共查询到20条相似文献,搜索用时 359 毫秒
1.
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
2.
Otolith microstructure and microchemistry were examined in juveniles of Australasian shortfinned eel, Anguilla australis, from Australia and New Zealand. Patterns in otolith increment widths were similar in these two stocks. A marked increase
in otolith increment width was found from age 138 to 198 d (mean ± SD: 164 ± 18.6 d) from Australia, 161 to 208 d (185 ± 17.3 d)
from the western coast of New Zealand and 161 to 211 d (187 ± 18.9 d) from the eastern coast. These changes coincided with
a drastic decrease in otolith Sr:Ca ratios, suggesting that metamorphosis began at these ages in each species. The duration
of metamorphosis estimated from otolith microstructure was the same in the different stocks, 17 to 41 d (mean ± SD: 27 ± 5.4 d).
Ages at recruitment were 186 to 239 d (mean ± SD: 208 ± 17.4 d) from Australia, 214 to 263 d (232 ± 19.8 d) from the western
coast of New Zealand and 208 to 266 d (237 ± 20.0 d) from the eastern coast. There was a significant difference in the age
between the Australian stock and the two stocks from New Zealand. No significant difference was found in the age between the
latter two stocks. The difference in the period for the recruitment between Australian and New Zealand stocks seems to reflect
their geographical separation.
Received: 1 March 1999 / Accepted: 19 July 1999 相似文献
3.
B. W. Molony 《Marine Biology》1996,125(3):439-446
Juvenile Ambassis vachelli, 40 to 50 d old, were used to test the effects of starvation and recovery-feeding on the widths of otolith increments. Three laboratory treatments (fed continuously; fed for 9d then starved for 15 d; starved for 9 d then fed for 15 d), were compared. Fish were also collected throughout the experiment from a field site to assess the natural fluctuations of increment widths. Growth, starvation and recovery were reflected in the widths of otolith increments. The width of increments deposited during starvation were similar in all fish, regardless of prior feeding history, despite the lower mortality recorded in starved fish with a history of intense feeding. Increment-width data were confounded by an ontogenetic decrease in increment widths with age. The results indicate that starvation and recovery are recorded in the increment widths of otoliths and are distinguishable from the effects of ontogenetic development. However, ontogenetic changes in the width of otolith increments confounded the interpretation of otolith-increment series. Therefore, the ontogenetic pattern of otolith increments must be known for each species before valid interpretation of otolith microstructure is possible. 相似文献
4.
Influence of temperature on the microstructure of statoliths of the thumbstall squid Lolliguncula brevis 总被引:4,自引:0,他引:4
A laboratory study investigating the influence of temperature on the microstructure of statoliths of Lolliguncula brevis is described. Groups of squid were subjected to various temperature regimes for periods in excess of 30 d. Statoliths extracted
from 20 squid were examined using a confocal microscope in laser scanning mode. The parts of the statoliths deposited during
the course of the experiments were identified using either putative daily increment counts or from checks produced in response
to capture and handling. These checks appear to consist of a series of prominent increments rather than reflecting a period
of interrupted statolith growth. Increments deposited during the experiment generally displayed reduced contrast and clarity
in comparison to the “wild” parts of the statolith, presumably in response to the constant conditions imposed in the laboratory.
Average statolith growth rates observed over the course of the experiment showed a strong positive relationship to ambient
temperature. A significant sex effect was apparent, with statoliths of female squid generally growing faster than those of
males. Observed statolith growth rates at 15 °C were generally below 1 μm d−1, suggesting that the widths of daily increments produced under these conditions may approach the resolution limits of a light
microscope. The implications for studies using increment numbers to estimate age are discussed.
Received: 23 July 1999 / Accepted: 17 February 2000 相似文献
5.
