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1.
The effects of starvation and emersion on the ammonia effluxes of Mytilus edulis L. were studied. Both fed and starved groups showed similar patterns of efflux during re-immersion, indicating no compensation
for starvation during anaerobic catabolism; this is taken as evidence that carbohydrate or lipid is the predominant energy
source at the outset of anaerobiosis. Instead of an overshoot of ammonia excreted during the 4 h following re-immersion, all
groups showed significantly reduced efflux rates independent of emersion duration. Such results suggest some conversion of
ammonia during the recovery period, as no significant drop in haemolymph ammonia occurred at this time. The level of ammonia
accumulation in haemolymph and mantle cavity fluid decreased exponentially with emersion duration, implying the stabilisation,
at a low rate, of ammonia production after a relatively long period of emersion (16 to 24 h). Oxygen levels of the mantle
cavity fluid dropped rapidly during emersion but never attained anoxia over 24 h of emersion, which may indicate some oxygen
uptake by emersed mussels. It has been concluded that the behaviour and physiological responses shown by M. edulis to emersion appear to reflect a need for respiratory gas exchange more than a response to desiccation – presumably in the
interest of energy-conservation. The reductions in ammonia efflux rate during emersion and, to a certain extent, immediately
after re-immersion have also been considered here to be energy-saving strategies that illustrate the importance of ammonia
in restoring normal levels of some amino acids following re-immersion.
Received: 26 August 1997 / Accepted: 27 May 1999 相似文献
2.
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
3.
Effects of emersion and elevated haemolymph ammonia on haemocyanin–oxygen affinity of Cancer
pagurus
The subtidal crab Cancer pagurus (L.) experiences involuntary periods of emersion associated with practices used in their marketing and distribution. During 24 h emersion, impaired gill function caused an increase of circulating total ammonia (TA=NH3+NH4+) of 0.35 mmol TA l-1 (167%). The oxygen-binding characteristics of the haemocyanin of C. pagurus were examined at 10°C in the presence of total ammonia (0.2-1.0 mmol TA l-1). The haemocyanin-oxygen affinity was decreased in the presence of TA ((logP50/(log[TA]=0.16). Emersion induced significant acidosis and elevated circulating levels of haemolymph TA, lactate and urate, but all had returned to normal levels within 24 h of re-immersion. The accumulation of haemocyanin-modulating substances during 24 h emersion compensated partially (40%) for the effect of the acidosis, but the net effect of the emersion period was a significant decrease in oxygen affinity, corresponding to an increase of P50 (10°C ) from 1.24 kPa (immersed) to 1.96 kPa (24 h emersion). The implications of the findings are considered in terms of the effects and adaptations to emersion. 相似文献
4.
The Norwegian lobsterNephrops norvegicus (L.) collected from Firth of Clyde, Scotland between December 1987 and March 1988, was unable to survive longer than 18 h experimental emersion at 10°C. During this time the partial pressure of oxygen (P
O2) in the venous blood decreased rapidly and the lobster supplemented cellular energy requirements by anaerobic metabolism. This was indicated by the rapid accumulation ofL-lactate in the blood. Although the survival rate increased (to ca 36 to 48 h) if lobsters were kept on ice, the accumulation ofL-lactate in the blood was not significantly different from lobsters at 10°C, despite the temperature difference. There was no indication thatN. norvegicus was able to further metabolize circulatingL-lactate during emersion. On emersion there was also a marked hyperglycemia in the blood due to the stress of handling and asphyxiation. There was fairly good agreement between results obtained during laboratory studies and simulated fishing activity in the Firth of Clyde. Both sets of results are discussed in the context of adaptation to air breathing within the Crustacea and an assesment of post-harvest treatment of lobsters. 相似文献
5.
