共查询到20条相似文献,搜索用时 15 毫秒
1.
The corallimorpharian Rhodactis rhodostoma (Ehrenberg, 1934) forms aggregations that dominate patches on some coral reef flats in the Red Sea. The outcomes and mechanisms
of competition for space between this corallimorpharian and other sessile organisms are poorly understood. Polyps of R. rhodostoma were observed to overgrow zoanthids, hydrozoan corals, sponges and encrusting macroalgae on a fringing reef at Eilat, northern
Red Sea. R. rhodostoma polyps also damaged, and in some cases overgrew, reef-building corals in the families Poritidae, Acroporidae and Pocilloporidae,
most of which form branching colonies with small polyps that are subordinate in coral competitive hierarchies. In contrast,
most stony corals in the families Faviidae and Mussidae had standoff interactions with R. rhodostoma, in which they prevented the corallimorpharians from damaging them or approaching closer than 1 to 3 cm. The latter corals
are ranked at the top of competitive hierarchies for Indo-Pacific corals, and they form massive colonies of large polyps which
may develop aggressive organs termed sweeper tentacles. Some soft corals that exude allelopathic chemicals also avoided overgrowth
by the corallimorpharians. Tentacles along the oral disk margin of R. rhodostoma polyps were swollen and bulbous during contacts with cnidarians. These bulbous marginal tentacles had significantly thicker
ectoderm and a higher proportion of holotrichous nematocysts than did the normally filiform marginal tentacles of R. rhodostoma polyps. It is concluded that, on the reef flat at Eilat, this corallimorpharian damages and overgrows a variety of sessile
competitors, including branching stony corals, via the application of specialised marginal tentacles filled with penetrating
nematocysts. R. rhodostoma is an intermediate competitor in the aggressive hierarchy among Indo-Pacific Anthozoa, including the reef-building corals.
Received: 1 July 1998 / Accepted: 24 March 1999 相似文献
2.
E. Mutlu 《Marine Biology》2001,138(2):329-339
The distribution of moon jellyfish (Aurelia aurita Linnaeus, 1758) in the Black Sea was determined from plankton samples collected above the anoxic zone (maximum depth 200 m)
in the summer, winter and spring during 1991–1995. Distribution was patchy. Average biomass ranged from 98 to 380 g m−2, and abundance varied from 2 to 14 individuals m−2. Biomass and abundance peaked in late spring and summer. The distribution was correlated with hydrographic features in the
Black Sea, with higher concentrations occurring at the peripheries of anticyclonic eddies. Centers of the two main cyclonic
gyres generally had a low biomass of A. aurita. From July 1992 to March 1995, the populations were largely concentrated in offshore regions. A. aurita were confined to the upper part of the mixed layer. Smaller A. aurita (≤1 cm) were present in early spring (March), and individuals reached maximum size in the summer. Release of the epyhrae
occurred in spring on the northwestern shelf of the sea when the seawater temperature was 11–12 °C. Microscopic analysis of
stomach contents showed that copepods and mollusks form their main diet.
Received: 3 September 2000 / Accepted: 29 September 2000 相似文献
3.
Morula cells (MCs), ubiquitous ascidian cells which participate in alloimmune reactions, were studied in allogeneic and xenogeneic
assays performed with Botryllus schlosseri (Pallas, 1766) colonies from the Mediterranean and the Pacific coast, USA. Experiments were performed on the morphological
level, on blood cells sampled or vitally labeled in situ and on histological sections. In non-interacting B. schlosseri during blastogenic cycles A to C, MCs congregate in tentacles of the zooids' siphons. During the takeover phase of blastogenesis
they disappear, appearing again in the siphons of the newly developed generation of zooids. In both compatible and incompatible
allogeneic reactions their numbers in interacting ampullae increased fourfold within 2 h after first contacts, reaching up
to 50% of the total blood-borne cells in ampulla lumens. In rejection processes most of these cells died, while in autologous
or allogeneic fusions they disappeared from interacting ampullae within days of the reaction. During allogeneic rejections,
we followed cases (up to 1 week) in which MCs crossed all morphological/physiological barriers between noncompatible colonies
and entered the tunic matrices and blood systems of the interacting partners, forming successful microchimerism. In xenogeneic
assays with Botrylloides sp., MCs concentrated at the xenogeneic boundary, but they never crossed into the other species. One week after fusion or
rejection interactions, large numbers of macrophages clearing dead cells were found in contact areas. This is the first evidence
for compartmentalization of specific cellular defense reactions in the tunicate circulatory system.