Sessile marine invertebrate larvae can recognize suitable settlement substrata by using various environmental cues, including
organic/microbial biofilms. In laboratory choice assays, the effect of biofilms of varying ages on the settlement behaviour
of two fouling organisms was assessed. The species included the arborescent cheilostome bryozoan Bugula flabellata (Thompson) and the solitary ascidian Ciona intestinalis (L.), both of which are characteristic of temperate sublittoral hard substratum assemblages in northwest Europe. Experiments
were carried out using polystyrene petri dish substrata preconditioned with multispecies biofilms from natural laboratory-aquarium
seawater for 1, 3, 6 or 12 d. Unfilmed (new, initially sterile) dishes were used as control substrata. Whereas the coronate
larvae of B. flabellata generally were inhibited by biofilming, irrespective of film age, the settlement of tadpole larvae of C. intestinalis was facilitated on biofilmed substrata, and numbers of settled larvae generally increased with biofilm age: the highest mean
numbers were counted on 12 d-old biofilms. In C. intestinalis, settlement and metamorphosis are processes which can be temporally separate and are possibly induced by different environmental
cues. This study therefore distinguished between C. intestinalis larvae which were attached to the biofilm surface by the anterior, and those larvae entrapped by the biofilm but not settled
in the conventional meaning of the term. As reported in previous studies, we did observe that such entrapped larvae could
subsequently attach and develop successfully into sessile juveniles. Both the numbers of “attached” and “trapped” tadpoles
increased with biofilm age. Assuming that “settlement” is essentially a process involving the active behavioural response
of larvae to environmental cues, it seems that the facilitated attachment of C. intestinalis onto biofilmed substrata is due to the combined effect of active habitat selection and passive deposition/“entrapment” of
larvae onto the “sticky” substratum.
Received: 21 August 1996 / Accepted: 21 November 1996 相似文献
6.
Otolith microstructure and microchemistry of the tropical eel Anguilla bicolor pacifica Schmidt were examined in glass eels collected at the mouth of the Dumoga River, North Sulawesi Island, Indonesia. Ages of
the glass eels examined (age at recruitment) ranged from 124 to 202 d (167 ± 19.3 d; mean ± SD), hatching being estimated
as having occurred between November 1995 and March 1996. Otolith increment widths markedly increased from age 101 to 172 d
(135 ± 18.2 d; mean ± SD), coincident with a drastic decrease in otolith Sr:Ca ratios, suggesting that metamorphosis began
during that period. The duration of metamorphosis was estimated as 20 to 40 d, on the basis of otolith microstructural characteristics.
The fluctuation patterns in otolith increment widths and Sr:Ca ratios were similar to those of the temperate Japanese eel
A. japonica.
Received: 20 May 1998 / Accepted: 7 October 1998 相似文献
7.
Juvenile squids were grown in individual 2.6-l floating enclosures and were fed either a high- or a low-ration diet of fish
and the crustacean Acetes. Squids were maintained for a maximum of 44 days in two experiments. The high-ration individuals reached a significantly
larger size in both experiments (27, 25.5 mm mean mantle length, ML) compared to their low-ration siblings (19 mm mean ML)
in both experiments. The statolith increment widths prior to the start of the experiment were significantly wider (between
3 and 4 μm) compared to the increment widths after the start of the experiment (between 2 and 3 μm) both for the low- and
the high-ration squids. High-ration squids also had significantly wider increments and larger statoliths than their low-ration
siblings. Even though we detected consistent trends in daily statolith increment widths for the different feeding regimes,
we could not detect variation in increment widths at a daily level of resolution (i.e. as a result of differences in day-to-day
food intake at an individual level). This was probably due to the relatively consistent diet experienced by each individual.
These experiments revealed that ration level influences squid growth rate, statolith size and daily statolith increment width.
Received: 30 March 2000 / Accepted: 30 October 2000 相似文献
8.
Juveniles of the planehead filefish Stephano-lepishispidus (Pisces: Monacanthidae) (Linnaeus, 1766) are a major component of the Sargassum spp. community, yet little is known of their ecology. In this study, the otolith record of age, growth, and ontogeny in S.
hispidus was examined. Juveniles caught off Beaufort Inlet, North Carolina (USA) on 30 June 1996 were marked with alizarin complexone
and reared in a flow-through, outdoor tank for up to 19 days. Examination of marked otoliths at several time intervals showed
that increment formation was not significantly different than one increment per day, and thus, increment number was used to
estimate age. Depth-distribution, morphology, and meristics of larvae and juveniles collected (1990–1992) between Cape Romain,
South Carolina, and Cape Hatteras, North Carolina, were examined to identify the timing of the larval to juvenile transition.