Differential thermal analysis (DTA) was used to measure the freezing temperature of nine species of red brown intertidal macroalgae from the coast of Maine, USA in 1991. Using slow and rapid cooling rates approximating those found in the field for Ascophyllum nodosum (L.) Le Jol. we found that, for a given rate, the freezing points of all species were similar: -7.06 to -8.02°C for slow cooling (ca. 0.25°C min-1) and -3.42 to -4.56°C for rapid cooling (ca. 5.0°C min-1). In the low shore species, Fucus evanescens C. Ag., photosynthesis was inhibited to a greater extent when plants were frozen or thawed rapidly than after slow freezing or thawing. However, in the upper shore species, F. spiralis (L.), photosynthesis recovered rapidly and completely regardless of freezing rate. Rapidly frozen F. evanescens also experienced greater loss of plasmalemmal integrity, evidenced by a greater loss of cellular contents on re-immersion, than those frozen slowly. Light-limited photosynthesis following freezing was more severely inhibited than light-saturated photosynthesis. Respiration was generally enhanced immediately after freezing, but then declined to rates below those of unfrozen controls within 2 h following re-immersion, with control rates of respiration being achieved after a 24 h recovery period. Our data suggest that the physiological consequences of winter emersion at sub-zero temperatures may vary widely between individual plants of freezing-susceptible species, due to the wide variations in freezing rate associated with microhabitat effects. 相似文献
6.
To determine the effects food ration and feeding regime on growth and reproduction of Strongylocentrotus droebachiensis (Müller), sea urchins in laboratory aquaria were fed kelp (Laminaria longicruris) supplied at either a high (H, ad libidum daily) or a low (L, ad libidum 1 d wk−1) ration in two successive 12-wk intervals during the reproductive period. After 24 wk, urchins fed the high ration continuously
(HH) or for the last 12 wk only (LH) had a significantly greater mean gonad index [(gonad weight/total body weight) × 100]
and body weight than urchins fed the low ration continuously (LL) or for the last 12 wk only (HL). Urchins in the HL treatment
had a significantly greater gonad index than those in the LL treatment; there was no significant difference in gonad index
between the LH and HH treatments. Females had a greater gonad index than males in the low ration (LL and HL) treatments at
the end of the experiment; there was no significant difference between sexes in the high ration (LH, HH) treatments. Gametogenesis
proceeded to maturation in all treatments and some individuals spawned at the end of the experiment. Females in the high ration
(HH and LH) treatments had a greater proportion of nutritive phagocytes in their ovaries than females in the low ration treatments,
but there was no effect of feeding treatment on oocyte or ovum size. Feeding treatment had no effect on the relative abundance
of nutritive phagocytes in the testes, although the proportion of spermatocytes was higher (and that of spermatozoa lower)
in the high ration than in the low ration treatments. Urchins in the high ration treatments had a lower mean jaw height index
[(jaw height/test diameter) × 100] and greater mean test diameter than those in the low ration treatments at the end of the
experiment, although these differences were not statistically significant. Feeding rate on kelp at the end of the experiment
was significantly greater for urchins in the low ration than in the high ration treatments. Our experimental results show
that even relatively low rations of kelp support somatic and gonadal growth in S. droebachiensis. Increasing the supply of kelp, particularly during the period of active gametogenesis, results in maximal rates of growth
and reproduction. These results suggest that populations of S. droebachiensis in barrens may derive a substantial proportion of their nutrition from drift kelp, which may contribute to their persistence
in these habitats. They also explain the large body size, high reproductive effort and fecundity of urchins grazing on kelp
beds. These findings have important implications for understanding the dynamics of natural populations of S. droebachiensis and for development of effective aquacultural practices.
Received: 17 February 1997 / Accepted: 5 March 1997 相似文献
7.
