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1.
Nutrients were added separately and combined to an initial concentration of 10 μM (ammonium) and/or 2 μM (phosphate) in a series of experiments carried out with the giant clam Tridacna maxima at 12 microatolls in One Tree Island lagoon, Great Barrier Reef, Australia (ENCORE Project). These nutrient concentrations
remained for 2 to 3 h before returning to natural levels. The additions were made every low tide (twice per day) over 13 and
12 mo periods for the first and second phase of the experiment, respectively. The nutrients did not change the wet tissue
weight of the clams, host C:N ratio, protein content of the mantle, calcification rates or growth rates. However, ammonium
(N) enrichment alone significantly increased the total population density of the algal symbiont (Symbiodinium sp.: C = 3.6 · 108 cell clam−1, N = 6.6 · 108 cell clam−1, P = 5.7 · 108 cell clam−1, N + P = 5.7 · 108 cell clam−1; and C = 4.1 · 108 cell clam−1, N = 5.1 · 108 cell clam−1, P = 4.7 · 108 cell clam−1, N + P = 4.5 · 108 cell clam−1, at the end of the first and second phases of the experiment, respectively), although no differences in the mitotic index
of these populations were detected. The total chlorophyll a (chl a) content per clam but not chlorophyll a per cell also increased with ammonium addition (C = 7.0 mg chl a clam−1, N = 13.1 mg chl a clam−1, P = 12.9 mg chl a clam−1, N + P = 11.8 mg chl a clam−1; and C = 8.8 mg chl a clam−1, N = 12.8 mg chl a clam−1; P = 11.2 mg chl a clam−1, N + P = 11.3 mg chl a clam−1, at the end of the first and second phases of the experiment, respectively). The response of clams to nutrient enrichment
was quantitatively small, but indicated that small changes in inorganic nutrient levels affect the clam–zooxanthellae association.
Received: 2 June 1997 / Accepted: 9 June 1997 相似文献
2.
Deposit-feeders can respond to seasonal fluctuations in food concentration both functionally (e.g. by adjusting feeding rates)
and physiologically (e.g. by changing the concentration of bacteriolytic agents in gut fluids). Laboratory feeding experiments
were carried out (11 to 21 July 1997) with the arenicolid polychaete worm Abarenicola pacifica (Healy and Wells). Objectives were to test for separate and interactive effects of sediment food concentration and temperature
(6, 11, and 16 °C) on deposit-feeder functional (feeding rates) and physiological (bacteriolytic activity of gut fluids) responses.
Food concentration was varied experimentally using sieved (1 mm) natural sediments (Md φ=2.00; 0.6% organic) mixed with combusted
(500 °C, 8 h) sediments for final concentrations of 25, 50, and 100% natural sediment. Sediment food quality was measured
as: (1) bioavailable amino acids (EHAA), (2) chlorophyll a (chl a), and (3) bacterial abundance. Feeding rates were inferred from egestion rates (ER, g h−1) and analyzed with respect to worm size. Bacteriolytic activity of midgut fluids was assayed turbidimetrically against two
bacterial isolates, after worms had fed on experimental sediments for 15 d. Temperature and food concentration both significantly
affected feeding rates, with maxima occurring at 50 and 100% natural sediment mixtures, and at high (16 °C) temperature. ER
was positively, but not significantly correlated with EHAA and chl a; a positive, significant correlation was detected between ER and sediment bacterial abundance. Overall, functional responses
agreed with earlier compensatory intake models for deposit-feeders. However, the size and direction of these responses was
temperature-sensitive, suggesting that these models need to be adjusted for changes in absorption rates. No effects of ambient
temperature or food concentration on bacteriolytic rates were observed, possibly due to compensatory mechanisms or the presence
of multiple bacteriolytic agents in gut fluids.
Received: 28 June 1999 / Accepted: 14 March 2000 相似文献
3.