All indicators suggested the transition occurred between 17 and 20 days. Mean otolith increment widths exhibited a marked
change at about 20 days, coinciding with the timing of the larval to juvenile transition and a change in the depth distribution
from bottom to surface waters. Increment width of individual juveniles, however, did not exhibit the same pattern; only 40%
conformed to the pattern identified for all fish. Thus, the record of the larval to juvenile transition is clear at the population
level, but unresolved at the individual level.
Received: 1 November 1999 / Accepted: 18 December 2000 相似文献
9.
We assessed the efficacy of tetracycline, calcein and strontium chloride for validating the periodicity of otolith growth-increments
in eight species of tropical marine gobies (family Gobiidae). We compared the number of fishes in which the otoliths were
successfully marked when each of these chemicals was administered by intraperitoneal injection or immersion bath at a range
of doses and immersion times. All three chemicals could produce a detectable mark in the otoliths of five reef-flat gobies,
Asterropteryx semipunctatus, Amblygobius bynoensis, Istigobius goldmanni, Valenciennea muralis and Amblygobius phalaena; however, tetracycline injection at 50 mg kg−1 is recommended because it produced a brighter otolith mark than calcein and is cheaper and quicker to detect than strontium
chloride. Calcein immersion treatment of 125 mg l−1 for 24 h was the most successful treatment for two estuarine gobiids, Favonigobius reichei and Glossogobius biocellatus. No treatment produced a detectable mark in the otoliths of the coral-dwelling goby Gobiodon histrio. Adequate care in the preparation of otoliths was found to be essential for detection of the validation mark produced by
tetracycline and calcein. Otolith growth-increments were deposited daily in the seven species of goby for which validation
was possible.
Received: 15 October 1999 / Accepted: 15 June 2000 相似文献
10.
The structure of the larval fish assemblages in three large estuarine systems on the KwaZulu-Natal coast of South Africa
was examined using a combination of univariate, distributional and multivariate techniques. The database was comprised of
a full annual set of larval fish samples taken from each estuarine system: Durban Harbour, Richards Bay Harbour and St Lucia
Estuary. The mean monthly densities of each species in each system were used in the species matrix, and the mean monthly values
of salinity, temperature and turbidity were used in the environmental matrix. The mean species diversity and evenness index
were significantly higher in Durban Harbour (H′ = 1.03, J′ = 0.65) than in the other two systems. The cumulative dominance curve showed that St Lucia Estuary has a high dominance
of a few species, with Richards Bay Harbour intermediate and Durban Harbour being the most diverse. Classification and MDS
(multiple-dimensional scaling) analyses of larval fish densities in all three systems grouped together into three main clusters
on the basis of system. The species similarity matrix (inverse analysis) clustered into five groups at the 25% similarity
level. The MDS analysis of the same matrix showed that the groups separated out according to the degree of estuarine association
of a species and hence habitat type. The species most responsible for system groupings were: Glossogobius callidus, Gilchristella aestuaria, Stolephorus holodon, Croilia mossambica and Gobiid 12. The “best fitting” of the environmental variables to explain the larval fish community patterns in each system
was turbidity on its own (weighted Spearman's rank correlation, ρw = 0.55). The relationship of larval densities to environmental conditions was shown to be species-specific with estuarine
species (e.g. G. callidus and G. aestuaria), having a strong positive correlation with temperature and turbidity but negative correlations with salinity. In summary,
much longer term studies with more sites within each system are needed to assess whether the larval fish assemblages are stable
or at an equilibrium (both spatially and temporally) and whether these assemblages are indicative of the relative “health”
and nursery function of the system.
