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1.
The shortfin mako shark, Isurus oxyrinchus, is a highly streamlined epipelagic predator that has several anatomical and physiological specializations hypothesized to
increase aerobic swimming performance. A large swim-tunnel respirometer was used to measure oxygen consumption (MO2) in juvenile mako sharks (swimming under controlled temperature and flow conditions) to test the hypothesis that the mako
shark has an elevated maintenance metabolism when compared to other sharks of similar size swimming at the same water temperature.
Specimen collections were conducted off the coast of southern California, USA (32.94°N and 117.37°W) in 2001-2002 at sea-surface
temperatures of 16.0–21.0°C. Swimming MO2 and tail beat frequency (TBF) were measured for nine mako sharks [77–107 cm in total length (TL) and 4.4 to 9.5 kg body mass]
at speeds from 28 to 54 cm s−1 (0.27–0.65 TL s−1) and water temperatures of 16.5–19.5°C. Standard metabolic rate (SMR) was estimated from the extrapolation to 0-velocity
of the linear regression through the LogMO2 and swimming speed data. The estimated LogSMR (±SE) for the pooled data was 2.0937 ± 0.058 or 124 mg O2 kg−1 h−1. The routine metabolic rate (RMR) calculated from seventeen MO2 measurements from all specimens, at all test speeds was (mean ± SE) 344 ± 22 mg O2 kg−1h−1 at 0.44 ± 0.03 TL s−1. The maximum metabolic rate (MMR) measured for any one shark in this study was 541 mg O2 kg−1h−1 at 54 cm s−1 (0.65 TL s−1). The mean (±SE) TBF for 39 observations of steady swimming at all test speeds was 1.00 ± 0.01 Hz, which agrees with field
observations of 1.03 ± 0.03 Hz in four undisturbed free-swimming mako sharks observed during the same time period. These findings
suggest that the estimate of SMR for juvenile makos is comparable to that recorded for other similar-sized, ram-ventilating
shark species (when corrected for differences in experimental temperature). However, the mako RMR and MMR are apparently among
the highest measured for any shark species. 相似文献
2.
Total mercury and methylmercury concentrations in fish from the Mojana region of Colombia 总被引:1,自引:0,他引:1
Marrugo-Negrete J Verbel JO Ceballos EL Benitez LN 《Environmental geochemistry and health》2008,30(1):21-30
Total mercury (T-Hg) and methylmercury (MeHg) concentrations have been measured in the muscle tissue of 16 fish species consumed
in the Mojana region of Colombia. T-Hg analysis was performed by cold-vapor atomic-absorption spectroscopy (CV-ASS) and MeHg
analysis by gas chromatography with electron-capture detection. Higher T-Hg and MeHg concentrations were detected in carnivorous
species (T-Hg = 0.371 ± 0.172 (μg g−1 fresh wt, MeHg = 0.346 ± 0.171 μg g−1 fresh wt) than in non-carnivorous fish (T-Hg = 0.155 ± 0.108 μg g−1 fresh wt, MeHg = 0.146 ± 0.102 μg g−1 fresh wt). In the different species mercury was present almost completely as the methylated form, with percentages between
80.5 and 98.1% (mean 92.0 ± 3.4%). In 13.5% of fish-tissue samples T-Hg concentrations exceeded the maximum level recommended
by the World Health Organization for human consumption (Hg = 0.5 μg g−1 fresh wt). Although mean T-Hg concentrations in all fish samples (0.269 ± 0.181 μg g−1 fresh wt) did not exceed this limit, risk assessment suggested that the consumption of 0.12 kg fish day−1 could increase the risk of mercury poisoning of the inhabitants of this region. 相似文献
3.
