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1.
José Juan Barrera-Alba Sônia Maria Flores Gianesella Gleyci Aparecida Oliveira Moser Flávia Marisa Prado Saldanha-Corrêa 《Hydrobiologia》2008,598(1):229-246
Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates and growth efficiencies were studied
in July 2001 and January 2002 during both spring and neap tides, along a tidal cycle, at three sites in a subtropical estuary.
Major freshwater inputs located in the Northern region led to differences in both phytoplankton and bacterioplankton biomass
and activity along the estuary. While in the Northern region phytoplankton is light-limited, with mean phytoplankton production
(PP) between 1.1 and 1.9 μg C l−1 h−1 and mean specific growth rates (PSG) between 0.14 and 0.16 d−1, the Southern region registered values as high as 24.7 μg C l−1 h−1 for PP and 2.45 d−1 (mean PP between 3.4 and 7.3 μg C l−1 h−1; mean PSG between 0.28 and 0.57 d−1). On the other hand, maximum bacterial production (BP: 63.8 μg C l−1 h−1) and specific growth rate (BSG: 32.26 d−1) were observed in the Northern region (mean BP between 3.4 and 12.8 μg C l−1 h−1; mean BSG between 1.98 and 6.67 day−1). These bacterial activity rates are among the highest recorded rates in estuarine and coastal waters, indicating that this
system can be highly heterotrophic, due to high loads of allochthonous carbon (mainly derived from mangrove forest). Our results
also showed that, despite that BP rates usually exceeded PP, in the Southern region BP may be partially supported (∼45%) by
PP, since a significant regression was observed between BP and PP (r = 0.455, P < 0.001).
Handling editor: P. Viaroli 相似文献
2.
We assessed the effect of salinity on plant growth and leaf expansion rates, as well as the leaf life span and the dynamics
of leaf production and mortality in seedlings of Avicennia germinans L. grown at 0, 170, 430, 680, and 940 mol m−3 NaCl. The relative growth rates (RGR) after 27 weeks reached a maximum (10.4 mg g−1 d−1) in 170 mol m−3 NaCl and decreased by 47 and 44% in plants grown at 680 and 940 mol m−3 NaCl. The relative leaf expansion rate (RLER) was maximal at 170 mol m−3 NaCl (120 cm m−2 d−1) and decreased by 57 and 52% in plants grown at 680 and 940 mol m−3 NaCl, respectively. In the same manner as RGR and RLER, the leaf production (P) and leaf death (D) decreased in 81 and 67% when salinity increased from 170 to 940 mol m−3 NaCl, respectively. Since the decrease in P with salinity was more pronounced than the decrease in D, the net accumulation of leaves per plant decreased with salinity. Additionally, an evident increase in annual mortality
rates (λ) and death probability was observed with salinity. Leaf half-life (t
0.5) was 425 days in plants grown at 0 mol m−3 NaCl, and decreased to 75 days at 940 mol m−3 NaCl. Thus, increasing salinity caused an increase in mortality rate whereas production of new leaves and leaf longevity
decreased and, finally, the leaf area was reduced. 相似文献
3.
Food and growth relations of the marine microzooplankter,Synchaeta cecilia (Rotifera) 总被引:2,自引:2,他引:0
David A. Egloff 《Hydrobiologia》1988,157(2):129-141
The trophic interactions of the marine rotifer Synchaeta cecilia were investigated by determining its feeding and growth rates on a wide variety of marine phytoplankton and by determining
its susceptibility to predation by the calanoid copepod, Acartia tonsa. Reproduction of S. cecilia was sustained in four-day feeding trails by 13 of 37 algal species tested. Growth-supporting species included species of
Cryptophyceae, Dinophyceae, Chlorophyceae and Haptophyceae in sizes from 4 to 47 μm. Within these taxa, other species in the
acceptable size range failed to support growth. No species of Cyanophyceae, Bacillariophyceae, or Chrysophyceae supported
growth of the rotifer. S. cecilia can be maintained on unialgal cultures of Cryptophyceae but growth is enhanced by a combination of two or three species;
a mixture of Chroomonas salina (Cryptophyceae), Heterocapsa pygmaea (Dinophyceae), and Isochrysis galbana (Haptophyceae) has sustained laboratory stocks of S. cecilia for over four years. The expected response of S. cecilia to food quantity was observed: as food concentration was increased from 58 to 1154 μg C 1−1, the population growth constant increased from 0.17 to 0.60 d−1 at 20°C. This is equivalent to population doubling times of 4.0 and 1.1 days at H. pygmaea densities of 500 and 104 cells ml−1, respectively. The susceptibility of S. cecilia to predation was investigated by determining its rate of capture by the omnivorous marine copepod Acartia tonsa. At prey densities of 5 to 35 μg C 1−1 (0.3 to 1.9 individuals 1−1), A. tonsa readily ingested S. cecilia at rates up to 3 μg C copepod−1 day−1. 相似文献
4.
