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1.
Sexual reproduction of the scyphomedusa Aurelia aurita in relation to temperature and variable food supply 总被引:1,自引:0,他引:1
The effects of food availability and temperature on sexual maturation and female reproductive output of the scyphomedusa
Aurelia aurita was examined in two populations from the contrasting environments of Southampton Water and Horsea Lake, England. Trends in
oogenesis and subsequent reproductive output differed markedly between the two populations. In Southampton Water, the onset
of sexual maturation occurred earliest in the larger medusae, but eventually all females became ripe, the smallest being 45 mm
bell diameter (BD). The decrease in minimum size at maturity was correlated with increasing temperature. In A. aurita from Horsea Lake, size at maturity varied on a seasonal basis, with the smallest ripe female being only 19 to 20 mm BD. There
were spring and autumn periods of sexual maturation in this population. During the autumn period, it is likely that food limitation
was playing a more critical role in determining medusa size, with decreasing temperature indirectly affecting A. aurita by limiting primary and secondary production. In similar-sized ripe medusae, fecundity was greater in Southampton Water,
but the planula larvae produced were significantly smaller than those in Horsea Lake. It is suggested that in Horsea Lake,
the quality of the larvae are greater in terms of biochemical content to ensure survival of the few gametes produced (i.e.
K-strategy). Comparison of the reproductive effort of the two A. aurita populations revealed that medusae from Southampton Water, which experience greater food availability, are able to direct
more energy to reproduction than Horsea Lake medusae. In the latter, A. aurita medusae appear to partition the available food resources into either somatic growth (and therefore increased future fecundity)
when food is abundant, or reproductive growth when food is scarce.
Received: 24 June 1997 / Accepted: 23 March 1998 相似文献
2.
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
3.
The ctenophore Mnemiopsis leidyi A. Agassiz, 1865 is known to be eaten by the scyphomedusan Chrysaora quinquecirrha (Desor, 1948), which can control populations of ctenophores in the tributaries of Chesapeake Bay. In the summer of 1995,
we videotaped interactions in large aquaria in order to determine whether M. leidyi was always captured after contact with medusae. Surprisingly, M. leidyi escaped in 97.2% of 143 contacts. The ctenophores increased swimming speed by an average of 300% immediately after contact
with tentacles and 600% by mid-escape. When caught in the tentacles of C. quinquecirrha, the ctenophores frequently lost a portion of their body, which allowed them to escape. Lost parts regenerated within a few
days. The striking ability of M. leidyi to escape from C. quinquecirrha may be critically important in maintaining ctenophore populations in situ.
Received: 14 November 1996 / Accepted: 4 December 1996 相似文献
4.
From September to November 1991, UV-absorbing mycosporine-like amino acids (MAAs) were monitored in a natural population of
the sea urchin Sterechinusneumayeri from a coastal area of Anvers Island (Antarctic Peninsula). MAA concentrations were determined for specific tissues (gonad,
digestive tract and body wall) from adults collected at four depths (intertidal, 8, 15 and 24 m). Four MAAs were identified:
mycosporine-glycine, shinorine, porphyra-334 and paly-thine. Concentrations of MAAs among replicate individuals varied considerably.
Ovaries had high concentrations of MAAs (84 to 1389 μg g−1 dry wt), while testes had non-detectable levels. The relative abundance of specific MAAs in ovaries appeared to be related
to the spawning cycle. Digestive-tract samples had MAA concentrations as high as 3000 μg g−1 dry wt, but the mean MAA content in intertidal individuals decreased by 70% over 3 mo during spring. The body walls of sea
urchins had very low amounts of MAAs (≤ 0.08 μg g−1 dry wt). There were significant depth differences in the␣total MAA content of the ovary ( p <0.001), ( p <0.015), digestive tract ( p <0.001), and body wall with organisms from the intertidal and 8 m depth having the highest concentrations of MAAs. Biological
dosimetry indicated that UV-B (280 to 320 nm) wavelengths penetrated 3 to 7 m below the sea ice during the study period. The
total MAA content in ovaries decreased with depth on all sample dates; however, the MAA content of the digestive tract and
body wall did not exhibit a consistent pattern of change with depth. The MAA content of tissues did not change significantly
with the temporal gradient of light exposure that was established by both ozone depletion and increasing photoperiod, except
in the digestive tract sampled from intertidal specimens. Adult urchins are probably well-protected from UV exposure by the
water column and a calcareous test; however, the results of this study suggest that, even under ice cover, depth of habitation
is a determinant of MAA content in S. neumayeri. Large daily and seasonal fluctuations in the light regime, which are characteristic of Antarctic coastal environments, apparently
do not provide reliable cues to elicit a detectable, temporal, biochemical response.
