<0.5 mg m−3) and summer (January/March: 0.5–1.0 mg m−3). During the spring bloom, diatoms made up to 90% of the total phytoplankton carbon (0.01–189 μg l−1), followed by a maximum of thecate dinoflagellates (0.08–34 μg l−1), and sporadic high biomass of phytoflagellates during summer. Heterotrophic algal groups such as Gymnodinium and Gyrodinium spp. dominated (70%, in the 5- to 25-μm size range) shortly before the main diatom bloom, and small peaks were observed within
spring and early summer periods (0–0.4 μg l−1). Phytoflagellates dominated earlier (spring) with higher carbon biomass (8 μg l−1) and post-bloom periods (summer) when carbon biomass ranged between 1 and 4 μg l−1.
Accepted: 6 September 2000 相似文献
6.
The ability of photoautotrophic picoplankton Synechococcus to degrade urea was examined in the euphotic zone of Lake Biwa. Samples were divided into pico (0.2–2.0 μm) and larger (>2.0
μm) size fractions by filtration. The rates of urea degradation (the sum of the rates of incorporation of carbon into phytoplankton
cells and of liberation of CO2 into water) measured by radiocarbon urea were 8 and 17 μmol urea m−3 day−1 in June and July, respectively, for the picophytoplankton in the surface water, and 196 and 96 μmol urea m−3 day−1, respectively for the larger phytoplankton. The rates decreased with depth, somewhat similar to the vertical profiles of
the photosynthetic rate. The urea degradation rates were obviously high under light conditions. In daylight, urea was degraded
into two phases, carbon incorporation and CO2 liberation, whereas in the dark it was degraded only into the CO2 liberation phase. The contribution of picophytoplankton to total phytoplankton in urea degradation was high in the subsurface
to lower euphotic layer. Urea degradation activity was higher in the picophytoplankton fraction than in the larger phytoplankton
fraction. Shorter residence times of urea were obtained in the upper euphotic zone. The contribution of picophytoplankton
to urea cycling was 4% to 35%. The present results suggest that the picophytoplankton Synechococcus is able to degrade urea and effectively makes use of regenerated urea as a nitrogen source in the euphotic layer, and that
picophytoplankton play an important role in the biogeochemical nitrogen cycle in Lake Biwa.
Received: June 25, 1998 / Accepted: February 10, 1999 相似文献
7.
Laura Alonso-Sáez Evaristo Vázquez-Domínguez Clara Cardelús Jarone Pinhassi M. Montserrat Sala Itziar Lekunberri Vanessa Balagué Maria Vila-Costa Fernando Unrein Ramon Massana Rafel Simó Josep M. Gasol 《Ecosystems》2008,11(3):397-409
Data from several years of monthly samplings are combined with a 1-year detailed study of carbon flux through bacteria at
a NW Mediterranean coastal site to delineate the bacterial role in carbon use and to assess whether environmental factors
or bacterial assemblage composition affected the in situ rates of bacterial carbon processing. Leucine (Leu) uptake rates
[as an estimate of bacterial heterotrophic production (BHP)] showed high interannual variability but, on average, lower values
were found in winter (around 50 pM Leu−1 h−1) as compared to summer (around 150 pM Leu−1 h−1). Leu-to-carbon conversion factors ranged from 0.9 to 3.6 kgC mol Leu−1, with generally higher values in winter. Leu uptake was only weakly correlated to temperature, and over a full-year cycle
(in 2003), Leu uptake peaked concomitantly with winter chlorophyll a (Chl a) maxima, and in periods of high ectoenzyme activities in spring and summer. This suggests that both low molecular weight
dissolved organic matter (DOM) released by phytoplankton, and high molecular weight DOM in periods of low Chl a, can enhance BHP. Bacterial respiration (BR, range 7–48 μg C l−1 d−1) was not correlated to BHP or temperature, but was significantly correlated to DOC concentration. Total bacterial carbon
demand (BHP plus BR) was only met by dissolved organic carbon produced by phytoplankton during the winter period. We measured
bacterial growth efficiencies by the short-term and the long-term methods and they ranged from 3 to 42%, increasing during
the phytoplankton blooms in winter (during the Chl a peaks), and in spring. Changes in bacterioplankton assemblage structure (as depicted by denaturing gradient gel electrophoresis
fingerprinting) were not coupled to changes in ecosystem functioning, at least in bacterial carbon use. 相似文献
8.