Received: 28 April 1999 / Accepted: 30 May 2000 相似文献
11.
A. I. Arkhipkin 《Marine Biology》1997,129(1):103-111
Statolith microstructure was studied in 56 Ancistrocheirus lesueurii (25 to 423 mm of mantle length, ML) caught in the central-east Atlantic. Statolith growth increments were grouped into three
main growth zones, distinguished mainly by increment width. The second transition in the statolith microstructure (from Zone
2 to Zone 3) coincides with the life history shift from epipelagic and upper mesopelagic to a bathyal habitat. Second-order
bands (mean 27.65 growth increments) and sub-bands (mean 13.6 growth increments) within statolith microstructure appeared
to be related to the lunar cycle. Striking sexual dimorphism is reflected in the age and growth rates: males live ca. 1 yr,
while females only start maturing at this age and obviously live >1.5 yr. A. lesueurii is a slow growing squid, attaining 25 to 30 mm ML at the age of 100 d. After ontogenetic migrations into bathypelagic waters
at ML > 30 to 35 mm, growth rates gradually decrease to the minimum known values for squids. Based on back-calculated hatching
dates, A. lesueurii hatches throughout the year with a peak between November and March.
Received: 28 August 1996 / Accepted: 31 January 1997 相似文献
12.
M. Thiel 《Marine Biology》2000,137(4):661-674
The population dynamics and reproductive biology of an ascidian- and a sponge-dwelling amphipod were examined. The two undescribed
amphipod species, Leucothoe“ascidicola” and L.“spongicola”, are closely related to each other, and occur in ascidians and sponges, respectively, along the Florida Atlantic coast.
L. “ascidicola” was abundant in solitary ascidians during fall 1997, disappeared during spring/early summer, and became abundant again in
September 1998. During the time when L. “ascidicola” were absent from their hosts, a copepod became a frequent inhabitant of the ascidians but disappeared again when L.“ascidicola” returned to the ascidians in September 1998. The numbers of L.“spongicola” in sponges increased substantially during spring, when high reproductive activity was observed. Following this reproductive
peak, both adult and juvenile amphipods apparently left the sponges, and during the summer amphipod numbers in the sponges
were very low. Another small amphipod species, which often co-occurred with L.“spongicola”, showed less seasonal variation and was found in sponges throughout the whole study period. The percentage of ovigerous
females per host unit was usually lower in the ascidian-dwelling than in the sponge-dwelling amphipods. In solitary ascidians,
L.“ascidicola” amphipods usually occurred in groups of several adults, yet there never was more than one ovigerous female per ascidian.
In contrast, several ovigerous L.“spongicola” females were found to cohabit in the same spongocoel. This suggests that intrasexual aggression may be stronger among reproductive
amphipod females in the ascidians than in sponges. The size distributions of juvenile cohorts indicate that juvenile L.“ascidicola” remain for relatively long time periods in the parental ascidian, where they may reach sexual maturity. In contrast, in
L.“spongicola”, only cohorts of very small juveniles could be identified, indicating that juveniles disperse shortly after emerging from
the female's brood pouch. It is concluded that extended parental care is of very short duration or does not occur in the sponge-dwelling
amphipod L. “spongicola”, possibly because fast-growing sponges with a highly branched spongocoel system do not allow long-lasting coexistence of
parent-offspring groups. In contrast, the discrete character of the solitary ascidians may enhance the potential for exclusion
of other species, resource monopolization by reproductive females, and furthermore for long-lasting extended parental care
in the ascidian-dwelling amphipod. Groups of single parents together with cohorts of large juveniles are reported in the literature
for amphipods and isopods from brachiopods, bivalves and ascidians, suggesting that these discrete biotic microhabitats may
favor the evolution of extended parental care in peracarid crustaceans.
Received: 30 July 1999 / Accepted: 8 May 2000 相似文献
13.
