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1.
The role of ambient and enhanced ultraviolet-B radiation (UVB; 280 to 315 nm) in a natural sand-associated microbenthic community
was studied in a 3-week experiment by incubating intact sediment cores from a shallow bay in an outdoor flow-through system
with 27 aquaria. After sampling of initial cores, the remaining cores (one per aquarium) were given one of three treatments:
no, ambient, and moderately enhanced UVB, and sampled, nine at a time, after 5, 12, and 19 d. The response of the community
was studied by analysing algal and meiofaunal composition and biomass, chlorophyll a content, composition of pigments and fatty acids, and content of UV-absorbing compounds (state variables), as well as carbon
fixation and allocation, and bacterial productivity (rate variables). Among rate variables, significant effects of UVB-treatments
were found for carbon fixation and allocation, while bacterial productivity was not affected. For state variables, a significant
response was observed for the composition of microalgae and fatty acids, and for chlorophyll a content. The effect of treatments was mainly observed as differences in development with time (two-way analysis of variance,
treatment × time interaction). Towards the end of the experiment, the no-UVB treatment most often differed from one or both
of the two treatments with UVB exposure, the latter showing lower values. There were marked successional changes in the community,
irrespective of treatment. The microalgal community changed from being dominated by coccoid cyanobacteria and epipsammic diatoms
to a dominance of epipelic diatoms and filamentous cyanobacteria. The pattern of carbon allocation, as well as an increased
C/N ratio of the sediment, suggested limitation of growth, perhaps by nutrients, at the end of the experiment. This may possibly
have acted synergistically with UVB exposure to create the treatment effects. The new knowledge gained from our experiment
is that ambient UVB can exert a stress on the function of sand-associated microbenthic communities in shallow waters and that
this effect coincides with structural differences in the community. More experiments in natural or semi-natural systems are
needed to allow better prediction of microbenthic community-level responses to UVB.
Received: 11 November 1997 / Accepted: 12 June 1998 相似文献
2.
Frederico P. Brandini Eduardo T. da Silva Franciane M. Pellizzari Alessandra L. O. Fonseca Luciano F. Fernandes 《Marine Biology》2001,138(1):163-171
Production rates, chlorophyll concentrations and general composition of periphytic diatom communities growing on glass slides
were studied in relation to environmental parameters during one seasonal cycle in the Bay of Paranaguá, southern Brazil. Slides
were routinely submersed at 1, 2 and 3 m depth and recovered weekly for microscopic examinations, analyses of chlorophyll,
cell counts and in situ photosynthetic incubations using the Winkler titration method. Water samples were also collected at
surface and bottom layers for determinations of temperature, salinity, nutrients and chlorophyll in the water. The periphytic
community was mainly formed by epipelic and epipsammic species, dominated by Navicula phyllepta, Cylindrotheca closterium, Navicula spp. and Amphora sp. Weekly chlorophyll a and cell accumulations on slides varied from <1–32 mg m−2 and up to 31 × 108 cells m−2, respectively. Photosynthetic rates varied from <1 to 35 mg oxygen mg chlorophyll a
−1 h−1, with higher values in summer. Daily production varied from 5 to 3,600 mg oxygen m−2 day−1 (<0.01–1.4 g carbon m−2 day−1). Multiple regression analysis revealed that vertical differences in light conditions and grazing pressure jointly affected
the influence of temperature on the seasonal patterns of cell densities and chlorophyll concentrations according to depth.
Received: 27 April 2000 / Accepted: 16 August 2000 相似文献
3.
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
4.
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
5.
The distribution and abundance of transparent exopolymer particles (TEP) was determined in and below pack ice of the Laptev
Sea from July to September 1995. Samples were collected from the lowermost 10 cm of ice floes and at 10 cm below the ice–water
interface. Abundance of bacteria, protists and TEP was determined, and the sea ice–water boundary layer was characterized
using temperature, salinity and molecular viscous shear stress. TEP, with a distinct size distribution signal, were found
in highest concentrations inside the sea ice, ranging from not detectable to 16 cm2 l−1 (median: 2.9 cm2 l−1). In the water, concentrations were one order of magnitude lower, ranged from below detection to 2.7 cm2 l−1 (median: 0.2 cm2 l−1) and decreased after the middle of August, whereas abundances of autotrophic flagellates (AF), diatoms, heterotrophic flagellates
(HF) and ciliates increased. The abundance of TEP decreased with its size in all samples following a power law relationship.