9.
Fast repetition rate fluorometry (FRRF) was successfully applied to various studies in modern oceanography. In this study, for the first time, the seasonality of phytoplankton photosynthetic parameters in a deep alpine lake was observed using FRRF in combination with the traditional 14C incubation technique. Special attention was given to the differences in photosynthetic behaviour during mixed and stratified conditions, characterised especially during summer by a deep chlorophyll maximum (DCM) dominated by the filamentous cyanobacterial species Planktothrix rubescens. Maximum light-utilisation efficiency (α*14C) was in the range of 0.01–0.03 mgC (mg Chl-a)−1 h−1 (μmol phot. m−2 s−1)−1, while maximum quantum yields for carbon fixation (ΦC,max) varied from 0.01–0.07 molC (mol phot.)−1. Higher values occurred during thermal stratification indicating acclimation of the phytoplankton assemblage. These findings were supported by FRRF-based estimates, although cyanobacterial blooms could not be characterised by FRRF-excitation due to methodological deficiencies. In general, however, instantaneous photosynthetic rates measured by FRRF-excitation correlate well at sub-saturating light-intensities with conventional 14C-uptake rates, although they operate on different time-scales. 相似文献
10.
Temporal patterns of primary production in a large ultra-oligotrophic Antarctic freshwater lake 总被引:3,自引:1,他引:2
A large ultra-oligotrophic Antarctic freshwater lake, Crooked Lake, was investigated between January 1993 and November 1993.
The water column supported a small phytoplankton community limited by temperature, nutrient availability and, seasonally,
by low photosynthetically active radiation. Chlorophyll a concentrations were consistently low (<1 g l−1) and showed no obvious seasonal patterns. Production rates were low, ranging from non-detectable to 0.56 g C l−1 h−1, with highest rates generally occurring towards the end of the austral winter and in spring. The pattern of carbon fixation
indicated that the phytoplankton was adapted to low light levels. Chlorophyll a specific photosynthetic rates (assimilation numbers) ranged from non-detectable to 1.27 gC (g chlorophyll a)−1 h−1. Partitioning of photosynthetic products revealed carbon incorporation principally into storage products such as lipids at
high light fluxes with increasing protein synthesis at depth. With little allochthonous input the data suggest that lake dynamics
in this Antarctic system are driven by phytoplankton activity.
Received: 21 February 1997 / Accepted: 18 May 1997 相似文献
11.
Production rates, abundance, chlorophyll a (Chl a) concentrations and pigment composition were measured for three size classes (<2 μm, 2–11 μm and >11 μm) of phytoplankton
from May to December 2000 in deep, mesotrophic, alpine lake Mondsee in Austria. The study focuses on differences among phytoplankton
size fractions characterised by their surface area to volume ratio ([mm2 l−1: mm3l−1]), pigment distribution patterns and photosynthetic rates. Particular attention was paid to autotrophic picophytoplankton
(APP, fraction <2 μm) since this size fraction differed significantly from the two larger size fractions. Among the three
fractions, APP showed the highest surface area to volume ratios and a high persistence in the pattern of lipophilic pigments
between temporarily and spatially successive samples (about 80% similarity of pigment composition between samples over seasons
and depths). The epilimnetic abundance of APP varied seasonally with an annual maximum of 180 × 103 cells ml−1 in June (at 4–9 m). The minimum (October at 12 m) was more than an order of magnitude lower (4.9 × 103 ml−1). APP peaked during autumn and contributed between 24% and 42% to the total area-integrated Chl a (10–23 mg m−2) and between 16% and 58% to total area-integrated production (5–64 mg m−2 h−1) throughout seasons. 相似文献
12.