J. G. Wakibia J. J. Bolton D. W. Keats L. M. Raitt 《Journal of applied phycology》2006,18(3-5):565-573
As a possible means of improving the livelihoods of local villagers, off-bottom rope cultivation of commercial eucheumoids was investigated on the southern Kenyan coast at three sites, representative of the variety of environments. The morphotypes used were brown Eucheuma denticulatum and green and brown Kappaphycus alvarezii. The study was carried out over a 15 month period from August 2001 until October 2002. Relative growth rates were highest at a sandy flat in a mangrove system (Gazi; 5.6% d−1), and lowest in an intertidal reef flat (Kibuyuni; 3.2% d−1) with a lagoon being intermediate (Mkwiro; 4.8% d−1). The brown E. denticulatum had the highest growth rate of 4.7% d−1 compared to the green and brown K. alvarezii which were 4.3% d−1 and 4.2% d−1, respectively. Growth was more variable at Kibuyuni and Mkwiro. The growth was higher during the southeast monsoon (4.7% d−1) than during the northeast monsoon (4.0% d−1). This is part of a larger study and the effects of water motion, salinity, temperature, thallus nitrogen, and ‘ice-ice’ syndrome on growth of morphotypes is discussed. The water motion was observed to increase thallus nitrogen and hence the growth of eucheumoids. The ‘ice-ice’ condition affected both brown E. denticulatum and brown K. alvarezii but not green K. alvarezii. The results suggest that commercial cultivation of eucheumoids in Kenya will be feasible. 相似文献
5.
Knowledge of how energetic parameters relate to fluctuating factors in the natural habitat is necessary when evaluating the
role of gelatinous zooplankton in the carbon flow of coastal waters. In laboratory experiments, we assessed feeding, respiration
and growth of the ctenophore, Pleurobrachia pileus, and constructed carbon budgets. Clearance rates (F, l d−1) of laboratory-reared Acartia tonsa as prey increased as a function of ctenophore polar length (L, mm) as F = 0.17L
1.9. For ctenophores larger than about 11 mm, clearance rate was depressed in containers of 30–50 l volume. Clearance rates on
field-collected prey were highest on the copepod, Centropages typicus, intermediate on the cladoceran, Evadne
nordmanni and low on the copepods, Acartia clausi and Temora longicornis. Specific growth rates of 8–10 mm P. pileus increased with increasing prey concentrations to a maximum of 0.09 d−1 attained at prey carbon densities of 40 and 100 μg C l−1 of Artemia salina and A. tonsa, respectively. Weight-specific respiration rates increased hyperbolically with prey concentration. From experiments in which
growth, ingestion and respiration were measured simultaneously, a carbon budget was constructed for individuals growing at
maximum rates; from the measured parameters, the assimilation efficiency and net growth efficiency were estimated to be 22
and 37%, respectively. We conclude that the predation rates of P. pileus depend on ctenophore size, prey species, prey density and experimental container volume. Because the specific growth rates,
respiration, assimilation and net growth efficiencies all were affected by food availability, knowledge of the ambient prey
field is critical when evaluating the role of P.
pileus in the carbon flow in coastal waters. 相似文献
6.
