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1.
We characterized the prey field and the lipid classes/fatty acids in the flesh of age 0 juvenile cod (Gadus morhua) during their late-summer/fall arrival and settlement into eelgrass (Zostera marina) in coastal Newfoundland. Examination of available prey demonstrated a high abundance of small zooplankton (Acartia, Microsetella and Oithona sp.) with no larger Calanus sp. prey. Breakpoint analysis showed significant changes in the accumulation of relative (mg g−1 wet weight) and absolute (μg fish−1) amounts of lipid with standard length at the time of settlement (~60 mm standard length). Settling juvenile cod showed an
alternate lipid utilization strategy where they catabolized phospholipids (PL) to a greater extent than triacylgylcerols (TAG).
Polyunsaturated fatty acids (PUFA) content in cod flesh decreased as fish grew indicating that nearshore zooplankton quality
was not optimal for PL formation. The dramatic reduction in cod PL was likely due to both catabolism of muscle and a lack
of dietary PUFA suitable for PL synthesis. However, juvenile cod continued to grow, leading to decreased lipid stores and
suggesting that cod settling into eelgrass are under intense selection pressure for growth prior to the onset of winter, possibly
as a means of escaping gape-limited predation. These data contrast better-studied freshwater and estuarine systems in which
lipid storage is critical for successful overwintering. 相似文献
2.
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
3.
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
4.
Feeding rates of the jellyfish Aurelia aurita on fish larvae 总被引:4,自引:0,他引:4
We quantified feeding rates of field caught Aurelia aurita feeding on yolk sac cod (Gadus morhua) larvae in a series of incubation experiments. A short-time (~1 h) functional response experiment with a wide range of prey concentrations (0.5–16 prey l−1, initial concentration) revealed that ingestion rates increased linearly over this range, such that clearance rates were similar between the different prey concentrations. This suggests that A. aurita is capable of efficiently utilizing dense prey patches. This indication was further supported by a linear increase of prey captured by A. aurita during 2.5 h of feeding at extremely high prey concentration (>200 prey l−1). Clearance rate in darkness scaled with jellyfish diameter to a power of ~1.7 for jellyfish 3.9–9.5 cm in diameter. The jellyfish did not alter their umbrella pulse frequency in response to presence of fish larvae. There were no significant differences between A. aurita feeding rates in light and darkness for yolk sac prey ages 0–7 days (at 7.5°C). Although prey vision and escape abilities of fish may develop rapidly during early larval ontogeny, these factors apparently have little impact on interactions with predators such as A. aurita during the yolk sac stage. 相似文献
5.
The effect of irradiance, prey concentration and pH on the growth and grazing responses of the mixotrophic prymnesiophyte
Chrysochromulina ericina under N-and P-replete conditions was studied using the pedinophyte Marsupiomonas pelliculata as prey. The two organisms were inoculated in monocultures and in mixed cultures at different predator: prey ratios at three
irradiances and allowed to grow for 4–7 days. All cultures were non-axenic. Algal densities and pH were monitored throughout
the experiments and growth and grazing rates were measured. An increase in growth of C. ericina cultures at irradiances of 25 and 70 μmol photons m−2 s−1 was observed after the addition of prey, while growth of C. ericina cultures at the high irradiance (150 μmol photons m−2 s−1) was unaffected by the addition of prey. However, although the growth of C. ericina increased at low irradiance (25 μmol photons m−2 s−1), it did not reach the same level as monocultures at the high irradiance (150 μmol photons m−2 s−1), suggesting that phagotrophy can only partly replace photosynthesis in C. ericina. Maximum growth rates of C. ericina at irradiances of 25 and 70 μmol photons m−2 s−1 were obtained at concentrations of > 0.15–0.3×105
M. pelliculata ml−1, corresponding to 50–100 μg C 1−1. Ingestion of M. pelliculata cells by C. ericina did not generally follow Michaelis—Menten kinetics. Deviation from the expected saturation kinetics was especially pronounced
at irradiances of 70 and 150 μmol photons m−2 s−1. At these irradiances ingestion of M. pelliculata cells by C. ericina decreased at high concentrations of M. pelliculata, indicating an increased uptake of bacterial prey in these cultures. The growth rate of C. ericina was affected in both monocultures and in mixed cultures when pH increased above 8.6, and growth stopped around pH 9. The
prey alga M. pelliculata tolerated high pH better and, consequently, took over in the mixed cultures when pH exceeded 9. The ecological significance
of mixotrophy in the genus Chrysochromulina is discussed.