Photosynthetic rates of eight seagrass species from Zanzibar were limited by the inorganic carbon composition of natural
seawater (2.1 mM, mostly in the form of HCO3
−), and they exhibited more than three time higher rates at inorganic carbon saturation (>6 mM). The intertidal species that grew most shallowly, Halophila ovalis, Halodule wrightii and Cymodocea rotundata, showed the highest affinity for inorganic carbon (K
1/2 = ca. 2.5 mM), followed by the subtidal species (K
1/2 > 5 mM). Photosynthesis of H. wrightii, C. rotundata, Cymodocea serrulata and Enhalus acoroides was >50% inhibited by acetazolamide, a membrane-impermeable inhibitor of carbonic anhydrase, indicating that extracellular
HCO3
− dehydration is an important part of their inorganic carbon uptake. Photosynthetic rates of H. wrightii, Thalassia hemprichii, Thalassodendron ciliatum, C. serrulata and E. acoroides were strongly reduced by changing the seawater pH from 8.2 to 8.6 in a closed system. In H. ovalis, C. rotundata and Syringodiumisoetifolium, photosynthesis at pH 8.6 was maintained at a higher level than could be caused by the ca. 30% CO2 concentration which remained in the closed experimental systems at that pH, pointing toward HCO3
− uptake in those species. It is suggested that the ability of H. ovalis and C. rotundata to grow in the high, frequently air-exposed, intertidal zone may be related to a capability to take up HCO3
− directly, since this is a more efficient way of HCO3
− utilisation than extracellular HCO3
− dehydration under such conditions. The inability of all species to attain maximal photosynthetic rates under natural conditions
of inorganic carbon supports the notion that seagrasses may respond favourably to any future increases in marine CO2 levels.
Received: 19 March 1997 / Accepted: 31 March 1997 相似文献
8.
Blood oxygen-binding characteristics of bigeye tuna (Thunnus obesus), a high-energy-demand teleost that is tolerant of low ambient oxygen 总被引:1,自引:0,他引:1
We found blood from bigeye tuna (Thunnus obesus) to have a significantly higher O2 affinity than blood from other tunas. Its P50 (partial pressure of oxygen, PO2 required to reach 50% saturation) was 1.6 to 2.0 kPa (12 to 15 mmHg) when equilibrated with 0.5% CO2. Previous studies employing similar methodologies found blood from yellowfin tuna (T. albacares), skipjack tuna (Katsuwonus pelamis), and kawakawa (Euthynnus affinis) to have a P50 of 2.8 to 3.1 kPa (21 to 23 mmHg). These observations suggest that bigeye tuna are more tolerant of low ambient oxygen than
other tuna species, and support similar conclusions derived from laboratory whole-animal studies, depth-of-capture data, and
directly-recorded vertical movements of fish in the open ocean. We also found the O2 affinity of bigeye tuna blood to be essentially unaffected by a 10 C° open-system temperature change (as is the blood of
all tuna species studied to date). The O2 affinity of bigeye tuna blood was, however, more affected by a 10 C° closed-system temperature change than the blood of any
tuna species yet examined. In other words, bigeye tuna blood displayed a significantly enhanced Bohr effect (change in log
P50 per unit change in plasma pH at P50) when subjected to the inevitable changes in partial pressure of carbon dioxide (PCO2) and plasma pH that accompany closed-system temperature shifts, than when subjected to changes in plasma pH accomplished
by changing PCO2 alone. In vivo, the resultant large decrease in O2 affinity (i.e. the increase in P50) that occurs as the blood of bigeye tuna is warmed during its passage through the vascular counter-current heat exchangers
ensures adequate rates of O2 off-loading in the swimming muscles of this high-energy-demand teleost.
Received: 12 March 1999 / Accepted: 18 December 1999 相似文献
9.
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
10.
Free amino acids and energy metabolism in eggs and larvae of seabass, Lates calcarifer 总被引:3,自引:0,他引:3
Contents of free amino acids (FAA), protein and ammonium ions together with rates of ammonia excretion and oxygen consumption
were measured in order to study the role of FAA as an energy substrate in developing eggs and larvae of seabass (Lates calcarifer) maintained in seawater (30 ppt) at 28 °C without feeding. Initially eggs contained 25.3 nmol ind−1 of FAA of which 21.5 nmol was rapidly utilised by the developing eggs and larvae during the period up to 40 h post spawning
(PS) when nearly all the yolk had been resorbed. During the same period, a net increase in protein content of 1.7 μg ind−1 was observed, indicating that the major part of the amino acids lost from the free pool had been polymerised into body proteins.
Assuming that the balance of the FAA after protein synthesis was used entirely for energy metabolism, FAA appeared to be an
important energy substrate during the embryonic stages (2 to 16 h PS); after hatching, the contribution of FAA to energy metabolism
was less significant. From 50 h PS until the end of the study period at 100 h PS, amino acids derived from somatic protein
were used for energy metabolism. For the overall period from just after spawning up to 100 h PS, the data indicate that ca.