Lesser sandeel (Ammodytes tobianus) is abundant in near-shore areas where it is a key prey. It exhibits the behaviour of alternating between swimming in schools
and lying buried in the sediment. We first determined the species’ standard metabolic rate (SMR), critical partial pressure
of oxygen
and maximal oxygen uptake
The sandeel were then exposed to an acute stepwise decline in water oxygen pressure (18.4, 13.8, 9.8, 7.5, 5.8, 4.0, and
3.1 kPa
). Swimming speed and routine- and post-experimental blood lactate levels were measured, in addition to levels associated
with strenuous exercise. The SMR was 69.0 ± 8.4 mg O2 kg−1 h−1 and the
about seven times as high. The
was found to be 4.1 kPa. A rapid decrease (within 1 h) in
from 18.4 to 3.1 kPa had no significant effect on routine swimming speed (0.9 ± 0.06 bl s−1), but steady levels at the lowest
(3.1 kPa) gradually reduced the swimming speed by 95% after 40 min. The routine blood lactate levels were 2.2 ± 0.6 mmol
l−1, while the levels in the strenuously exercised groups were significantly higher with 5.4 ± 1.6 and 5.8 ± 1.3 mmol l−1. The highest levels were observed in post-experimental fish with 7.5 ± 2.7 mmol l−1. We argue that, as sandeel showed no decrease in swimming speed (to offset stress) nor an increased speed to escape the hypoxia,
the fish either rely on a low SMR and being a reasonable strong oxygen regulator
as a mean to cope when exposed to acute hypoxia, or that the hypoxia simply developed too fast for the fish to decide on
an appropriate strategy. Not showing a behavioural response may in the present case be maladaptive, as the consequence was
major physiological stress which the fish however appears tolerant towards. The high routine blood lactate levels suggest
that anaerobic metabolism is associated with swimming in sandeel, which may be related to the specific lifestyle of the fish
where they regularly bury in the sediment. 相似文献
4.
While qualitative observations of jellyfish intraguild predation abound in the literature, there are only few rate measurements
of these interactions. We quantified predation rates among two common jellyfish in northern boreal waters, Cyanea capillata and its prey Aurelia aurita, both of which also feed on crustacean zooplankton and fish larvae. A series of incubation experiments using a wide range
of prey concentrations (0.38–3.8 m−3) in large containers (2.6 m3) was carried out. By replenishing the prey continuously as they were captured we maintained a nearly constant prey concentrations.
Ingestion rates increased linearly up to prey concentrations of 1.92 m−3, yielding maximum clearance rates of ∼2.37 ± 0.39 m3 predator−1 h−1 for C. capillata predators 16 ± 2.3 cm in diameter. Mean ingestion rate at saturated prey concentrations (1.92–3.85 m−3) was 4.01 ± 0.78 prey predator−1 h−1. Behavioral observations suggested that predators did not alter their swimming behavior during meals, and thus that feeding
rates were generally handling limited rather than encounter limited. Predators captured more prey than needed, and semi-digested
prey was often discarded when fresh prey was encountered. 相似文献
5.
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
6.
E. Amato L. Alcaro I. Corsi C. Della Torre C. Farchi S. Focardi G. Marino A. Tursi 《Marine Biology》2006,149(1):17-23
In order to gain preliminary knowledge about the threat to marine ecosystems due to leakage of chemical warfare agents (CWAs)
and other pollutants from rusting bombshells on the seabed, a case study was conducted in a dumping area in the southern Adriatic
Sea (depth 200–300 m). Following electroacoustic and magnetometric surveys of the CWA dumping area, an integrated ecotoxicological
approach was used. This approach was based on analysis of CWA residues and their metabolites, including arsenic, in sediment
and organisms, as well as multimarker methodology including the Health Assessment Index, histological lesion analysis and
enzyme assays. Two sentinel species were selected, the blackbelly rosefish [Helicolenus dactylopterus (Delaroche, 1809)] and the European conger (Conger conger L., 1758). Sediment analysis revealed the presence of CWA degradation products, including 1-4-thioxane and 1-4-dithiane.
Tissues of fish from the CWA dumping site showed higher levels of arsenic than those from the reference site. Neither CWAs
nor their metabolites were detected in fish tissues. Arsenic levels recorded in blackbelly rosefish were well above those
reported for other fish species from the southern Adriatic, much higher than the FDA limit for food (2.6 mg kg−1) and close to the LD50 calculated for mammals (20 mg kg−1 body weight). The presence of pollutants in the CWA dumping site was also confirmed by pathological lesions in both species
and EROD activity, two to three times higher than in fish from the reference site (16.45±8.08 and 8.05±5.87 pmol min−1 mg protein−1 in blackbelly rosefish and 269±24.92 and 78.71 pmol min−1 mg protein−1 in European conger, respectively). Cholinesterase activity seemed unaffected in muscle of both species, whereas in brain
they were one-third of those recorded in fish from the reference site (14.22±10.05 and 72.87 nmol min−1 mg protein−1, respectively). This suggests that acetylcholinesterase is sensitive to CWAs. In conclusion, the agreement of all the chemical
and biological parameters investigated suggests that the integrated ecotoxicological approach used is appropriate to reveal
the presence and biological effects of CWAs in the marine ecosystem.