Published online: 4 July 2002 相似文献
6.
Peter J. Edmunds 《Marine Biology》2009,156(9):1797-1808
This study tested the effects of acclimatization on the response of corals to elevated temperature, using juvenile massive
Porites spp. and branching P. irregularis from Moorea (W149°50′, S17°30′). During April and May 2006, corals were acclimatized for 15 days to cool (25.7°C) or ambient
(27.7°C) temperature, under shaded (352 μmol photons m−2 s−1) or ambient (554 μmol photons m−2 s−1) natural light, and then incubated for 7 days at ambient or high temperature (31.1°C), under ambient light (659 μmol photons
m−2 s−1). The response to acclimatization was assessed as biomass, maximum dark-adapted quantum yield of PSII (F
v/F
m), and growth, and the effect of the subsequent treatment was assessed as F
v/F
m and growth. Relative to the controls (i.e., ambient temperature/ambient light), massive Porites spp. responded to acclimatization through increases in biomass under ambient temperature/shade, and low temperature/ambient
light, whereas P. irregularis responded through reduced growth under ambient temperature/shade, and low temperature/ambient light. Acclimatization affected
the response to thermal stress for massive Porites spp. (but not P. irregularis), with an interaction between the acclimatization and subsequent treatments for growth. This interaction resulted from a
lessening of the negative effects of high temperature after acclimatizing to ambient temperature/shade, but an accentuation
of the effect after acclimatizing to low temperature/shade. It is possible that changes in biomass for massive Porites spp. are important in modulating the response to high temperature, with the taxonomic variation in this effect potentially
resulting from differences in morphology. These results demonstrate that corals can acclimatize during short exposures to
downward excursions in temperature and light, which subsequently affects their response to thermal stress. Moreover, even
con-generic taxa differ in this capacity, which could affect coral community structure.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Andrew McMinn Andrew Pankowskii Chris Ashworth Ranjeet Bhagooli Peter Ralph Ken Ryan 《Marine Biology》2010,157(6):1345-1356
Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes
were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica.
Maximum oxygen export from sea ice was 0.95 mmol O2 m−2 h−1 (~11.7 mg C m−2 h−1) while from the sediment it was 6.08 mmol O2 m−2 h−1 (~70.8 mg C m−2 h−1). When the ice was present O2 export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)−1 h−1 while those from the benthos were up to 1.53 mg C (mg Chl-a)−1 h−1. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice
was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned
between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production. 相似文献
8.
The effects of light exposure on the photosynthetic activity of kleptoplasts were studied in the sacoglossan mollusc Elysia viridis. The photosynthetic activity of ingested chloroplasts was assessed in vivo by non-destructively measuring photophysiological
parameters using pulse amplitude modulation (PAM) fluorometry. Animals kept under starvation were exposed to two contrasting
light conditions, 30 μmol photons m−2 s−1 (low light, LL), and 140 μmol photons m−2 s−1 (high light, HL), and changes in photosynthetic activity were monitored by measuring the maximum quantum yield of photosystem
II (PSII), F
v/F
m, the minimum fluorescence, F
o, related to chlorophyll a content, and by measuring rapid light-response curves (RLC) of relative electron transport rate (rETR). RLCs were characterised
by the initial slope of the curve, αRLC, related to efficiency of light capture, and the maximum rETR level, rETRm,RLC, determined by the carbon-fixation metabolism. Starvation induced the decrease of all photophysiological parameters. However,
the retention of photosynthetic activity (number of days for F
v/F
m > 0), as well as the rate and the patterns of its decrease over time, varied markedly with light exposure. Under HL conditions,
a rapid, exponential decrease was observed for F
v/F
m, αRLC and rETRm,RLC, F
o not showing any consistent trend of variation, and retention times ranged between 6 and 15 days. These results suggested
that the retention of chloroplast functionality is limited by photoinactivation of PSII reaction center protein D1. In contrast,
under LL conditions, a slower decrease in all parameters was found, with retention times varying from 15 to 57 days. F
v/F
m, αRLC and rETRm,RLC exhibited a bi-phasic pattern composed by a long phase of slow decrease in values followed by a rapid decline, whilst F
o decayed exponentially. These results were interpreted as resulting from lower rates of D1 photoinactivation under low light
and from the gradual decrease in carbon provided by photosynthesis due to reduction of functional photosynthetic units. 相似文献
9.