Received: 23 October 1997 / Accepted: 17 February 1998 相似文献
4.
Genetic differentiation between North Sea and Baltic Sea Hediste diversicolor (O.F. Müller, 1776) (Polychaeta: Nereididae) populations was studied by allozyme electrophoresis on starch gel. Thirteen
loci were analyzed in eight populations. The level of genetic variation was very low (mean H
o = 0.000 to 0.015). Differentiation between H. diversicolor populations is quite high (F
ST = 0.892) and reflected by three enzyme loci (MDH-I*, MDH-II*, IDH-I*). The reduced gene flow (N
m<1) may be explained by the limited dispersal capacity of the species. Regardless of whether found in the North Sea or Baltic
Sea, there appear to be two different genetic types which are parapatric or sympatric in some places. The two types hybridize
at three localities, but no signs of hybridization have been found at one (Tallinn).
Received: 26 June 1997 / Accepted: 10 September 1997 相似文献
5.
Dark survival strategies in marine phytoplankton assessed by cytometric measurement of metabolic activity with fluorescein diacetate 总被引:5,自引:0,他引:5
F. J. Jochem 《Marine Biology》1999,135(4):721-728
Cytometric quantification of cellular fluorescence upon cleavage of fluorescein diacetate (FDA) is presented as a sensitive
and rapid technique to assess phytoplankton metabolic activity during exposure to prolonged darkness of 10 to 12 d. Two distinct
types of metabolic response to darkness are distinguished: Type I cells (Brachiomonas submarina, Pavlova lutheri, Chrysochromulina hirta) adapt to prolonged darkness by reducing their metabolism to a lower level of activity (∼10% of initial in P. lutheri, C. hirta, ∼0.5% in B. submarina) within few days, whereas Type II cells (Prymnesium parvum, Bacteriastrum sp., unidentified pennate diatom) continue with unchanged activity. Type I cells were able to maintain their initial cell
abundance and commenced rapid cell growth upon re-illumination after 12 d of darkness. Among Type II cells, diatoms were able
to maintain cell abundance and growth capacity as well, whereas P. parvum was not. Type I cells are expected to exhibit competitive advantages in environments with frequent or long dark periods.
Bacterivory further supports dark survival in C. hirta.
Received: 10 May 1999 / Accepted: 20 September 1999 相似文献
6.
The shortjaw mudsucker, Gillichthys seta, an intertidal goby endemic to the Sea of Cortez, has been proposed to be the paedomorphic derivative of the longjaw mudsucker,
Gillichthys mirabilis. G. mirabilis is a disjunct species, with populations found along the Pacific coast of central California to central Baja California, and
with isolated populations found in the northern Sea of Cortez. Previous studies have suggested that the endemic paedomorph
form speciated in sympatry with the Sea of Cortez population of G. mirabilis. Alternatively, this speciation event could have occurred before the separation of G. mirabilis populations into two disjunct entities. To test these alternative hypotheses, we collected adult individuals from both species
throughout their ranges from December 1997 to November 1998. We amplified and sequenced 142 partial [527 base pairs (bp)]
mitochondrial cytochrome b regions and 18 nuclear creatine kinase introns (140 bp). We found that Pacific populations of G. mirabilis separated into two distinct clades, possibly reflecting a phylogeographic break found in other fish species along the Baja
California coast at Punta Eugenia. These two Pacific populations were well separated from Sea of Cortez populations. Furthermore,
our results indicate that the split between Sea of Cortez and Pacific populations of G. mirabilis occurred well after the speciation event that separated G. mirabilis from its paedomorphic counterpart, G. seta.
Received: 30 March 2000 / Accepted: 4 September 2000 相似文献
7.