The relation of TEP to the microbial community differed between the sea ice and water, being positively correlated with bacteria
and diatoms in the ice and negatively correlated with HF in the sea water. The presence of a pycnocline significantly influenced
the abundance of organisms, diatom composition and TEP concentrations. Pennate diatoms dominated by Nitzschia frigida were most abundant inside the ice. Though bacteria have the potential to produce exopolymeric substances (EPS), the results
of this study indicate that the majority of TEP at the ice–water interface in first-year Arctic summer pack ice are produced
by diatoms.
Received: 19 August 1999 / Accepted: 4 July 2000 相似文献
6.
Laboratory culture experiments were performed to study the changes in size-fractionated Fe concentrations during the growth
of the oceanic diatom Chaetoceros sp. Fe concentration was estimated for three size fractions: large labile particles (>0.2 μm), small colloidal particles
(0.2 μm to 200 kDa) and soluble species (<200 kDa). The size-fractionated Fe concentration in the nutrient-enriched filtered
seawater medium without diatom cells became stable within 4 d after the spike of FeCl3 solution. Light irradiation by white fluorescent tubes with a 14 h light:10 h dark cycle did not significantly alter concentrations
of the size-fractionated Fe. For the phytoplankton culture experiment, Fe-starved diatom cells were inoculated into the nutrient-enriched
media aged for 19 d after the addition of FeCl3. With the growth of diatom cells, total acid-labile Fe concentrations decreased from 0.60 to 0.46 nM during 7 d of incubation. However, only the concentration of the small colloidal particles showed a significant decrease;
the concentration of the other size fractions remained relatively constant. Although the media still contained sufficient
amounts Fe as large labile particles and soluble species, diatom cells appeared to be Fe-limited once Fe as small colloidal
particles had been used up. These results suggest that Fe in the small colloidal particle fraction was the most dynamic size
fraction during the growth of the diatom Chaetoceros sp. In addition, to better understand Fe dynamics in the ocean, we must consider the influence of phytoplankton growth on
small colloidal Fe [which is typically included in the dissolved Fe fraction (<0.2 μm)].
Received: 9 December 1999 / Accepted: 5 May 2000 相似文献
7.
Short-term effects of temperature and irradiance on oxygenic photosynthesis and O2 consumption in a hypersaline cyanobacterial mat were investigated with O2 microsensors in a laboratory. The effect of temperature on O2 fluxes across the mat–water interface was studied in the dark and at a saturating high surface irradiance (2162 μmol photons
m−2 s−1) in the temperature range from 15 to 45 °C. Areal rates of dark O2 consumption increased almost linearly with temperature. The apparent activation energy of 18 kJ mol−1 and the corresponding Q
10 value (25 to 35 °C) of 1.3 indicated a relative low temperature dependence of dark O2 consumption due to mass transfer limitations imposed by the diffusive boundary layer at all temperatures. Areal rates of
net photosynthesis increased with temperature up to 40 °C and exhibited a Q
10 value (20 to 30 °C) of 2.8. Both O2 dynamics and rates of gross photosynthesis at the mat surface increased with temperature up to 40 °C, with the most pronounced
increase of gross photosynthesis at the mat surface between 25 and 35 °C (Q
10 of 3.1). In another mat sample, measurements at increasing surface irradiances (0 to 2319 μmol photons m−2 s−1) were performed at 25, 33 (the in situ temperature) and 40 °C. At all temperatures, areal rates of gross photosynthesis saturated
with no significant reduction due to photoinhibition at high irradiances. The initial slope and the onset of saturation (E
k = 148 to 185 μmol photons m−2 s−1) estimated from P versus E
d curves showed no clear trend with temperature, while maximal photosynthesis increased with temperature. Gross photosynthesis
was stimulated by temperature at each irradiance except at the lowest irradiance of 54 μmol photons m−2 s−1, where oxygenic gross photosynthesis and also the thickness of the photic zone was significantly reduced at 40 °C. The compensation
irradiance increased with temperature, from 32 μmol photons m−2 s−1 at 25 °C to 77 μmol photons m−2 s−1 at 40 °C, due to increased rates of O2 consumption relative to gross photosynthesis. Areal rates of O2 consumption in the illuminated mat were higher than dark O2 consumption at corresponding temperatures, due to an increasing O2 consumption in the photic zone with increasing irradiance. Both light and temperature enhanced the internal O2 cycling within hypersaline cyanobacterial mats.
