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1.
Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology.
Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show
here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence
dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish,
Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and
leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined.
Critical speed was 27.5 ± 1.0 cm s−1 (30.9 BL s−1), and in situ speed was 13.6 ± 0.6 cm s−1. Fastest individuals were 44.6 and 25.0 cm s−1, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed.
Unfed larvae swam 172 ± 29 h at 8–10 cm s−1 (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was
2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional
swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction
to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming
SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left
(more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates
the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction.
Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours,
and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to
behaviour of other settlement-stage pomacentrid larvae that are older and larger. 相似文献
2.
Wrasses are abundant reef fishes and the second most speciose marine fish family, yet little is known of their larval swimming
abilities. In August 2010 at Moorea, Society Islands, we measured swimming ability (critical speed, Ucrit) of 80 settlement-stage
larvae (11–17 mm) of 5 labrid species (Thalassoma quinquevittatum [n = 67], Novaculichthys taeniourus [n = 6], Coris aygula [n = 5], Halichoeres trimaculatus [n = 1] and H. hortulanus [n = 1]) and 33 new recruits of T. quinquevittatum. Median (mdn) larval Ucrit was 7.6–12.5 cm s−1. In T. quinquevittatum (n = 67), larvae of 12.5–14.5 mm swam faster (mdn 16.9 cm s−1) than smaller or larger larvae (mdn 3.9 and 3.2 cm s−1, respectively). Labrid larvae Ucrit is similar to that of other similar-sized tropical larvae, so labrids and species with
comparable settlement sizes should have similar abilities to influence dispersal. Ucrit of T. quinquevittatum recruits decreased to 47–56% of larval Ucrit in 2 days, implying rapid physiological changes at settlement. 相似文献
3.
Late larvae of the serranid coral trout Plectropomus leopardus (Lacepède), captured in light traps, were released during the day both in open water and adjacent to two reefs, and their
behaviour was observed by divers at Lizard Island, northern Great Barrier Reef. Coral trout larvae (n = 110) were present in light-trap catches from 18 November to 3 December 1997, including new moon (30 November). The swimming
speed of larvae in open water or when swimming away from reefs was significantly greater (mean 17.9 cm s−1) than the speed of larvae swimming towards or over reefs (mean 7.2 cm s−1). Near reefs, larvae swam at average depths of 2.7 to 4.2 m, avoiding 0 to 2 m. In open water, swimming depth varied with
location: larvae >1 km east of Lizard Island swam steeply downward to >20 m in 2 to 4 min; larvae >1 km west oscillated between
2.6 and 13 m; larvae 100 to 200 m east of Lizard Island oscillated between 0.8 and 15 m. Nearly all larvae swam directionally
in open water and near reefs. In open water, the average swimming direction of all larvae was towards the island, and 80%
(4 of 5) swam directionally (p < 0.05, Rayleigh's test). Larvae swam directionally over the reef while looking for settlement sites. The frequency of behaviours
by larvae differed between two reefs of different exposure and morphology. Depending on site, 26 to 32% of larvae released
adjacent to reefs swam to open water: of these, some initially swam towards or over the reef before swimming offshore. In
some cases, offshore-swimming seemed to be due to the presence of predators, but usually no obvious cause was observed. Depending
on the reef, 49 to 64% of the larvae settled. Non-predatory reef residents aggressively approached 19% of settlers. Between
5 and 17% of the larvae were eaten while approaching the reef or attempting to settle, primarily by lizardfishes but also
by wrasses, groupers and snappers. A higher percentage of larvae settled in the second week of our study than in the first.
Average time to settlement was short (138 s ± 33 SE), but some larvae took up to 15 min to settle. Average settlement depth
was 7.5 to 9.9 m, and differed between locations. No settlement took place on reef flats or at depths <4.2 m. Larvae did not
appear to be selective about settlement substrate, but settled most frequently on live and dead hard coral. Late-stage larvae
of coral trout are capable swimmers with considerable control over speed, depth and direction. Habitat selection, avoidance
of predators and settlement seem to rely on vision.
