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1.
The zoeal larvae of brachyuran crabs must feed soon after hatching on a diet that includes large micro- and mesozooplankton
in order to satisfy nutritional requirements. However, newly hatched larvae have been shown to ingest a variety of dinoflagellates,
perhaps using microbial carbon sources to sustain them until they encounter more favored prey. Ingestion of dinoflagellates
by larval crabs has been documented previously under conditions in which the larvae were exposed to algae provided in monoculture
or in defined mixtures of cells. We report here on experiments conducted on the hatching stage of five crab species to determine
if ingestion of dinoflagellates occurred when they were provided in combination with Artemia sp. nauplii or after a period of feeding on mesozooplankton. Quantitative measurements of chl a in the larval guts provided evidence of ingestion of algal cells. Active ingestion of the dinoflagellate Prorocentrum micans at specified intervals during an extended feeding period was determined on larvae of two crab species using fluorescently
labeled cells provided for brief periods at prescribed time intervals. Stage 1 larvae of four of the five crab species ingested
dinoflagellates when they were provided in combination with nauplii and larvae of all five species ingested cells after feeding
solely on nauplii for 24 h. Ingestion of algal cells was first evident in the larval guts after 6 h of feeding at both low
(200 cell ml−1) and high (1,000 cells ml−1) prey densities. Higher prey densities resulted in higher gut chl a. Larvae continuously exposed to dinoflagellates actively ingested cells at every 3 h interval tested over a 36 h period.
Results confirm previous studies that larvae will ingest dinoflagellates even when they are encountered in a mixed prey field
or when having previously fed. Ingestion of cells may occur on a continual basis over time. 相似文献
2.
Most studies on feeding by herring larvae (Clupea harengus) have taken place in clear, open waters, but several herring stocks around the world spawn in inshore and estuarine regions.
An example is the spring-spawning Blackwater Estuary (Essex, England) stock. Samples were collected in this estuary to examine
prey selectivity and feeding levels in relation to biological and environmental conditions. Herring larvae negatively selected
copepod nauplii, but positively selected the copepodite and adult stages of Acartia spp. Gastropod larvae were also positively selected. Particles >150 μm width were preferred, whilst particles smaller than
this value were preferentially rejected. Concentrations of potential prey items in the water were in the range of 6.0 to 49.7
organisms l−1 with a median concentration of 15.0 organisms l−1 (n = 26). These values are towards the low end of prey concentrations quoted in the literature as being required to sustain
herring larval growth and survival. However, theoretical considerations suggest that, in this environment, levels of tidally-induced
turbulence enhance encounter rates between larval herring and their prey. On the other hand, turbidity is also related to
tidal current speed and might reduce feeding success by decreasing underwater light levels. Measurements at two sites in the
estuary confirmed that tidally-induced turbidity reduced the effective water depth in which herring larvae could visually
feed by up to 50% at times of peak current speed. However, with the gut-content data available in the present study, it was
not possible to discern any clear relationships between feeding success and the state of the tide. Feeding success appeared
to be more strongly influenced by surface light-levels.
Received: 24 June 1998 / Accepted: 17 February 1999 相似文献
3.
Patricia N. Pochelon Henrique Queiroga Guiomar Rotllant Antonina dos Santos Ricardo Calado 《Marine Biology》2011,158(9):2079-2085
In Portuguese waters, Nephrops norvegicus larvae hatch at 400–800 m depth and need to perform a vertical migration to food-rich shallower waters to find suitable prey.
The effect of suboptimal feeding on digestive enzymes activity of N. norvegicus larvae during this early period of their larval life remains unknown. Protease and amylase activities were investigated ex situ using flurometry in laboratory-hatched larvae exposed to different feeding and/or starving scenarios in the 24 h following
hatching, the period during which they typically accomplish their upward vertical migration. Amylase activity was very low
in comparison with protease activity, indicating that carbohydrates are not a primary energy reserve. Larvae starved for 12 h
and subsequently fed displayed no increase in amylase activity, which suggests that feeding may be required before 12 h post-hatch
to trigger amylase activity. Protease activity was high under all feeding conditions, and the increase in protease activity
under sustained starvation indicated the catabolism of protein reserves. The ability of first-stage N. norvegicus larvae to metabolize protein reserves may play a decisive role for their survival during their first vertical migration,
as it enables them to overcome the deleterious effects of short-term starvation and/or suboptimal feeding. 相似文献
4.
