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1.
Ammonium concentrations of ∼1 M are commonly cited as being the threshold for inhibition of NO3
− uptake, but the applicability of this threshold to phytoplankton from different taxonomic classes has rarely been examined.
Additionally, little is known about the influence of environmental variables (e.g. growth temperature) on the interaction
between ambient NH4
+ and NO3
− uptake. Four species of estuarine phytoplankton, two diatom [Chaetoceros sp., and Thalassiosira weissflogii (Grunow) Fryxell et Hasle] and two dinoflagellate [Prorocentrum minimum (Pavillard) Schiller, and Gyrodinium uncatenum Hulburt], were grown on NO3
− at several different temperatures (4, 10, 15, or 20 °C), and the impact of NH4
+ additions on NO3
− uptake/assimilation (non-TCA-extracted) and assimilation (TCA-extracted) was assessed. For all species at all temperatures,
NO3
− uptake/assimilation and assimilation rates decreased in a roughly exponential manner with increasing NH4
+ concentrations but were not completely inhibited even at elevated NH4
+ concentrations of 200 μM. Estimated half-inhibition concentrations (K
i) were significantly greater in the diatom species (mean ± SE; 2.70 ± 0.67 μM) than in the dinoflagellate species (1.26 ± 0.55 μM). Half-inhibition constants were positively related to temperature-limited relative growth rate although not significantly.
The observed inhibition of NO3
− uptake and assimilation, as a percentage of NO3
− uptake in the absence of NH4
+, averaged about 80% and ranged from 49 to 100%. For all species, a significant (P < 0.001) positive correlation was found between percent inhibition of NO3
− assimilation and temperature-limited relative growth rate. Two experiments on Chesapeake Bay phytoplankton during an April
1998 diatom bloom showed that in short-term (∼1 h) temperature manipulation experiments, percent inhibition of NO3
− uptake/assimilation was also positively related (P = 0.05) to experimental temperature. The observed relationships between temperature-limited relative growth rate and percent
inhibition of NO3
− assimilation rates for the species tested suggest that at the enzyme level, the inhibitory mechanism of NO3
− assimilation is similar among species, but at the whole cell level may be regulated by species-specific differences in the
accumulation of internal metabolites. These findings add not only to our understanding of species-specific variability and
the role of growth temperature, but also provide additional data with which to evaluate current models of NH4
+ and NO3
− interactions.
Received: 31 August 1998 / Accepted: 7 December 1998 相似文献
2.
Phytoplankton blooms are strongly impacted by microzooplankton grazing in coastal North Pacific waters 总被引:1,自引:0,他引:1
Phytoplankton growth and microzooplankton grazing were measured in two productive coastal regions of the North Pacific: northern
Puget Sound and the coastal Gulf of Alaska. Rates of phytoplankton growth (range: 0.09–2.69 day−1) and microzooplankton grazing (range: 0.00–2.10 day−1) varied seasonally, with lowest values in late fall and winter, and highest values in spring and summer. Chlorophyll concentrations
also varied widely (0.19–13.65 μg l−1). Large (>8 μm) phytoplankton cells consistently dominated phytoplankton communities under bloom conditions, contributing
on average 65% of total chlorophyll biomass when chlorophyll exceeded 2 μg l−1. Microzooplankton grazing was an important loss process affecting phytoplankton, with grazing rates equivalent to nearly
two-thirds (64%) of growth rates on average. Both small and large phytoplankton cells were consumed, with the ratio of grazing
to growth (g:μ) for the two size classes averaging 0.80 and 0.42, respectively. Perhaps surprisingly, the coupling between microzooplankton
grazing and phytoplankton growth was tighter during phytoplankton blooms than during low biomass periods, with g:μ averaging 0.78 during blooms and 0.49 at other times. This tight coupling may be a result of the high potential growth
and ingestion rates of protist grazers, some of which feed on bloom-forming diatoms and other large phytoplankton. Large ciliates
and Gyrodinium-like dinoflagellates contributed substantially to microzooplankton biomass at diatom bloom stations in the Gulf of Alaska,
and microzooplankton biomass overall was strongly correlated with >8 μm chlorophyll concentrations. Because grazing tended
to be proportionally greater when phytoplankton biomass was high, the absolute amount of chlorophyll consumed by microzooplankton
was often substantial. In nearly two-thirds of the experiments (14/23), more chlorophyll was ingested by microzooplankton
than was available for all other biological and physical loss processes combined. Microzooplankton were important intermediaries
in the transfer of primary production to higher trophic levels in these coastal marine food webs.