Physical and Chemical Impacts on Marine Organisms, a Bilateral Seminar in Italy–Japan held in November 2004. 相似文献
7.
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
8.
Ammonium concentrations of ∼1 M are commonly cited as being the threshold for inhibition of NO3
− uptake, but the applicability of this threshold to phytoplankton from different taxonomic classes has rarely been examined.
Additionally, little is known about the influence of environmental variables (e.g. growth temperature) on the interaction
between ambient NH4
+ and NO3
− uptake. Four species of estuarine phytoplankton, two diatom [Chaetoceros sp., and Thalassiosira weissflogii (Grunow) Fryxell et Hasle] and two dinoflagellate [Prorocentrum minimum (Pavillard) Schiller, and Gyrodinium uncatenum Hulburt], were grown on NO3
− at several different temperatures (4, 10, 15, or 20 °C), and the impact of NH4
+ additions on NO3
− uptake/assimilation (non-TCA-extracted) and assimilation (TCA-extracted) was assessed. For all species at all temperatures,
NO3
− uptake/assimilation and assimilation rates decreased in a roughly exponential manner with increasing NH4
+ concentrations but were not completely inhibited even at elevated NH4
+ concentrations of 200 μM. Estimated half-inhibition concentrations (K
i) were significantly greater in the diatom species (mean ± SE; 2.70 ± 0.67 μM) than in the dinoflagellate species (1.26 ± 0.55 μM). Half-inhibition constants were positively related to temperature-limited relative growth rate although not significantly.
The observed inhibition of NO3
− uptake and assimilation, as a percentage of NO3
− uptake in the absence of NH4
+, averaged about 80% and ranged from 49 to 100%. For all species, a significant (P < 0.001) positive correlation was found between percent inhibition of NO3
− assimilation and temperature-limited relative growth rate. Two experiments on Chesapeake Bay phytoplankton during an April
1998 diatom bloom showed that in short-term (∼1 h) temperature manipulation experiments, percent inhibition of NO3
− uptake/assimilation was also positively related (P = 0.05) to experimental temperature. The observed relationships between temperature-limited relative growth rate and percent
inhibition of NO3
− assimilation rates for the species tested suggest that at the enzyme level, the inhibitory mechanism of NO3
− assimilation is similar among species, but at the whole cell level may be regulated by species-specific differences in the
accumulation of internal metabolites. These findings add not only to our understanding of species-specific variability and
the role of growth temperature, but also provide additional data with which to evaluate current models of NH4
+ and NO3
− interactions.
Received: 31 August 1998 / Accepted: 7 December 1998 相似文献
9.
Oxygen consumption and tail beat frequency were measured on saithe (Pollachius virens) and whiting (Merlangius merlangus) during steady swimming. Oxygen consumption increased exponentially with swimming speed, and the relationship was described by a power function. The extrapolated standard metabolic rates (SMR) were similar for saithe and whiting, whereas the active metabolic rate (AMR) was twice as high for saithe. The higher AMR resulted in a higher scope for activity in accordance with the higher critical swimming speed (U
crit) achieved by saithe. The optimum swimming speed (U
opt) was 1.4 BL s−1 for saithe and 1.0 BL s−1 for whiting with a corresponding cost of transport (COT) of 0.14 and 0.15 J N−1 m−1. Tail beat frequency correlated strongly with swimming speed as well as with oxygen consumption. In contrast to swimming speed and oxygen consumption, measurement of tail beat frequency on individual free-ranging fish is relatively uncomplicated. Tail beat frequency may therefore serve as a predictor of swimming speed and oxygen consumption of saithe and whiting in the field. 相似文献
10.
Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa 总被引:1,自引:0,他引:1
Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O2 and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O2 concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured
at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness
decreased the O2 concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell
surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O2 h−1 foraminifer−1. The net photosynthesis averaged 5.3 ± 2.7 nmol O2 h−1. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O2 h−1, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O2 h−1). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross
photosynthesis versus scalar irradiance curves (P vs E
o curves) showed light saturation irradiances (E
k) of 75 and 137 μmol photons m−2 s−1 in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m−2 s−1. The light compensation point of the symbiotic association was 50 μmol photons m−2 s−1. Radial profile measurements of scalar irradiance (E
o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E
d).
Received: 26 January 1998 / Accepted: 11 April 1998 相似文献
11.