It has been hypothesized that marine fish larvae in the advanced stages of starvation would show increased density (ρ = mass
volume−1) from water loss due to osmoregulation failure. Changes in larval buoyancy are currently attributed to swim bladder regulation
and protein synthesis or catabolism. Osmoregulation-related changes in density is an alternative mechanism, the importance
of which remains untested in the laboratory and the influence of which on vertical distributions is unknown. We provide evidence
that loss of osmotic control is a plausible mechanism for increased density of larval cod (Gadus morhua L.). Furthermore, our results show that this mechanism is not restricted to larvae in the advanced stages of starvation.
“Relative” larval densities are estimated using a modified density gradient. We use a gravimetric method to separate the effects
of nutrition from osmoregulation failure. We assessed the importance of sampling strata on estimates of larval density. Proportional
sampling within three depth strata (stratified sample) produced the least biased method for determining the “average” density
of a population of larvae in laboratory culture. Larvae sampled from the bottom third of the culture tank were significantly
more dense then those sampled from the surface. This was true for larvae of all ages. The average change in density from hatching
till death from starvation for larvae sampled in the surface stratum was nominal (Δρ = 5.0 × 10−4 g cm−3), while the change for those sampled from the bottom stratum was large (Δρ = 3.8 × 10−3 g cm−3). These large density differences suggest that larvae sampled from the bottom stratum were either osmotically stressed or
were facultatively changing their density via regulatory pathways. Preliminary observations suggest that vitality is lower
amongst those larvae which are sampled near the bottom. The small change in average density of larvae sampled from the surface
stratum was due to starvation. The density differences we observed between “osmotically stressed” and “starving” larvae could
readily have been misconstrued as differences in feeding and growth experienced by individual larvae. The potential bias of
increased density from osmoregulation failure must be considered as a factor in experimental designs developed to assess the
effect of fed and starved treatments on buoyancy for larvae of all ages. The simple bioassay we describe may prove useful
both as a means of assessing larval condition and as a mechanism for evaluating factors affecting larval vertical distributions
in the field.
Received: 13 January 1997 / Accepted: 3 February 1997 相似文献
5.
Four species of microalgae (Chaetoceros muelleri, Tetraselmis suecica, Tahitian Isochrysis sp. (T-iso) and Dunaliella tertiolecta) with distinctly different fatty acid profiles were grown in continuous culture and fed to prawn larvae (Penaeus japonicus, P. semisulcatus and P. monodon) as monospecific diets. The best two diets (C. muelleri and T. suecica) were also fed as a mixed diet. Experiments were run until the larvae fed the control diet of C. muelleri metamorphosed to Mysis 1. The survival and development (i.e. performance) of the larvae were affected by algal diet, and
the diets were ranked in the order of decreasing nutritional value: C. muelleri ≥ T. suecica > T-iso > D. tertiolecta. Larvae fed a mixed diet of C. muelleri and T. suecica (2:3 by dry weight) performed as well or better than those fed C. muelleri, and the performance of both these groups of larvae was better than those fed T. suecica. The lipid and carbohydrate compositions of the algae had little or no effect on the lipid and carbohydrate compositions
of the larvae or their performance. However, the larvae that performed best (i.e. those fed C. muelleri) had significantly more lipid and carbohydrate than those that performed worst (i.e. those fed D. tertiolecta). Larvae fed C. muelleri or the mixed-algae diet had higher proportions of the essential fatty acids eicosapentaenoic acid [EPA, 20:5(n-3)] and arachidonic acid [ARA, 20:4(n-6)] than the larvae fed on other diets. Furthermore, the larvae fed T. suecica, which showed intermediate performance between larvae fed C. muelleri and T-iso or D. tertiolecta, also had higher proportions of EPA and ARA. Both C. muelleri and T. suecica contained EPA and ARA, but T-iso and D. tertiolecta did not, except for trace amounts of EPA in T-iso. The fatty acid ARA appears to be much more important in the diet of larval prawns than has so far been considered. The level
of the essential fatty acid docosahexaenoic acid [DHA, 22:6(n-3)] in the algal diet and the larvae was not related to the performance of the larvae; only C. muelleri and T-iso contained DHA. However, the nauplii contained large proportions of DHA, suggesting that these were sufficient to meet the
larval requirements for DHA during their development to Mysis 1. Mixed-algae diets could improve the performance of larvae
by providing a more comprehensive range of fatty acids.