Received: 7 July 1998 / Accepted: 26 January 1999 相似文献
4.
Critical swimming speeds of late-stage coral reef fish larvae: variation within species,among species and between locations 总被引:3,自引:0,他引:3
The swimming abilities of larval fishes are important for their survival, potentially affecting their ability to avoid predators,
obtain food and control dispersal patterns. Near settlement swimming abilities may also influence spatial and temporal patterns
of recruitment. We examined Critical speed (U-crit) swimming ability in late stage larvae of 89 species of coral reef fishes from the Great Barrier Reef and the Caribbean.
Coefficients of variation in U-crit calculated at the individual level were high (28.4%), and this was not explained by differences in size or condition
factor of these same larvae. Among species U-crit ranged from 5.5 cm s−1 to 100.8 cm s−1 (mean=37.3 cm s−1), with 95% of species able to swim faster than the average current speed around Lizard Island, suggesting that most species
should be capable of influencing their spatial and temporal patterns of settlement. Inter-specific differences in swimming
ability (at both the family and species levels) were significantly correlated with size and larval morphology. Correlations
were found between swimming performance and propulsive area, fineness ratio and aspect ratio, and these morphological parameters
may prove useful for predicting swimming ability in other taxa. Overall, the swimming speeds of larvae from the same families
at the two locations were relatively similar, although the Lutjanidae and Acanthuridae from the Caribbean were significantly
slower than those from the great barrier reef. Differences in swimming speed and body form among late stage larvae suggests
that they will respond differently to factors influencing survival and transport during their pelagic phase, as well as habitat
use following settlement. 相似文献
5.
Herring (Clupea harengus L.) larvae from spring and autumn spawning stocks were reared at different constant temperatures from 5° to 17 °C. At equivalent developmental stages, the spring larvae were longer than the autumn larvae and the larvae reared at low temperatures were longer than those reared at high temperatures. At hatching and at the end of the yolk-sac stage, the larvae were induced, by a probe, to make C-start escape responses, which were recorded and analysed using a high-speed video recording at 400 frames s-1. The response was rapid and of short duration. The tailbeat frequency and swimming speed were measured during the burst of swimming following the C-start at different test temperatures and in larvae with different temperature histories. The tail-beat frequency was strongly temperature-dependent, rising from 19 Hz at 5 °C to 37 Hz at 17 °C with no effect of temperature history, season or developmental stage. The burst-swimming speed ranged at hatching from 75 to 90 mm s-1 at 5 °C to 110 to 160 mm s-1 at 17 °C and at yolk resorption from 90–115 mm s-1 at 5 °C to 175–190 mm s-1 at 17 °C. The longer, spring-spawned larvae swam faster than the shorter autumn-spawned larvae. When the swimming speeds were expressed as body lengths (L) s-1, these differences disappeared. Larvae swam from 7–9 L s-1 at 5 °C to 15–20 L s-1 at 17 °C at hatching, and from 8–9 L s-1 at 5 °C to 15–17 L s-1 at 17 °C at yolk resorption. There was, however, a significantly faster specific swimming speed by the larvae reared at 12 °C in spring 1991.Honorary Research Fellow of the Scottish Association for Marine ScienceUnfortunately, Karen Fretwell was drowned in an accident on 9 January 1993 相似文献
6.
Effect of amino acids on the swimming activity of newly hatched turbot larvae (Scophthalmus maximus)
The swimming behaviour of newly hatched turbot (Scophthalmus maximus L.) larvae was observed in artificial seawater (ASW) and in solutions of 21 l-amino acids at a concentration of 10−5
M. The behaviour of 20 larvae was analysed in each solution. Each larva was observed for 1 min. Individual movements were recorded
on video and analysed using a computer-assisted program. The larvae swam in convoluted, randomised three-dimensional paths,
rested and started swimming again. There were large variations in the swimming behaviour of turbot larvae during ontogeny.