The genetic relationships among South-East Asian populations of the scad mackerels Decapterus macarellus, D. macrosoma and D. russelli (Pisces: Carangidae) were investigated. In 1995 and 1996, 216 fish were sampled in seven localities spanning the seas of
Indonesia and were examined for restriction-site polymorphisms using ten restriction enzymes for the mitochondrial (mt) DNA
control region, amplified by the polymerase chain-reaction. The inferred phylogeny of haplotypes led to the recognition of
three distinct mitochondrial lineages or phylads consistent with the distinctions of current taxonomy. All 15 mtDNA haplotypes
found in D. macarellus and all 9 haplotypes found in D. macrosoma were arranged as star-like clusters, suggesting recent evolutionary history. In contrast, the phylad formed by 6 haplotypes
in D. russelli from the Sulawesi Sea exhibited diffuse topology, suggesting that ancestral lineages of this species have been retained to
the present. Average nucleotide-divergence estimates between haplotypes of different phylads were between 0.042 and 0.135,
suggesting ancient separation, in consistency with published allozyme data. High levels of haplotype diversity, but no geographical
heterogeneity, was detected within D. macarellus from the Molucca Sea and the Banda Sea. Populations of D. macrosoma exhibited both significant differences between adjacent regions (Sunda Strait and Java Sea), and broadscale genetic homogeneity
from the South China Sea to the Sulawesi Sea via the Java Sea and Makassar Strait. The geographic isolation of the D. macrosoma population sampled in the Sunda Strait suggests that this region constitute a sharp transition zone between the Indian Ocean
and the Sunda Shelf. Near-monomorphism of haplotypes and low nucleotide diversity (d
X) were observed in the samples of D. macrosoma from the continental shelf (haplotype-diversity estimates, h, = 0.00 to 0.25 ± 0.08 and d
X = 0.000 to 0.002). This was in contrast to the comparatively high haplotype and nucleotide diversities observed in other
pelagic fish species including D. macarellus (h = 0.82 ± 0.05, d
X = 0.012 to 0.015) and D. russelli (h = 0.63 ± 0.12, d
X = 0.016), and in the oceanic D. macrosoma population sampled in the Sunda Strait (h = 0.67 ± 0.31, d
X = 0.005). We hypothesise that this may be the consequence of recent and perhaps repeated bottleneck events that have affected
the D. macrosoma population sampled on the continental shelf.
Received: 29 September 1997 / Accepted: 3 September 1999 相似文献
8.
Life history of Gonatus onyx (Cephalopoda: Teuthoidea): deep-sea spawning and post-spawning egg care
A reproductive strategy consisting of deep- water spawning and egg-care was inferred for the midwater squid Gonatus onyx Young, 1972. Brooding females and associated eggs and hatchlings, captured between 1250 and 1750 m depth off southern California,
are described. Brooding females appear to be senescent and lack tentacles. Large eggs of this species (3 mm) at cold temperatures
(3 °C at capture depth) may require as long as 9 mo to develop. The high lipid content of the digestive gland in adult females
of this species may provide fuel to support such an extended “brooding” period.
Received: 22 February 1999 / Accepted: 25 May 2000 相似文献
9.
The morphology and ultrastructure of the otolith settlement-mark was examined in 44 tropical reef-fish species spanning nine
families. A classification scheme based on similar otolith characteristics is presented. Three major categories are identified
based on changes in increment width and optical qualities of the settlement-mark. Of the 44 species examined, 39 possessed
“abrupt” settlement-marks (Type I) characterised by a rapid decrease in increment width (up to 50% reduction) over settlement.