Received: 22 April 1998 / Accepted: 3 December 1998 相似文献
6.
The effects of two fixed photoperiodic regimes on the rate of somatic growth and segment proliferation in the semelparous
polychaete Nereis (Neanthes) virens Sars has been investigated. The two photoperiods (16 h light:8 h dark and 8 h light:16 h dark, hereafter LD 16:8 and LD 8:16)
were close to the extremes experienced naturally by N. (N.) virens in the course of a year. The experiments were carried out during the ambient winter and all worms (including four-setiger
larvae raised out of season) showed elevated feeding, growth and enhanced segment-proliferation rates when reared under LD
16:8, compared to worms reared under LD 8:16. The rate of replacement of lost segments after caudal ablation was also higher
under LD 16:8. The number of segments present when the segment proliferation rate had fallen to zero was higher in individuals
grown from birth under LD 16:8 compared to those grown under LD 8:16. Feeding activity showed a degree of spontaneous recovery
under LD 8:16 from January onwards, but remained lower than under LD 16:8. This difference continued into the following spring,
and was not attributable to differences in sexual maturity. We conclude that the rate of feeding in N. (N.) virens and other indicators of somatic growth rate such as rates of caudal regeneration and segment proliferation are directly influenced
by the photoperiod, but that the seasonal cycle of growth also includes a circa-annual component modifying the response to
static photoperiods according to the time of year.
Received: 20 October 1998 / Accepted: 4 February 1999 相似文献
7.
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
8.
Investigations of factors affecting feeding success in fish larvae require knowledge of the scales of variability of the
feeding process itself and the indices used to assess this variability. In this study, we measured short-term (diel) variability
in feeding rates of wild haddock (Melanogrammus aeglifinus) larvae four times per day during a 10-d cruise in the northern North Sea. Feeding activity was evaluated using indices of
gut fullness, prey digestive state and biochemical measurements (tryptic enzyme activity). The gut fullness and the enzyme
activity indices indicated moderate to high rates of food consumption throughout the cruise. Time series analysis of the three
indices showed significant diel variability in all indices and enabled identification of significant lags between food uptake
and peak digestive enzyme activity. The typical pattern of food consumption and digestion was characterized by maximal ingestion
of prey early in the evening (19:00 hrs) and peak digestive enzyme activity at 01:00 hrs. The time scale over which enzyme
activities reacted to prey ingestion was ca. 6 h, and is consistent with expectations from controlled laboratory experiments
with other larval fish species. Significant diel variability in tryptic enzyme activity suggests that attempts to relate this
measure of feeding success to other variables (e.g. food concentrations) should take care to accommodate natural cycles in
feeding activity before making statistical comparisons.
Received: 29 October 1998 / Accepted: 18 June 1999 相似文献
9.