14% of the total aerobic energy metabolism was derived from amino acid catabolism.
Received: 26 September 1997 / Accepted: 1 April 1998 相似文献
11.
E. Pfeiler 《Marine Biology》1997,127(4):571-578
Bonefish (Albula sp.) larvae (leptocephali) from the Gulf of California complete metamorphosis in ˜10 d in natural seawater (35‰S; Ca2+ conc = 10.5 mM). The increase in ossification that occurs near the end of the non-feeding metamorphic period, in addition to the ability
of larvae to complete metamorphosis in dilute seawater (8‰ S) prompted the present study, where the effects of varying the
external calcium ion concentration, [Ca2+]e, of artificial seawater (ASW) on the survival, development and internal (whole-body) calcium ion content, (Ca2+)i, of unfed metamorphosing larvae were investigated. Early-metamorphosing larvae placed in␣ASW, where [Ca2+]e = 10.1 mM, survived for up to 10 d and developed normally without exogenous nutrients. In shorter-term experiments (4 to 5 d), no differences
in survival were found for larvae in ASW with [Ca2+]e rang-ing from 1.5 to 10.1 mM. However, in Ca2+-free ASW, most larvae died within 27 h and no larvae survived more than 42 h; the median lethal time (LT50), and its 95% confidence limits, were 14.5 (10.0 to 20.9) h. High mortality (81% after 20 h) also occurred in 1.0 mM Ca2+ ASW, but 2 of 16 larvae tested survived for 96 h. The 96 h median tolerance limit (TLM), corrected for control mortality, was 1.2 mM Ca2+. In natural seawater, larval (Ca2+)i remained relatively constant ( = 0.419 mg larva−1)␣in early- and intermediate-metamorphosing larvae, and then increased to a mean value of 0.739 mg larva−1 in advanced larvae, indicating that Ca2+ was␣taken up from the medium at this stage; the increase in (Ca2+)i corresponded to the period of ossification of the vertebral column. Internal (whole-body) magnesium ion content (Mg2+)i showed no significant change during metamorphosis ( = 0.089 mg larva−1). No significant differences in (Ca2+)i were found in advanced larvae in natural seawater and those in ASW, with [Ca2+]e ranging from 2.0 to 10.1 mM. However, clearing and staining revealed that ossification of the vertebral column had not yet occurred in advanced larvae
from 2.0 to 10.1 mM Ca2+ ASW. Also, low [Ca2+]e (1.0 to 2.0 mM) usually produced deformed larvae that swam erratically, at times showing “whirling” behavior.
Received: 21 August 1996 / Accepted: 26 August 1996 相似文献
12.
Effect of temperature fluctuations and food supply on the growth and metabolism of juvenile sea scallops (Placopecten magellanicus) 总被引:1,自引:0,他引:1
On the eastern shore of Nova Scotia late summer atmospheric systems cause upwelling of shelf water; the associated temperature
variations of 10 °C with a 6 to 8 d period are comparable in magnitude to the seasonal variation. A laboratory study was undertaken
to assess the effects of these temperature fluctuations on sea scallop (Placopecten magellanicus) growth and metabolism. In a factorial design, scallops were subjected to constant (10 °C) or a variable (6 to 15 °C) 8 d
temperature cycle, and either a low (seston in filtered seawater) or high (seston supplemented with cultured phytoplankton)
food diet. During the 48 d experiment scallop mortality was low and growth positive in all treatments. Shell and total tissue
growth rate did not differ between temperature treatments, but growth in the high food treatments was 40 to 50% higher than
in the low food treatments. However, soft tissue (excluding adductor) growth did show a temperature treatment effect; growth
rates were significantly higher in the fluctuating temperature treatment, due in part to greater gonad development. Weight-standardized
rates of scallop oxygen consumption (V
sO2 , μmol O2 g−1 h−1) were 20 to 25% higher in high food than in low food treatments, consistent with the expected increase in respiration due
to the higher growth rates. Scallop metabolism did not acclimate to the fluctuating temperature cycle; V
sO2 and ammonium excretion (V
sNH+
4, μmol O2 g−1 h−1) remained dependent on ambient temperature throughout the experiment. V
sNH+
4 Q10 (2.77) was higher than V
sO2 Q10 (2.01) which was reflected in a decrease in the O:N ratio at 15 °C, indicating a shift toward increased protein catabolism
and a stressed state. At 10 °C, V
sO2 and V
sNH+
4 in the variable temperature treatments were 15 to 18% lower than in the constant temperature treatments, a difference that
was not detected in growth measurements. Results demonstrate that the metabolism of Placopecten magellanicus, unlike some bivalve species, is tightly coupled to fluctuations in ambient temperature. Although an absence of compensatory
acclimation had a minimal effect on growth in this study, if high temperatures were combined with low food conditions a reduction
in scallop production could result.