Luz Allende Guillermo Tell Horacio Zagarese Ana Torremorell Gonzalo Pérez José Bustingorry Roberto Escaray Irina Izaguirre 《Hydrobiologia》2009,624(1):45-60
Shallow lakes often alternate between two possible states: one clear with submerged macrophytes, and another one turbid, dominated
by phytoplankton. A third type of shallow lakes, the inorganic turbid, result from high contents of suspended inorganic material,
and is characterized by low phytoplankton biomass and macrophytes absence. In our survey, the structure and photosynthetic
properties (based on 14C method) of phytoplankton were related to environmental conditions in these three types of lakes in the Pampa Plain. The
underwater light climate was characterized. Clear-vegetated lakes were more transparent (K
d 4.5–7.7 m−1), had high DOC concentrations (>45 mg l−1), low phytoplankton Chl a (1.6–2.7 μg l−1) dominated by nanoflagellates. Phytoplankton productivity and photosynthetic efficiency (α ~ 0.03 mgC mgChla
−1 h−1 W−1 m2) were relatively low. Inorganic-turbid lakes showed highest K
d values (59.8–61.4 m−1), lowest phytoplankton densities (dominated by Bacillariophyta), and Chl a ranged from 14.6 to 18.3 μg l−1. Phytoplankton-turbid lakes showed, in general, high K
d (4.9–58.5 m−1) due to their high phytoplankton abundances. These lakes exhibited the highest Chl a values (14.2–125.7 μg l−1), and the highest productivities and efficiencies (maximum 0.56 mgC mgChla
−1 h−1 W−1 m2). Autotrophic picoplankton abundance, dominated by ficocianine-rich picocyanobacteria, differed among the shallow lakes independently
of their type (0.086 × 105–41.7 × 105 cells ml−1). This article provides a complete characterization of phytoplankton structure (all size fractions), and primary production
of the three types of lakes from the Pampa Plain, one of the richest areas in shallow lakes from South America.
Handling editor: J. Padisak 相似文献
13.
Abstract
Seasonal variation in bacterioplankton abundance, biomass, and bacterioplankton production was studied over eight years in
hypertrophic Lake S?byg?rd. Biologically, the lake is highly variable; this is due mainly to large interannual variation in
fish recruitment. Bacterioplankton production was low during winter, typically 1–3 × 107 cells l−1 h−1, and high during summer, albeit greatly fluctuating with maximum rates typically ranging from 60 to 90 × 107 cells l−1 h−1 (or 0.4 to 0.6 mg C l−1 day−1). Less pronounced variations were found in bacterioplankton abundance, which typically ranged from 3–8 × 109 cells l−1 in winter to 15–30 × 109 cells l−1 during summer. The specific growth rate of bacterioplankton varied from 0.02–0.2 d−1 in winter to 0.5–2.3 day−1 during summer. Interpolated mean bacterioplankton production, in terms of carbon, ranged from 0.08 to 0.16 mg C l−1 day−1, corresponding to 1.6–5.5% of the phytoplankton production, while biomass ranged from 0.28 to 0.36 mg C l−1, corresponding to 1.9–4.6% of the phytoplankton biomass. We conducted regression analysis, relating the bacterioplankton
variables to a number of environmental variables, and evaluated the interannual parameter variability. Chlorophyll a and phytoplankton production contributed less to the variation in the bacterioplankton variables than in most previous analyses
using data from less eutrophic systems. We suggest that the proportion of phytoplankton production that is channelized through
bacterioplankton in lakes decreases with increasing trophic state and decreasing mean depth. This probably reflects a concurrent
increase in fish predation on macrozooplankton and loss by sedimentation. An important part of the residual variation in the
equations hitherto proposed in the literature could be explained by variation in macrozooplankton biomass and pH > 10.2. A
negative effect of high pH on bacterioplankton production was confirmed by laboratory experiments. The impact of different
zooplankton varies considerably, with Daphnia seeming to have a negative impact on bacterioplankton abundance and, thereby, indirectly on bacterioplankton production,
while Bosmina, rotifers, and cyclopoid copepods seem to stimulate both abundance and production. Bosmina apparently also stimulate the bacterioplankton specific growth rate.