Profiles of diarrhetic shellfish poisoning (DSP) toxins produced throughout the growth cycle and the cell cycle of the toxigenic
marine dinoflagellate Prorocentrum lima were studied in triplicate unialgal batch cultures. Cells were pre-conditioned at 18 ± 1 °C, under a photon flux density
(PFD) of 90 ± 5 μmol m−2 s−1 on a 14 h light:10 h dark photoperiod. In exponential growth phase, cultures were synchronized in darkness for 17 d. After
dark synchronization, cultures were transferred back to the original photoperiod regime. Cells were harvested for DSP toxin
analysis by LC-MS (liquid chromatography with mass spectrometry), and double-stranded (nuclear) DNA was quantified by flow
cytometry. The cell populations became asynchronous within approximately 3 d after transition from darkness to the 14 h light:10 h
dark photoperiod. This may be due to the prolonged division cycle (5 to 7 d) that is not tightly phased by the photoperiod.
Unlike other planktonic Prorocentrum spp., cytokinesis in P. lima occurred early in the dark and ceased by “midnight”. Cellular levels of the four principal DSP toxins, okadaic acid (OA),
OA C8-diol-ester (OA-D8), dinophysistoxin-1 (DTX1) and dinophysistoxin-4 (DTX4), ranged from 0.37 to 6.6, 0.02 to 1.5, 0.04
to 2.6, and 1.8 to 7.8 fmol cell−1, respectively. No toxin production was evident during the extended period of dark synchronization nor during the initial
period when NH4 was consumed as the major nitrogen source. Soon after the cells were returned to the 14 h light:10 h dark cycle and they
began to take up NO3, cellular levels of all four toxins gradually increased. This increase in DSP toxins usually occurred in the light, marked
by a rise in DTX4 levels that preceded an increase in the cellular concentration of OA and DTX1 (delayed by 3 to 6 h). Thus,
DTX4 synthesis is initiated in the G1 phase of the cell cycle and persists into S phase (“morning” of the photoperiod), whereas
OA and DTX1 production occurs later during S and G2 phases (“afternoon”). No toxin production was measured during cytokinesis,
which happened early in the dark. The evidence indicates that toxin synthesis is restricted to the light period and is coupled
to cell cycle events.
Received: 3 September 1998 / Accepted: 30 March 1999 相似文献
10.
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
11.
Recruitment of capelin in the Barents Sea fail when juvenile herring and cod are abundant and the potential for feeding competition
of wild sympatric capelin and herring larvae and small cod juveniles were investigated. The frequency of gut evacuation after
capture of capelin larvae were also studied in mesocosms. Small capelin larvae (<35 mm length) fed on small prey including
phytoplankton, invertebrate eggs and nauplii, bivalves, other invertebrate larvae and small copepods. Calanus copepodites were only observed in large capelin larvae (>26 mm length). Calanus copepodites were the major food sources for contemporary herring larvae (25–35 mm length) and Calanus and euphausiids were the major prey for small juvenile herring (37–60 mm length) and cod (18–40 mm length). Capelin larvae
reared in mesocosms evacuated the guts shortly after capture. Capelin larvae had a smaller mouth and fed on smaller prey than
herring and cod of the same length. This implies that the small capelin larvae, in contrast to sympatric small herring and
cod, are not tightly linked to the food chain involving Calanus and euphausiids. Thus, exploitative competition between capelin larvae and planktivorous fish that rely on Calanus and euphausiids in the Barents Sea may be relaxed. 相似文献
12.