Serena Caplins Miguel Angel Penna-Diaz Erick Godoy Nelson Valdivia J. M. Turbeville Martin Thiel 《Marine Biology》2012,159(6):1363-1374
Understanding the impact of environmental stressors on predator activity is a prerequisite to understanding the underlying
mechanisms shaping community structure. The nemertean Prosorhochmus nelsoni is a common predator in the mid-intertidal zone on rocky shores along the Chilean coast, where it can reach very high abundances
(up to 260 ind m−2) in algal turfs, algal crusts, barnacle crusts, and mixed substrata. Tidal and diurnal scans revealed that the activity of
P. nelsoni is primarily restricted to night and early-morning low tides and is relatively low when air temperatures are high. On average,
larger worms crawled faster than smaller worms, with their maximum velocity being influenced by substratum type. Their estimated
rate of predation is 0.092 prey items nemertean−1 day−1, just below the laboratory rate of ~0.2 amphipods nemertean−1 day−1 previously estimated for this species. P. nelsoni consumes a diverse spectrum of prey items (i.e., amphipods, isopods, decapods, barnacles, and dipterans) and is possibly
exerting a significant influence on its prey populations. We suggest that the opportunistic predatory behavior of this intertidal
predator is caused by the trade-off between immediate persistence (e.g., avoidance of desiccation) and long-term survival
through successful foraging. 相似文献
10.
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
11.
The fate of 100 marked recruits of the rhizophytic alga Halimeda incrassata was followed in Puerto Morelos reef lagoon, Mexican Caribbean (20°52′N, 86°51′W), until death of the last individual from
April 2005–2007. Juvenile mortality was relatively high (19%), the half-life of adult thalli was 13 months and maximal lifespan
was 2 years. First age of sexual reproduction was 10 months, but only 6% of the marked thalli reproduced sexually. A subsequent
static life-table approach (February–April 2008) at two sites indicated low spatial variation in transition probabilities
between the life stages. Recruits were found throughout the year (density 2–11 thalli m−2) and were mostly of clonal origin. In a disturbed area, the density of sexual recruits was ~0.01 thalli m2. Temporal fluctuations in population size depended on mortality rates, which increased slightly after hurricanes Emily (July
2005) and Wilma (October 2005), but might otherwise be regulated by density-dependent processes. 相似文献
12.
Howard I. Browman Jeannette Yen David M. Fields Jean-François St-Pierre Anne Berit Skiftesvik 《Marine Biology》2011,158(12):2653-2660
Paraeuchaeta norvegica (8.5 mm total length) and yolk-sac stage Atlantic cod larvae (4 mm total length) (Gadus morhua) larvae were observed in aquaria (3 l of water) using silhouette video photography. This allowed direct observations (and
quantitative measurement) of predator–prey interactions between these two species in 3-dimensions. Tail beats, used by cod
larvae to propel themselves through the viscous fluid environment, also generate signals detectable by mechanoreceptive copepod
predators. When the prey is close enough for detection and successful capture (approximately half a body-length), the copepod
launches an extremely rapid high Reynolds number attack, grabbing the larva around its midsection. While capture itself takes
place in milliseconds, minutes are required to subdue and completely ingest a cod larva. The behavioural observations are
used to estimate the hydrodynamic signal strength of the cod larva’s tail beats and the copepod’s perceptive field for larval
fish prey. Cod larvae are more sensitive to fluid velocity than P. norvegica and also appear capable of distinguishing between the signal generated by a swimming and an attacking copepod. However, the
copepod can lunge at much faster velocities than a yolk-sac cod larva can escape, leading to the larva’s capture. These observations
can serve as input to the predator–prey component of ecosystem models intended to assess the impact of P. norvegica on cod larvae. 相似文献
13.