Richard Brill Yonat Swimmer Carina Taxboel Katherine Cousins Timothy Lowe 《Marine Biology》2001,138(5):935-944
We hypothesize that the morpho-physiological adaptations that permit tunas to achieve maximum metabolic rates (MMR) that
are more than double those of other active fishes should result in high water and ion flux rates across the gills and concomitant
high osmoregulatory costs. The high standard metabolic rates (SMR) of tunas and dolphin fish may, therefore, be due to the
elevated rates of energy expenditure for osmoregulation (i.e. teleosts capable of achieving exceptionally high MMR necessarily
have SMR). Previous investigators have suggested a link between activity patterns and osmoregulatory costs based on Na+-K+ ATPase activity in the gills of active epipelagic and sluggish deep-sea fishes. Based on these observations, we conclude
that high-energy-demand fishes (i.e. tunas and dolphin fish) should have exceptionally elevated gill and intestinal Na+-K+ ATPase activity reflecting their elevated rates of salt and water transfer. To test this idea and estimate osmoregulatory
costs, we measured Na+-K+ ATPase activity (V
max) in homogenates of frozen samples taken from the gills and intestines of skipjack and yellowfin tunas, and the gills of dolphin
fish. As a check of our procedures, we made similar measurements using tissues from hybrid red tilapia (Oreochromis mossambicus ×O. niloticus). Contrary to our supposition, we found no difference in Na+-K+ ATPase activity per unit mass of gill or intestine in these four species. We estimate the cost of osmoregulation to be at
most 9% and 13% of the SMR in skipjack tuna and yellowfin tuna, respectively. Our results, therefore, do not support either
of our original suppositions, and the cause(s) underlying the high SMR of tunas and dolphin fish remain unexplained.
Received: 7 September 2000 / Accepted: 4 December 2000 相似文献
12.
Predation on Euphausia pacifica by demersal fishes: predation impact and influence of physical variability 总被引:2,自引:0,他引:2
The importance of Euphausia pacifica Hansen to the demersal fish community off Sendai Bay, northern Japan, was studied based on a total of 256 trawl samples collected
during May, October and November, from 1989 to 1992. The samples were classified into 16 assemblages according to year, month
and depth. The importance of E. pacifica to the total diet of each of the assemblages was measured using an index considering both fish diet and species composition.
A total of 24 fish species out of 87 were found to ingest E. pacifica. Of these, Gadus macrocephaus and Theragra chalcogramma had the highest predation impact due to their dominance in the fish assemblages and the high proportion of E. pacifica in their diets. The contribution of E. pacifica to the total diet of the fish assemblage was highest in the shallow (≤300 m) regions during May, accounting for an average
of 38.5% for the 4 years. However, during May 1990, when the warm Kuroshio Extension prevailed, the contribution was higher
in the deep (>300 m; 22.6%) region, reflecting active and/or passive movements of E. pacifica. The average predation impact was maximal in the May/shallow assemblage (mean ± SE; 4.6 ± 1.4 kg wet wt km2 d−1) and was minimal in the November/shallow assemblage (0.4 ± 0.3). Annual estimates of consumption by demersal fish fishes
ranged from 43 to 128 metric tons, representing 15 to 64% of the annual commercial catch of E. pacifica by local fisheries. It is therefore suggested that the fisheries on E. pacifica have the potential to considerably impact the demersal fish assemblages.
Received: 3 December 1997 / Accepted: 10 June 1998 相似文献
13.
Holothuroidea represent the dominant benthic megafauna in hadal trenches (~6,000–11,000 m), but little is known about their
behaviour and functional role at such depths. Using a time-lapse camera at 8,074 m in the Peru–Chile Trench (SE Pacific Ocean),
we provide the first in situ observations of locomotory activity for the elasipodid holothurian Elpidia atakama Belyaev in Shirshov Inst Oceanol 92:326–367, (1971). Time-lapse sequences reveal ‘run and mill’ behaviour whereby bouts of feeding activity are interspersed by periods of locomotion.
Over the total observation period (20 h 25 min), we observed a mean (±SD) locomotion speed of 7.0 ± 5.7 BL h−1, but this increased to 10.9 ± 7.2 BL h−1 during active relocation and reduced to 4.8 ± 2.9 BL h−1 during feeding. These observations show E. atakama translocates and processes sediment at rates comparable to shallower species despite extreme hydrostatic pressure and remoteness
from surface-derived food. 相似文献
14.