Received: 12 November 1999 / Accepted: 4 October 2000 相似文献
3.
Cell growth of a coastal marine diatom, Chaetoceros sociale, in the presence of different premixed organic-Fe(III) complexes [EDTA-Fe(III) (100:1 and 2:1), citric-Fe(III) (100:1) and
fulvic-Fe(III) (0.1, 0.2 and 1 ppm C)] and solid amorphous hydrous ferric oxide [am-Fe(III) or Fe(III) hydroxide] were experimentally
measured in culture experiments at 10 °C under 3000 lux fluorescent light. Fulvic-Fe(III) (0.1 and 0.2 ppm C) and citric-Fe(III)
(100:1) induced maximal cell yields of C. sociale. The order of cell yields was: fulvic-Fe(III) (0.1 and 0.2 ppm C) ≥ citric-Fe(III) (100:1) > EDTA-Fe(III) (2:1) ≫ solid am-Fe(III) > EDTA-Fe(III)
(100:1) ≫ fulvic-Fe(III) (1 ppm C). The short-term iron uptake rates by C. sociale in fulvic-Fe(III) (0.1 and 0.2 ppm C) and citric-Fe(III) (100:1) media were about five to six times faster than those in
EDTA-Fe(III) (100:1) and solid am-Fe(III) media. The dissociative precipitation rates of premixed organic-Fe(III) complexes
in seawater at 10 °C were determined by simple filtration (0.025 μm) involving γ-activity measurements of 59Fe. The order of estimated initial Fe(III) dissociative precipitation rates of these organic-Fe(III) complexes in seawater
were nearly consistent with those of cell yields in the culture experiments and short-term iron uptake rates by C. sociale [except for fulvic-Fe(III) (1 ppm C) medium]. In fulvic-Fe(III) (0.1 and 0.2 ppm C), citric-Fe(III) (100:1) and EDTA-Fe(III)
(2:1) media, the concentrations of dissolved organic-Fe(III) complexes in initial culture experiments are prone to supersaturate
under the culture conditions. The supersaturated dissolved organic-Fe(III) complex in seawater supplies biologically available
inorganic Fe(III) species in culture media through its dissociation at high pH and high levels of seawater cations. Therefore,
the natural dissolved organic-Fe(III) complexes supplied by riverine input may play an important role in supplying bioavailable
iron in estuarine mixing system and coastal waters.
Received: 6 September 1998 / Accepted: 8 April 1999 相似文献
4.
Sexuality and cyst formation of the spring-bloom dinoflagellate Scrippsiella hangoei in the coastal northern Baltic Sea 总被引:3,自引:0,他引:3
The temporal sequence and the magnitude of the sexual reproduction and subsequent cyst deposition of the common spring-bloom
dinoflagellate Scrippsiella hangoei (Schiller) Larsen was studied during spring 1996 on the SW coast of Finland, Baltic Sea. The abundances of the different
size of fractions of S. hangoei (14 to 18 μm, 18 to 22 μm and >22 μm) were monitored in the water column, and the deposition of resting cysts was measured
using moored sediment traps. Cyst sedimentation rates were measured throughout the seasonal cycle in order to estimate cyst
resuspension rates for the quantitative assessment of the fraction of population undergoing encystment. The onset of sexual
reproduction, indicated by a significant increase of the small cells (14 to 18 μm) representing gametes, occurred in a nutrient
replete environment well before the exponential growth phase and peak abundances of vegetative cells. Gamete formation was
followed by high abundances of large cells (>22 μm) representing planozygotes, and subsequent sedimentation of resting cysts.
Approximately 60% of the asexually growing bloom population was estimated to form planozygotes, suggesting that encystment
was an important factor in bloom termination and possibly plays a role in the regulation of the magnitude of the bloom. Finally
encystment accounted for 40% of the entire S. hangoei population, resulting in a considerable loss of the bloom population and an input of the vernal phytoplankton biomass to
the benthos.
Received: 11 December 1998 / Accepted: 8 April 1999 相似文献
5.