Received: 30 November 1999 / Accepted: 11 April 2000 相似文献
8.
A series of experiments investigated the potential role of microbial mats in nutrition of the early settlement stages of Penaeus semisulcatus. From 3 days post-metamorphosis, the microbial mat supported high growth and survival rates in postlarvae, equivalent to
that supported by a control diet of Artemia nauplii and mussel. Examination of gut contents indicated that benthic postlarvae feed indiscriminately on the microbial
mat. However, when postlarvae were fed separated size-fractions of the microbial mat, only the fraction containing a high
concentration of infauna (mainly nematodes) was able to support the same growth as intact microbial mat. This appears to be
due to the low nitrogen content (0.4–0.9 mmol g−1) of the various size-fractions, compared to that of infauna (4.0 mmol g−1). The stable isotope composition of the dietary size-fractions and postlarval shrimp tissue supports the hypothesis that
the shrimp assimilated C and N primarily from the associated infauna. This may be due to selective feeding that is not apparent
from stomach contents, due to rapid digestion of fauna soft tissues, or to differential assimilation of infaunal prey relative
to other microbial mat components. The results demonstrate that microbial mats may support survival and growth in early-stage
penaeid shrimp postlarvae on intertidal mud flats. 相似文献
9.
Potential dietary effects on the fatty acid composition of the common jellyfish Aurelia aurita 总被引:2,自引:0,他引:2
Fatty acid composition of the natural and aquarium-reared common jellyfish Aurelia aurita was investigated. Fatty acid composition of the aquarium-reared A. aurita clearly reflected that of the diet, brine shrimp (Artemia). In the same way, fatty acid composition of the natural A. aurita was assumed to reflect those of natural diets. Samples of natural A. aurita were collected from April 1995 to September 1995 in the Seto Inland Sea, Japan, and their fatty acids were analyzed by gas
chromatography and mass spectrometry. Variation of fatty acid compositions was seasonal rather than dependent on body size.
Two major seasonal groups were divided by the cluster analysis of the A. aurita fatty acid composition: the April–June and the August–September clusters. The April–June cluster was characterized by high
contents of the (n − 3)-fatty acids of diatom origin, accumulated via the grazing food chain. By contrast, the August–September cluster was
characterized by an increase in (n − 6)-fatty acids of macroalgal origin, probably transferred via the detritus food chain. These results suggest that the diet
of natural A. aurita may shift between the diatom-based food chain and the detritus-based food chain.
Received: 12 April 2000 / Accepted: 1 December 2000 相似文献
10.
C. H. McKenzie D. Deibel R. J. Thompson B. A. MacDonald R. W. Penney 《Marine Biology》1997,129(3):407-416
Water samples from six bays were taken over a 5-year period (1988 to 1992) to determine the distribution and abundance of
loricate choanoflagellates in coastal Newfoundland, and to assess the impact that these organisms might have on this cold
ocean food web. Scanning electron microscopy was used to study the morphology of these flagellates, allowing us to identify
11 species of loricate choanoflagellates. Parvicorbicula socialis (Meunier) Deflandre was the most abundant species (80 × 103 cells l−1), particularly during the spring diatom bloom. Single-cell species, such as Bicosta spini fera (Throndsen) Leadbeater and Calliacantha natans (Grontved) Leadbeater, were found more commonly after the spring diatom bloom in the summer months. Many of the single-cell
choanoflagellates were attached to bacteria-rich microaggregates and debris in the water column and in unpoisoned sediment
traps. The P. socialis cell flux was calculated to be 5.3 × 106 cells m−2 d−1 in late May sediment traps. P. socialis in the upper 100 m of the water column was removing 0.3% of the standing crop of bacteria each day (April/May), and the equivalent
of 7.4% of the daily bacterial production over the water column. Diel studies of P. socialis in Conception Bay suggest that the sharp decline in population numbers observed in midnight samples may be related to the
high number of grazing zooplankton observed during the same period. Pelagic tunicate and zooplankton fecal pellets were found
to contain large numbers of choanoflagellate costae, thus providing a direct link from the microbial loop to the macrozooplankton.