Mytilus edulis L., Ruditapes philippinarum (Adams & Reeve) and Tapes decussatus L. were fed particles of the same shape (spherical), the same density (2.1 g cm−3) and the same chemical composition (SiO2), but which varied in diameter from 5 to 37 μm. Findings obtained at different particle concentrations (mean ± SD) of 51 ± 2,
105 ± 18 and 171 ± 17 mg l−1 invariably indicate that significant proportions of all particles with diameters larger than from between 7.5 and 22.5 μm
were preferentially rejected as pseudofaeces. We define the preferential ingestion index (PII) as the ratio between average
particle volume in pseudofaeces and average particle volume in food. Whatever the particle concentration or the species, this
PII was always statistically higher than 1. Irrespective of particle concentration, PII values in M. edulis were lower than in T. decussatus (averages of 1.2 and 2, respectively). PII values in M. edulis were also lower than in R. philippinarum maintained at particle concentrations above 171 ± 17 mg l−1. We suggest that preferential size-dependent rejection of larger particles could be of significant adaptive value in the
natural environment, either if there are large inorganic particles, or if the average organic content of smaller particles
is higher.
Received: 11 January 1997 / Accepted: 8 March 1997 相似文献
15.
The kinetics of ammonium assimilation was investigated in Ulva pertusa (Chlorophyceae, Ulvales) from northeastern New Zealand. Ammonium assimilation exhibited Michaelis–Menten kinetics with a
maximum rate of assimilation (V
max) of 54 ± 5 μmol g−1 dry weight h−1 and half-saturation constant (K
m) of 23 ± 8 μM. In contrast, values for ammonium uptake were considerably higher with a V
max of 316 ± 59 μmol g−1 dry weight h−1 and K
m of 135 ± 46 μM. At environmentally relevant ammonium concentrations (5 μM), assimilation accounted for most (70%) of the
ammonium taken up. Darkness decreased the maximum rate of ammonium assimilation by 83%. We investigated the hypothesis that
rates of biosynthetic processes are greater in the early part of the day in Ulva. Consistent with this hypothesis, the maximum rate of ammonium assimilation in U. pertusa peaked in the morning and coincided with low levels of the photosynthetic product sucrose, which peaked in the afternoon.
There was a diurnal cycle in the rate of ammonium uptake and assimilation in light and dark, but the amplitude was much greater
for assimilation than uptake. Moreover, our data suggest that net ammonium assimilation only occurs during the day in U. pertusa. We suggest that two major roles for diurnal cycles are minimisation of interspecific competition for resources and metabolic
costs. 相似文献
16.
Diel swimming behaviors of juvenile anchovies (Anchoa spp.) were observed using stationary hydroacoustics and synoptic physicochemical and zooplankton profiles during four unique
water quality scenarios in the Neuse River Estuary, NC, USA. Vertical distribution of fish was restricted to waters with DO
greater than 2.5 mg O2 l−1, except when greater than 70% of the water column was hypoxic and a subset of fish were occupying water with 1 mg O2 l−1. We made the prediction that an individual fish would select a swim speed that would maximize net energy gain given the abundance
and availability of prey in the normoxic waters. During the day, fish adopted swim speeds between 7 and 8.8 bl s−1 that were near the theoretical optimum speeds between 7.0 and 8.0 bl s−1. An exception was found during severe hypoxia, when fish were swimming at 60% above the optimum speed (observed speed = 10.6 bl s−1, expected = 6.4 bl s−1). The anchovy is a visual planktivore; therefore, we expected a diel activity pattern characteristic of a diurnal species,
with quiescence at night to minimize energetic costs. Under stratified and hypoxic conditions with high fish density coupled
with limited prey availability, anchovies sustained high swimming speeds at night. The sustained nighttime activity resulted
in estimated daily energy expenditure over 20% greater than fish that adopted a diurnal activity pattern. We provide evidence
that the sustained nighttime activity patterns are a result of foraging at night due to a lower ration achieved during the
day. During severe hypoxic events, we also observed individual fish making brief forays into the hypoxic hypolimnion. These
bottom waters generally contained higher prey (copepod) concentrations than the surface waters. The bay anchovy, a facultative
particle forager, adopts a range of behaviors to compensate for the effects of increased conspecific density and reduced prey
availability in the presence of stratification-induced hypoxia. 相似文献
17.
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
18.