Received: 8 February 1996; Accepted: 16 July 1996 相似文献
14.
J. Carlos Roseiro P. J. Partidário N. Lobo M. J. Marçal 《Applied microbiology and biotechnology》1999,52(4):546-552
The change of dilution rate (D) on both Methylophilus methylotrophus NCIMB11348 and Methylobacterium sp. RXM CCMI908 growing in trimethylamine (TMA) chemostat cultures was studied in order to assess their ability to remove
odours in fish processing plants. M. methylotrophus NCIMB11348 was grown at dilution rates of 0.012–0.084 h−1 and the biomass level slightly increased up to values of D around 0.07 h−1. The maximum cell production rate was obtained at 0.07 h−1 corresponding to a maximum conversion of carbon into cell mass (35%). The highest rate of TMA consumption was 3.04 mM h−1 occurring at D=0.076 h−1. Methylobacterium sp. RXM CCMI908 was grown under similar conditions. The biomass increased in a more steep manner up to values of D around 0.06 h−1. The maximum cell production rate (0.058 g l−1h−1) was obtained in the region close to 0.06 h−1 where a maximum conversion of the carbon into cell mass (40%) was observed. The maximum TMA consumption was 2.33 mM h−1 at D=0.075 h−1. The flux of carbon from TMA towards cell synthesis and carbon dioxide in both strains indicates that the cell is not excreting
products but directing most of the carbon source to growth. Carbon recovery levels of approximately 100% show that the cultures
are carbon-limited. Values for theoretical maximum yields and maintenance coefficients are presented along with a kinetic
assessment based on the determination of the substrate saturation constant and maximum growth rate for each organism.
Received: 25 February 1999 / Received revision: 14 May 1999 / Accepted: 17 May 1999 相似文献
15.
Brandon K. Swan James M. Watts Kristen M. Reifel Stuart H. Hurlbert 《Hydrobiologia》2007,576(1):111-125
The Salton Sea currently suffers from several well-documented water quality problems associated with high nutrient loading.
However, the importance of phosphorus regeneration from sediments has not been established. Sediment phosphorus regeneration
rates may be affected by benthic macroinvertebrate activity (e.g. bioturbation and excretion). The polychaete Neanthes
succinea (Frey and Leuckart) is the dominant benthic macroinvertebrate in the Salton Sea. It is widely distributed during periods
of mixing (winter and spring), and inhabits only shallow water areas following development of anoxia in summer. The contribution
of N. succinea to sediment phosphorus regeneration was investigated using laboratory incubations of cores under lake temperatures and dissolved
oxygen concentrations typical of the Salton Sea. Regeneration rates of soluble reactive phosphorus (SRP) were lowest (−0.23–1.03
mg P m−2 day−1) under saturated oxygen conditions, and highest (1.23–4.67 mg P m−2 day−1) under reduced oxygen levels. N. succinea most likely stimulated phosphorus regeneration under reduced oxygen levels via increased burrow ventilation rates. Phosphorus
excretion rates by N. succinea were 60–70% more rapid under reduced oxygen levels than under saturated or hypoxic conditions. SRP accounted for 71–80% of
the dissolved phosphorus excreted under all conditions. Whole-lake SRP regeneration rates predicted from N. succinea biomass densities are highest in early spring, when the lake is mixing frequently and mid-lake phytoplankton populations
are maximal. Thus, any additional phosphorus regenerated from the sediments at that time has potential for contributing to
the overall production of the lake.
Guest Editor: John M. Melack
Saline Water and their Biota 相似文献
16.