Received: 19 February 1997 / Accepted: 26 March 1997 相似文献
5.
In this study eight different species of barnacles were found within nine species of sponges from the Red Sea. This brings
to 11 the number of sponge-symbiotic barnacles reported from the Red Sea, two of these are new Acasta species (not described herein) and one (A. tzetlini Kolbasov) is a new record for this sea. This number is much higher than that of symbiotic barnacles found within sponges
from either the N. Atlantic (2) or the Mediterranean (4). Two possible explanations for this are the presence of numerous
predators in coral reefs and scarcity of available substrate for settlement. These factors can lead to high incidence of symbiotic
relationships. Of the nine sponge species, only one (Suberites cf. clavatus) had previously been known to contain barnacles. Even at the family level, this is the first record of symbiotic barnacles
in two out of the seven sponge families (Latrunculiidae, Theonellidae). Our present findings strengthen the apparent rule
that the wider the openings in a barnacle shell, the fewer the host taxa with which it will associate, usually from one or
two closely related families, and the more frequent it will associate with elastic sponges. Most Neoacasta laevigata found on Carteriospongia foliascens were located on the same side as the sponge's ostia, i.e. facing the incoming water. This adaptation allows the barnacles
to catch more suspended particles from the water, provides them with more oxygen and prevents their exposure to discharged
sponge waste. The highest density of barnacles observed on one face of a “leaf ” (with ostia) was 0.389 barnacles cm−2 (one barnacle per 2.57 cm2) and on average 0.181 ± 0.68, while the average on the other side was only 0.068 ± 0.52 barnacles cm−2. As indicated by the Morisita index, these barnacles most frequently (58%, n = 12) had a clumped spatial distribution (while the rest were randomly distributed), as is to be expected from such sessile
organisms with internal fertilization via copulation. The presence of N. laevigata induced the growth of secondary perpendicular projections of its host C. foliascens. Of the N. laevigata examined, 17% brooded 324 ± 41 embryos each, of 286 ± 17 μm total length; only 5.7% (n = 123) were found to be dead. Size distribution analysis of skeletal elements from dead barnacles showed them to be significantly
larger than the skeletal elements of the population of live barnacles ( p < 0.05).
Received: 26 June 1998 / Accepted: 1 December 1998 相似文献
6.
The benthic crustacean Saduria entomon occurs frequently in deeper parts of the Gulf of Gdańsk. It is one of a few species able to survive oxygen deficiencies in
its natural environment. The anaerobic heat production of S. entomon during 40 h of anoxia was determined. Additionally, the effects of size, sex and activity of the organism on its heat production
were investigated. Average heat production of S. entomon was 0.25 ± 0.16 mJ g−1 wet wt s−1 (n=55, avg. length 39 ± 6 mm). The amount of heat produced decreased with increasing body size. The heat production of S. entomon males was greater than that of females ( p<0.05). Specimens kept in chambers with glass beads and water were less active and had lower metabolic rates than those placed
in chambers containing water only (more active). During 40 h of anoxia S. entomon gradually decreased its heat production to 5–16% of aerobic level, demonstrating the high adaptation of this species to changeable
oxygen conditions in the Baltic Sea.
Received: 31 July 1997 / Accepted: 21 January 1998 相似文献
7.