Received: 17 March 1997 / Accepted: 9 May 1997 相似文献
11.
Comparison of herbivory in the closely-related marine fish genera Girella and Kyphosus 总被引:2,自引:0,他引:2
Specimens of the nominally herbivorous, closely-related, fish genera Girella and Kyphosus were collected from Australian waters in 1994 and 1995. The diet of three Girella species (G. cyanea, G. elevata, and G. tricuspidata) consisted mainly of chlorophytes and rhodophytes, with an animal component of␣15.9 ± 4.2% in G. tricuspidata. The diet of four species of Kyphosus (K. bigibbus, K. cinerascens, K. sydneyanus, and K. vaigiensis) included phaeophytes, chlorophytes and rhodophytes, and almost no animal material. Concentration of total short-chain fatty
acids in the posterior intestine was <11.4 mM in the Girella spp. and >39.2 mM in the Kyphosus spp. These results suggest that microbial fermentation plays a role in algal digestion in Kyphosus spp., but not in Girella spp. Girellids and kyphosids appear to function quite differently as herbivores. Girellids should be considered as omnivores
that complement readily-available energy from algae with protein from invertebrates. Kyphosids appear to be strict herbivores
that can derive adequate nutrition from algae poor in easily assimilable energy, through microbial fermentation in the hindgut.
Received: 8 July 1996 / Accepted: 2 August 1996 相似文献
12.
The production dynamics and carbon balance of Thalassia testudinum in the lower Laguna Madre, Texas, USA, were examined during the 1995 summer period based on in situ photosynthesis vs irradiance
(PI) measurements and continuous measurements of underwater photon-flux density (PFD). The validity of applying the H
sat model, used to calculate production for Zostera marina as the product of the maximum rate of photosynthesis (P
max) and daily hours of saturating irradiance (H
sat) was assessed for T. testudinum by comparison with integrated production estimates derived through numerical integration. Gross integrated production values
were combined with dark-respiration measurements of photosynthetic (PS) and non-photosynthetic (NPS) tissues and areal biomass
to generate daily whole-plant carbon balance. Production and whole-plant carbon balance are discussed in relation to surface
and underwater PFD measurements, biomass and other physical and chemical parameters collected during a 1 yr period from January
to December 1995. The H
sat model significantly underestimated production during all summer months, averaging 70% of integrated production over the entire
study period. Gross integrated production ranged between 11.5 mg C g−1 leaf dry wt d−1 in June (during a period of unseasonably low PFDs caused by a drift-alga mat covering the seagrass bed) to 26.7 mg C g−1 leaf dry wt d−1 in July. Modeled net carbon gain was highest in July at 454 mg C m−2 d−1 (1.4 g dry wt m−2 d−1), sufficient to account for measured rates of leaf production in the study area and representative of T. testudinum populations of low productivity. During part of the summer period, however, the population was in negative carbon balance.
The relatively low productivity of this population and the periods of negative carbon balance are attributed to low net photosynthesis:dark
respiration (P
net:R
d) ratios, sporadic low-light periods, the small fraction of PS tissue relative to whole-plant biomass (5 to 13%) and nutrient
limitation. Production models are sensitive to both light availability and the proportion of PS tissue supporting NPS biomass
as reflected in whole-plant P
net:R
d ratios.
Received: 13 August 1997 / Accepted: 6 March 1998 相似文献
13.