Olivier Maire Jean-Michel Amouroux Jean-Claude Duchêne Antoine Grémare 《Marine Biology》2007,152(6):1293-1307
The filtration activity of the Mediterranean mussel, Mytilus galloprovincialis, was assessed under different concentrations and compositions of seston by using a new automated image acquisition and analysis
system. This approach allowed for frequent and simultaneous measurements of valve gape and exhalant siphon area. Filtration
rates were measured through clearance measurements whereas pumping rates were measured using hot-film probes. The average
filtration rate (17.5 l g h−1 DW−1 for a 0.36 g DW mussel) recorded during the present study was higher than those available for Mytilus edulis when standardized to flesh dry weight but almost equivalent (17.5 l h−1 g DW−1 for a 53 mm shell length mussel) to those rates when standardized to shell length. Immediately after the addition of algal
cells (Isochrysis galbana; 4.5 μm in size), valve gape, exhalant siphon area and filtration rate increased quickly as mussels reached their maximum
filtration activity. These three parameters then gradually decreased until complete closure of the shell. The algal cell concentration
inducing this transition was close to 800 cells ml−1 and 0.5 μg Chl a l−1. When algal concentration was maintained above this threshold by successive algal additions, both valve gape and exhalant
siphon area remained maximal. Temporal changes in the exhalant siphon area were continuous as opposed to those of valve gape.
Therefore, despite the significant correlation between these two parameters, valves and siphon were sometimes dissociated
due to a reduction of the area or even a closure of the exhalant siphon while the valves remained open. The velocity of exhaled
water tended to be constant irrespective of exhalant siphon area and thus pumping rates were a linear function of exhalant
siphon area. Consequently, reductions in exhalant siphon area and pumping rate were almost similar in M. galloprovincialis. Our results thus clearly support the hypothesis that exhalant siphon area constitutes a better proxy of pumping rate than
valve gape as already suggested for Mytilus edulis. Finally, the high filtration rates measured during the present study together with the high concentrations of inorganic
matter (> 40 mg DW l−1) requested to alter those rates suggest that the studied mussels were well adapted to oligotrophic waters featuring strong
hydrodynamism and frequent sediment resuspension events. 相似文献
4.
To assess the effects of both temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis (O.F. Müller), individuals collected December 1996 (winter experiment) and June 1997 (summer experiment) were maintained
for 3 months in one of four experimental treatments: (1) 3 °C and fed ad libitum (high ration), (2) 3 °C and fed one-seventh of the maximum ration (low ration), and (3) 12 °C and fed the high ration; (4) 12 °C and fed
the low ration. All individuals were fed an artificial diet and exposed to only 1 h of light every day. At the end of both
experiments, mean gonad indices of sea urchins fed the high ration had increased significantly (11–24% and 6–19% in the winter
and summer experiments, respectively), while the gonad indices of individuals fed the low ration did not change. At the high
ration (both experiments), the increase in gonad index of sea urchins occurred primarily as the result of a significant increase
in the mass of nutritive phagocytes, as revealed by histological analyses. Primary oocytes were significantly larger in individuals
held at 3 °C than at 12 °C throughout the winter experiment, regardless of food ration; during the summer experiment, primary
oocytes were significantly larger in individuals receiving the high ration, regardless of the temperature at which they were
held. These results suggest that: (1) food availability is the most important factor regulating energy storage and the relative
size of gonads throughout the year, (2) temperature affects the rate of growth and maturation of primary oocytes during the
later stages of oogenesis, and (3) once gametogenesis has been initiated, mature ova will be produced, even under conditions
of low food availability. Conditions of high food availability in summer and low temperature in winter would thus favor reproductive
output in sea urchin populations.
Received: 1 March 2000 / Accepted: 4 October 2000 相似文献
5.
The accumulation of lipofuscin, which is an indictor of physiological age, in the brain of juvenile European lobster (Homarus gammarus L.) was monitored for 22 mo in three experimental temperature regimes that simulated seasonal variation in temperature in
the geographic range of this species. Metabolic rate responses to changes in temperature were estimated by measuring the activity
of the electron transport system (ETS) in muscle tissue and in vivo rates of oxygen consumption. Lipofuscin accumulation oscillated
with simulated seasonal changes in temperature and was described by seasonalised von Bertalanffy growth functions. The incremental
accumulation in lipofuscin between sampling dates was linearly related to the number of degree days that accumulated between
dates, irrespective of the amplitude of temperature fluctuation that had occurred. ETS activity increased with acclimation
temperature and was modelled using a polynomial function. This indicated a lower temperature sensitivity in the temperature
mid-range (12 to 16 °C), although the Q10 for this mid-range was 2.1. ETS activity in lobsters acclimated to 8 and 18 °C and assayed at 13 °C was similar, indicating
no compensation for changes in environmental temperature. Oxygen consumption rate was significantly higher at 14 °C than at
10.5 °C and had a Q10 of 3.6, again suggesting no compensation to temperature change. The absence of metabolic compensation in response to temperature
change in H. gammarus is consistent with the predictability of changes in temperature and food availability in the sub-littoral environment of
this species. As lipofuscin accumulates according to metabolic rate, and metabolic rate in H. gammarus is directly correlated with temperature, geographic differences and long-term temporal trends in temperature will need to
be considered when converting physiological age indices, obtained from lipofuscin estimates, to a chronological scale.