Aspects of denitrification and benzoate degradation were studied in two estuarine microbial mat communities on the California
coast by measuring the depth distributions of potential denitrification rates, genetic potential for denitrification, nitrate
concentration, benzoate mineralization rates, total bacterial abundance, and abundance of a denitrifying strain (TBD-8b) isolated
from one of the sites. Potential denitrification was detected in microbial mat cores from both Elkhorn Slough and Tomales
Bay. Maximum denitrification rates were more than two orders of magnitude higher at Elkhorn Slough (3.14 mmol N m−2 d−1) than at Tomales Bay (0.02 mmol N m−2 d−1), and at both sites, the maximum rates occurred in the 0–2 mm depth interval. Ambient pore [NO3+NO2] was substantially higher at Elkhorn Slough than at Tomales Bay. Incorporation and mineralization of benzoate was maximal
near the mat surface at Elkhorn Slough. The areal rate of benzoate utilization was 1045 nmol C m−2 d−1, which represented utilization of 70% of the added substrate in 24 h. Total bacterial and TBD-8b abundances were greatest
near the surface at both Tomales Bay and Elkhorn Slough, and TBD-8b represented less than 0.2% of the total. Genetic potential
for denitrification, quantified by hybridization with a nitrite reductase gene fragment, was present below the mat surface
at average levels representing presence of the gene in approximately 10% of the total cells. 相似文献
7.
Abstract
If predators select for or against contaminant-degrading bacteria, it will affect bacterial survival and has important implications
for bioremediation. Protozoa are important predators of bacteria. In order to determine whether protozoa preyed differentially
on bacteria with different degradation abilities, two ciliates (Euplotes sp. and Cyclidium sp.) and three strains of PAH-degrading bacteria (Vibrio spp., degrading naphthalene, anthracene, or phenanthrene) were isolated from sediment from New York/New Jersey Harbor. By
manipulating growth conditions, bacterial strains with different PAH-degradation abilities and different cell properties were
produced. Stepwise regression models were used to analyze how clearance rates on suspended bacteria and grazing rates on bacteria
attached to particles were affected by bacterial size, hydrophobicity, C:N ratio, protein content, and PAH-degradation ability.
Clearance rates ranged from 0 to 49 nl ciliate−1 h−1 for Euplotes sp. and from 0 to 1.7 nl ciliate−1 h−1 for Cyclidium sp. Clearance rates of both ciliates were positively correlated with bacterial size, hydrophobicity, and protein content,
and negatively correlated with C:N ratio. PAH degradation ability had no (for Euplotes sp.) or small (for Cyclidium sp.) effects on clearance rates. The models accounted for 63–75% of the variation in clearance rates on different bacteria.
Only Euplotes sp. grazed on attached bacteria, at rates from 3 to 176 bacteria ciliate−1 h−1. A regression model with only C:N ratio and protein content explained 45% of the variation in grazing rates. These models
indicate that multiple properties of bacteria affect their susceptibility to predation by ciliates, but PAH-degradation ability
per se has little effect.
Received: 5 May 1998; Accepted: 14 September 1998 相似文献
8.
Abstract
The bacterial colonization and development of the ectoenzymatic glucosidase activity and glucose uptake were followed together
with bacterial growth (measured as thymidine incorporation) in laboratory experiments, using phytoplankton-derived particles
incubated in rolling tanks. Bacterial colonization of the particles was rapid. In the particles, bacterial turnover rates
(production/biomass) were low (0.02 to 0.14 d−1). In the ambient water, turnover rates increased from 0.1 d−1 to 23.3 d−1, until the end of the experiment. In the control, lacking any particles, turnover of bacteria ranged from 0.3 to 7.6 d−1. Similarly, glucose uptake rates, per bacterium, were 1 to 2 orders of magnitude lower for particle-attached bacteria than
for their free-living counterparts. Generally, Km values for glucosidase activity declined, over the incubation period, in particles and free-living bacteria until 168 h,
and slightly increased, thereafter, to values of approximately 0.1 μM. Particle-attached bacteria exhibited significantly
lower uptake rates of both thymidine and glucose, per bacterium, throughout the incubation. The per-cell ectoenzymatic activity
was similar in particle-associated and free-living bacteria during the initial phase of the experiment, but was significantly
higher after ≈200 h. Dissolved total (TCHO), as well as monomeric carbohydrates (MCHO), declined continuously in both particles
and ambient water; they remained constant in the control; TCHO comprised about 50% of the dissolved organic carbon (DOC) in
the particles. In ambient water TCHO contribution to DOC varied, with only one exception, between 25 and 45%; and in the control,
between 20 and 50%. The shift detectable in the relation between ectoenzymatic activity and uptake of glucose between free-living
and attached bacteria over the incubation period may reflect changes in the physiological status of the bacteria.