In ASW the mean frequency of trajectories longer than a body length of 4 mm larva−1 min−1 increased from 1.2 at Day 1, to 10 at Day 4. Analysing the data (Dunnett's method) revealed that the frequency of swimming
trajectories increased in the presence of glycine, histidine and glutamine, and decreased in the presence of proline. The
total distance swum increased for glycine but decreased for proline. The threshold concentration for glycine detected by turbot
larvae was 10−5
M. The straightness index did not change in the presence of the amino acids. The possible role of these changes in behaviour
is discussed.
Received: 12 June 1997 / Accepted: 13 January 1998 相似文献
7.
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
8.
The transport of eel early life stages may be critical to their population dynamics. This transport from ocean spawning to
freshwater, estuarine and coastal nursery areas is a combination of physical and biological processes (including swimming
behavior). In New Jersey, USA, the American eel (Anguilla rostrata) enters estuaries as glass eels (48.7–68.1 mm TL) in contrast to the Conger eel (Conger oceanicus) that enters as larger (metamorphosing) leptocephali (68.3–117.8 mm TL). To begin to understand the mechanisms of cross-shelf
transport for these species, we measured the potential swimming capability (critical swimming speed, U
crit) under ambient conditions throughout the ingress season. A. rostrata glass eels were collected over many months (January–June) at a range of temperatures (4–21°C), with relative condition declining
over the course of the ingress period as temperatures warmed. C. oceanicus occurred later in the season (April–June) and at warmer temperatures (14–24.5°C). Mean U
crit values for A. rostrata (11.7–13.3 cm s−1) and C. oceanicus (14.7–18.6 cm s−1) were comparable, but variable, with portions of the variability explained by water temperature, relative condition, ontogenetic
stage, and fish length. Travel times to Little Egg Inlet, New Jersey, estimated using 50% U
crit values, indicate it would take A. rostrata ~30 and ~60 days to swim from the shelf edge and Gulf Stream, respectively. Travel times for C. oceanicus were shorter, ~20 days from the shelf edge, and ~45 days from the Gulf Stream. Despite differences in life stage, our results
indicate both species are competent swimmers, and suggest they are capable of swimming from the Gulf Stream and/or edge of
the continental shelf to estuarine inlets. 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.
Myong Hwan Sohn Kyung Won Seo Yong Seok Choi Sang Joon Lee Young Sil Kang Yang Soon Kang 《Marine Biology》2011,158(3):561-570
The marine dinoflagellate Cochlodinium polykrikoides is a harmful and highly motile algal species. To distinguish between the motility characteristics of solitary and chain-forming
cells, the swimming trajectories and speeds of solitary cells and 2- to 8-cell chains of C. polykrikoides were measured using a digital holographic particle tracking velocimetry (PTV) technique. C. polykrikoides cells exhibited helical swimming trajectories similar to other dinoflagellate species. The swimming speed increased as the
number of cells in the chain increased, from an average of 391 μm s−1 (solitary cells) to 856 μm s−1 (8-cell chain). The helix radius R and pitch P also increased as the number of cells in the chain increased. R increased from 9.24 μm (solitary cell) to 20.3 μm (8-cell chain) and P increased from 107 μm (solitary cell) to 164 μm (8-cell chain). The free thrust-generating motion of the transverse flagella
and large drag reduction in the chain-forming cells seemed to increase the swimming speed compared to solitary cells. The
measured swimming speeds agreed with those from field observations. The superior motility of chain-forming C. polykrikoides cells may be an important factor for its bloom, in addition to the factors reported previously. 相似文献
11.