Received: 27 April 2000 / Accepted: 21 July 2000 相似文献
6.
Oxygen transport by the hemocyanin of the protobranch mollusc Solemya reidi Bernard was studied in native hemolymph samples. Clams were collected from two different reducing environments, beneath log
booms in Alberni Inlet, British Columbia, Canada, and from the sewage effulent in Santa Monica Bay, California, USA. The hemocyanin
concentration in a pooled hemolymph sample (n = 10 individuals) was 33.5 mg ml−1. The mean hemolymph pH of five Alberni clams maintained for 3 wk in mud was 7.96 ± 0.06. No significant variation in hemocyanin
oxygen-affinity or cooperativity was found for hemocyanin in whole hemolymph samples from these five individually studied
clams. There was a significant difference only at 15 °C in the oxygen affinity of hemocyanin in pooled whole-hemolymph samples
from S. reidi collected from Alberni Inlet compared with clams collected from Santa Monica Bay. Little effect of temperature on hemocyanin
oxygen-affinity was found for temperatures below 20 °C; above 20 °C, the oxygen affinity was reduced for clams from both sites.
Temperature and pH had no apparent affect on hemocyanin cooperativity. Moderate Bohr shifts were found at all temperatures
examined. The presence of physiologically relevant concentrations of thiosulphate in hemocyanin samples resulted in a decrease
in hemocyanin oxygen-affinity, opposite to the effect on hemocyanin found for the hydrothermal vent crab Byth-ograea thermydron, but thiosulphate had no effect on hemocyanin cooperativity.
Received: 2 September 1997 / Accepted: 6 February 1998 相似文献
7.
Symbiotic dinoflagellate algae (Symbiodinium sp.) isolated from the scleractinian coral Plesiastrea versipora and incubated in homogenized host tissue released 4 to 7 times as much glycerol (14 to 46 nmol glycerol/106 algae) as those incubated in seawater (3 to 6 nmol glycerol/106 algae) after 4 h incubation in the light. During this period, no release of triglycerides was detected. Intracellular glycerol
increased 2- to 3-fold in algae incubated in host homogenate, but remained unchanged in algae incubated in seawater at a concentration
of 0.82 ± 0.47 nmol glycerol/106 algae. In each incubation condition, intracellular triglyceride levels increased. However, in algae incubated in host homogenate,
the intracellular levels of triglycerides reached only about 75% of the amount reached in algae incubated in seawater (max.
18.55 ± 2.40 nmol glycerol/106 cells). Host homogenate did not stimulate the release of glycerol from algae during dark incubation. These data show that
the glycerol released by algae incubated in host-tissue homogenate was derived from increased synthesis of glycerol or from
diversion of some glycerol or other photosynthetic intermediates from incorporation into algal triglyceride stores, and did
not come from existing stores.
Received: 20 December 1996 / Accepted: 9 January 1997 相似文献
8.
On-line determination of respiration rates at steady-state dissolved oxygen tensions was performed in a thermostatted measuring
chamber equipped with a galvanic oxygen electrode. The measuring chamber is designed to completely exclude gas bubbles from
the liquid phase and is named a mono-phase oxystat. Additions of oxygenated water to maintain steady-state dissolved oxygen
tensions are controlled by a computer, and the respiration rate is determined from the rate of these additions. An external
loop with a flow cell in a spectrophotometer makes it possible to determine and control the concentration of algal cells in
the mono-phase oxystat and allowed simultaneous determination of respiration and filtration rates of filter-feeding invertebrates.
Because the system maintains steady-state conditions the experiments do not suffer from time limitations. The response time
of the system is negligible compared to the response time of other open systems.
Received: 7 November 1996 / Accepted: 6 December 1996 相似文献
9.