Received: 3 February 1997; Accepted: 6 November 1997 相似文献
9.
The influence of diet on the growth of Stenonema vicarium (Walker) (Ephemeroptera: Heptageniidae) 总被引:1,自引:1,他引:0
Laboratory studies compared the growth rate of Stenonema vicarium (Walker) nymphs on diets of detritus and natural stream periphyton. In three consecutive runs of the experiment, growth rates
were consistently higher on periphyton (mean growth rate = 2.1% wet wt. d−1) than detritus (mean = 1.8% wet wt. d−1). The starting date of each run also significantly influenced growth rates. In each treatment growth rates generally decreased
over the course of the 3 runs, and ca. one-half of the nymphs in the last run did not molt or grow. It appeared that growth
of S. vicarium may be partially controlled by seasonal factors. 相似文献
10.
Protozoan growth rates in Antarctic lakes 总被引:1,自引:0,他引:1
The growth rates of heterotrophic nanoflagellates (HNAN), mixotrophic cryptophytes, dinoflagellates and ciliates in field
assemblages from Ace Lake in the Vestfold Hills (eastern Antarctica) and Lakes Fryxell and Hoare (McMurdo Dry Valleys, western
Antarctica), were determined during the austral summers of 1996/1997 and 1997/1998. The response of the nanoflagellates to
temperature differed between lakes in eastern and western Antarctica. In Ace Lake the available bacterial food resources had
little impact on growth rate, while temperature imposed an impact, whereas in Lake Hoare increased bacterial food resources
elicited an increase in growth rate. However, the incorporation of published data from across Antarctica showed that temperature
had the greater effect, but that growth is probably controlled by a suite of factors not solely related to bacterial food
resources and temperature. Dinoflagellates had relatively high specific growth rates (0.0057–0.384 h−1), which were comparable to Antarctic lake ciliates and to dinoflagellates from warmer, lower latitude locations. Temperature
did not appear to impose any significant impact on growth rates. Mixotrophic cryptophytes in Lake Hoare had lower specific
growth rates than HNAN (0.0029–0.0059 h−1 and 0.0056–0.0127 h−1, respectively). They showed a marked seasonal variation in growth rate, which was probably related to photosynthetically
active radiation under the ice at different depths in the water column. Ciliates' growth rates showed no relationship between
food supply and mean cell volume, but did show a response to temperature. Specific growth rates ranged between 0.0033 and
0.150 h−1 for heterotrophic ciliates, 0.0143 h−1 for a mixotrophic Plagiocampa species and 0.0075 h−1 for the entirely autotrophic ciliate, Mesodinium rubrum. The data indicated that the scope for growth among planktonic Protozoa living in oligotrophic, cold extreme lake ecosystems
is limited. These organisms are likely to suffer prolonged physiological stress, which may account for the highly variable
growth rates seen within and between Antarctic lakes.
Accepted: 7 December 1999 相似文献
11.
Herrera-Valencia VA Contreras-Pool PY López-Adrián SJ Peraza-Echeverría S Barahona-Pérez LF 《Current microbiology》2011,63(2):151-157
The aim of this study was to investigate the potential of the green microalga Chlorella saccharophila as a source of oil for biodiesel production. We evaluated for the first time, the effect of salinity and/or nitrogen depletion
(ND) on cell growth, lipid accumulation and lipid profile in this microalga. The fatty acid methyl esters (FAME) identified
for C. saccharophila in this study consisted of C-16:0, C-18:0, C-18:1 cis, and C-18:1 trans. Among these, C-18:1 (indicator of biodiesel quality)
was the main FAME found, representing approximately 76 and 80% of total FAME under normal and ND growing conditions, respectively.