Annual cycles of phytoplankton community-structure and bloom dynamics in the Neuse River Estuary, North Carolina 总被引:6,自引:0,他引:6
The spatiotemporal distributions of major phytoplankton taxa were quantified to estimate the relative contribution of different
microalgal groups to biomass and bloom dynamics in the eutrophic Neuse River Estuary, North Carolina, USA. Biweekly water
samples and ambient physical and chemical data were examined at sites along a salinity gradient from January 1994 through
December 1996. Chemosystematic photopigments (chlorophylls and carotenoids) were identified and quantified using high-performance
liquid chromatography (HPLC). A recently-developed factor-analysis procedure (CHEMTAX) was used to partition the algal group-specific
chlorophyll a (chl a) concentrations based on photopigment concentrations. Results were spatially and temporally integrated to determine the ecosystem-level
dynamics of phytoplankton community-constituents. Seasonal patterns of phytoplankton community-composition changes were observed
over the 3 yr. Dinoflagellates reached maximum abundance in the late winter to early spring (January to March), followed by
a spring diatom bloom (May to July). Cyanobacteria were more prevalent during summer months and made a large contribution
to phytoplankton biomass, possibly in response to nutrient-enriched freshwater discharge. Cryptomonad blooms were not associated
with a particular season, and varied from year to year. Chlorophyte abundance was low, but occasional blooms occurred during
spring and summer. Over the 3 yr period, the total contribution of each algal group, in terms of chl a, was evenly balanced, with each contributing nearly 20% of the total chl a. Cryptomonad, chlorophyte, and cyanobacterial dynamics did not exhibit regular seasonal bloom patterns. High dissolved inorganic-nitrogen
loading during the summer months promoted major blooms of cryptomonads, chlorophytes, and cyanobacteria.
Received: 12 September 1997 / Accepted: 12 December 1997 相似文献
6.
D. Raby M. Mingelbier J. J. Dodson B. Klein Y. Lagadeuc L. Legendre 《Marine Biology》1997,127(4):665-672
Epifluorescence microscopy was used to analyze the stomach contents of bivalve larvae collected in the Baie des Chaleurs
(western Gulf of St. Lawrence, Canada) in order to document food-particle sizes, compare feeding among taxa, and compare the
diet with the in situ phytoplankton community. Stomach contents were mainly composed of small autotrophic flagellates (<5
μm) and cyanobacteria (<2 μm), reflecting the microbial food web which characterizes these waters. More than half (55%) of
all veligers examined contained algal cells of 5 to 15 μm, whereas only 3% had cells of 15 to 25 μm. Differences in the size
ranges of ingested algal cells among similar-sized larvae of different species suggests that veligers actively selected food
particles. Among the smallest veligers (185 to 260 μm), scallops (Placopecten magellicanus) and mussels (Mytilus edulis) ingested more <5 μm and 5 to 15 μm algae than clams (Mya arenaria). Among larger veligers (261 to 405 μm), clams contained significantly more <5 μm cells than mussels, whereas mussels contained
significantly more 5 to 15 μm algae than clams. Algal cells of 15 to 25 μm were preferentially ingested by mussel veligers.
Feeding also differed between different-sized veligers within taxa, i.e. the smallest clam veligers ingested fewer of 5 to
15 μm algae than the larger size classes. Mussel veligers ingested significantly more 15 to 25 μm and fewer <5 μm cells as
their size increased. The dominance of ultraplankton in the nearshore waters of Baie des Chaleurs and in the stomach contents
suggests that veliger larvae may be an important export path for carbon produced by small phytoplankton.
Received: 17 July 1996 / Accepted: 20 September 1996 相似文献
7.
Contribution of salps to carbon flux of marginal ice zone of the Lazarev Sea, southern ocean 总被引:3,自引:0,他引:3
In order to estimate the in situ grazing rates of Salpa thompsoni and their implications for the development of phytoplankton blooms and for the sequestration of biogenic carbon in the high
Antarctic, a repeat-grid survey and drogue study were carried out in the Lazarev Sea during austral summer of 1994/1995 (December/January).
Exceptionally high grazing rates were measured for S. thompsoni at the onset of a phytoplankton bloom (0.2 to 0.8 μg chlorophyll a l−1) in December 1994, with up to ≃160 μg of plant pigments consumed by an individual salp of 7 to 10 cm length per day. Dense
salp swarms extended throughout the marginal ice zone, consuming up to 108% of daily phytoplankton production and 21% of the
total chlorophyll a stock. Due to the much faster sinking rates and higher carbon content of salp faecal pellets, the efficiency of downward
carbon flux through salps is much higher than through the other major grazers, krill and copepods. S. thompsoni can thus export large amounts of biogenic carbon from the euphotic zone to the deep ocean. With the observed ingestion rates
during December 1994, this flux could have attained levels of up to 88 mg C m−2 d−1, accounting for the bulk of the vertical transport of carbon in the Lazarev Sea. However, in January 1995, when phytoplankton
concentrations exceeded a threshold level of 1.0 to 1.5 μg chlorophyll a l−1, salps experienced a drastic reduction in their feeding efficiency, possibly as a result of clogging of their filtering apparatus.