Artemia franciscana was grown on Isochrysis galbana Green (clone T. Iso) at saturated food concentrations (13 to 20 mg C l−1) for 11 d at 26 to 28 °C, and 34 ppt salinity. Three groups of brine shrimp were used in the feeding experiments: metanauplius
III and IV (Group 1), post-metanauplius II and III (Group 2) and post-metanauplius VIII (Group 3), corresponding to 4-, 7-
and 11-d-old animals, respectively. The ingestion rate, clearance rate and carbon balance were estimated for these stages
at different concentrations of 14C-labeled I. galbana ranging from 0.05 to 30 mg C l−1. The handling time of algae was determined for all three groups. The ingestion rate (I, ng C ind−1 h−1) increased as a function of animal size and food concentration. In all three groups, the ingestion rate increased to a maximum
level (I
max) and remained constant at food concentrations ≥10 mg C l−1 (saturated food concentrations). The clearance rate (CR, μl ind−1 h−1) increased with increasing food concentration up to a maximum rate (CR
max), after which it decreased for even higher food concentrations. The functional response of A. franciscana was most consistent with Holling's Type 3 functional response curve (sigmoidal model), which for the two oldest groups (Group 2
and 3) differed significantly from a Type 2 response (p < 0.05). The gut passage time for the three groups of A. franciscana, feeding on saturated food concentration (20 mg C l−1), varied between 24 and 29 min. As the nauplii developed to pre-adult stage the handling time of the algae increased as a
function of animal size. The assimilation rate (ng C ind−1 h−1) in the youngest stages (Group 1 and 2) increased with increasing food concentrations, reaching a maximum level close to
10 mg C l−1. At higher food concentrations the assimilation rate decreased, and the proportions of defecated carbon increased, reaching
60 to 68% in the post-metanauplius stages (Group 3). The assimilation efficiency (%) was high at the lowest food concentrations
in all three groups (89 to 64%). At higher concentrations, the assimilation efficiency decreased, reaching 56 to 38% at the
highest concentrations.
Received: 2 February 2000 / Accepted: 25 March 2000 相似文献
10.
I. B. Kuffner 《Marine Biology》2001,138(3):467-476
The effects of water flow and ultraviolet radiation (UVR, 280–400 nm) on the reef coral Porites compressa Dana were explored in a manipulative flume experiment. The aim of this study was to determine whether this coral responds
to changes in the UVR environment by adjusting the tissue concentration of UV-absorbing compounds (mycosporine-like amino
acids, MAAs), and to see whether such an acclimation is affected by water flow. Also, calcification rate and chlorophyll-a concentration were measured during the experiment to estimate the potential costs (in the form of slowed growth and/or reduced
photosynthetic capacity) to the coral–alga symbiosis of being exposed to UVR and producing MAAs. Branches of P. compressa from a single male colony were exposed to high or low flow (15 cm s−1 and 3 cm s−1, respectively) and ambient or no UVR in an outdoor, continuous-flow seawater system. Chlorophyll-a and MAA concentrations were determined after zero, 3 and 6 weeks of exposure to the experimental conditions. Increase in
buoyant weight during the two 3-week periods was used to calculate calcification rate. The presence of UVR had a significant
positive effect on total MAA concentration in the P. compressa colonies; however, there were significant interactions present. In colonies exposed to UVR, MAA concentration increased and
then decreased to initial levels in high water flow, and increased steadily in low water flow. In colonies receiving no UVR,
MAA concentration decreased steadily, declining 23% in 6 weeks. The absence of UVR did not result in higher chlorophyll-a concentrations, but the calcification rate was slightly affected by UVR. This study supports the putative photoprotective
role of MAAs in P. compressa, and suggests that the costs of mitigating the effects of ambient UVR are detectable, but they are very small.
Received: 29 February 2000 / Accepted: 20 September 2000 相似文献
11.
Y. Shrivastava G. G. Mahambre C. T. Achuthankutty B. Fernandes S. C. Goswami M. Madhupratap 《Marine Biology》1999,135(4):663-670
The cladoceran Diaphanosoma celebensis Stingelin is reported on for the first time from Indian waters (Mandovi estuary, Goa). Amictic females were maintained in
the laboratory (temperature 24 ± 1 °C and salinity 17 psu) for three successive generations in order to follow the parthenogenetic
reproductive behaviour, growth, survival and neonate production. The mean life span and body length of adult females in the
three generations showed some variations and ranged from 9 to 12.5 d and 842 to 932 μm, respectively. The mean length of the
neonates produced also varied (283 to 446 μm) in the three generations. Cladoceran preference for three phytoplankton food
sources, i.e. Isochrysis galbana (Parke), Chaetoceros calcitrans (Paulsen) and Tetraselmis gracilis (Kylin), was determined. Growth was faster in the initial stage with all three diets but slowed down in later life. Increased
food concentrations resulted in higher neonate production but reduced the life span of females. However, long-term feeding
experiments revealed that the percentage survival was high with I. galbana and low with C. calcitrans.