The reproductive biology of the jellyfish Catostylus mosaicus (Quoy and Gaimard 1824) (Scyphozoa: Rhizostomeae) was investigated in New South Wales, Australia. Medusae were gonochoristic.
There was a 1:1 ratio of male and female medusae and there was no evidence of sexual dimorphism. Oocytes arose from the gastrodermis
and maintained contact with the gastrodermis, via trophocytes, throughout gametogenesis. Spermatogenesis occurred within follicles
that arose from invagination of the gastrodermis. Detailed sampling of gonads over a period of 3.25 yr in Botany Bay, and
over 2.5 yr in Lake Illawarra, indicated that gametogenesis occurred almost continuously during the year. Oocytes were smaller,
or were absent from the ovaries during 3 of the 4 winters sampled at Botany Bay and during all 3 winter periods sampled at
Lake Illawarra. Comparisons were made with other locations, although these were sampled less frequently. When medusae were
present at a location, similar trends were observed. The size at which medusae matured varied, but during non-winter periods
and at two locations, all medusae exceeding 130 mm diam were considered mature.
Received: 6 January 2000 / Accepted: 3 July 2000 相似文献
8.
Using a biopsy dart system, samples of skin tissue were collected from southern right whales (Eubalaena australis) in 1995 on two wintering grounds, southwest Australia (n = 20) and the Auckland Islands of New Zealand (n = 20); and on offshore feeding grounds at Latitudes 40 to 43°, south of Western Australia (n = 5). A variable section of the mitochondrial DNA control-region (289 nucleotides) was amplified and sequenced from these
45 individuals (21 males, 20 females and 4 of unknown sex), distinguishing a total of seven unique sequences (i.e. mtDNA haplotypes).
Two haplotypes were found on both wintering grounds (including a common type representing 45% of each sample), and five types
were unique to only one wintering ground. An analysis of variance adapted for molecular information revealed significant genetic
differentiation between the two wintering grounds (p = 0.017). The feeding-ground sample was too small for statistical comparison with the wintering grounds, but included two
haplotypes found only in the Auckland Islands as well as the common haplotype found on both wintering grounds. The nucleotide
diversity and differentiation of mtDNA among the right whales was similar to that among humpback whales (Megaptera novaeangliae) from the same regions (Baker et al. 1998), but haplotype diversity was significantly reduced, perhaps as a result of more
intensive hunting during the last century and continued illegal hunting during this century.
Received: 16 March 1998 / Accepted: 18 December 1998 相似文献
9.
J. H. M. Kouwenberg H. I. Browman J. A. Runge J. J. Cullen R. F. Davis J.-F. St-Pierre 《Marine Biology》1999,134(2):285-293
The copepod Calanus finmarchicus Gunnerus is a key component of the planktonic food web in the Gulf of St. Lawrence, Canada. In this region, productivity-determining
biophysical interactions occur in the upper 0 to 30 m of the water column. The eggs and nauplii of C. finmarchicus are found in this layer. Measurements of the diffuse attenuation coefficients for solar ultraviolet-B radiation (280 to 320 nm,
UV-B) at various locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates)
of 3 to 4 m at a wavelength of 310 nm. This represents a significant percentage of the summer mixed-layer water column: organisms
residing in this layer are exposed to UV-B radiation. Laboratory experiments using a Xenon-arc-lamp based solar simulator
revealed that C. finmarchicus embryos exposed to UV-B exhibited high wavelength-dependent mortality. The strongest effects occurred under exposures to
wavelengths below 312 nm. A significant percentage of nauplii hatched from eggs exposed to these wavelengths exhibited malformations
indicative of errors in pattern formation during embryogenesis. At the shorter wavelengths (<305 nm), UV-B-induced mortality
was strongly dependent on cumulative exposure. The biological weighting function (BWF) derived for UV-B-induced mortality
in C. finmarchicus eggs is similar to that reported for naked DNA. This suggests that the UV-B-induced mortality effect on C. finmarchicus embryos is a direct result of DNA damage. There was no evidence of a detrimental effect of ultraviolet-A radiation (320 to
400 nm). Calculations based upon the BWF indicate that, under current noon surface irradiance, 50% of C. finmarchicus eggs located at or very near (within 10 cm) the ocean surface will be dead after 2.5 h of exposure. Under solar spectral
irradiance simulating a 20% decrease in ozone layer thickness, this time drops to 2.2 h. These are first-order estimates based
upon irradiance taken at a time of day during which the values would be maximal. Nonetheless, they illustrate the relative
changes in UV-B effects that will result from ozone layer depletions expected over the coming decades. It is also important
to point out that variability in cloud cover, water quality, and vertical distribution and displacement within the mixed layer,
can all have a greater effect on the flux of UV-B radiation to which C. finmarchicus eggs are exposed than will ozone layer depletion at these latitudes.