A series of laboratory (short-term exposure in small beakers) studies and a 19 d mesocosm (6 m3 polyethylene bags filled with fjord water) study were conducted on blue mussel, Mytilus edulis, larvae and plantigrades exposed to a concentration gradient of the detergent linear alkylbenzene sulphonate (LAS, 0 to 39 mg l−1). LAS is increasingly found in nearshore environments receiving wastewater from urban treatment plants. The aims were to
observe physiological effects on swimming, grazing and growth in the laboratory and effects on settling and population development
at in situ conditions (in field mesocosms) in order to evaluate the damages on ciliated meroplankton caused by LAS. In the
laboratory the larvae showed a 50% mortality at 3.8 mg LAS l−1 after 96 h exposure whether or not food was provided. Additionally the swimming behaviour was affected at 0.8 mg LAS l−1 (i.e. a more compact swimming track, a smaller diameter of the swimming tracks, and reduced swimming speed). The larval particle
grazing was reduced 50% at 1.4 mg LAS l−1. The specific growth rate of the larvae was reduced to half at 0.82 mg LAS l−1 over 9 d. During the mesocosm experiment, the larval population showed a dramatic decrease in abundance within 2 d at concentrations
as low as 0.08 mg LAS l−1, both due to a significantly increased mortality, but also due to settling. The settling success was reduced at the same
LAS concentration as that at which mortality was observed to increase significantly. In addition to reduced settling rate,
the larvae showed delayed metamorphosis and reduced shell growth as a response to LAS. Our hypothesis that the larval ciliary
apparatus, crucial for normal swimming, orientation, and settling behaviours and for particle uptake, was damaged due to LAS
exposure is supported by our results. This is confirmed by the physiological data (grazing, growth) and in the direct video-based
observations of larval performance (swimming) and provides a reasonable explanation for what was observed in the bags (abundance,
settling, mortality). These physiological effects on blue mussel larvae/plantigrades occurred at LAS concentrations reported
to occur in estuarine waters.
Received: 15 January 1997 / Accepted: 12 February 1997 相似文献
12.
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
13.
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
14.
Effects of low dissolved oxygen on early development and swimming behaviour of veliger larvae of the scavenging gastropod
Nassarius festivus were studied. Embryonic development was significantly delayed when dissolved oxygen level was reduced to 3.0 mg O2 l−1 and no embryo hatched successfully at 0.5 mg O2 l−1. Veliger larvae hatched at 4.5 mg O2 l−1 had significantly smaller velar lobe, shell length and shell width. Median 48-h LC50 value of the veliger larvae was estimated at 1.25 mg O2 l−1 with lower swimming speed (swimming velocity and dispersal velocity) being recorded for the survivors exposed to reduced
oxygen levels. The percentage of veliger larvae that developed into crawling juveniles was significantly reduced and metamorphosis
was delayed at 4.5 mg O2 l−1 whereas all larvae at 3.5 mg O2 l−1 died before they underwent metamorphosis. Juveniles developed at 4.5 mg O2 l−1 were also smaller than those at 6.0 mg O2 l−1. Results indicated that dissolved oxygen levels well above hypoxia levels (2.8 mg O2 l−1) have already had significant impact on the hatching success and larval development in gastropods, which may lead to long-term
decreases in population growth. 相似文献
15.
Respiration rates and elemental composition (carbon and nitrogen) were determined for four dominant oncaeid copepods (Triconia borealis, Triconia canadensis, Oncaea grossa and Oncaea parila) from 0–1,000 m depth in the western subarctic Pacific. Across the four species of which dry weight (DW) varied from 2.0
to 32 μg, respiration rates measured at in situ temperature (3°C) increased with DW, ranging from 0.84 to 7.4 nl O2 individual−1 h−1. Carbon (C) and nitrogen (N) composition of the four oncaeid species ranged from 49–57% of DW and 7.0–10.3% of DW, respectively,
and the resultant C:N ratios were 4.8–8.3. The high C contents and C:N ratios were reflected by large accumulation of lipids
in their body. Specific respiration rates (SR, a fraction of body C respired per day) ranged between 0.5 and 1.3% day−1. Respiration rates adjusted to a body size of 1 mg body N (i.e. adjusted metabolic rates, AMR) of the four oncaeid species
[0.6–1.1 μl O2 (mg body N)−0.8 h−1 at 3°C] were significantly lower than those (1.7–5.1) reported in the literature for oithonid and calanoid copepods at the
same temperature. The present results indicate that lower metabolic expenditure due to less active swimming (pseudopelagic
life mode) together with rich energy reserve in the body (as lipids) are the characters of oncaeid copepods inhabiting in
the epi- and mesopelagic zones of this region. 相似文献
16.