We studied benthic harpacticoid grazing on diatom algae from two sites on the White Sea intertidal sandflat. Diatoms from sediments and from harpacticoid gut contents were sampled in situ, identified and counted, and grazing rates were calculated by two ways: (1) using potential daily ration estimations and (2) from the gut content and gut-residence time data. Paraleptastacus kliei did not contain any diatoms in the guts and presumably fed on other objects (bacteria or flagellates). Two other dominating species studied, Heterolaophonte minuta and Huntemannia jadensis, contained an average of 604 and 222 diatom cells per specimen. Diet composition differed significantly from the natural algal community. Two diatoms of intermediate cell size (Nitzschia palea var. debilis and Navicula sp.) contributed 92–97% of gut content for H. minuta and 58–81% for Hn. jadensis, whereas these diatoms amounted to only about 10% of biomass in native community. Mean consumption rates were estimated as 50–200 μg of wet biomass/day/cm2, so the harpacticoids grazed only between 3 and 11% of the total microalgae biomass per day. The grazing impact on the two preferred diatom populations, however, was much more intensive, 10–30% per day for Navicula sp. and 55–228% for N. palea. Therefore, native harpacticoid populations demonstrate highly selective feeding and could be strongly limited by their food in spite of seemingly plentiful total abundance of microphytobenthos. This disproportionally high grazing pressure upon some species apparently could affect the structure of microalgae communities resulting in low relative abundance of mid-sized forms. We hypothesize that a very dynamic spatio-temporal distribution of epibenthic harpacticoids (short-living micropatches) may be the possible adaptation to such local food limitation. 相似文献
14.
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
15.
Abundance and temporal distribution of viable (able to germinate) resting stage cells of planktonic diatoms in bottom sediments
have been investigated almost monthly during 1989 to 1992 in Hiroshima Bay, western part of Seto Inland Sea, Japan. The abundance
of viable resting stages in bottom sediments was enumerated with the extinction dilution method (most probable number method,
MPN). In bottom sediments of Hiroshima Bay, dominantly distributed species and/ or genera of the diatom resting stages were
Skeletonema costatum, Chaetoceros spp. and Thalassiosira spp. Viable resting stages of these diatoms were densely distributed on the orders of 103 to 106 (MPN g−1 wet sediments), and persisted in bottom sediments throughout the investigation period. Conversely, vegetative cells of these
diatoms fluctuated remarkably in the water column and disappeared sporadically. Survival of the resting stages in a collected
sediment sample was also determined with the MPN method, at different storage temperatures (5, 10, 15, 20, 25 °C). The survival
test demonstrated that the diatom resting stages could survive in the dark for several months or years in sediments. Resting
stages survived longer at the lower storage temperature, and the order of longevity was consistent within three diatoms (Chaetoceros spp. > Thalassiosira spp. > S. costatum) at each storage temperature. The present study suggests that these diatom resting stages in the coastal bottom sediments
could serve as a “seed bank”, analogous to those of terrestrial plants. The seed bank would ensure the survival of diatoms
within highly fluctuating coastal environments, while it would also be the source of sporadic and autochthonous diatom blooms
in coastal waters.
Received: 29 November 1996 / Accepted: 16 December 1996 相似文献
16.
To elucidate the effects of temperature and algal cell concentration on pumping of water in the ascidian Ciona intestinalis a number of different experiments were performed. Beat frequency of the lateral cilia in the openings of the branchial sac
was measured in intact specimens using a microprojection objective and a monochrome CCD video camera. At constant low algal
cell concentration, beat frequencies increased linearly with temperature from 4.0 Hz (±0.5) at 7.4 °C to 13.6 Hz (±1.6) at
20.1 °C. At a constant temperature of 15 °C, beat frequency decreased with increasing algal cell concentration from approximately
3000 to >10 000 Rhodomonas sp. cells ml−1. The decrease was observed both in experiments where the ascidians had been acclimated to a fixed algal cell concentration
and in experiments with changing concentrations. Effect of algal cell concentration on squirting/siphon closure and flow velocity
in the exhalent siphon was measured using a thermistor. At low algal cell concentrations, flow velocity in the exhalent siphon
was stable, apart from a few short squirts. At very high algal cell concentrations, the flow velocity was reduced and much
less stable, with prolonged squirting. The effect of gut content on filtration was studied in experiments with specimens acclimated
to high algal cell concentrations. Results showed a close relation between gut clearance and filtration rate. From the experimental
results and a qualitative analysis of the Ciona-pump it was concluded that the ciliary beat frequency is proportional to the water flow through the sea squirt and that changes
in pumping caused by temperature or algal cell concentration are under nervous control or governed by enzyme kinetics, rather
than being a result of physico-mechanical properties, i.e. pump efficiency versus flow resistance, of the ascidian pump.
Received: 6 October 1997 / Accepted: 8 October 1998 相似文献
17.