This triggered a dramatic reversal in the relationship, during which a dense phytoplankton bloom developed in conjunction
with the collapse of the salp population. Increases in the biomass and geographic range of the tunicate S. thompsoni have occurred in several areas of the southern ocean, often in parallel with a rise in sea-surface temperature during sub-decadal
periods of warming anomalies.
Received: 10 August 1997 / Accepted: 21 October 1997 相似文献
8.
Mytilus edulis L., Ruditapes philippinarum (Adams & Reeve) and Tapes decussatus L. were fed particles of the same shape (spherical), the same density (2.1 g cm−3) and the same chemical composition (SiO2), but which varied in diameter from 5 to 37 μm. Findings obtained at different particle concentrations (mean ± SD) of 51 ± 2,
105 ± 18 and 171 ± 17 mg l−1 invariably indicate that significant proportions of all particles with diameters larger than from between 7.5 and 22.5 μm
were preferentially rejected as pseudofaeces. We define the preferential ingestion index (PII) as the ratio between average
particle volume in pseudofaeces and average particle volume in food. Whatever the particle concentration or the species, this
PII was always statistically higher than 1. Irrespective of particle concentration, PII values in M. edulis were lower than in T. decussatus (averages of 1.2 and 2, respectively). PII values in M. edulis were also lower than in R. philippinarum maintained at particle concentrations above 171 ± 17 mg l−1. We suggest that preferential size-dependent rejection of larger particles could be of significant adaptive value in the
natural environment, either if there are large inorganic particles, or if the average organic content of smaller particles
is higher.
Received: 11 January 1997 / Accepted: 8 March 1997 相似文献
9.
Growth and development of Calanus spp. (Copepoda) during spring phytoplankton succession in the North Sea 总被引:1,自引:0,他引:1
Experiments were carried out to determine growth and development rates of the herbivorous copepod Calanus finmarchicus (Gunnerus) under natural conditions during the phytoplankton spring bloom in the northern North Sea. From 28 April to 25 May 1983 copepodite stages I, IV and V were incubated for a 3-d period on board a ship in vessels with naturally occurring phytoplankton or cultured algae as food. Highest rates of growth and development were achieved while the diatom Chaetoceros sp. was the dominant phytoplankton organism. These rates decreased considerably when this chain-forming diatom was succeeded after one week by the small-celled diatom Thalassiosira conferta. Again one week later, during the bloom of the succeeding colonial microflagellate Corymbellus aureus, copepodite stage IV still managed to maintain moderate rates of growth and development, but these rates dropped to almost zero in CV, suggesting the start of a resting stage. Nevertheless, brood collected from this generation and from Calanus helgolandicus (Claus) was raised in the laboratory to the adult stage at high speed. Since temperature and the total phytoplankton concentration in the sea remained almost constant it seems that the retardation and arrestment of growth and development were an immediate response to a qualitative change of the food composition related to the successive blooms of different algal species. 相似文献
10.
Eggs and embryos of the sea urchin Paracentrotus lividus were used as a model to study the effect at the cellular level of potential anti-mitotic compounds extracted from the diatom
Thalassiosira rotula. Eggs and embryos incubated in a water-soluble diatom extract, corresponding to 5 × 106 and 107 cells ml−1, were totally blocked (i.e. cell division was blocked) at the one-cell stage. At lower concentrations (2.5 and 1.25 × 106 cells ml−1), the first mitotic division was inhibited in 32 ± 26% and 25 ± 3.5% of the zygotes, respectively, demonstrating the dose-dependent
effect of diatom extracts on sea urchin development. Immunofluorescence dyes, specific for DNA and α-tubulin subunits, were
used to stain nuclei and microtubules in sea urchin embryos during various phases of development. Images with the confocal
laser scanning microscope showed that tubulin was not organised in filaments at the sperm aster and cortex levels, and that
the pronuclei were not fused in embryos incubated soon after fertilisation with water-soluble diatom extracts corresponding
to 107 cells ml−1. At lower diatom-extract concentrations (4 × 106 cells ml −1), fusion of the pronuclei occurred but the mitotic spindle was not formed. Microtubules were clearly de-polymerised and the
chromatin appeared globular and compacted at the centre of the cell. A similar structure was observed for sea urchin embryos
incubated with 0.1 mM colchicine, a potent anti-mitotic compound. When sea urchin embryos were incubated in water-soluble diatom extracts at different
times prior to the first mitotic division, microtubules appeared de-polymerised at each step, from pronuclear fusion to telophase,
and cell division was blocked. At the histological level, embryos incubated with 4 × 106 cells ml−1 diatom extract showed nuclear fragmentation without cytokinesis. The possible use of sea urchin embryos as a bioassay to
test for other unknown compounds with cytotoxic activity in phytoplankton species is discussed.
