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1.
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
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.
Five pelagic Halobates species occupy a vast area from 40∘ north to 40∘ south in the three major oceans. Oceanic diffusion, constantly acting to disperse these insects, must be an important factor
in determining their life history and distribution. We investigated the effects of oceanic diffusion on the following aspects
of these insects. (1) The estimated radius of a patch of Halobates could be expanded by oceanic diffusion alone from an initial point of origin to 1250 km in 60 d. This distance is about 1/12
of the maximum distributional range of H. micans in the Pacific Ocean. Mutual encounter rates due to oceanic turbulence could be as high as 11 d−1 even at low population densities (100 ind km−2). This suggests that individuals from their original habitat could find mates even when they had been carried a long distance.
Thus, extensive gene mixing may occur over the whole range of a species' distribution. (2)␣Estimated growth rates are rather
low (0.0026 to 0.0079 d−1) compared with those of other insects. However, they are offset by a long life span (over 90 d) and an extended oviposition
period (perhaps over 2␣months). Thus, pelagic Halobates spp. appear to have adopted a strategy of slow growth and prolonged longevity to cope with living in an unstable physical
environment that is constantly disturbed by storms and winds.
Received: 5 February 1995 / Accepted: 30 October 1997 相似文献
4.
A marine algicidal gliding bacterium Cytophaga sp. strain J18/M01 was isolated in 1990 from a station in northern Harima-Nada, the Seto Inland Sea, Japan, using the harmful
red tide alga Chattonella antiqua (Hada) Ono as a susceptible organism. The bacterium can prey upon various species of microalgae. Temporal fluctuations of
this bacterium and Chattonella spp. [C. antiqua and C. marina (Subrahmanyan) Hara et Chihara] were investigated weekly at the above station in the summer of 1997 and 1998, using immunofluorescence
assay employing highly specific polyclonal antibodies for the bacterium. In the summer of 1997, the cell density of Chattonella spp. showed a maximum value (70 cells ml−1) on 8 July, and decreased thereafter. The bacterium Cytophaga sp. J18/M01 was commonly detected around a few hundreds of cells per milliliter or less. The number of Cytophaga sp. J18/M01 increased after the peak of Chattonella spp., and the maximum cell number of the bacterium was 1350 ml−1. This algicidal bacterium also followed the changes of total amounts of microalgal biomass (chlorophyll a+pheophytin) when Chattonella spp. were absent. In the summer of 1998, Chattonella spp. were relatively less abundant (maximum 21 cells ml−1), and the algicidal bacterium Cytophaga sp. J18/M01 showed a close relationship with the change of total microalgal biomass. The present study suggests that the
algicidal bacterium Cytophaga sp. J18/M01 preyed upon, not only harmful red tide microalgae, but also other common microalgae such as diatoms, and the
bacterium presumably plays an important role in regulating microalgal biomass in natural marine environments.
Received: 20 April 2000 / Accepted: 1 December 2000 相似文献
5.
Spatial and temporal pattern in seagrass community composition and productivity in south Florida 总被引:4,自引:1,他引:3
We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance
of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites,
delimiting 12,800 km2 of seagrass beds in the 17,000-km2 survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km2. The range of T. testudinum was almost as extensive (6,400 km2), followed by Syringodium filiforme (4,400 km2), Halodule wrightii (3,000 km2) and Halophila engelmanni (50 km2 ). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m−2day−1, with a range of 0.05–3.29 g m−2 day−1. Specific productivity ranged between 3.2 and 34.2 mg g−1 day−1, with a mean of 18.3 mg g−1 day−1. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the
study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 1010 g S. filiforme, which translate to a yearly production of 9.4 × 1011 g T. testudinum leaves and 2.4 × 1011 g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing
these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as
a benchmark against which future change in the system can be quantified.
Received: 30 January 2000 / Accepted: 24 July 2000 相似文献
6.
The predation impact of the two chaetognaths Eukrohnia hamata and Sagitta gazellae on mesozooplankton standing stock were investigated in three depth layers during two 24 h stations occupied in the vicinity
of Marion Island in late austral summer (April/May) 1986. The zooplankton community at both stations was dominated by small
copepods (Oithona spp., Microcalanus spp.), which accounted for >95% of total zooplankton abundance. Chaetognaths comprised <2% of total zooplankton abundance.