Throughout its geographic range, the temperate-zone anemone Anthopleura elegantissima is the host of one or both of two distinctively different symbiotic microalgae: a dinoflagellate Symbiodinium (zooxanthellae, ZX) and a chlorophyte (zoochlorellae, ZC). Given the broad vertical intertidal and latitudinal range of this
anemone, we investigated the role of temperature in determining whether A. elegantissima supports one algal symbiont over the other and whether temperature regulates the observed distributions of natural populations
of ZX and ZC. Temperature appears to be a key factor in regulating both the photophysiology and metabolism of this algal–cnidarian
association. In anemones containing ZX, neither algal densities nor chlorophyll content varied with temperature (6–24 °C);
in contrast, anemones with ZC displayed reduced densities and chlorophyll content at the highest temperature treatment (24 °C).
Both ZX and ZC photosynthetic rates were directly related to temperature, as were anemone respiration rates. The higher photosynthetic
rates, maintenance of a stable algal density and chlorophyll content, and higher potential contribution of algal carbon toward
animal respiration (CZAR) suggest that the ZX are the more viable symbiont as temperature increases, but we suggest alternative
reasons why ZC are preserved in this symbiotic association. Elevated temperatures reduce ZC densities and chlorophyll, suggesting
that higher temperatures affect this relationship in a negative fashion, presumably due to a higher cost of maintaining ZC
by the association; alternatively, these costs may be affiliated with the deterioration of the ZC themselves. These results
suggest that temperature may be one of the most significant environmental parameters that sets the intertidal microhabitat
and latitudinal distribution patterns of the two algal taxa observed in the field.
Received: 2 November 1998 / Accepted: 25 October 2000 相似文献
18.
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
19.
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
20.
A. Sakka Hlaili B. Grami Hassine Hadj Mabrouk M. Gosselin D. Hamel 《Marine Biology》2007,151(2):767-783
Phytoplankton growth and microzooplankton grazing were investigated in the restricted Bizerte Lagoon in 2002 and 2004. The
2002 study, carried out at one station from January to October, showed significant seasonal variations in phytoplankton dynamics.
High growth rates (0.9–1.04 day−1), chlorophyll a (Chl a) concentrations (6.6–6.8 μg l−1) and carbon biomass (392–398 μg C l−1) were recorded in summer (July), when several chain-forming diatoms had intensively proliferated and dominated the carbon
biomass (74%). In 2004, four stations were studied during July, a period also characterized by the high proliferation of several
diatoms that made up 70% of the algal carbon biomass. In 2004, growth rates (0.34–0.45 day−1) and biomass of algae (2.9–5.4 μg Chl a l−1 and 209–260 μg C l−1) were low, which may be related to the lower nutrient concentrations recorded in 2004. Microzooplankton >5 μm were mainly
composed of heterotrophic dinoflagellates and ciliates. Microzooplankton biomass peaked during summer (2002 320–329, 2004
246–361 μg C l−1), in response to the enhanced phytoplankton biomass and production. The grazer biomass was dominated by ciliates (71–76%)
in July 2002 and by heterotrophic dinoflagellates (52–67%) in July 2004. Throughout the year and at different stations, microzooplankton
grazed actively on phytoplankton, removing 26–58% of the Chl a and 57-84% of the primary production. In 2002, the highest grazing impact was observed on the large algae (>10 μm) during
the period of diatom dominance. These results have a significant implication for carbon export to depth. Indeed, the recycling
of most of the diatom production by the microbial food web in the upper water column would reduce the flux of material to
the seafloor. This should be considered when modeling the carbon cycling in coastal environments and under conditions of diatom
dominance. During both studies, ciliates had higher growth rates (0.5–1.5 day−1) and a higher carbon demand (165–470 μg C l−1 day−1) than dinoflagellates (0.1–0.5 day−1, 33–290 μg C l−1 day−1). Moreover, when grazer biomass was dominated by ciliates (in July 2002), herbivory accounted for 71–80% of the C ingested
by microzooplankton while it accounted only for 14–23% when dinoflagellates dominated the grazer biomass (in July 2004). These
results suggest that, in contrast to findings from open coastal waters, ciliate species of the restricted Bizerte Lagoon were
more vigorous grazers of the large algae (diatoms) than were dinoflagellates. 相似文献