José Juan Barrera-Alba Sônia Maria Flores Gianesella Gleyci Aparecida Oliveira Moser Flávia Marisa Prado Saldanha-Corrêa 《Hydrobiologia》2008,598(1):229-246
Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates and growth efficiencies were studied
in July 2001 and January 2002 during both spring and neap tides, along a tidal cycle, at three sites in a subtropical estuary.
Major freshwater inputs located in the Northern region led to differences in both phytoplankton and bacterioplankton biomass
and activity along the estuary. While in the Northern region phytoplankton is light-limited, with mean phytoplankton production
(PP) between 1.1 and 1.9 μg C l−1 h−1 and mean specific growth rates (PSG) between 0.14 and 0.16 d−1, the Southern region registered values as high as 24.7 μg C l−1 h−1 for PP and 2.45 d−1 (mean PP between 3.4 and 7.3 μg C l−1 h−1; mean PSG between 0.28 and 0.57 d−1). On the other hand, maximum bacterial production (BP: 63.8 μg C l−1 h−1) and specific growth rate (BSG: 32.26 d−1) were observed in the Northern region (mean BP between 3.4 and 12.8 μg C l−1 h−1; mean BSG between 1.98 and 6.67 day−1). These bacterial activity rates are among the highest recorded rates in estuarine and coastal waters, indicating that this
system can be highly heterotrophic, due to high loads of allochthonous carbon (mainly derived from mangrove forest). Our results
also showed that, despite that BP rates usually exceeded PP, in the Southern region BP may be partially supported (∼45%) by
PP, since a significant regression was observed between BP and PP (r = 0.455, P < 0.001).
Handling editor: P. Viaroli 相似文献
17.
E. A. Pakhomov H. M. Verheye A. Atkinson R. K. Laubscher J. Taunton-Clark 《Polar Biology》1997,18(3):180-192
Mesozooplankton abundance, community structure and grazing impact were determined during late austral summer (February/March)
1994 at eight oceanic stations near South Georgia using samples collected with a Bongo and WP-2 nets in the upper 200-m and
100-m layer, respectively. The zooplankton abundance was generally dominated by copepodite stages C3–C5 of six copepod species:
Rhincalanus gigas, Calanus simillimus, Calanoides acutus, Metridia spp., Clausocalanus laticeps and Ctenocalanus vanus. Most copepods had large lipid sacs. All copepods accounted for 41–98% of total zooplankton abundance. Juvenile euphausiids
were the second most important component contributing between 1 and 20% of total abundance. Pteropods, mainly Limacina inflata, were important members of the pelagic community at two sites, accounting for 44 and 53% of total abundance. Average mesozooplankton
biomass in the upper 200 m was 8.0 g dry weight m−2, ranging from 4.3 to 11.5 g dry weight m−2. With the exception of Calanussimillimus, gut pigment contents and feeding activity of copepod species were low, suggesting that some species, after having stored
large lipid reserves, had probably started undergoing developmental arrest. Daily mesozooplankton grazing impact, measured
using in situ gut fluorescence techniques and in vitro incubations, varied widely from <1 to 8% (mean 3.5%) of phytoplankton
standing stock, and from 5 to 102% (mean 36%) of primary production. The highest grazing impact was found northeast of the
island co-incident with the lowest phytoplankton biomass and primary production levels.
Received: 30 October 1996 / Accepted: 23 February 1997 相似文献
18.
Elżbieta E. Kopczyńska Nicolas Savoye Frank Dehairs Damien Cardinal Marc Elskens 《Polar Biology》2007,31(1):77-88
Variations of phytoplankton assemblages were studied in November–December 2001, in surface waters of the Southern Ocean along
a transect between the Sub-Antarctic Zone (SAZ) and the Seasonal Ice Zone (SIZ; 46.9°–64.9°S; 142°–143°E; CLIVAR-SR3 cruise).