Information about foraging speeds is particularly valuable when the impact of a predator species upon a community of prey has to be defined, as in the case of great cormorants. We measured the swim speed of 12 (six males and six females) free-ranging great cormorants Phalacrocorax carbo, foraging off the Greenland coast during the summer of 2003, using miniaturized data-loggers. Although mean body mass of males was 27% greater than that of females, and mean swim speed of males were 29–57% higher than that of females during foraging phases (but not descent phases) of dives, these differences in speeds were not significant due to high variances. Birds descended to the mean maximum depth of 4.7 m at an average speed of 1.6±0.5 m s−1, a speed similar to that measured in captive cormorants in previous studies. Although bursts of up to 4 m s−1 were recorded, speed usually decreased during the deepest (foraging) phase of dives, being on average 0.8±0.6 m s−1. Speeds measured here should be taken with caution, because the large propeller loggers used to measure speed directly decreased descent speeds by up to 0.5 m s−1 when compared to smaller depth-only loggers. Cormorants in Greenland seem to combine two searching strategies, one requiring low speed to scan the water column or benthos, and one requiring high speed to pursue prey. These two strategies depend on the two main habitats of their prey: pelagic or demersal. 相似文献
17.
Carl Van Colen J. Lenoir A. De Backer B. Vanelslander M. Vincx S. Degraer T. Ysebaert 《Marine Biology》2009,156(10):2161-2171
The role of multi-species benthic diatom films (BDF) in the settlement of late pediveliger larvae of the bivalve Macoma balthica was investigated in still-water bioassays and multiple choice flume experiments. Axenic diatom cultures that were isolated
from a tidal mudflat inhabited by M. balthica were selected to develop BDF sediment treatments characterized by a different community structure, biomass, and amount of
extracellular polymeric substances (EPS). Control sediments had no added diatoms. Although all larvae settled and initiated
burrowing within the first minute after their addition in still water, regardless of treatment, only 48–52% had completely
penetrated the high diatom biomass treatments after 5 min, while on average 80 and 69% of the larvae had settled and burrowed
into the control sediments and BDF with a low diatom biomass (<3.5 μg Chl a g−1 dry sediment), respectively. The percentage of larvae settling and burrowing into the sediment was negatively correlated
with the concentration of Chl a and EPS of the BDF. This suggests higher physical resistance to bivalve penetration by the BDF with higher diatom biomass
and more associated sugar and protein compounds. The larval settlement rate in annular flume experiments at flow velocities
of 5 and 15 cm s−1 was distinctly lower compared to the still-water assays. Only 4.6–5.8% of the larvae were recovered from BDF and control
sediments after 3 h. Nonetheless, a clear settlement preference was observed for BDF in the flume experiments; i.e., larvae
settled significantly more in BDF compared to control sediments irrespective of flow speed. Comparison with the settlement
of polystyrene mimics and freeze-killed larvae led to the conclusion that active selection, active secondary dispersal and,
at low flow velocities (5 cm s−1), passive adhesion to the sediment are important mechanisms determining the settlement of M. balthica larvae in estuarine biofilms. 相似文献
18.
Salps have higher filtration rates than most other holoplankton, and are capable of packaging and exporting primary production
from surface waters. A method of kinematic analysis was employed to accurately measure salp feeding rates. The data were then
used to explain how diverse body morphologies and swimming motions among species and lifecycle stages influence salp feeding
performance. We selected five species, representing a range of morphologies and swimming styles, and used digitized outlines
from video frames to measure body-shape change during a pulse cycle. Time-varying body volume was then calculated from the
digitized salp outlines to estimate the amount of fluid passing through the filtering mesh. This non-invasive method produced
higher feeding rates than other methods and revealed that body volume, pulse frequency and degree of contraction are important
factors for determining volume filtered. Each species possessed a unique combination of these three characteristics that resulted
in comparable filtration (range: 0.44–15.33 ml s−1) and normalized filtration rates (range: 0.21–1.27 s−1) across species. The convergence of different species with diverse morphologies on similar normalized filtration suggests
a tendency towards a flow optimum. 相似文献
19.