In this study, juvenile colonies of massive Porites spp. (a combination of P. lutea and P. lobata) from the lagoon of Moorea (W 149°50′, S 17°30′) were damaged and exposed to contrasting conditions of temperature and flow
to evaluate how damage and abiotic conditions interact to affect growth, physiological performance, and recovery. The experiment
was conducted in April and May 2008 and consisted of two treatments in which corals were either undamaged (controls) or damaged
through gouging of tissue and skeleton in a discrete spot mimicking the effects of corallivorous fishes that utilize an excavating
feeding mode. The two groups of corals were incubated for 10 days in microcosms that crossed levels of temperature (26.7 and
29.6°C) and flow (6 and 21 cm s−1), and the response assessed as overall colony growth (change in weight), dark-adapted quantum yield of PSII (F
v/F
m), and healing of the gouged areas. The influence of damage on growth was affected by temperature, but not by flow. When averaged
across flow treatments, damage promoted growth by 25% at 26.7°C, but caused a 25% inhibition at 29.6°C. The damage also affected
F
v/F
m in a pattern that differed between flow speeds, with a 10% reduction at 6 cm s−1, but a 4% increase at 21 cm s−1. Regardless of damage, F
v/F
m at 21 cm s−1 was 11% lower at 26.7°C than at 29.6°C, but was unaffected by temperature at 6 cm s−1. The lesions declined in area at similar rates (4–5% day−1) under all conditions, although the tissue within them regained a normal appearance most rapidly at 26.7°C and 6 cm s−1. These findings show that the response of poritid corals to sub-lethal damage is dependent partly on abiotic conditions,
and they are consistent with the hypothesis that following damage, calcification and photosynthesis can compete for metabolites
necessary for repair, with the outcome affected by flow-mediated mass transfer. These results may shed light upon the ways
in which poritid corals respond to biting by certain corallivorous fishes. 相似文献
14.
The photosynthetic adaptive features of non-dormant seeds in Posidonia oceanica were studied in order to evaluate the effects of light on germination success. Transmission electron micrographs showed the
presence of chloroplasts in the epidermal cells, close to the nucleus at the periphery of the cytoplasm. The well-developed
thylakoid membranes and the presence of starch granules indicated that the chloroplasts were photosynthetically active. The
relationship between photosynthesis versus irradiance in P. oceanica seeds incubated at 15 and 21°C was analysed. The net photosynthesis in the non-dormant seed of P. oceanica was positive and compensated its respiration demand (90 μmol quanta m−2 s−1) at both temperatures. Net photosynthesis was negative at the other irradiance values. To test the effects of light on germination
success, seeds were placed both in dark and light conditions. Germination success was significantly higher in light rather
than in dark condition. The characteristics observed in the photosynthesis in P. oceanica seed could be a mechanism to guarantee seedling survival in temperate waters, demonstrating though the specialized nature
of this species. 相似文献
15.
The shallow kelp forest at Santa Catalina Island, California (33.45 N, −118.49 W) is distinguished by several canopy guilds
ranging from a floating canopy (Macrocystis pyrifera), to a stipitate, erect understory canopy (Eisenia arborea), to a short prostrate canopy just above the substratum (Dictyopteris, Gelidium, Laminaria, Plocamium spp.), followed by algal turfs and encrusting coralline algae. The prostrate macroalgae found beneath E. arborea canopies are primarily branching red algae, while those in open habitats are foliose brown algae. Densities of Corynactis californica, are significantly greater under E. arborea canopies than outside (approximately 1,200 versus 300 polyps m−2 respectively). Morphological differences in macroalgae between these habitats may affect the rate of C. californica particle capture and serve as a mechanism for determining polyp distribution and abundance. Laboratory experiments in a unidirectional
flume under low (9.5 cm s−1) and high (21 cm s−1) flow speeds examined the effect of two morphologically distinct macroalgae on the capture rate of Artemia sp. cysts by C. californica polyps. These experiments (January–March 2006) tested the hypothesis that a foliose macroalga, D. undulata, would inhibit particle capture more than a branching alga, G. robustum. G. robustum, found predominantly under the E. arborea canopy did not affect particle capture. However, D. undulata, found predominantly outside of the canopy, inhibited particle capture rates by 40% by redirecting particles around C. californica polyps and causing contraction of the feeding tentacles. These results suggest that the morphology of flexible marine organisms
may affect the distribution and abundance of adjacent passive suspension feeders. 相似文献
16.