Survival, developmental and consumption rate (Artemia nauplii ingested per day) as well as predation efficiency (ingested per available Artemia nauplii) were studied during the larval development of the shallow-water burrowing thalassinid Callianassa tyrrhena (Petagna, 1792), which exhibits an abbreviated type of development with only two zoeal stages and a megalopa. The larvae,
hatched from berried females from S. Euboikos Bay (Aegean Sea, Greece), were reared at 10 temperature–food density combinations
(19 and 24 °C; 0, 2, 4, 8 and 16 Artemia nauplii d−1). Enhanced starvation resistance was evident: 92 and 58% of starved zoeas I molted to zoea II, while metamorphosis to megalopa
was achieved by 76 and 42% of the hatched zoeas at 19 and 24 °C, respectively. The duration of both zoeal stages was affected
by temperature, food density and their interaction. Nevertheless, starvation showed different effects at the two temperatures:
compared to the fed shrimp, the starved zoeae exhibited accelerated development at 19 °C (8.4 d) but delayed metamorphosis
at 24 °C (5.9 d). On the other hand, both zoeal stages were able to consume food at an increased rate as food density and
temperature increased. Predation efficiency also increased with temperature, but never exceeded 0.6. Facultative lecithotrophy,
more pronounced during the first zoeal stage of C.tyrrhena, can be regarded as an adaptation of a species whose larvae can respond physiologically to the different temperature–food
density combinations encountered in the wide geographical range of their natural habitat.
Received: 28 February 1998 / Accepted: 21 October 1998 相似文献
13.
Most marine fishes undergo a pelagic larval phase, the early life history stage that is often associated with a high rate
of mortality due to starvation and predation. We present the first study that examines the effects of prey swimming behavior
on prey-capture kinematics in marine fish larvae. Using a digital high-speed video camera, we recorded the swimming velocity
of zooplankton prey (Artemia franciscana, Brachionus rotundiformis, a ciliate species, and two species of copepods) and the feeding behavior of red drum (Sciaenops ocellatus) larvae. From the video recordings we measured: (1) zooplankton swimming velocity in the absence of a red drum larva; (2)
zooplankton swimming velocity in the presence of a red drum larva; and (3) the excursion and timing of key kinematic events
during prey capture in red drum larvae. Two-way ANOVA revealed that: (1) swimming velocity varied among zooplankton prey;
and (2) all zooplankton prey, except rotifers and ciliates, increased their swimming velocity in the presence of a red drum
larva. The kinematics of prey capture differed between two developmental stages in S. ocellatus larvae. Hyoid-stage larvae (3–14 days old) fed on slow swimming B. rotundiformis (rotifers) while hyoid-opercular stage larvae (15 days and older) ate fast moving A. franciscana. Hyoid-opercular stage red drum larvae had a larger gape, hyoid depression and lower jaw angle, and a longer gape cycle duration
relative to their hyoid-stage conspecifics. Interestingly, the feeding repertoire within either stage of red drum development
was not affected by prey type. Knowledge of the direct relationship between fish larvae and their prey aids in our understanding
of optimal foraging strategies and of the sources of mortality in marine fish larvae. 相似文献
14.
One concept of evolutionary ecology holds that a living fossil is the result of past evolutionary events, and is adapted
to recent selective forces only if they are similar to the selective forces in the past. We describe the present environment
of the living coelacanth Latimeria chalumnae Smith, 1939 at Grande Comore, western Indian Ocean and report depth-dependent cave distribution, temperature, salinity and
oxygen values which are compared to the fish's distribution and its physiological demands. We studied the activity pattern,
feeding behaviour, prey abundance and hunting success to evaluate possible links between environmental conditions, feeding
ecology and evolutionary success of this ancient fish. Transmitter tracking experiments indicate nocturnal activity of the
piscivorous predator which hunts between approximately 200 m below the surface to 500 m depth. Fish and prey density were
measured between 200 and 400 m, both increase with depth. Feeding tracks and feeding strikes of the coelacanth at various
depths were simulated with the help of video and laser techniques. Along a 9447 m video transect a total of 31 potential feeding
strikes occurred. Assuming 100% hunting success, medium-sized individuals would obtain 122 g and large females 299 g of prey.
Estimates of metabolic rates revealed for females 3.7 ml O2 kg−1 h−1 and for males 4.5 ml O2 kg−1 h−1. Today coelacanths are considered to be a specialist deep-water form and to inhabit, with their ancient morphology, a contemporary
environment where they compete with advanced, modern fish.
Received: 5 July 1999 / Accepted: 11 November 1999 相似文献
15.