Received: 7 May 1998 / Accepted: 9 December 1998 相似文献
11.
Is kelp detritus a good food for suspension feeders? Effects of kelp species, age and secondary metabolites 总被引:2,自引:0,他引:2
The food quality of detrital particles derived from three species of kelps was evaluated in a laboratory feeding experiment
utilizing two species of suspension feeders, the serpulid polychaete Pseudochitonopomaoccidentalis and the mussel Mytilustrossulus. Fresh and aged kelp particles were also evaluated, and growth in all treatments was compared to growth on ad libidum phytoplankton
rations. Fresh particles from Laminariagroenlandica, aged particles from Agarumfimbriatum and Alariamarginata, and mixed phytoplankton promoted the highest growth rates in both consumers. Growth was inversely related to total polyphenolic
concentration in the fresh kelp particles. The increase in quality of both Agarumfimbriatum and Alariamarginata particles with age corresponded with a rapid loss of polyphenolic secondary metabolites and an increase in total nitrogen.
Received: 26 November 1996 / Accepted: 9 January 1997 相似文献
12.
Cadmium accumulation in the female shore crab Carcinus maenas during the moult cycle and ovarian maturation 总被引:2,自引:0,他引:2
The influence of moulting and ovarian maturation on cadmium accumulation in the tissues of female shore crabs Carcinus maenas exposed to 1 mg Cd l−1 in the water was investigated. Cadmium accumulation in all tissues examined was markedly increased in crabs in the postmoult
stages (A and B) compared to crabs in all other moult stages. During the moult cycle, average cadmium accumulation in the
midgut gland ranged from 29 μg Cd g−1 dw at premoult stage (D2) to 589 μg Cd g−1 dw at postmoult stage (A). Average cadmium concentrations in the haemolymph ranged from 0.56 μg Cd ml−1 at intermoult stage (C4) to 4.6 μg Cd ml−1 at postmoult stage (A), while the gills accumulated from 103 μg Cd g−1 dw in intermoult stage (C3) to 352 μg Cd g−1 dw in postmoult stage (A). Cadmium concentration in gills and haemolymph was also significantly higher in crabs in late premoult
stage (D3) compared to C4-crabs, while midgut gland cadmium concentration remained elevated in C1- and C3- intermoult stages relative to C4. During ovarian maturation the cadmium accumulation in midgut gland, gills, ovaries and haemolymph decreased. Average cadmium
concentration in the midgut gland decreased from 63 μg g−1 dw in ovarian Stage I to 19 μg g−1 dw in ovarian Stage VI. The same pattern was observed for gills, haemolymph and ovaries. The present study demonstrates that
cadmium accumulation in the female shore crab strongly depends on the physiological status of the animal. A possible association
between physiological calcium requirements and cadmium accumulation during moulting is discussed.
Received: 20 January 2000 / Accepted: 20 July 2000 相似文献
13.
One of the best-known features of diatom biology is the reduction in mean cell size during vegetative multiplication by binary
fission. We examined changes in copper toxicity and copper accumulation during cell-size reduction in Haslea ostrearia (Simonsen), a pennate diatom responsible for greening in oyster-ponds. We selected three strains with apical axes of different
lengths: 40 μm (S40), 65 μm (S65) and 85 μm (S85). Each strain was grown separately in batch culture and exposed to a range
of copper overloads (0 to 1.57 μM) that were added to the culture immediately after cell inoculation. Significant differences in sensitivity to copper were
observed among the three strains. S85 exhibited highest sensitivity, followed by S40, while S65 displayed the highest tolerance.