Risk to humans of consuming metals in anchovy (<Emphasis Type="Italic">Coilia</Emphasis> sp.) from the Yangtze River Delta 总被引:1,自引:0,他引:1
Fengyan Liu Jiachun Ge Xin Hu Teng Fei Yuehua Li Yuan Jiang Zhiqiang Xu Shuyan Ding John P. Giesy 《Environmental geochemistry and health》2009,31(6):727-740
Concentrations of metals were determined in four species of anchovy (Coilia sp.) from the Yangtze River, Taihu Lake, and Hongze Lake in Jiangsu Province, China. Concentrations of Cr in anchovy fish
muscle ranged from 2.6 × 10−2 to 5.0 mg/kg ww, and Coilia nasus taihuensis in Jiaoshan, Taihu Lake contained the highest concentrations of Cr, which was almost 111-fold higher than the mean value
at other locations. Concentrations of Pb ranged from 1.5 × 10−2 to 1.3 × 10−1 mg/kg ww. Comparisons of concentrations of lead (Pb) among the four species indicated that anadromous species contained higher
concentrations of Pb than did freshwater species. However, concentrations of Pb in C. nasus from the Nanjing and Haimen locations in the Yangtze River were not significant higher than those of two freshwater species:
C. nasus taihuensis from Taihu Lake and C. brachygnathus from Hongze Lake (Duncan’s test, α = 0.05). While concentrations of Cd and Zn ranged from 7.0 × 10−4 to 3.6 × 10−3 mg/kg ww and 3.4 to 4.8 mg/kg ww, respectively, there were no significant differences in concentrations among the eight locations.
The only concentration of the metals studied that exceeded the Chinese National Standard was Cr in Coilia from Jiaoshan, Taihu Lake, which was 2.5-fold higher than the standard. These results indicate that people who consume the
genus Coilia are not at risk due to concentrations of metals, except Cr in C. nasus taihuensis from Jiaoshan in Taihu Lake. Concentrations of all of the metals studied except for Cr were similar to or less than those
of metals in most other areas in the world. 相似文献
17.
Bacterial abundance, production, and extracellular enzyme activity were determined in the shallow water column, in the epiphytic
community of Thalassia
testudinum, and at the sediment surface along with total carbon, nitrogen, and phosphorus in Florida Bay, a subtropical seagrass estuary.
Data were statistically reduced by principle components analysis (PCA) and multidimensional scaling and related to T. testudinum leaf total phosphorus content and phytoplankton biomass. Each zone (i.e., pelagic, epiphytic, and surface sediment community)
was significantly dissimilar to each other (Global R = 0.65). Pelagic aminopeptidase and sum of carbon hydrolytic enzyme (esterase, peptidase, and α- and β-glucosidase) activities
ranged from 8 to 284 mg N m−2 day−1 and 113–1,671 mg C m−2 day−1, respectively, and were 1–3 orders of magnitude higher than epiphytic and sediment surface activities. Due to the phosphorus-limited
nature of Florida Bay, alkaline phosphatase activity was similar between pelagic (51–710 mg P m−2 day−1) and sediment (77–224 mg P m−2 day−1) zones but lower in the epiphytes (1.1–5.2 mg P m−2 day−1). Total (and/or organic) C (111–311 g C m−2), N (9.4–27.2 g N m−2), and P (212–1,623 mg P m−2) content were the highest in the sediment surface and typically the lowest in the seagrass epiphytes, ranging from 0.6 to
8.7 g C m−2, 0.02–0.99 g N m−2, and 0.5–43.5 mg P m−2. Unlike nutrient content and enzyme activities, bacterial production was highest in the epiphytes (8.0–235.1 mg C m−2 day−1) and sediment surface (11.5–233.2 mg C m−2 day−1) and low in the water column (1.6–85.6 mg C m−2 day−1). At an assumed 50% bacterial growth efficiency, for example, extracellular enzyme hydrolysis could supply 1.8 and 69% of
epiphytic and sediment bacteria carbon demand, respectively, while pelagic bacteria could fulfill their carbon demand completely
by enzyme-hydrolyzable organic matter. Similarly, previously measured T. testudinum extracellular photosynthetic carbon exudation rates could not satisfy epiphytic and sediment surface bacterial carbon demand,
suggesting that epiphytic algae and microphytobenthos might provide usable substrates to support high benthic bacterial production
rates. PCA revealed that T. testudinum nutrient content was related positively to epiphytic nutrient content and carbon hydrolase activity in the sediment, but
unrelated to pelagic variables. Phytoplankton biomass correlated positively with all pelagic components and sediment aminopeptidase
activity but negatively with epiphytic alkaline phosphatase activity. In conclusion, seagrass production and nutrient content
was unrelated to pelagic bacteria activity, but did influence extracellular enzyme hydrolysis at the sediment surface and
in the epiphytes. This study suggests that seagrass-derived organic matter is of secondary importance in Florida Bay and that
bacteria rely primarily on algal/cyanobacteria production. Pelagic bacteria seem coupled to phytoplankton, while the benthic
community appears supported by epiphytic and/or microphytobenthos production. 相似文献
18.