H. Zenitani 《Marine Biology》1999,134(4):645-652
The size-specific nutritional conditions of larval sardines, Sardinops melanostictus, from the main Kuroshio Current and its offshore waters off eastern Japan were assessed by lipid analysis. A rapid lipid
analysis technique (diagnostic kits for human serum lipids) was used to measure the different lipid components of individual
sardine larvae as indicators of their nutritional condition. Size-specific growth trajectories of individual larvae were estimated
by the biological intercept method, and the recent daily growth rate of standard length (SL) was calculated from the 3 d outer increment width on the otolith. Relationships between the amount of larval phospholipid
(PL; tissue weight indicator) and SL, and the recent daily growth rate of larva (Gr) and SL, could be expressed by the equations PL = 0.459 SL
1.77 and Gr = 0.0809 SL − 0.341, respectively. There was no notable difference in these values between the two survey areas. The relationship between
the amount of triglyceride (TG) and SL could be expressed allometrically (TG = 0.013 SL
2.63). The relationship between the index of starvation tolerance (TG/PL) and SL could be expressed by the allometric equation TG/PL = 0.0288 SL
0.865, suggesting that larger sardine have a higher starvation tolerance than smaller sardine. The TG of the 8 to 9 mm SL size-class larvae in the offshore area was higher than in the main Kuroshio Current. To test whether
the TG for each larval sardine in the 8 to 9 mm SL size-class could be correlated with variables (temperature, chlorophyll a and distribution density of the sardine larvae) measured at the sampling stations, correlation analyses were performed. A
highly significant negative correlation between TG and distribution density of the sardine larvae was found. A density-dependence effect seemed to influence the fluctuation
of the larval storage energy component for short-term needs.
Received: 12 March 1998 / Accepted: 26 March 1999 相似文献
14.
Age and growth of Electrona antarctica (Pisces: Myctophidae), the dominant mesopelagic fish of the Southern Ocean 总被引:1,自引:0,他引:1
Numerically and in biomass, the lanternfish Electrona antarctica is the dominant fish in the vast pelagic region of the Southern Ocean bounded on the north by the Antarctic Convergence and
in the south by the Antarctic continental shelf. It is an important krill predator, and in turn is important in the diets
of flighted and swimming seabirds. Further, it is the southernmost and coldest-dwelling representative of the globally distributed
fish family Myctophidae. The present study was undertaken to estimate the species' growth rate and average life span, to incorporate
the information in a basic energy budget, and to compare the growth of E. antarctica with more northerly confamilials. Fishes were aged using primary growth increments that were resolved on sagittal otoliths
using three sequential techniques: thin-section grinding and polishing, etching, and scanning electron microscopy (SEM). Based
on increment width (0.8 to 1.2 μm), continuity, and previous studies on confamilials, the microincrements were assumed to
be deposited on a daily basis. Montages of SEM photomicrographs were constructed for each sagitta to allow the daily rings
to be counted over the entire life span of 31 individuals representing the entire size range of the species. Results suggest
a larval stage of 30 to 47 d and a maximum life span of 3.5 yr, with females growing faster than males in the last 1.5 yr
of life and reaching a larger maximum size. Construction of a simple energy budget using the best information available suggests
that a surplus of energy is available to support the observed growth rates (0.05 to 0.07 mm d−1). The results of the present study contrast markedly with previous estimates of an 8 to 11 yr maximum age for E. antarctica. These results provide important data addressing the ecology and population dynamics of the pelagic Antarctic ecosystem.
E. antarctica is the end-member species in the continuum of vertically migrating myctophids that extend from the equator to the polar circle.
Its growth rate is consonant with that of all other myctophid species examined using primary growth increments to determine
age. The present study, in conjunction with earlier studies, suggests that growth rates of mesopelagic species are far higher
than previously thought.
Received: 12 September 1997 / Accepted: 25 July 1998 相似文献
15.