E. hamata constituted >95% of the total chaetognath stock. The general trend in both species was decreasing abundance with increasing
depth, which appeared to be correlated to the distribution of copepods (r
2 = 0.45; P <0.05). Gut-content analysis showed that copepods (mainly Oithona spp., Calanus spp. and Rhincalanus gigas) and ostracods were the main prey of both species, accounting for 87 and 61% of the total number of prey in E. hamata and S.␣gazellae stomachs, respectively. In the guts of S.␣gazellae, pteropods (Limacina spp.) and chaetognaths were also well represented. The mean number of prey items (NPC) for E. hamata ranged from 0.02 to 0.06 prey individual−1 which corresponds to an individual feeding rate (Fr) of between 0.05 and 0.12 prey d−1. For S.␣gazellae, the NPC values were higher, varying between 0.04␣and 0.20 prey individual−1, or between 0.15 and 0.76 prey d−1. The daily predation impact of the two chaetognaths was estimated at between 0.3 and 1.2% of the copepod standing stock or
between 7 and 16% of the daily copepod production. Predation by S. gazellae on chaetognaths accounted for up to 1.6% of the chaetognath standing stock per day.
Received: 26 November 1996 / Accepted: 31 October 1997 相似文献
7.
Growth and development rates were determined for nauplii of Calanus finmarchicus (Gunnerus) in the near-shore waters of a western Norwegian fjord from in situ mesocosm incubations. The major food source
for the nauplii was diatoms, but Phaeocystis sp., dinoflagellates and ciliates were also part of the diet. At local temperatures ranging from 4.8 to 5.2 °C the cumulative
median development time from hatching to Nauplius VI was 19 d. The time taken to molt to the next naupliar stage was approximately
constant (3 d) from Stages IV to VI, but Stage III needed the longest development time (5 d). The instantaneous growth rate
in terms of body carbon was negative from hatching to Nauplius Stage II, but as high as 0.25 to 0.30 d−1 from Stage III to V. Enhancement of food resources by nutrient addition led to no significant change in specific growth rates.
Additionally, the cohorts from different nutrient regimes showed almost equal development time, size and body carbon within
stages. Length–weight relationships of nauplii from the two different food resources were: W
low resources = 4.17 × 10−6 × L
2.03 (r
2 = 0.84) and W
high resources = 4.29 × 10−6 × L
2.05 (r
2 = 0.92), where weight (W) is in micrograms of C and body length (L) in micrometers. The natural body morphology of naupliar stages I to VI is illustrated with digital images, including the
final molt from Nauplius VI to Copepodid Stage I. In general, development of the nauplii was faster than that of the copepodids
of C. finmarchicus, and structural growth was exponential from naupliar stages III to VI. This study validates our earlier results that nauplii
of C. finmarchicus can obtain high growth and nearly maximal developmental rates at relatively low food levels (∼50 μg C l−1), suggesting that nauplii exhibit far less dependence on food supply than copepodids.
Received: 30 July 1999 / Accepted: 7 March 2000 相似文献
8.
Environmental preferences of yellowfin tuna (Thunnus albacares) at the northern extent of its range 总被引:5,自引:0,他引:5
B. A. Block J. E. Keen B. Castillo H. Dewar E. V. Freund D. J. Marcinek R. W. Brill C. Farwell 《Marine Biology》1997,130(1):119-132
We used acoustic telemetry to examine the small-scale movement patterns of yellowfin tuna (Thunnus albacares) in the California Bight at the northern extent of their range. Oceanographic profiles of temperature, oxygen, currents and
fluorometry were used to determine the relationship between movements and environmental features. Three yellowfin tuna (8
to 16 kg) were tracked for 2 to 3 d. All three fish spent the majority of their time above the thermocline (18 to 45 m in
depth) in water temperatures >17.5 °C. In the California Bight, yellowfin tuna have a limited vertical distribution due to
the restriction imposed by temperature. The three fish made periodic short dives below the thermocline (60 to 80 m), encountering
cooler temperatures (>11 °C). When swimming in northern latitudes, the depth of the mixed layer largely defines the spatial
distribution of yellowfin tuna within the water column. Yellowfin prefer to spend most of their time just above the top of
the thermocline. Oxygen profiles indicated that the tunas encountered oceanic water masses that ranged most often from 6.8
to 8.6 mg O2 l−1, indicating no limitation due to oxygen concentrations. The yellowfin tuna traveled at speeds ranging from 0.46 to 0.90 m
s−1 (0.9 to 1.8 knots h−1) and frequently exhibited an oscillatory diving pattern previously suggested to be a possible strategy for conserving energy
during swimming.
Received: 14 February 1997 / Accepted: 14 April 1997 相似文献
9.
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
10.
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
11.