Larvae of the marine cheilostomatid bryozoan Bugula neritina (L.) were prevented from settling for 1, 4 and 8 h by mechanical agitation, following which settlement and metamorphosis
success were examined. Settlement rates were significantly affected by swimming time, which decreased from 100% after 2 h
to 93.7 ± 4.3% after 8 h. Similarly, metamorphosis to the feeding ancestrula was significantly impaired following a swimming
time of 8 h, declining from 93.7 ± 4.3% after 1 h to 65.9 ± 7.0% after 8 h. The resultant colonies grew well for the first
3 wk, following which time, growth patterns became erratic. Growth rate was in all cases highly variable, and did not correlate
with enforced swimming times. Larval protein composition was examined after 1, 4 and 8 h swimming time, and post-larval composition
1, 2, 5, 24 and 48 h after settlement using sodium-dodecyl-sulphate polyacrylamide-gel electrophoresis (SDS-PAGE). Individual
protein content was measured using a densitometer. Larvae did not consume protein during swimming, however a protein measuring
170 kdaltons was consumed during metamorphosis. These results are discussed in the context of larval settlement and energetics.
Received: 19 July 1998 / Accepted: 3 December 1998 相似文献
16.
Elvira Morote María Pilar Olivar Anna Bozzano Fernando Villate Ibon Uriarte 《Marine Biology》2011,158(6):1349-1361
Feeding ecology was analysed for the first time in the larvae of the European hake (Merluccius merluccius) to determine whether their diet and selectivity were constrained by environmental conditions and how these feeding characteristics
were related to ontogeny, prey availability and visual capabilities. Larvae collected during both day and night were analysed,
and it was found that feeding incidence was high, regardless of the time of day. Examination of the visual system corroborated
the hypothesis that hake larvae should be able to cope with a wide range of photic conditions and to forage even at low light
intensity. A clear preference for adult calanoid copepods and, especially, for Clausocalanus spp. was observed in all sizes analysed. Prey number increased with larval size, but prey size did not. This finding indicates
that hake larvae behave as selective and specialist predators that consume an increasing number of prey rather than larger
prey during larval growth. 相似文献
17.
The pattern of settlement over time of three broadcast spawning coral species (Cyphastrea serailia, Acanthastrea lordhowensis, and Goniastrea australensis) from the Solitary Islands (30°00′S; 153°20′E) was studied in 1995 and 1996 in order to determine the maximum length of time
these larvae could remain in the water column and still retain the ability to settle and metamorphose. Larvae were maintained
in aquaria and the number which had settled on biologically-conditioned tile pairs was monitored every 5 to 10 d. While the
majority of larvae settled quickly after becoming competent, some larvae survived and settled for extended periods after spawning.
Competency periods ranged from 26 d for C. serailia to 56 d for G. australensis and 78 d for A. lordhowensis. These data greatly extend the known competency periods for larvae of broadcast-spawning corals and indicate the potential
for transport of broadcast-spawned coral larvae over large distances. Medium to long-distance larval dispersal of the species
studied provides a mechanism for their widespread distribution in subtropical regions, on reefs which are often widely spaced
and relatively isolated.
Received: 27 May 1997 / Accepted: 27 November 1997 相似文献
18.
Levels of total RNA, total DNA, 18S ribosomal RNA (rRNA), poly(A) messenger RNA (mRNA), and two mRNAs coding for abundant
myofibrillar proteins were estimated in laboratory-reared Atlantic cod larvae (Gadusmorhua Linnaeus) under conditions of feeding and starvation. DNA probes specific for cod 18S rRNA, β-actin mRNA and myosin heavy
chain mRNA were developed. In two experiments on newly hatched larvae in fed and starved treatments, changes in 18S rRNA and
mRNA were similar to changes in total RNA during the first weeks after hatching. RNA levels in fed and starved larvae in both
experiments were stable, or increased, over the first 3 d after hatching, and then decreased to minima at 9 d. RNA levels
increased after 9 d, with the degree and timing of the increase varying among the individual classes of RNA. Complete mortality
of starved larvae in both experiments was observed shortly after 11 d, corresponding to exhaustion of endogenous yolk reserves.