Type I settlement-marks were found in all nine families examined. The 39 species spanned the whole range of possible larval
durations (Pomacentrus moluccensis, 15 d ± 0 SE; Naso hexacanthus, 91.2 d ± 2.97 SE). Four of the 44 species possessed “zonal” settlement-marks (Type II), featuring a band of increments that
are wider than pre-settlement increments. Species in this category are the labrids Corisaygula, Thalassoma bifasciatum, T. lunare and an unidentified acanthurid (Acanthurus sp. 2). One species of acanthurid (N. brevirostris) possessed a “gradual” settlement-mark (Type III), manifest as a gradual decrease in increment width during the settlement
period. A possible fourth type was identified from the literature. Gnatholepis thompsoni and Coryphopterus glaucofraenum possessed a settlement-mark with increment widths that increased post-settlement. Available data suggest a poor relationship
between the structure of the settlement-mark and the magnitude of metamorphosis (previously reported as internal and external
morphological change). Evidence suggests that the increment profile over early development and the increment transitions associated
with the settlement event are taxon-specific and may enable late-larval stage fishes to be identified to species level.
Received: 21 May 1997 / Accepted: 3 February 1999 相似文献
10.
Two populations of Marenzelleria spp. from the North Sea and the Baltic Sea that had already been characterized by allozyme electrophoresis and found genetically
different in 1994 were again examined in 1997. The genetic identity (I = 1.0) examined in 1994 and 1997 shows that the structures of the populations of genetic Type I in the North Sea (Ringkobing
Fjord) and genetic Type II in the Baltic Sea (Darss–Zingst Bodden chain) are stable. Three diagnostic gene loci that were
determined additionally (citrate synthase, one locus; alanine aminotransferase, two loci) support the hypothesis of the existence
of two sibling species of the genus Marenzelleria in Europe. In addition, the activities of ten electrophoretically separated enzyme systems were measured in the worms immediately
after removal from their habitat and after they had been kept in the laboratory for 2 months. Under both conditions four enzymes
showed significant differences between genetic types. The higher activity of the alanine aminotransferase of the North Sea
worms (Type I) is discussed in the context of the different preferred salinities of the two Marenzelleria sibling species.
Received: 21 January 1999 / Accepted: 13 July 1999 相似文献
11.
Predation rates and prey selection of the pelagic mysid shrimp, Mysis mixta, were studied experimentally in the northern Baltic Sea in 1998 during their most intensive growth period, from June to October.
Functional responses during 5 months were determined by providing the mysids with a natural zooplankton assemblage, diluted
to several different concentrations. The results show that ingestion rate increased, along with mysid growth, from early summer
to autumn and that saturation level was reached between 400 and 500 μg C l−1. Ingestion rates increased with increasing prey concentration, and sigmoidal curves explained mostly the variation in ingestion
rates (explanatory levels of 86–97%). Prey selection was evident in June, July and August, though weaker during the latter
2 months. Selection differed between the studied months but, generally, copepods were more positively selected than cladocerans.
Rotifers were the main prey during June and July, when mysids were small, while larger mysids fed on copepods and cladocerans.
Of the copepods, Eurytemora affinis was a truly selected species. This study shows that mysids feed on many zooplankton taxa and that they undergo ontogenetic
diet shifts.
Received: 19 July 2000 / Accepted: 19 October 2000 相似文献
12.
The Kumamoto oyster Crassostrea sikamea is distinguished from the closely related Pacific oyster C. gigas by concordant differences in 16S rDNA, allozymes, and a one-way gametic incompatibility. After repeated failures to find
this oyster in its native habitat, we speculated in 1994 that “the Kumamoto oyster may be extinct in Japan”. In September
1996, we sampled small, deep-cupped oysters from the Ariake Sea and typed these for 16S rDNA and ITS-1 DNA markers previously
shown to be diagnostic for the three most common oysters in the Ariake Sea, C. gigas, C. sikamea and C. ariakensis. Our earlier suggestion of the demise of C. sikamea proved incorrect. Of the 256 oysters sampled, 181 (71%) were C. gigas, 53 (21%) were C. sikamea, and 22 (9%) were C. ariakensis; no interspecific hybrids were observed. The distributions of C. sikamea and C. ariakensis are clumped in the Ariake Sea: C. sikamea occurs on the eastern and northern shores, C. ariakensis occurs only in the northern part. These results emphasize the value of molecular markers for discriminating these morphologically
plastic species both in the field and in aquaculture.
Received 6 July 1998 / Accepted 8 October 1998 相似文献
13.