During commercial handling of Nephropsnorvegicus (L.) there are a number of situations when the prawns may be exposed to very high ambient ammonia levels. These experiments
evaluated the effects of increased levels of ambient total ammonia (TA = NH3 + NH4
+) on␣blood ammonia, ammonia efflux rates and on the cardio-ventilatory performance of N. norvegicus. When prawns were taken from <1 to 2000 μmol TA l−1 medium, blood TA concentrations increased rapidly for the first 2 h but tended to drop thereafter. Original blood TA levels
were restored 6 h after the prawns were transferred back from seawater containing 2000 to <1 μmol TA l−1. Sudden exposure to 500, 1000, 2000 or 4000 μmol TA l−1 medium induced blood TA concentrations to increase respectively to 50, 30, 33 and 36% of external concentrations (normally,
internal TA values are much higher than external levels). Immediately after transfer back to seawater with low ammonia concentration
( <1 μmol TA l−1), excretion rates were higher than those of control prawns, and the absolute amounts of TA excreted were considerably higher
than those calculated to have accumulated in the haemolymph. Heart rate (HR) and scaphognathite rate (SR) were not altered
when prawns were subjected to sudden alterations in ambient ammonia ( <1 to 2000 to <1 μmol TA l−1). When water ammonia concentrations were altered more gradually, both rates increased, but only at 4000 μmol TA l−1. These results show that N. norvegicus is able to remove ammonia from the haemolymph and/or transform ammonia into some other substance when subjected to increased
levels of ambient ammonia. Possible mechanisms involved (e.g. active transport across the gills; storage in some other tissue;
glutamate synthe sis) are discussed.
Received: 20 May 1996 / Accepted: 1 July 1996 相似文献
12.
In situ measurements of seagrass photosynthesis in relation to inorganic carbon (Ci) availability, increased pH and an inhibitor
of extracellular carbonic anhydrase were made using an underwater pulse amplitude modulated (PAM) fluorometer. By combining
the instrument with a specially designed Perspex chamber, we were able to alter the water surrounding a leaf without removing
it from the growing plant. Responses to Ci within the chamber showed that subtidal plants of the seagrasses Cymodocea serrulata and Halophila ovalis had photosynthetic rates that were limited by the ambient Ci concentration depending on the irradiance that was available
during short-term photosynthesis–irradiance trials. Relative electron transport rates (RETRs) at light saturation (up to 500 μ
mol photons m−2 s−1) increased by 66–100% when the Ci concentration was increased from ca. 2.2 to 6.2 mM. On the other hand, intertidal plants
of the same species exhibited a much lesser limitation of photosynthesis by Ci at any irradiance (up to 1500 μ mol photons
m−2 s−1). Both species were able to use HCO−
3 efficiently, and there was stronger evidence for direct uptake of HCO−
3 rather than extracellular dehydration of HCO−
3 to CO2 prior to Ci uptake. Subtidally, H. ovalis and C. serrulata grew to 10 and 12 m, respectively, where ambient irradiances were approximately 16 and 11% of those at the surface. Maximum
RETRs (at light saturation) were lower for these deep-growing plants than for the intertidally growing ones. For both species,
the onset of light saturation of photosynthesis (E
k) occurred at approximately 100 μ mol photons m−2 s−1 for the deep water populations, which was four and two times lower than for the shallow populations of C. serrulata and H. ovalis, respectively. This, and the differences in maximal photosynthetic rates (RETR
max), reflects an acclimation of the deep-growing populations to the lower light environment. The results presented here show
that photosynthesis, as measured in situ, was limited by the availability of Ci for the deeper growing plants in Zanzibar,
while the intertidally growing plants photosynthesised at close to Ci saturation. The latter result is contrary to previous
conclusions regarding Ci limitations for these intertidal plants, and, in general, our findings highlight the need for performing
similar experiments in situ rather than under laboratory conditions.
Received: 4 April 2000 / Accepted: 31 August 2000 相似文献
13.
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
14.
The aim of our investigations was to determine, via oxygen and carbon-dioxide respirometry, how much energy dolphins (Tursiops truncatus) require when swimming at different speeds. Experiments were conducted on two female bottlenose dolphins (mean mass 162 kg)
in the dolphinarium in Nuremberg Zoo, Germany, between March and August 1997. Animals were stationed in a respiration chamber
for a minimum of 90 s after performing a variety of activities. We measured respiration frequency and oxygen requirements
during (1) resting, (2) swimming at various velocities and (3) leaping to various heights. Resting metabolic rate of our bottlenose
dolphins (2.15 W kg−1) was comparable to previously published data. Metabolic rate in swimming dolphins increased to 2.47 W kg−1 at 2 m s−1, while leaps to 2.2 and 3 m height required a power input of 3.5 and 4 W kg−1, respectively. Transport costs of swimming dolphins were lowest (1.16 J kg−1 m−1, corresponding to 0.12 J N−1 m−1) at a speed of 2.5 m s−1, yielding an optimal range speed of between 1.9 and 3.2 m s−1 (corresponding to minimum cost of transport ±10%). Breathing rates during all experiments correlated very well with oxygen
consumption (r
2 > 0.89) and could be used to derive metabolic rates in unencumbered dolphins at sea.