When symbiotic dinoflagellate algae (Symbiodinium sp., isolated from the coral Plesiastrea versipora) were incubated with NaH14CO3 in the light in seawater, they released 22.69±9.16 nmol carbon/106 algae. Release of photosynthetically fixed carbon was stimulated more than six-fold for algae incubated in host-tissue homogenate
(148.54±97.03 nmol C/106 algae) and more than four-fold (102.00±49.16 nmol C/106 algae) for algae incubated in a low molecular weight fraction (≤1 000 M
r
) prepared from host homogenate. Soluble released 14C-labelled products, as determined by chromatography and autoradiography, were the same when algae were incubated in either
host homogenate or the low molecular weight fraction. After 4 h incubation in the light (300 mol photons m−2 s−1),␣intracellular␣glycerol increased in algae incubated with the low molecular weight fraction (an increase of 0.39 to␣0.67 nmol glycerol/106 algae) compared with little or no increase in algae incubated in seawater (0 to 0.12 nmol glycerol/106 algae). Partial inhibition of triglyceride synthesis (up to 51%) was also observed when algae were incubated in the low molecular
weight fraction. All these effects are the same as those observed when algae were incubated in host homogenate. These data
indicate that the “host release-factor” activity of P.␣versipora is a compound of low molecular weight.
Received: 13 February 1997 / Accepted: 24 October 1997 相似文献
19.
Helen S. Findlay Michael A. Kendall John I. Spicer Stephen Widdicombe 《Marine Biology》2010,157(4):725-735
Ocean acidification and global warming are occurring concomitantly, yet few studies have investigated how organisms will respond
to increases in both temperature and CO2. Intertidal microcosms were used to examine growth, shell mineralogy and survival of two intertidal barnacle post-larvae,
Semibalanus balanoides and Elminius modestus, at two temperatures (14 and 19°C) and two CO2 concentrations (380 and 1,000 ppm), fed with a mixed diatom-flagellate diet at 15,000 cells ml−1 with flow rate of 10 ml−1 min−1. Control growth rates, using operculum diameter, were 14 ± 8 μm day−1 and 6 ± 2 μm day−1 for S. balanoides and E. modestus, respectively. Subtle, but significant decreases in E. modestus growth rate were observed in high CO2 but there were no impacts on shell calcium content and survival by either elevated temperature or CO2. S. balanoides exhibited no clear alterations in growth rate but did show a large reduction in shell calcium content and survival under
elevated temperature and CO2. These results suggest that a decrease by 0.4 pH(NBS) units alone would not be sufficient to directly impact the survival of barnacles during the first month post-settlement.
However, in conjunction with a 4–5°C increase in temperature, it appears that significant changes to the biology of these
organisms will ensue. 相似文献
20.
Heterotrophic nitrogen-fixation (acetylene reduction) was measured during decomposition (under dark conditions) of Rhizophora mangle L. and Avicennia germinans (L.) Stearn leaf litter. Nitrogen-fixation rates in leaf litter increased following 24 d incubation, then decreased after
≃44 d for both species. Maximum rates of 66.2 and 64.6 nmol C2H4 g−1 dry wt h−1 were reached by R. mangle and A. germinans leaf litter, respectively. Higher fixation rates of leaf litter were associated with an increase in water content and sediment
particles on leaf surfaces of both species. Rates of nitrogen fixation by diazotrophs attached to sediment particles were
not significantly different from zero. With additions of d-glucose, ethylene production rates increased by factors of 625-, 34- and 7-fold for sediment, R. mangle and A.␣germinans leaf litter, respectively, compared to rates prior to enrichment. These organically enhanced rates of nitrogen fixation on
leaves could be accounted for by increased activity associated with attached sediment particles and not the leaf material.
Total phenolics [reported as tannic acid equivalent (TAE) units] decreased nitrogen-fixation rates when added to d-glucose-enriched sediment at >20 mg TAE l−1. Phenolic compounds could explain the initial lag in rates of nitrogen fixation during leaf-litter decomposition of R. mangle (initial content of 110.8 mg TAE g−1 dry wt), but not of A. germinans (initial content of 23.4 mg TAE g−1 dry wt). The higher phenolic content and reportedly lower carbon substrate of R. mangle did not result in species-specific differences in either the magnitude or temporal pattern of nitrogen fixation compared
to A. germinans leaf litter. We conclude that the availability of organic substrates leached from the leaf litter along with colonization
by the heterotrophic diazotrophs (as indicated by sediment accumulation) controls nitrogen-fixation rates in a similar manner
in the leaf litter of both species.
Received: 8 August 1997 / Accepted: 4 December 1997 相似文献