Under a normal growing condition this microalga showed 154.63 mg l−1 d−1, 63.33 mg l−1 d−1, and 103.73 mg l−1 of biomass productivity, lipid productivity, and FAME yield, respectively. The higher biomass productivity (159.58 mg l−1 d−1), lipid productivity (99.33 mg l−1 d−1), and FAME yield (315.53 mg l−1) were obtained under the ND treatment. In comparison to other related studies, our results suggest that C. saccharophila can be considered as a suitable source of oil for biodiesel production. 相似文献
12.
Measurements of plankton community structure and trophic resourcespotentially available to planktonic copepods were made in
the mangroveestuaries of six rivers in Northeastern Australia. The Pascoe, Claudie,Lockhart, McIvor and Daintree Rivers represent
wet tropical systems on CapeYork, whereas the Haughton River estuary has restricted freshwater inflowbecause of a drier climate
and freshwater diversion for agriculture. TheHaughton River was sampled approximately monthly between October 1992 andMay
1994, and had a mean abundance of zooplankton >37 μm of 200l−1 (range 60–500 l−1). The Cape Yorkrivers were sampled infrequently, and zooplankton abundances ranged between0.4 and 1400 l−1. The zooplankton of all rivers was dominatedby copepods, particularly representatives of the genus Oithona which werecharacteristic
of a distinct mangrove fauna. Physical forcing influencedthe zooplankton of mangrove estuaries much more than the measured
biologicalvariables. The water column was characterised by high concentrations ofparticulate matter, up to 3.3 mg l−1 C and 1.1 mgl−1 N, of low food quality (as indicated by the C:N ratio).Phytoplankton biomass (as chlorophyll a) in all six rivers was on
averagefour-fold greater than in neighbouring coastal waters (1.1–12.6μg l−1), and 25% of this chlorophyll a wasderived from cells >10 μm, and thus potentially available tocopepods. The degree of mixing,
determined by the combination of tidal stateand the extent of freshwater input, appears to drive both the quantity andquality
of particulate material available to higher consumers and thedistribution of zooplankton communities within mangrove estuaries.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Light irradiation had remarkable effects on callus growth of Oldenlandia affinis with an optimum intensity of 35 μmol m−2 s−1. Biosynthesis of kalata B1, the main cyclic peptide in O. affinis, was induced and triggered with rising irradiation intensities. The highest concentration of kalata B1, 0.49 mg g−1 DW characterised by the maximum productivity of 3.88 μg per litre and day was analysed at 120 μmol m−2 s−1, although callus growth was repressed. The light saturation point was established to be 35 μmol m−2 s−1, where kalata B1 productivity was in a similar order (3.41 μg per day) due to the higher growth index. O. affinis suspension cultures were shown to accumulate comparable specific kalata B1 concentrations in a delayed growth associated
production pattern. These were dependent on irradiation intensity (0.16 mg g−1 at 2 μmol m−2 s−1; 0.28 mg g−1 at 35 μmol m−2 s−1). The batch cultivation process resulted in a maximum productivity of 27.30 μg per litre and day with culture doubling times
of 1.16 d−1. Submers operation represented a 8-fold product enhancement compared to callus cultivation. 相似文献
14.