Received: 18 December 1998 / Accepted: 27 April 1999 相似文献
15.
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
16.
Spatial and temporal distributions of copepods to leeward and windward of Oahu, Hawaiian Archipelago 总被引:1,自引:0,他引:1
The spatial and temporal distributions of two island-associated copepod species, Undinula vulgaris Dana and Labidocera madurae Scott, were compared to the distributions of two open ocean species, Cosmocalanus darwinii Lubbock and Scolecithrix danae Lubbock, along 28-km windward and leeward transects off the island of Oahu, Hawaii. Samples were taken in September and December
1985 and April and June 1986. A warm, low salinity pool on the leeward side was a prominent feature during all transects except
December. The abundances of the two oceanic species did not change significantly between leeward and windward stations, with
distance from shore, or between September 1985 and April 1986 samples. As expected, very high abundances of U. vulgaris occurred at some nearshore stations, up to 3 g dry wt m−2 for adults alone. Calculations of respiratory loss at these densities (0.7 g C m−2 d−1) suggest a high local productivity would be required to meet these demands. L. madurae, a surface-dwelling species normally restricted to within 1 km of shore, was an effective indicator species of nearshore
water movement. It was more common in offshore samples on the leeward transects, rarely being found offshore on the windward
side, consistent with prevailing currents and the presence of the leeward warm, low salinity pool. The occurrence of a strong
mixing event in April 1986 resulted in L. madurae being distributed throughout the upper 100 m of the water column. The presence of oceanic species close to shore on the windward
side also coincided with this wind-driven event. The primary environmental influence on vertical distributions was daytime
cloud cover, with U. vulgaris tending to be found shallower on cloudy days. Of the two oceanic species, S. danae exhibited the most pronounced vertical migration, however, vertical distributions were not significantly correlated with
environmental factors for either species. The abundant nearshore U. vulgaris population cannot be explained by differences in vertical distribution between it and the two oceanic species that might
allow a physical mechanism to concentrate U. vulgaris. A high population growth rate is likely necessary to explain U. vulgaris' dominance.
Received: 26 June 1998 / Accepted: 31 March 1999 相似文献
17.
We investigated the effects of addition of dissolved organic matter (DOM) on the growth and chemical composition of Nodularia spumigena cells under conditions of P or N deficiency. Semi-continuous monocultures of N. spumigena Mertens were established. The cells were exposed to the following treatments: nutrient-sufficient (+NP), nitrogen-deficient
without DOM (−N) and with DOM (−NDOM), and phosphorus-deficient without DOM (−P) and with DOM (−PDOM). The −NDOM treatment
had the highest N. spumigena cell density (6.1 × 107 cells l−1) during the experiment, whereas the P-deficient treatments had the lowest cell numbers (0.53 to 0.66 × 107 cells l−1). Both −P and −PDOM treatments yielded P-deficient N. spumigena cells. Dissolved organic nitrogen may provide N and increase N. spumigena yield under conditions of N deficiency. On the other hand, N. spumigena cells did not use DOM as a P source.
Received: 19 July 1999 / Accepted: 20 October 1999 相似文献
18.
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
19.
Determination of basic population parameters in long-lived Crustacea is hindered by a lack of appropriate methods for age
determination. This study uses the pigment lipofuscin as an age marker in the common Antarctic decapod Notocrangon antarcticus (Pfeffer, 1887) from the eastern Weddell Sea. Resin brain sections of the lateral somacluster of the olfactory lobe of 189
specimens were digitally recorded by confocal microscopy and images were subsequently analyzed. A modal progression analysis
of the lipofuscin concentration–frequency distribution revealed a total of eight regularly spaced modes presumed to reflect
consecutive annual age classes. All eight modes contained females, and the first four contained males. No regular modes were
obvious in the comparable length-frequency distribution. The average yearly pigment accumulation was nearly linear and estimated
as 0.02% area fraction year−1, which is considerably lower than rates published for species from lower latitudes. This is probably explained by the effect
of low water temperature on metabolism and lipofuscin accumulation rate. The growth parameters CL∞ and k from the von Bertalanffy growth function were 22.3 mm and 0.79 year−1 for females, respectively, and 16.9 mm and 0.64 year−1 for males, respectively. Mortality, estimated from catch curves, amounted to 0.44 year−1 in females and 0.92 year−1 in males, whereas P/B, calculated from the mass specific growth rate method, was slightly lower. The results indicate that the lipofuscin-inferred
population parameters are an improvement over what can be learned about N. antarcticus with traditional methods.
Received: 1 August 2000 / Accepted: 21 September 2000 相似文献
20.
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