Observations of copepod feeding and vertical distribution under natural turbulent conditions in the North Sea 总被引:1,自引:0,他引:1
We present results of simultaneous measurements of turbulent-dissipation rate, zooplankton vertical distribution and copepod
gut pigments in the northern North Sea. Analysis shows that some, but not all, copepods (by species, sex and stage) exhibit
significant dependence on turbulence in respect to vertical distribution and feeding rate. Oithona similis (female and copepodite stages) exhibits an avoidance of the surface layer when turbulence is strong there. For the range
of turbulence (10−7 to 10−3 m2 s−3) and ambient chlorophyll concentration (0.5–0.8 μg l−1) encountered, Calanus spp. and Metridia lucens exhibited a significant negative response in feeding-rate index with increasing turbulence. Centropages typicus and Pseudocalanus spp. also exhibited a negative response but of less significance.
Received: 12 October 2000 / Accepted: 11 December 2000 相似文献
14.
This paper reports on the feeding biology of a predatory and of a facultatively predatory nematode, Enoploides longispiculosus and Adoncholaimus fuscus, respectively. Both species represent genera which are common and abundant in the littoral of the North Sea and in adjacent
estuaries. Observations on the foraging behaviour of both species are given, and for the former species, a range of prey from
its natural habitat is identified. Respiration was determined using a polarographic oxygen electrode technique and compared
to consumption determined as predation rates on the monhysterid nematode Diplolaimelloides meyli. The daily C-loss due to respiration accounted for 15% of the measured C-consumption in E. longispiculosus and for 111% in A. fuscus, proving the observed feeding rates in the latter species to have been inadequate for the maintenance of its aerobic metabolism.
Daily respiration rates at an average environmental temperature were 219 ng C ind−1 d−1 for adults of A. fuscus and 21.9 ng C ind−1 d−1 for adults of E. longispiculosus. Using radiotracer techniques, no uptake of bacterial cells or of organic matter in the dissolved phase was demonstrated
for E. longispiculosus. In A. fuscus, however, a significant drinking of label in the dissolved or volatile fraction occurred; bacterial cells were taken up at
a level insignificant to the nematode's daily C-ration. It is concluded that E. longispiculosus has a fairly strict predatory feeding strategy, while A. fuscus gains a majority of C from additional foraging strategies, among which the uptake of dissolved material and scavenging on
macrofauna carcasses (as reported in the literature) may be of particular importance.
Received: 28 August 1998 / Accepted: 8 March 1999 相似文献
15.
The isopod Munnopsurus atlanticus occupies bathyal depths in both the Bay of Biscay (NE Atlantic; between 383 and 1022 m) and in the Catalan Sea (Northwestern
Mediterranean; between 389 and 1859 m). The species was dominant in both assemblages, reaching bathymetric peaks of abundance
on the upper part of the continental slope (400 m depth) in the Bay of Biscay and at ˜600 m in the Catalan Sea. Both the Atlantic
and the Mediterranean populations are bivoltines. Demographic analysis of the Bay of Biscay population revealed the production
of two generations per year with different potential longevity (5 mo for G1 and 11 mo for G2). The mean cohort-production interval (CPI) was estimated at 8 mo, and results of the demographic analysis were also used
to estimate production for the Catalan Sea populations. Mean annual density (D) and biomass (B) were higher in the Bay of
Biscay (D = 356.7 individuals 100 m−2; B = 0.803 mg dry wt m−2 yr−1) than in the Mediterranean (D = 16.3 individuals 100 m−2; B = 0.078 mg dry wt m−2 yr−1). Also, mean annual production was an order of magnitude higher in the Atlantic (between 4.063 and 4.812 mg dry wt 100 m−2 yr−1 depending on the method used) than in the Catalan Sea (between 0.346 and 0.519 mg dry wt 100 m−2 yr−1). M. atlanticus feeds on a wide variety of benthic and pelagic food sources. In both study areas, phytodetritus was not important in the
diet of M. atlanticus. In contrast, gut-content data suggested an indirect coupling with phytoplankton production in both areas via foraminiferans.
The life history and the recorded production are considered in respect to both the dynamics and levels of primary production
and the total mass flux in the respective study areas. Differences in the secondary production of both populations seemed
to be more consistently explained by differences in total mass flux than by differences in the primary production levels;
this is also consistent with the variety of food sources exploited by M. atlanticus.