Miriam Schutter Sander Kranenbarg René H. Wijffels Johan Verreth Ronald Osinga 《Marine Biology》2011,158(4):769-777
In this study, we tested the hypothesis that the importance of water flow for skeletal growth (rate) becomes higher with increasing
irradiance levels (i.e. a synergistic effect) and that such effect is mediated by a water flow modulated effect on net photosynthesis.
Four series of nine nubbins of G. fascicularis were grown at either high (600 μE m−2 s−1) or intermediate (300 μE m−2 s−1) irradiance in combination with either high (15–25 cm s−1) or low (5–10 cm s−1) flow. Growth was measured as buoyant weight and surface area. Photosynthetic rates were measured at each coral’s specific
experimental irradiance and flow speed. Additionally, the instantaneous effect of water flow on net photosynthetic rate was
determined in short-term incubations in a respirometric flowcell. A significant interaction was found between irradiance and
water flow for the increase in buoyant weight, the increase in surface area, and specific skeletal growth rate, indicating
that flow velocity becomes more important for coral growth with increasing irradiance levels. Enhancement of coral growth
with increasing water flow can be explained by increased net photosynthetic rates. Additionally, the need for costly photo-protective
mechanisms at low flow regimes could explain the differences in growth with flow. 相似文献
19.
In situ measurements of photosynthetic irradiance responses of two Red Sea sponges growing under dim light conditions 总被引:6,自引:0,他引:6
Photosynthetic responses to irradiance by the photosymbionts of the two Red Sea sponges Theonella swinhoei (Gray) and Clionavastifica (Hancock) growing under dim light conditions were measured in situ (in September 1997) using a newly developed underwater
pulse amplitude modulated (PAM) fluorometer. Relative rates of photosynthetic electron transport (ETR) were calculated as
the effective quantum yield of photosystem II (Y ) multiplied with the photosynthetic photon flux (PPF). Photosynthesis versus irradiance (P-I ) curves, obtained within minutes, showed that individual specimens of both sponges, growing under very low light conditions,
feature lower light saturation points as well as lower maximal ETRs than individuals growing under higher light. Evaluations
of such curves using low irradiances of the actinic light source (20 to 130 μmol photons m−2 s−1) showed a general decrease in Y, with a shoulder from the lowest irradiance applied till 20 to 30 μmol photons m−2 s−1. Point measurements yielded ETRs close to what could be estimated from the P-I curves. These point measurements also revealed good correlations between the diurnally changing ambient irradiances (1 to
50 μmol photons m−2 s−1) and average ETR values for both species. Further analysis showed that although Y values varied considerably between the different point measurements, they did not decrease significantly with light under
these very low irradiances. Therefore, PPF rather than Y seems to determine the in situ diel photosynthetic performance at the low ambient irradiances experienced by these sponges.
Received: 22 November 1997 / Accepted: 8 April 1998 相似文献
20.
Adult Vinciguerria nimbaria are the main prey of tuna during the tuna fishing season (late autumn and winter) in the equatorial Atlantic (0–4°N, and
~15°W). V. nimbaria trophic behavior in the fishing grounds was studied in relation to hydrobiological factors to determine its role in the trophic
food web. Sampling stations spaced by 20 nautical miles were set up along a 15°W north–south transect from 4°N to 0°40S. At
each station, the temperature and vertical fluorescence profiles were recorded. Nitrate and chlorophyll a analyses were performed on water sampled at different levels in the euphotic zone. Vertical plankton hauls were carried out
at depths of 0–100 and 0–200 m using a standard WP2 net fitted with a 200-μm mesh gauze. Vinciguerria nimbaria adults were collected using a young-fish mid-water trawl net (10 × 15 m opening mouth, 10 mm cod end mesh). The weight of
the stomach contents, the stomach fullness index, the number of prey, the frequency of occurrence and the prey preponderance
were recorded for 20 fish from each haul. An oligotrophic typical tropical structure (TTS) was found between 1° and 4°N where
small zooplankton was relatively abundant above or near the thermocline. In the TTS, V. nimbaria behaved as an epipelagic fish, feeding on the dominant small prey during the daytime. In turn, it was a prey for tuna. In
the equatorial zone, where zooplankton was more abundant than in the north equatorial zone, V. nimbaria behaved as a mesopelagic fish and as an opportunistic mesozooplankton feeder. It consumed a wide range of sizes of food,
feeding on the most abundant species of zooplankton as well as the largest zooplankton species, possibly while migrating towards
the surface in the late afternoon or in the deep layer. 相似文献