Received: 23 June 1998 / Accepted: 8 February 1999 相似文献
13.
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
14.
On the roofs of subtidal crevices, the giant cuttlefish (Sepia apama) of southern Australia lays clutches of lemon-shaped eggs which hatch after 3 to 5 mo. Diffusion of oxygen through the capsule
and chorion membrane to the perivitelline fluid and embryo was modelled using the equation V˙
O2 = G
O2(P
O2out−P
O2in), where V˙
O2 = rate of oxygen consumption, G
O2 = oxygen conductance of the capsule, and P
O2 values = oxygen partial pressures across the capsule. During development, V˙
O2 rose exponentially as the embryo grew, reaching 5.5 μl h−1 at hatching. Throughout development, the capsule dimensions enlarged by absorption of water into the perivitelline space,
increasing G
O2 by a combination of increasing surface area, and decreasing thickness of the capsule. These processes maintained P
O2in high enough to allow unrestricted V˙
O2 until shortly before hatching. Diffusion limitation of respiration in hatching-stage embryos was demonstrated by (1) increased
embryonic V˙
O2 when P
O2out was experimentally raised, (2) greater V˙
O2 of resting individuals immediately after hatching, and (3) reduced V˙
O2 of hatchlings at experimental P
O2 levels higher than P
O2in before hatching. Thus, low P
O2in may be the stimulus to hatch. Potential problems of diffusive gas-exchange are mitigated by the relatively low incubation
temperature (12 °C), which may be a factor limiting the distribution of the species to cool, southern waters.
Received: 14 August 1999 / Accepted: 24 January 2000 相似文献
15.
The diatom Cylindrotheca closterium was exposed to transient light- and osmotic conditions as occur during its tidal emersion. The objective was to analyze how
this simulated emersion contributes to the production of active oxygen species (AOS) and via this, to oxidative cell damage.
Light- and salinity conditions were varied in factorial combination: low light (no UVB) or high light (unweighted UVB-dose
rates of respectively 0.01; 0.07; 0.24; 1.03 W m−2) at normal (30 psu) or high salinity (60 psu). UVB (0.01–0.24 W m−2) and high salinity had a significant, negative effect on the photosynthetic efficiencies ΔF/F
m’ (steady-state quantum yield) and F
v/F
m (maximum yield). UVB at 1.03 W m−2 (15 kJ m−2 d−1) almost arrested electron transport. At ecologically relevant UVB levels, i.e. below 0.24 W m−2 (≈3.4 kJ m−2 d−1) with UVB:PAR<0.4:100 (PAR photosynthetically active radiation) only dynamic photoinhibition was observed (protection via
heat dissipation). Non-photochemical quenching was positively correlated with the de-epoxidation of diadinoxanthin (DD) to
diatoxanthin (DT). A decreasing ratio DT/(DD+DT) after 4 h of UVB at >0.07 W m−2 and at 60 psu indicated a reversal of the diatom xanthophyll cycle (diminished photoprotection) which may be caused by an
enhanced AOS production. Oxidative stress and -damage to C. closterium cells were assessed applying fluorescent indicator dyes, via confocal microscopy and quantitative image analysis. AOS production
rates (cellular DCF fluorescence) were stimulated by UV, and were ~50% higher at 60 psu. AOS production decreased with an
increasing pre-exposure (0–4 h) to normal UVB (0.24 W m−2), which indicated a stimulation of the antioxidative defence. Non-protein thiols (indicator CMF) and glutathione pools (HPLC-analyzed)
decreased with UVB-dose rates (0.01–0.24 W m−2), most likely due to AOS-mediated thiol oxidation. Hypersalinity (60 psu) and UVB (0.01–0.24 W m−2) caused membrane depolarization (dye DIBAC4(3)) and phospholipid hydrolysis (phospholipase A2 dye: bis-BODIPY FL-C11-PC). AOS production may have diminished the membrane polarity, and peroxidized the membrane lipids (HPLC-analyzed malondialdehyde)
which enhanced PLA2 activity. The dyes indicated an increased oxidative (lipid) damage at a 15% inhibition of photosynthesis in this diatom,
at UVB levels and salinities that can be expected in situ during its periodic tidal emersion. 相似文献
16.