Kanesa May Duncan 《Environmental Biology of Fishes》2006,76(2-4):139-149
Juvenile scalloped hammerhead sharks, Sphyrna lewini, are apex predators within their nursery ground in Kāne‘ohe Bay, Ō‘ahu, Hawai‘i. Understanding daily maintenance requirements of a top-level predator is an important step toward understanding its ecological impact within a nursery ecosystem. Juvenile S. lewini were fed a range of daily ration levels to examine the effect of feeding rate on growth and gross conversion efficiency. The von Bertalanffy growth model yielded the best fit to the data, predicting a maintenance ration of 115 kJ kg−1 day−1 (3.4% body weight (BW) day−1) and a maximum growth rate of 38 kJ kg−1 day−1. This finding is in agreement with the previous prediction of high energetic requirements for S. lewini. In combination with the hypothesized food limitation within Kāne‘ohe Bay, this result may explain the observed high mortality rates of S. lewini. Gross conversion efficiency, K
1, ranged from −36% to 34%, with maximum efficiency at feeding levels of 5.1% BW day−1. The growth conversion efficiency of S.␣lewini is similar to that of lemon sharks and teleost fishes. Growth rates of juvenile S. lewini are possibly restricted by their high metabolic rate, limited food availability and foraging inexperience. By directly examining the effect of ration size on growth and food conversion, it was possible to resolve discrepancies between earlier studies, which used respiratory metabolism and gut content analyses. 相似文献
15.
Gametophyte cells of brown algae Laminaria japonica were employed both in a modified silicone tubular membrane-aerated photobioreactor (bubble-less cultivation mode) and a bubble-column
photobioreactor (bubbling cultivation mode), to study different gas–liquid mixing modes on cell growth rate and cell physiological
status. With an inoculum density of 50 mg DCW l−1, in modified artificial Pacific seawater (APSW) medium at 13°C, light intensity of 60 μE m−2 s−1, light cycle of 16/8 h L/D, and aeration rate of 60 ml min−1, the specific growth rates were 0.082 d−1 for bubble-less mode and 0.070 d−1 for bubbling mode with biomass, in the form of dry cell density, increasing 10.9 and 6.8 times, respectively, during the
36 days’ photolithotrophic cultivation. The specific oxygen evolution rate under bubble-less mode was 39.6% higher than under
bubbling mode on the 18th day. The gametophyte cells grew in cell aggregates with clump sizes, at day 36, of 1.5 mm and 0.5 mm
diameter under bubble-less and bubbling mode respectively and cell injury percentages of 5.1% and 21.1%, respectively. The
silicone tubular membrane-aerated photobioreactor was better suited for the cultivation of fragile macroalgal gametophyte
cells due to the absence of hydrodynamic shear stress caused by fluid turbulence and the presence of a bubble-less gas supply. 相似文献
16.
In order to study the N and P balances in the Driss I reservoir, we measured concentrations in the water of these elements,
their sedimentation rates, and their input by the river Inaouen and output through the dam.
Supply and loss of N and P were calculated from samples collected every 48 hours and were for N 15 and 27. 5 mg m−2 d−1 and for P 33.6 and 1.1 mg m−2 d−1 respectively. The sedimentation rates, determined using sediment traps, were high, about 75 mg m−2 d−1 for N and 34 mg m−2 d−1 for P.
Phosphate input came from point sources and was mainly in particulate form. A large fraction of the phosphate sedimented in
the form of calcium bound phosphate, with some iron bound phosphate. Bioavailability was, however, low, as the particulate
phosphate disappeared rapidly from the epilimnion because of the high sedimentation rate. The ratio Tot-N/Tot-P of the sedimented
particulate matter varied between 0.05 and 7.74 and depended on primary production and watergate management. 相似文献
17.
High-rate biological conversion of sulfide and nitrate in synthetic wastewater to, respectively, elemental sulfur (S0) and nitrogen-containing gas (such as N2) was achieved in an expanded granular sludge bed (EGSB) reactor. A novel strategy was adopted to first cultivate mature granules
using anaerobic sludge as seed sludge in sulfate-laden medium. The cultivated granules were then incubated in sulfide-laden
medium to acclimate autotrophic denitrifiers. The incubated granules converted sulfide, nitrate, and acetate simultaneously
in the same EGSB reactor to S0, N-containing gases and CO2 at loading rates of 3.0 kg S m−3 d−1, 1.45 kg N m−3 d−1, and 2.77 kg Ac m−1 d−1, respectively, and was not inhibited by sulfide concentrations up to 800 mg l−1. Effects of the C/N ratio on granule performance were identified. The granules cultivated in the sulfide-laden medium have
Pseudomonas spp. and Azoarcus sp. presenting the heterotrophs and autotrophs that co-work in the high-rate EGSB-SDD (simultaneous desulfurization and denitrification)
reactor. 相似文献
18.