Received: 2 March 1998 / Accepted: 18 December 1998 相似文献
10.
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
11.
Although scyphomedusae have received increased attention in recent years as important predators in coastal and estuarine
environments, the factors affecting zooplankton prey vulnerability to these jellyfish remain poorly understood. Current models
predicting feeding patterns of cruising entangling predators, such as Chrysaora quinquecirrha (Desor, 1948), fail to account for the selection of fast-escaping prey such as copepods. Nevertheless, our analysis of gastric
contents of field-collected medusae showed that this scyphomedusa fed selectively on the calanoid copepod Acartia tonsa (Dana, 1846) and preferentially ingested adult over copepodite stages. We measured feeding rates in a planktonkreisel while
simultaneously videotaping predator–prey interactions. C. quinquecirrha consumed adult A. tonsa ten times faster than copepodites. Differences in prey behavior, in the form of predator–prey encounter rates or post-encounter
escape responses, could not account for the elevated feeding rates on adults. Prey size, however, had a dramatic impact on
the vulnerability of copepods. In experiments using heat-killed prey, feeding rates on adults (1.5 times longer than copepodites)
were 11 times higher than on copepodites. In comparison, medusae ingested heat-killed prey at only two to three times the
rate of live prey. These results suggest that during scyphomedusan–copepod interactions, prey escape ability is important,
but ultimately small size is a more effective refuge from predation.
Received: 26 September 1997 / Accepted: 20 May 1998 相似文献
12.
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
13.
The euphausiid Euphausia crystallorophias Holt and Tattersall, 1906 is considered to be a neritic species. It has been found in greatest abundance along the Antarctic
continental margins, often in association with regions of pack ice. Although E. crystallorophias has been observed at some islands to the west of the Antarctic Peninsula, the species has not previously been reported from
islands of the maritime- or sub-Antarctic further north. During an oceanographic transect in November 1997 from South Georgia
to the South Sandwich Islands, acoustic observations revealed a dense, discrete pelagic target at 50 m. The target was fished
and was found to be an aggregation of small E. crystallorophias. The fishing location (54.48°S; 30.61°W) was >1500 km from the Antarctic continent, and >250 km from the nearest land, in
water of several thousands of metres depth – clearly a non-neritic environment. Examination of hydrographic data revealed
that the E. crystallorophias swarm had been located within a fast-flowing band of water that had characteristics of water found near the Antarctic Peninsula.
This band was ≃150 km wide, and had a speed ranging from 9 to 22 km d−1 in a north-easterly direction. The possible origins of this E. crystallorophias swarm are explored in the light of the eddy-dominated current patterns prevalent in the Weddell–Scotia Confluence region,
and with reference to published growth-rate estimates for the species. We discuss the potential for long-distance dispersal
of E. crystallorophias and other neritic species in fast current jets, and examine how such oceanographic features could facilitate long-distance
dispersal, colonization, and gene flow.
Received: 23 November 1998 / Accepted: 25 March 1999 相似文献
14.