A key regulatory mechanism underlying the switch between aerobic and anaerobic metabolism amongst anoxia-tolerant marine
molluscs is reversible protein phosphorylation. To assess the role of cAMP-dependent protein kinase (PKA) in aerobic–anaerobic
transitions, the effects of anoxia on the activity and subcellular distribution of PKA were assessed in foot and hepatopancreas
of the marine periwinkle, Littorina littorea. Exposure to N2 gas at 5 °C caused a rapid decline in the percentage of total enzyme present as the free catalytic subunit (PKAc) in both
tissues; the percentage of PKAc fell from ∼30% in controls to 3% after 1 h anoxia and remained low over 72 h. Total PKA also
fell by 30% after 72 h anoxia in hepatopancreas but rebounded during aerobic recovery. Freezing at −8 °C elicited parallel
results for both percentage of PKAc and total PKA, suggesting that PKA responses to freezing were stimulated by the ischemia
that develops when hemolymph freezes. Anoxia also led to a shift in PKA subcellular distribution in hepatopancreas (but not
in foot), the percentage of total PKA activity associated with the nuclear fraction dropping from 25% in controls to 8% in
12 h anoxic snails with opposite changes in the cytosolic fraction. The catalytic subunit (PKAc) of foot PKA was purified
to a final specific activity of 63.5 nmol phosphate transferred per minute per milligram protein. Enzyme properties included
a molecular weight of 33 to 35 kDa, an activation energy from Arrhenius plots of 65.1 ± 4.8 kJ mol−1, and substrate affinity constants of 151 ± 6 μM for the phosphate acceptor, Kemptide, and 72 ± 9 μM for Mg.ATP. Activity was strongly reduced by mammalian PKA inhibitors (H-89, PKA-I), by neutral chloride salts (I50 values 165 to 210 mM) and by NaF (I50 62 mM). Reduced PKA activity under anoxic or freezing conditions would facilitate the observed suppression of the activities of
numerous enzymes that are typically PKA-activated and thereby contribute to the overall anoxia-induced metabolic rate depression.
Received: 19 November 1997 / Accepted: 30 September 1998 相似文献
17.
K. A. Tricklebank 《Marine Biology》2000,136(2):337-348
Parma microlepis (Günther) were collected from Malabar, an urban location close to the centre of Sydney, Australia, and from Jervis Bay, a
reference location 170 km south of the city centre. At each location, fish were collected from two sites separated by 100
to 200 m. The ultrastructure of normal liver tissue is described based on 20 female fish collected from Jervis Bay, where
fish are known to be exposed to low levels of organochlorine contaminants. Alterations in the endoplasmic reticulum, mitochondria,
lysosomes and nuclei of hepatocytes were identified and quantified in the liver tissue of fish from this location and compared
to alterations in 20 female fish collected from Malabar, where fish are exposed to higher concentrations of organochlorine
pesticides such as DDT compounds. There were significant differences in the percentage of hepatocytes with swollen mitochondria
(F = 124.025, df = 2, 2, P = 0.008) and atypical nuclei (F = 22.198, df = 2, 2, P = 0.043) between sites (100 to 200 m apart), but there were no clear differences between the percentage of structural alterations
in the hepatocytes of P. microlepis from Jervis Bay and Malabar. Associations between liver morphology and the organochlorines aldrin, dieldrin, DDE and chlordane
were examined using a Pearson correlation matrix. Significant correlations were detected between the percentage of hepatocytes
with dilated endoplasmic reticulum and the concentrations of the pesticide aldrin (r = 0.600, df = 11, r
crit(α = 0.05) = 0.553). Significant associations were also detected between the percentage of hepatocytes with disorganised endoplasmic
reticulum and the concentrations of dieldrin and DDE residues in fish (r = 0.576, r = 0.567, respectively, df = 13, r
crit (α = 0.05) = 0.514). However, there was little evidence that ultrastructural alterations in fish responded to increasing concentrations
of these pesticides in a consistent dose-response manner.