Flathead grey mullets Mugil cephalus are commonly found in Mediterranean lagoons, which are regularly subject to high environmental variations. Oxygen is one
of the factors that shows extremely high variation. The objective of this study was to test the effects of acute hypoxia exposure
at two experimental temperatures (i.e. 20 and 30°C) on the stamina (time to fatigue) in M. cephalus swimming at the minimal cost of transport (i.e. optimal swimming speed; U
opt). At each temperature, a relationship was established between swimming speed and oxygen consumption (MO2). This allowed estimation of U
opt at 45 cm s−1 (~1.12 Body Length s−1). Independent of temperature, stamina at U
opt was significantly reduced in severe hypoxia, i.e. at 15% of air saturation (AS). In these conditions, oxygen supply appears
therefore to be insufficient to maintain swimming, even at the low speed tested here. After the stamina test, MO2 measured in fish tested at 15% AS was significantly higher than that measured after the test in normoxia. Therefore, we suggest
that in hypoxia, fish used anaerobic metabolism to supplement swimming at U
opt, leading to an oxygen debt. Since flathead grey mullet is a hypoxia-tolerant species, it is possible that hypoxic conditions
less severe than those tested here may reduce stamina at low speed in less tolerant species. In addition, we suggest that
testing stamina at these speeds may be relevant in order to understand the effect of hypoxia on behavioural activities carried
out at low speed, such as food searching. 相似文献
20.
In situ measurements of seagrass photosynthesis in relation to inorganic carbon (Ci) availability, increased pH and an inhibitor
of extracellular carbonic anhydrase were made using an underwater pulse amplitude modulated (PAM) fluorometer. By combining
the instrument with a specially designed Perspex chamber, we were able to alter the water surrounding a leaf without removing
it from the growing plant. Responses to Ci within the chamber showed that subtidal plants of the seagrasses Cymodocea serrulata and Halophila ovalis had photosynthetic rates that were limited by the ambient Ci concentration depending on the irradiance that was available
during short-term photosynthesis–irradiance trials. Relative electron transport rates (RETRs) at light saturation (up to 500 μ
mol photons m−2 s−1) increased by 66–100% when the Ci concentration was increased from ca. 2.2 to 6.2 mM. On the other hand, intertidal plants
of the same species exhibited a much lesser limitation of photosynthesis by Ci at any irradiance (up to 1500 μ mol photons
m−2 s−1). Both species were able to use HCO−
3 efficiently, and there was stronger evidence for direct uptake of HCO−
3 rather than extracellular dehydration of HCO−
3 to CO2 prior to Ci uptake. Subtidally, H. ovalis and C. serrulata grew to 10 and 12 m, respectively, where ambient irradiances were approximately 16 and 11% of those at the surface. Maximum
RETRs (at light saturation) were lower for these deep-growing plants than for the intertidally growing ones. For both species,
the onset of light saturation of photosynthesis (E
k) occurred at approximately 100 μ mol photons m−2 s−1 for the deep water populations, which was four and two times lower than for the shallow populations of C. serrulata and H. ovalis, respectively. This, and the differences in maximal photosynthetic rates (RETR
max), reflects an acclimation of the deep-growing populations to the lower light environment. The results presented here show
that photosynthesis, as measured in situ, was limited by the availability of Ci for the deeper growing plants in Zanzibar,
while the intertidally growing plants photosynthesised at close to Ci saturation. The latter result is contrary to previous
conclusions regarding Ci limitations for these intertidal plants, and, in general, our findings highlight the need for performing
similar experiments in situ rather than under laboratory conditions.
Received: 4 April 2000 / Accepted: 31 August 2000 相似文献