Jordi Vives i Batlle R. C. Wilson S. J. Watts P. McDonald S. R. Jones S. M. Vives-Lynch A. Craze 《Radiation and environmental biophysics》2010,49(1):67-85
The basic principles underlying a four-discrete age group, logistic, growth model for the European lobster Homarus gammarus are presented and discussed at proof-of-concept level. The model considers reproduction, removal by predation, natural death,
fishing, radiation and migration. Non-stochastic effects of chronic low linear energy transfer (LET) radiation are modelled
with emphasis on 99Tc, using three endpoints: repairable radiation damage, impairment of reproductive ability and, at higher dose rates, mortality.
An allometric approach for the calculation of LD50/30 as a function of the mass of each life stage is used in model calibration. The model predicts that at a dose rate of 1 Gy day−1, lobster population reproduction and survival become severely compromised, leading eventually to population extinction. At
0.01 Gy day−1, the survival rate of an isolated population is reduced by 10%, mainly through loss of fecundity, comparable to natural migration
losses. Fishing is the main ecological stress and only dose rates in the range 0.03–0.1 Gy day−1 can achieve discernible effects above it. On the balance of radiation and other ecological stresses, a benchmark value of
0.01 Gy day−1 is proposed for the protection of lobster populations. This value appears consistent with available information on radiation
effects in wildlife. 相似文献
19.
Recent technological advances have led to the discovery that free-living, planktonic protozoa are ubiquitous in nature and
appear to be important components of pelagic food webs (e.g., fluorescent straining, flow cytometry). Despite this, limited
information exists tying their seasonality to rate processes that drive succession patterns. The abundance, and seasonal growth
and grazing loss of an entire protozoan assemblage were evaluated in Lake Michigan. The protozoan assemblage was species-rich
(100 taxa) and abundant throughout the year in Lake Michigan. Nano-sized protozoa (Hnano and Pnano, <20 μm in size) ranged
in abundance from 102 to 103 cells ml−1, while micro-protozoa (Hmicro and Pmico, >20 and <200 μm in size) ranged in abundance from 4 to 17 cells ml−1. The biomass of Hnano and Hmicro by itself represented more than 70–80% of crustacean zooplankton biomass, while Pnano and
Pmicro constituted nearly 50% of phytoplankton biomass. Protozoa exhibited growth rates comparable to other components of
the plankton in Lake Michigan, and some populations grew at rates similar to maximum rates determined in the laboratory (rates
of 1–2 day−1). Overall, it appears that macro-zooplankton predation is a major loss factor counter-balancing growth with only small differences
between the two rate processes (<0.1 day−1). Discrepancies between growth and grazing loss in the spring were likely attributed to sedimentation losses for larger species
of tintinnids and dinoflagellates (Codonella, Tintinnidium, and Gymnodinium) that can account for their occurrence in the deep chlorophyll layer. In the summer, carnivory among similar sized species
(Chromulina and small ciliates) may be additional loss factors impinging on the protozoan assemblage. 相似文献
20.
The effects of temperature (20, 24 and 28 °C) and irradiance (15 and 40 μmol photon m−2 s−1) on the nitrate and ammonium uptake rates of the subtropical red alga, Laurencia brongniartii, were investigated to prepare for tank cultivation. Nitrate uptake followed saturation kinetics and was faster at higher
irradiances and temperatures. In contrast, ammonium uptake was linear over the experimental range and was not affected by
an increase in temperature. A parameter, β, was calculated to compare substrate uptake rates of nitrate along the linear portion
of the uptake curve with that of ammonium. For nitrate, β was lower at low irradiance and higher at high irradiance (β = 0.007
± 0.003 and 0.030 ± 0.002 [μmol N L−1 (μmol N gww−1 d−)−1], respectively). However, β was 0.023 ± 0.002 and 0.034 ± 0.002 [μmol N L−1 (μmol N gww−1 d−1)−1] for ammonium, suggesting a preference for ammonium over nitrate. 相似文献