Allozyme variation in global populations of striped mullet, Mugil cephalus (Pisces: Mugilidae) 总被引:5,自引:0,他引:5
The striped mullet, Mugil cephalus Linnaeus, 1758, is one of the few species of marine shore fish with a worldwide circumtropical distribution. Because of this
distribution and the dependency of M. cephalus on coastal waters during various phases of its life cycle, as well as nearshore living habits, questions have been raised
regarding levels of genetic divergence and gene flow among transoceanic populations. To cast more light on this, allozyme
variation at 27 presumptive gene loci was investigated in ten globally diverse populations. The observed heterozygosity ranged
from 0.018 (Hawaii) to 0.081 (Florida), averaging 0.050. The proportion of polymorphic loci showed a similar trend. Several
populations were characterised by fixed allelic differences. Estimated gene diversities were very high, the allele frequency
variation among populations was found to be 68%; genetic distances reached 0.242, with an average of 0.117. Estimated rates
of gene flow were high among Mediterranean populations (Nm = 7.26), and between Mediterranean and East Atlantic populations (Nm= 2.86), but extremely low between non-contiguous populations within the Indian, Pacific and Atlantic Oceans, where Nm ranged from 0.03 to 0.05.
Received: 7 April 1997 / Accepted: 4 February 1998 相似文献
15.
P. J. Krug 《Marine Biology》1998,132(3):483-494
A San Diego population of the opisthobranch mollusc Alderia modesta (Lovén, 1844) exhibits poecilogony, the presence of two development modes within a single species. In spring, half of the
adults spawned masses containing ∼300 eggs with a mean diameter of 68 μm. After 3 d, these egg masses hatched planktotrophic
veligers with a maximum shell dimension of 116 μm. The remaining adults spawned masses containing ∼30 eggs with a mean diameter
of 105 μm. These egg masses hatched after 5 to 6 d, releasing lecithotrophic larvae with a maximum shell dimension of 186 μm.
About 1% of field-collected adults produced mixed clutches containing a continuum of larval sizes, spanning the size extremes
of planktotrophy and lecithotrophy and hatching larvae with a mean maximum shell dimension of 152 μm. Adults producing planktotrophic
and lecithotrophic larvae were interfertile, and no hybrid breakdown was observed through the F3 generation. When starved,
adults which previously produced only lecithotrophic larvae switched to producing planktotrophic larvae or mixed clutches
with both planktotrophic and lecithotrophic larvae. Sequence-polymorphisms from a portion of the mitochondrial cytochrome
c oxidase I gene support the conclusion that the two reproductive morphs represent a single species. Most of the lecithotrophic
larvae and a small percentage of the larvae from mixed clutches were metamorphically competent within 3 d of hatching. A. modesta is the only molluscan species as yet known to have both planktotrophic and pelagic lecithotrophic development within a single
natural population.
Received: 14 August 1997 / Accepted: 11 April 1998 相似文献
16.
Many holoplanktonic forms, such as medusae, spawn in response to environmental cues such as light or temperature. Few observations
of the time of reproduction have been made in salps. Small groups of mature aggregates of the salp Thalia democratica (Forskal, 1775), collected off the Great Barrier Reef of Australia, were held under constant light in early to mid-December
in the years 1990, 1993 and 1994. Sperm were shed between 0300 and 0600 hrs each day with a mean time of about 0450 hrs for
all individuals for all years combined. Solitary stages released chains of fertilizable female individuals between 0500 and
0700 hrs each day, with a mean time of 0540 hrs. Field observations suggested that similar timing occurred in nature. Advancing
the time of dusk from 1900 to 1700 or 1800 hrs. did not significantly alter the mean time of sperm shedding or chain release.
T. democratica aggregates, collected in the Mediterranean Sea in 1995 and maintained in constant light, had a broader distribution of individual
spawning times, with a mean time of 0625 hrs, which differed significantly from that of the Australian population. Coordination
of the events of sexual reproduction in T. democratica may improve fertilization success and be responsible for recognizable age cohorts within blooms of this species.
Received: 27 May 1997 / Accepted: 20 June 1997 相似文献
17.