Received: 23 June 1999 / Accepted: 20 September 1999 相似文献
12.
To determine how fertilisation varied with sperm concentration for two species of scallop, Chlamys (Equichlamys) bifrons (Lamarck) and C. asperrima (Lamarck), we performed a simple series of sperm dilution experiments, and measured egg size and sperm swimming speeds. C. bifrons eggs were much larger (average diam=116.5 μm), and sperm swimming speeds faster (209.8 μm s−1), than C. asperrima (71.2 μm, 166.0 μm s−1). In both species, maximum fertilisation occurred at an ambient sperm concentration of around 100 sperm μl−1; the maximum proportion of eggs fertilised was less than 0.70 in the C. bifrons experiments, but nearer 1.0 with C. asperrima. At high sperm concentrations (>100 sperm μl−1), fertilisation decreased (presumably due to polyspermy) with increasing sperm concentration, but decreased more rapidly
in C. bifrons than C. asperrima. A polyspermy-adjusted fertilisation kinetics model could be fitted to the experimental data, but unique parameter estimates
could not be determined.
Received: 7 October 1999 / Accepted: 8 July 2000 相似文献
13.
Growth rates and development times were determined for nauplii of the genera: Acartia, Centropages, Corycaeus, Oithona, Paracalanus, Parvocalanus and Temora in nearshore waters of Jamaica from in situ microcosm incubations. At these high local temperatures (∼28 °C), total naupliar
development time was short: 3 to 4 d inshore and 4 to 5 d offshore. Mean instantaneous growth rates (g) ranged from as high as 0.90 d−1 for Parvocalanuscrassirostris to as low as 0.41 d−1 for Corycaeus spp. In general, nauplii of cyclopoid copepods appeared to grow more slowly than those of calanoids of the same size. Naupliar
growth rates were significantly related to body size (r
2 = 0.43 to 0.50), but were unrelated to chlorophyll concentration in any measured size-fraction. This suggests that nauplii
are generally not limited by resources, but are growing at their maximum temperature and size-dependent rates.
Received: 30 May 1997 / Accepted: 13 May 1998 相似文献
14.
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
15.
Laboratory experiments were conducted to investigate the survival rate of Monoporeia affinis in sulphide-rich sediment with oxic overlying water, and the effect of amphipod bioturbation on sulphide and oxygen profiles.
As long as the oxygen content in the water is high, the amphipods seem to avoid quite high concentrations (>200 μmol l−1) of sulphide in the sediment by creating microhabitats where sulphide is rapidly oxidised. In cores with amphipods, a decrease
of sulphide concentration was found in upper layers, while an increase of sulphide was found in deeper layers. Aggregation
of amphipods generated pockets of light-brown sediment, characterised by high oxygen concentrations and no sulphide, and their
depth was clearly dependent on amphipod density. This indicates that M. affinis has a potential to recolonise sulphide-rich sediments, devoid of macroscopic life, after the overlying water column has become
oxygenated.
Received: 13 April 2000 / Accepted: 8 September 2000 相似文献
16.
Fluoride in Antarctic marine crustaceans 总被引:2,自引:0,他引:2
The concentration of fluoride in the body parts of a range of Antarctic crustaceans from a variety of habits was examined
with the aim of determining whether fluoride concentration is related to lifestyle or phylogenetic grouping. Euphausiids had
the highest overall fluoride concentrations of a range of Antarctic marine crustaceans examined; levels of up to 5477 μg g−1 were found in the exoskeleton of Euphausia crystallorophias. Copepods had the lowest fluoride levels (0.87 μg g−1 whole-body); some amphipods and mysids also exhibited relatively high fluoride levels. There was no apparent relationship
between the lifestyle of the crustaceans and their fluoride level; benthic and pelagic species exhibited both high and low
fluoride levels. Fluoride was concentrated in the exoskeleton, but not evenly distributed through it; the exoskeleton of the
head, carapace and abdomen contained the highest concentrations of fluoride, followed by the feeding basket and pleopods,
and the eyes. The mouthparts of E.␣superba contained almost 13 000 μg F g−1 dry wt. Antarctic krill tail muscle had low levels of fluoride. After long-term (1 to 5 yr) storage in formalin, fluoride
was almost completely lost from whole euphausiids.