Received: 20 October 1998 / Accepted: 24 November 1999 相似文献
18.
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
19.
The growth rates of two fish species, the winter flounder Pseudopleuronectes americanus (Walbaum) (19.3 to 42.6 mm total length, TL) and the tautog Tautogaonitis (Linnaeus) (23.9 to 55.9 mm TL), were used to evaluate habitat quality under and around municipal piers in the Hudson River
estuary, USA. Growth rates were measured in a series of 10 d field caging-experiments conducted at two large piers in the
summers of 1996 and 1997. Cages (0.64 m2) were deployed along␣transects that stretched from underneath the piers to beyond them, encompassing the pier edge (the transitional
zone between the pier interior and the outside). Growth in weight (G
w
) was determined at five locations along the transect, 40 m beneath the pier, 20 m beneath the pier, at the pier edge, 20 m
beyond the pier edge, and 40 m beyond. Under piers, mean growth rates of winter flounder and tautogs were negative (xˉG
W
= −0.02 d−1), and rates were comparable to laboratory-starved control fishes (xˉG
W
= −0.02 d−1). In contrast, mean growth rates at pier edges and in open waters beyond piers were generally positive (xˉG
W
ranged from −0.001 to +0.05 d−1), with growth at pier edges often being more variable and less rapid than at open-water sites. Analyses of stomach contents
upon retrieval of caged fishes revealed that dry weights of food were generally higher among fishes caged at open-water stations
(xˉ range = 0.02 to 0.72 mg dry wt) than at pier-edge (xˉ range = 0.01 to 0.54 mg) or under-pier (xˉ range = 0.03 to 0.11 mg) stations, although it was apparent that benthic prey were available at all stations on the transect.
Our results indicate poor feeding conditions among fishes caged under piers, and suboptimal foraging among fishes caged at
pier edges. Inadequate growth rates can lead to higher rates of mortality, and, based on these and other earlier experiments,
we conclude that under-pier environments are poor-quality habitats for some species of juvenile fishes.
Received: 12 March 1998 / Accepted: 9 November 1998 相似文献
20.
Grazing effects on nitrogen fixation in coral reef algal turfs 总被引:2,自引:0,他引:2
This study addressed whether grazing by the sea urchin Diadema antillarum influenced rates of nitrogen fixation by algal turf communities on Caribbean coral reefs. Because the turfs were nitrogen-limited,
we also assessed whether newly-fixed nitrogen was important for supporting net primary productivity by the turfs. We measured
acetylene reduction in turfs grown in treatments excluding or including D. antillarum in the presence of other herbivores at 3 m water depth on Tague Bay forereef, St. Croix, U.S. Virgin Islands. These were
the first measurements of acetylene reduction on coral reefs under quasi-natural conditions of high water-flow and photosynthetic
oxygen generation. Rates of acetylene reduction under these conditions were as high as any measured previously in coral reef
communities (mean 7.6 nmol C2H4 cm−2 h−1). Algal turfs grazed by D. antillarum and other herbivores had chlorophyll-specific acetylene reduction rates up to three times higher than when D. antillarum was excluded. High rates of nitrogen fixation by the turfs were sufficient to meet <2% of the nitrogen required to support
net chlorophyll-specific primary productivity over 24 h. Grazer-mediated increases in nitrogen fixation do not appear responsible
for a parallel enhancement of net primary productivity. Algal turfs at this site must be dependent primarily on external sources
of nitrogen.
Received: 1 July 1997 / Accepted: 5 September 1997 相似文献