Received: 22 February 1999 / Accepted: 3 February 2000 相似文献
16.
Frederico P. Brandini Eduardo T. da Silva Franciane M. Pellizzari Alessandra L. O. Fonseca Luciano F. Fernandes 《Marine Biology》2001,138(1):163-171
Production rates, chlorophyll concentrations and general composition of periphytic diatom communities growing on glass slides
were studied in relation to environmental parameters during one seasonal cycle in the Bay of Paranaguá, southern Brazil. Slides
were routinely submersed at 1, 2 and 3 m depth and recovered weekly for microscopic examinations, analyses of chlorophyll,
cell counts and in situ photosynthetic incubations using the Winkler titration method. Water samples were also collected at
surface and bottom layers for determinations of temperature, salinity, nutrients and chlorophyll in the water. The periphytic
community was mainly formed by epipelic and epipsammic species, dominated by Navicula phyllepta, Cylindrotheca closterium, Navicula spp. and Amphora sp. Weekly chlorophyll a and cell accumulations on slides varied from <1–32 mg m−2 and up to 31 × 108 cells m−2, respectively. Photosynthetic rates varied from <1 to 35 mg oxygen mg chlorophyll a
−1 h−1, with higher values in summer. Daily production varied from 5 to 3,600 mg oxygen m−2 day−1 (<0.01–1.4 g carbon m−2 day−1). Multiple regression analysis revealed that vertical differences in light conditions and grazing pressure jointly affected
the influence of temperature on the seasonal patterns of cell densities and chlorophyll concentrations according to depth.
Received: 27 April 2000 / Accepted: 16 August 2000 相似文献
17.
Spatial and temporal pattern in seagrass community composition and productivity in south Florida 总被引:4,自引:1,他引:3
We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance
of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites,
delimiting 12,800 km2 of seagrass beds in the 17,000-km2 survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km2. The range of T. testudinum was almost as extensive (6,400 km2), followed by Syringodium filiforme (4,400 km2), Halodule wrightii (3,000 km2) and Halophila engelmanni (50 km2 ). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m−2day−1, with a range of 0.05–3.29 g m−2 day−1. Specific productivity ranged between 3.2 and 34.2 mg g−1 day−1, with a mean of 18.3 mg g−1 day−1. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the
study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 1010 g S. filiforme, which translate to a yearly production of 9.4 × 1011 g T. testudinum leaves and 2.4 × 1011 g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing
these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as
a benchmark against which future change in the system can be quantified.
Received: 30 January 2000 / Accepted: 24 July 2000 相似文献
18.
Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive
X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly
higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates
that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase.
Received: 30 September 1999 / Accepted: 6 April 2000 相似文献
19.
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
20.
Otolith microstructure and microchemistry were examined in juveniles of American (Anguilla rostrata) and European (A. anguilla) eels. Otolith increment width markedly increased from age 132 to 191 d (156 ± 18.9 d; mean ± SD) in A. rostrata and 163 to 235 d (198 ± 27.4 d; mean ± SD) in A. anguilla, both of which were coincident with drastic decreases in otolith Sr:Ca ratios, suggesting that metamorphosis from leptocephalus
to glass eel began at those ages in each species. The duration of metamorphosis was estimated to be 18 to 52 d from otolith
microstructure, for both species studied. Ages at recruitment were 171 to 252 d (206 ± 22.3 d; mean ± SD) in A. rostrata and 220 to 281 d (249 ± 22.6 d; mean ± SD) in A. anguilla. In these two species, positive linear relationships were found in ages between the beginning of metamorphosis and recruitment,
suggesting that early metamorphosing larvae recruited at younger ages. Duration of the leptocephalus stage to recruitment
in A. anguilla was about 40 d longer than that in A. rostrata. The geographical segregation between the two species in the Atlantic Ocean seems to be involved in the differences in the
duration of the leptocephalus stage (age at metamorphosis).
Received: 8 November 1999 / Accepted: 8 May 2000 相似文献