After 5 to 6 d exposure to 0.47 μM copper, chlorophyll a, carbohydrate, protein and lipid content per g dry weight had not changed in any of the three strains studied, except for
a decrease of 16% in chlorophyll a in S85. At the end of the growth period with 0.47 μM copper, the amount of metal per unit surface area was similar for all strains, but the quantity of intracellular copper per
g dry weight was lower in S65 cells than in S40 and S85 cells. Notable differences in the kinetics of both adsorbed and intracellular
copper were observed between S40 and S85. Our results suggest that tolerance mechanisms may change during the vegetative life
of H. ostrearia. The differential sensitivities of the strains suggest that copper pollution may alter the cell composition of natural populations
of H. ostrearia by inducing selection for smaller cell size. Since auxosporulation results in the formation of larger cells with a higher
sensitivity to copper, H. ostrearia could gradually disappear from copper-contaminated environments. In addition, by inducing smaller cell size, copper contamination
would have an impact on filter-feeders such as oysters, whose diet is largely composed of diatoms.
Received: 26 March 1999 / Accepted: 2 December 1999 相似文献
14.
Martin G. J. Löder Cédric Meunier Karen H. Wiltshire Maarten Boersma Nicole Aberle 《Marine Biology》2011,158(7):1551-1580
Mesocosm experiments coupled with dilution grazing experiments were carried out during the phytoplankton spring bloom 2009.
The interactions between phytoplankton, microzooplankton and copepods were investigated using natural plankton communities
obtained from Helgoland Roads (54°11.3′N; 7°54.0′E), North Sea. In the absence of mesozooplankton grazers, the microzooplankton
rapidly responded to different prey availabilities; this was most pronounced for ciliates such as strombidiids and strobilids.
The occurrence of ciliates was strongly dependent on specific prey and abrupt losses in their relative importance with the
disappearance of their prey were observed. Thecate and athecate dinoflagellates had a broader food spectrum and slower reaction
times compared with ciliates. In general, high microzooplankton potential grazing impacts with an average consumption of 120%
of the phytoplankton production (P
p
) were measured. Thus, the decline in phytoplankton biomass could be mainly attributed to an intense grazing by microzooplankton.
Copepods were less important phytoplankton grazers consuming on average only 47% of P
p
. Microzooplankton in turn contributed a substantial part to the copepods’ diets especially with decreasing quality of phytoplankton
food due to nutrient limitation over the course of the bloom. Copepod grazing rates exceeded microzooplankton growth, suggesting
their strong top-down control potential on microzooplankton in the field. Selective grazing by microzooplankton was an important
factor for stabilising a bloom of less-preferred diatom species in our mesocosms with specific species (Thalassiosira spp., Rhizosolenia spp. and Chaetoceros spp.) dominating the bloom. This study demonstrates the importance of microzooplankton grazers for structuring and controlling
phytoplankton spring blooms in temperate waters and the important role of copepods as top-down regulators of microzooplankton. 相似文献
15.
Effect of temperature fluctuations and food supply on the growth and metabolism of juvenile sea scallops (Placopecten magellanicus) 总被引:1,自引:0,他引:1
On the eastern shore of Nova Scotia late summer atmospheric systems cause upwelling of shelf water; the associated temperature
variations of 10 °C with a 6 to 8 d period are comparable in magnitude to the seasonal variation. A laboratory study was undertaken
to assess the effects of these temperature fluctuations on sea scallop (Placopecten magellanicus) growth and metabolism. In a factorial design, scallops were subjected to constant (10 °C) or a variable (6 to 15 °C) 8 d
temperature cycle, and either a low (seston in filtered seawater) or high (seston supplemented with cultured phytoplankton)
food diet. During the 48 d experiment scallop mortality was low and growth positive in all treatments. Shell and total tissue
growth rate did not differ between temperature treatments, but growth in the high food treatments was 40 to 50% higher than
in the low food treatments. However, soft tissue (excluding adductor) growth did show a temperature treatment effect; growth
rates were significantly higher in the fluctuating temperature treatment, due in part to greater gonad development. Weight-standardized
rates of scallop oxygen consumption (V
sO2 , μmol O2 g−1 h−1) were 20 to 25% higher in high food than in low food treatments, consistent with the expected increase in respiration due
to the higher growth rates. Scallop metabolism did not acclimate to the fluctuating temperature cycle; V
sO2 and ammonium excretion (V
sNH+
4, μmol O2 g−1 h−1) remained dependent on ambient temperature throughout the experiment. V
sNH+
4 Q10 (2.77) was higher than V
sO2 Q10 (2.01) which was reflected in a decrease in the O:N ratio at 15 °C, indicating a shift toward increased protein catabolism
and a stressed state. At 10 °C, V
sO2 and V
sNH+
4 in the variable temperature treatments were 15 to 18% lower than in the constant temperature treatments, a difference that
was not detected in growth measurements. Results demonstrate that the metabolism of Placopecten magellanicus, unlike some bivalve species, is tightly coupled to fluctuations in ambient temperature. Although an absence of compensatory
acclimation had a minimal effect on growth in this study, if high temperatures were combined with low food conditions a reduction
in scallop production could result.