Received: 1 April 1998 / Accepted: 29 July 1998 相似文献
17.
Growth rates were determined for copepodites of the genera: Acartia, Centropages, Corycaeus, Oithona, Paracalanus, Parvocalanus and Temora in nearshore waters of Jamaica from in situ microcosm incubations. At these high local temperatures (∼28 °C), total copepodite
development time was as short as 4 to 5 d. Mean instantaneous growth rates (g) ranged from as high as 1.2 d−1 to as low as 0.1 d−1. In general, cyclopoid copepods appeared to grow more slowly than calanoids of the same size. Enhancement of resources by
nutrient addition caused a 32% increase in growth rates in experiments from a mesotrophic site, but only a 17% increase at
a more eutrophic site. Additionally, copepodites at both sites showed faster development and generally larger size at stage
in response to nutrient addition. Growth rates were positively related to chlorophyll concentration in the >2 μm size-fraction.
A significant relationship of growth rate to body size (r
2 = 0.45) emerged across a wide range of trophic status, but it was confounded with resource availability. It appears that
growth in tropical copepod copepodites may be frequently limited by resources in a size-dependent manner.
Received: 30 May 1997 / Accepted: 13 May 1998 相似文献
18.
In the Black Sea, during summer stratification, Calanus euxinus (Hulsemann) undertakes diel vertical migrations with an amplitude of about 117 m from oxygenated, warm (18 °C) surface layers
to hypoxic (∼0.8 mg O2 l−1) zones with lower temperature (7.9 °C). When such changes in temperature and oxygen concentration are reproduced in the laboratory,
total metabolism, basal metabolism and scope of activity of copepods decrease 7.2, 7.8 and 6.7 times, respectively, while
the frequency of locomotory acts and mechanical power decline 3.4- and 9.5-fold, respectively. These changes allowed the copepods
to conserve a significant portion of food consumed near the surface for transformation to lipid reserves. Diel respiratory
oxygen consumption of migrating individuals, calculated so as to include actual duration of residence in layers with different
temperature and oxygen concentrations, is estimated at 17.87 μg O2 ind−1. The net energy cost of vertical migration made up only 11.6% of the total. Copepods expend 78.6% of diel energy losses during
approximately 10 h in the surface layers, while about 5.4% is required during about 9 h at depth. Hypoxia is shown to have
a significant metabolic advantage during diel vertical migrations of C. euxinus in the Black Sea.
Received: 1 October 1999 / Accepted: 11 July 2000 相似文献
19.
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
20.
The red alga Portieria hornemannii (Lyngbye) Silva was selected to test the effects of enhanced nutrient availability on the production of carbon-based secondary
metabolites, because of its notable site-to-site variation in monoterpene production. On Guam, the major secondary metabolite
produced by this alga is ochtodene, a cyclic monoterpene. Quantitative high-performance liquid-chromatography analysis of
the extracts of P. hornemannii collected from six sites on Guam showed that both ochtodene and triglyceride concentrations differed significantly among
sites. Internal nitrogen and phosphorus content of the algae did not correlate with the observed variation in chemistry. Experimental
enhancement of N-alone, P-alone or N + P in the field for 5 wk failed to induce a significant change in ochtodene concentrations
in the alga, while triglyceride concentrations increased significantly in the N + P treatment. Ochtodene and triglyceride
concentrations did not change among similar treatments in shaded (18 d) and unshaded (11 d) fertilization experiments conducted
in the laboratory. Variation in ochtodene concentrations in P. hornemannii cannot be attributed to N and P availability; however, the decrease in ochtodene and triglyceride concentrations during the
shaded laboratory experiment suggests that light may be a factor influencing monoterpene biosynthesis. The difference in ochtodene
concentration between the initial and final sets of field controls collected for the unshaded laboratory experiment suggests
that temporal variation might also contribute to differences observed among the algae at the different sites.
Received 11 June 1996 / Accepted 20 July 1996 相似文献