Jessica R. Frost Anneke Denda Clive J. Fox Charles A. Jacoby Rolf Koppelmann Morten Holtegaard Nielsen Marsh J. Youngbluth 《Marine Biology》2012,159(2):239-253
The ecology of small, gelatinous zooplankton is not integrated into management of Dogger Bank (54° 00′ N, 3° 25′ E to 55°
35′ N, 2° 20′ E). In pursuit of this goal, gelatinous zooplankton and their potential prey were sampled along a transect across
the bank on June 10–16, 2007. Eleven species of small medusae and ctenophores were collected, with six abundant taxa occurring
in greater numbers below the thermocline and in the shallower, southeastern portion of the bank. There were no statistically
significant diel changes in distribution. In contrast, potential prey were distributed more evenly across the bank and throughout
the water column. Isotopic analyses revealed that gelatinous zooplankton fed on both smaller (100–300 μm) and larger (>300 μm)
mesozooplankton, but also potentially on each other. These ecological insights suggest that small medusae and ctenophores
should be integrated into sustainable management of Dogger Bank. 相似文献
18.
Fluoride in Antarctic marine crustaceans 总被引:2,自引:0,他引:2
The concentration of fluoride in the body parts of a range of Antarctic crustaceans from a variety of habits was examined
with the aim of determining whether fluoride concentration is related to lifestyle or phylogenetic grouping. Euphausiids had
the highest overall fluoride concentrations of a range of Antarctic marine crustaceans examined; levels of up to 5477 μg g−1 were found in the exoskeleton of Euphausia crystallorophias. Copepods had the lowest fluoride levels (0.87 μg g−1 whole-body); some amphipods and mysids also exhibited relatively high fluoride levels. There was no apparent relationship
between the lifestyle of the crustaceans and their fluoride level; benthic and pelagic species exhibited both high and low
fluoride levels. Fluoride was concentrated in the exoskeleton, but not evenly distributed through it; the exoskeleton of the
head, carapace and abdomen contained the highest concentrations of fluoride, followed by the feeding basket and pleopods,
and the eyes. The mouthparts of E.␣superba contained almost 13 000 μg F g−1 dry wt. Antarctic krill tail muscle had low levels of fluoride. After long-term (1 to 5 yr) storage in formalin, fluoride
was almost completely lost from whole euphausiids.
Received: 1 April 1998 / Accepted: 29 July 1998 相似文献
19.
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
20.
In situ seagrass photosynthesis measured using a submersible, pulse-amplitude modulated fluorometer 总被引:8,自引:0,他引:8
Assessments of photosynthetic activity in marine plants can now be made in situ using a newly developed, submersible, pulse-amplitude
modulated (PAM) fluorometer: Diving-PAM. PAM fluorometry provides a measure of chlorophyll a fluorescence using rapid-light curves in which the electron-transport rate can be determined for plants exposed to ambient
light conditions. This technique was used to compare the photosynthetic responses of seagrasses near Rottnest Island, Western
Australia. Several fluorescence parameters were measured as a function of time of day and water depth; electron-transport
rate (ETR), quantum yield, photochemical quenching and non-photochemical quenching and Photosystem II (PSII) photochemical
efficiency (F
v
:F
m
ratio) were measured. Results indicate that recent light-history plays a crucial role in seagrass photosynthetic responses.
Maximum ETR of Posidonia australis, Amphibolis antarctica and Halophila ovalis is influenced by the irradiance during the diurnal cycle, with low rates at dawn and dusk (<10 μmol electron m−2 s−1), highest rates in late morning (40 to 60 μmol electron m−2 s−1) and a mid-day depression. Maximum ETR and PSII photochemical efficiency varied widely between seagrass species and were
not correlated. A comparison of photochemical to non-photochemical quenching indicated that seagrasses in shallow water receiving
high light have a high capacity for non-photochemical quenching (e.g. light protection) compared to seagrasses in deep water.
These results indicate that in situ measurements of photosynthesis will provide new insights into the mechanisms and adaptive
responses of marine plants.
Received: 26 May 1997 / Accepted: 27 May 1998 相似文献