Received: 23 June 1998 / Accepted: 8 February 1999 相似文献
16.
Comparison of the bioavailability of Cr and Fe bound with natural colloids of different origins and sizes to two marine bivalves 总被引:4,自引:0,他引:4
Recent studies have demonstrated the significant role of colloidal microparticles or macromolecules in the biogeochemical
cycling of trace metals in aquatic environments. In this study, the influences of different colloidal organic carbon (COC)
concentrations, colloidal sizes and colloidal origins (estuarine vs coastal) on the bioavailability of two trace metals (Cr
and Fe) to the green mussel Perna viridis and the clam Ruditapes philippinarum were examined under laboratory conditions. Natural colloids were isolated by cross-flow ultrafiltration and were radiclabeled
with 59Fe and 51Cr before being exposed to the mussels and clams. The uptake of colloid-bound Cr and Fe was compared with the uptake of low
molecular weight complexed metals (<1 kDa). Both natural colloid-bound Cr and Fe were bioavailable to the green mussels and
clams. The uptake of both colloidal Cr and Fe by the two bivalves was much higher than that of their counterparts in a low
molecular weight fraction, implying that colloidal binding enhanced considerably the bioavailability of Cr and Fe to the bivalves.
The magnitude to which Cr uptake was enhanced, due to its binding with colloids, was much greater than that of Fe. There was
no significant difference in the measured dry weight concentration factor of the metals between the two COC concentrations.
Similarly, the COC concentration did not influence metal uptake when all the experiments were considered together. There was
generally no major difference in the metal bioavailability between the two different sizes of colloids isolated from the coastal
waters (1–10 kDa and 10 kDa-0.2 μm), whereas metals bound with the larger size colloids isolated from the estuarine waters
were more bioavailable than metals bound with the smaller size colloids. The bioavailability of Cr and Fe bound with the colloids
from estuarine waters was generally lower than those bound with colloids from the coastal waters. This study demonstrated
that the geochemical properties of colloids (origin) and the chemical properties of metals are critical in affecting the bioavailability
of colloid-bound metals to marine bivalves.
Published online: 21 June 2002 相似文献
17.
An experiment under laboratory conditions was conducted to test the hypothesis that development and growth of copepodite
stages in Calanus chilensis are temperature-dependent and not subject to food shortage in the upwelling area of the Humboldt Current, northern Chile.
Field data obtained from June 1994 to May 1995 in Bahía Mejillones (23°S) were used to define four combinations of temperature
and food under which copepodites were reared from Stage CIII to adulthood. The high temperature was 18.1 °C and the low temperature
13.1 °C, whereas the high food level was in the range of 6.8 to 24.8 μg l−1 chlorophyll a and the low level 1.0 to 6.8 μg l−1 chlorophyll a. As food a mixture of three unknown species of phytoflagellates and the diatom Navicula cryptocephala was used. This phytoplankton was initially obtained from the same sampling sites as copepods and kept in f/2 media at stable levels and composition throughout the experiment. The development rate (1/t), estimated from the time (t) elapsing between Stage CIV and adult, was significantly affected by both temperature and food, although low-food effects
were much more remarkable. Low-food conditions also significantly reduced body length and “structural” (lipid-discounted)
body mass at adulthood, while temperature only affected body length. The weight-specific growth rate was also affected by
food and temperature, but again food effects were much more drastic. The results indicate that C. chilensis is a highly sensitive species to lack of food, and is possibly subject to food shortage during its annual cycle in the coastal
upwelling area of northern Chile. Food limitation may help explain the seasonal pattern of adult size reported by previous
studies in the area and the lack of consistence between the number of generations predictable from a temperature-dependent
model and that observed in the field during the annual cycle.
Received: 10 September 1996 / Accepted: 29 October 1996 相似文献
18.