Total RNA content, RNA/DNA ratio, 18S rRNA levels, total mRNA pool, and actin and myosin heavy chain mRNA levels showed significant
differences in fed and starved first-feeding larvae after yolk exhaustion. In another experiment with 3- to 4-week-old cod
larvae, 18S rRNA levels were significantly lower in starved versus fed larvae after 3 d. Total RNA responded to feeding and
starvation within a similar time as 18S rRNA and the mRNAs examined. Analysis of bulk nucleic acids using fluorometric dyes
was simpler and faster than analysis of individual RNAs using hybridization probes, and provides valuable information on recent
growth and condition of individual larvae. However, analysis of specific RNAs can provide information on expression of the
corresponding genes and reveal the changes underlying trends seen in bulk RNA.
Received: 9 February 1996 / Accepted: 7 June 1999 相似文献
19.
Nicole E. Phillips 《Marine Biology》2011,158(10):2335-2342
This study evaluated whether larvae of the Indo-Pacific vermetid gastropod Dendropoma maximum are obligate planktotrophs, or whether they exhibit an intermediate feeding strategy. Experiments were conducted in Moorea,
French Polynesia (149°50′W, 17°30′S), Sep–Oct 2009, to examine D. maximum larval growth and metamorphic responses to different diets and amounts of food. Dendropoma maximum larvae required particulate food to undergo metamorphosis, but were able to survive and grow in the absence of food for up
to 20 days. Larvae in Low and Unfed food treatments exhibited phenotypic plasticity by growing a larger velum (the larval
feeding structure) compared with those in high food. Unfed D. maximum larvae had a slower initial growth rate; however, by 11-day post-hatch fed and unfed larvae had converged on the same mean
shell height (553 μm), which was only 10% larger than the initial size at hatching. Therefore, although the nutritional strategy
of D. maximum larvae is best described as obligate planktotrophy, it appears to approach an intermediate feeding strategy. 相似文献
20.
Moerisia lyonsi Boulenger (Hydrozoa) medusae and benthic polyps were found at 0 to 5‰ salinity in the Choptank River subestuary of Chesapeake
Bay, USA. This species was introduced to the bay at least 30 years before 1996. Medusae and polyps of M. lyonsi are very small and inconspicuous, and may occur widely, but unnoticed, in oligohaline waters of the Chesapeake Bay system
and in other estuaries. Medusae consumed copepod nauplii and adults, but not barnacle nauplii, polychaete and ctenophore larvae
or tintinnids, in laboratory experiments. Predation rates on copepods by medusae increased with increasing medusa diameter
and prey densities. Feeding rates on copepod nauplii were higher than on adults and showed no saturation over the range of
prey densities tested (1 to 64 prey l−1). By contrast, predation on copepod adults was maximum (1 copepod medusa−1 h−1) at 32 and 64 copepods l−1. Unexpectedly, M. lyonsi colonized mesocosms at the Horn Point Laboratory during the spring and summer in 4 years (1994 to 1997), and reached extremely
high densities (up to 13.6 medusae l−1). Densities of copepod adults and nauplii were low when medusa densities were high, and estimated predation effects suggested
that M. lyonsi predation limited copepod populations in the mesocosms. Polyps of M. lyonsi asexually produced both polyp buds and medusae. Rates of asexual reproduction increased with increasing prey availability,
from an average total during a 38 d experiment of 9.5 buds polyp−1 when each polyp was fed 1 copepod d−1, to an average total of 146.7 buds polyp−1 when fed 8 copepods d−1. The maximum daily production measured was 8 polyp buds and 22 medusae polyp−1. The colonizing potential of this hydrozoan is great, given the high rates of asexual reproduction, fairly wide salinity
tolerance, and existence of a cyst stage.
Received: 29 October 1998 / Accepted: 3 March 1999 相似文献