Two regions had characteristic but different phytoplankton assemblages. Nanoflagellates(<20 μm) and pico-plankton (∼2 μm)
occurred in similar concentrations along the transect, but were dominant in the SAZ, Sub-Antarctic Front (SAF), Polar Front
Zone (PFZ) and the Inter-Polar Front Zone (IPFZ), (46.9°–56.9°S). Along the entire transect their average cell numbers in
the upper 70 m of water column, varied from 3 × 105 to 1.1 × 106 cells l−1. Larger cells (>20 μm), diatoms and dinoflagellates, were more abundant in the Antarctic Zone-South (AZ-S) and the SIZ, (60.9°–64.9°S).
In AZ-S and SIZ diatoms ranged between 2.7 × 105 and 1.2 × 106 cells l−1, dinoflagellates from 3.1 × 104 to 1.02 × 105 cells l−1. A diatom bloom was in progress in the AZ-S showing a peak of 1.8 × 106 cells l−1. Diatoms were dominated by Pseudo-nitzschia spp., Fragilariopsis spp., and Chaetoceros spp. Pseudo-nitzschia spp. outnumbered other diatoms in the AZ-S. Fragilaropsis spp. were most numerous in the SIZ. Dinoflagellates contained autotrophs (e.g. Prorocentrum) and heterotrophs (Gyrodinium/Gymnodinium, Protoperidinium). Diatoms and dinoflagellates contributed most to the cellular carbon: 11–25 and 17–124 μg C l−1, respectively. Small cells dominated in the northern region characterized by the lowest N-uptake and new production of the
transect. Larger diatom cells were prevalent in the southern area with higher values of N-uptake and new production. Diatom
and nanoflagellate cellular carbon contents were highly correlated with one another, with primary production, and productivity
related parameters. They contributed up to 75% to the total autotrophic C biomass. Diatom carbon content was significantly
correlated to nitrate uptake and particle export, but not to ammonium uptake, while flagellate carbon was well correlated
to ammonium uptake, but not to export. Diatoms have contributed highly to particle export along the latitudinal transect,
while flagellates played a minor role in the export. 相似文献
19.
The diet of the kelp gull (Larus dominicanus), its foraging behaviour and the consumption rates on the Antarctic limpet (Nacella concinna) were studied during austral spring and summer 1992/1993 and 1993/1994 at Potter Peninsula, King George Island, Antarctica.
Prey information was obtained by collecting 237 pellets, foraging behaviour was observed by focal and instantaneous scan samplings,
and consumption rate was estimated by means of weekly sampling of limpets found in 5 nests and their respective middens. Limpets
were the most important prey followed by scavenged prey (penguin and seal carcasses), amphipods, snails, fish and euphausiids.
Foraging gulls spent 51% of the time searching for limpets, 10% moving between foraging areas, 9% in catching effort and 15%
handling prey. The number of gulls observed searching for limpets was inversely correlated with the tidal height. In the diet
limpets provide 102.3, 159.4 and 188.1 kJ gull−1 day−1 during incubation, hatching and brooding respectively; these values range between 15 and 27%, with a maximum of 40%, of the
basic daily energy requirements of kelp gulls. Total consumption rate estimations for the whole population of gulls at Potter
Peninsula reached between 3400 and 4800 limpets day−1, which represents approximately 10–14% of the total annual limpet mortality.
Received: 25 March 1996 / Accepted: 26 August 1996 相似文献
20.
North Lake, a small (330 ha. surface area) southwestern U.S.A. cooling water reservoir was found to contain less phytoplankton
production (104.0 mg C m−3 day−1), lower annual mean total organic carbon (3.7 mg l−1) and phytoplankton standing crops (0.9 ml m−3) than other local area reservoirs. Concentrations of inorganic P and N were at or below test detection limits during the
study year 1973–1974.In situ
14C non-filtration primary productivity techniques demonstrated significant (≃13 percent) stimulation of planktonic primary
productivity due to power plant entrainment. Optical counts showed no destruction of entrained phytoplankters. Populations
of Cyanophyta were never dominant, although they frequently bloom in most other local reservoirs. Thermal loading at North
Lake is thought to ultimately depress phytoplankton primary production and standing crop by causing nutrient limitation. 相似文献