A key regulatory mechanism underlying the switch between aerobic and anaerobic metabolism amongst anoxia-tolerant marine
molluscs is reversible protein phosphorylation. To assess the role of cAMP-dependent protein kinase (PKA) in aerobic–anaerobic
transitions, the effects of anoxia on the activity and subcellular distribution of PKA were assessed in foot and hepatopancreas
of the marine periwinkle, Littorina littorea. Exposure to N2 gas at 5 °C caused a rapid decline in the percentage of total enzyme present as the free catalytic subunit (PKAc) in both
tissues; the percentage of PKAc fell from ∼30% in controls to 3% after 1 h anoxia and remained low over 72 h. Total PKA also
fell by 30% after 72 h anoxia in hepatopancreas but rebounded during aerobic recovery. Freezing at −8 °C elicited parallel
results for both percentage of PKAc and total PKA, suggesting that PKA responses to freezing were stimulated by the ischemia
that develops when hemolymph freezes. Anoxia also led to a shift in PKA subcellular distribution in hepatopancreas (but not
in foot), the percentage of total PKA activity associated with the nuclear fraction dropping from 25% in controls to 8% in
12 h anoxic snails with opposite changes in the cytosolic fraction. The catalytic subunit (PKAc) of foot PKA was purified
to a final specific activity of 63.5 nmol phosphate transferred per minute per milligram protein. Enzyme properties included
a molecular weight of 33 to 35 kDa, an activation energy from Arrhenius plots of 65.1 ± 4.8 kJ mol−1, and substrate affinity constants of 151 ± 6 μM for the phosphate acceptor, Kemptide, and 72 ± 9 μM for Mg.ATP. Activity was strongly reduced by mammalian PKA inhibitors (H-89, PKA-I), by neutral chloride salts (I50 values 165 to 210 mM) and by NaF (I50 62 mM). Reduced PKA activity under anoxic or freezing conditions would facilitate the observed suppression of the activities of
numerous enzymes that are typically PKA-activated and thereby contribute to the overall anoxia-induced metabolic rate depression.
Received: 19 November 1997 / Accepted: 30 September 1998 相似文献
19.
In late summer (Antiprod I cruise, March 1977), antarctic waters of the southern part of the Indian Ocean contain low amounts of dissolved Vitamin B12: 1 ng l-1 on average. However, higher concentrations were recorded in two areas: in the subantarctic convergence zone and between 50° and 57°S, with values greater than 3,5 ng l-1. Despite nutrient-rich waters, primary production was low and the phytoplankton sparse. Abundance of diatoms was related, to a certain extent, to the concentration of Vitamin B12. An experimental approach (Antiprod II cruise, February and March 1980) was applied to (1) artificially enriched natural sea water, and (2) cultures of two diatom species isolated from antarctic waters, Nitzschia turgiduloides and Chaetoceros sp. The experiments demonstrated that antarctic diatoms in general do not require any of the three investigated vitamins for growth. However, Vitamin B12 has a slightly stimulating effect on growth. This may explain the observed relation between phytoplankton density and vitamin concentration in the Antarctic Ocean. This experimental approach elucidates the minor role of vitamins in the primary production of antarctic waters and provides indirect evidence of the major importance of turbulence as a limiting factor. 相似文献
20.
Cell growth of a coastal marine diatom, Phaeodactylum tricornutum (stock cultures), and two red tide marine flagellates, Heterosigma akashiwo and Gymnodinium mikimotoi (stock cultures), in the presence of soluble chelated Fe(III)-EDTA (1:2) and of four different phases of ferric oxide colloids were experimentally measured in culture experiments at 20°C under 3000 lux fluorescent light. Soluble Fe(III)-EDTA induced the maximal growth rates and cell yields. The short-term uptake rate of iron by H. akashiwo in Fe(III)-EDTA medium was about eight times faster than that in solid amorphous hydrous ferric oxide (Fe2O3·xH2O) medium. In culture experiments supplied with four different ferric oxide forms, the orders of cell yields are amorphous hydrous ferric oxide>-FeOOH (lepidocrocite)>Fe5O7(OH)·4H2O (hydrated ferric oxyhydroxide polymer >-FeOOH (goethite). The specific growth rates () at logarithmic growth phase in Fe(III)-EDTA, amorphous hydrous ferric oxide and -FeOOH media were significantly greater than those in Fe5O7 (OH)·4H2O and -FeOOH media. The thermodynamically stable forms such as Fe5O7(OH)·4H2O and -FeOOH supported a little or no phytoplankton growth. The iron solublities and/or proton-promoted iron dissolution rates of these colloidal ferric oxides in seawater at 20°C were determined by simple filtration techniques involving -activity measurements of 59Fe. The orders of solubilities and estimated dissolution rate constants of these ferric oxides in seawater were consistent with that of cell yields in the culture experiments. These results suggest that the availability of colloidal iron to provide a source of iron for phytoplankton is related to the thermodynamic stability and kinetic lability of the colloidal ferric oxide phases, which probably control the uptake rate of iron by phytoplankton. 相似文献