Results of isozyme electrophoresis were used to explore the genetic relationships between several Mediterranean morphs of
Cerithium (Gastropoda: Prosobranchia), for which taxonomy is currently uncertain because of high intraspecific variability and low
interspecific differentiation. The large species, classically known as C. vulgatum Bruguière, 1789 was identified at four sites (two in the French Mediterranean and two in southern Spain). Two different larval
types were found in the French sites, but poecilogony could not be demonstrated. Individuals collected from harbours were
not genetically distinct from open-sea populations of classic C. vulgatum. However, a population in the Embiez lagoon (French Mediterranean) which morphologically resembles C. vulgatum did display distinct genetic traits, supporting its status as a separate species. Of the small Cerithium species usually known as C. rupestre, two sympatric species (C.“rupestre” Risso, 1826 and C. lividulum Risso, 1826) were distinguished. Genotype frequencies within the analysed populations revealed much heterozygote deficiency.
F
ST
values (fixation index measuring the effects of population subdivision) suggest a higher genetic differentiation for C. lividulum populations than for C. vulgatum populations. We assume that a high larval dispersal capability (via planktotrophy) allows a high gene flow between populations
of C. vulgatum.
Received: 24 November 1998 / Accepted: 24 September 1999 相似文献
16.
J. M. Kalish J. M. Johnston D. C. Smith A. K. Morison S. G. Robertson 《Marine Biology》1997,128(4):557-563
Accelerator mass-spectrometry was used to measure radiocarbon in the earliest formed portions of selected blue grenadier,
Macruronus novaezelandiae, otoliths to provide a validation of fish-age estimates based on the quantification of opaque and translucent zones in otolith
thin-sections. Δ14C data from blue grenadier otoliths were compared with previous estimates of Δ14C in seawater-dissolved inorganic carbon at similar latitutes, longitudes, and depths to link variation in otolith Δ14C to time. Minimum otolith Δ14C was −76.9 ± 7.7‰, indicative of pre-bomb radiocarbon levels below the surface mixed-layer at latitudes where juvenile blue
grenadier are found. When plotted versus fish age estimated from otolith sections, the majority of the Δ14C data combined to define a curve reflecting the increase in bomb radiocarbon in temperate oceans of the Southern Hemisphere,
indicating that age-estimation procedures based on otolith thin-sections are satisfactory for determining blue grenadier age.
If otolith-section age estimates were correct, peak otolith Δ14C of 106.8 ± 7.9‰ occurred during the late 1960s, i.e. earlier than expected. This may be a manifestation of an increase in
the mixed-layer depth associated with increased frequency of zonal westerly winds at this time.
Received: 3 December 1996 / Accepted: 17 December 1996 相似文献
17.
James D. McCleave 《Marine Biology》2008,155(3):249-262
This study reviewed literature on spawning times for three north temperate species of anguillid eels estimated by sampling
for small leptocephali (larvae) at sea and for several temperate and tropical species by back-calculating from putative daily
ages derived from otolith increment analysis of glass eels that recruited to coastal waters. Estimates from otoliths of European
eels, Anguilla anguilla, American eels, Anguilla rostrata, and Japanese eels, Anguilla japonica, imply much more protracted spawning seasons than are indicated by sampling at sea during various times of year. European
eels are inferred to spawn year-round from otolith analysis, but the smallest, recently hatched leptocephali are found only
in late winter and spring. From otoliths, the spawning times of these three species are all estimated to occur much later
in the year than when small leptocephali are found at sea, indicating that ages appear to be underestimated. For these and
other temperate and tropical eels, there are inconsistencies in assigned ages among various studies, which are most extreme
for the European eel. This species has the longest larval migration and often has an opaque zone in the glass eels’ otoliths
where it is difficult to discern growth increments. These inconsistencies suggest that interpretation of otolith growth increments
is incorrect at least in some studies, and the apparently consistent mismatch between otolith and sea-sampling studies suggests
that increments may not always be formed at some period during the unusual early life history of anguillids. Because daily
increments may be formed in eels during most of their early life history, future research is needed to determine the cause
of the mismatch of glass eel aging studies and the apparent spawning times of eels offshore.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
James D. McCleaveEmail: |
18.
Zooplankton samples from the North Arabian Sea Environment and Ecosystem Research (NASEER) cruises were analyzed to determine
the basic taxonomic composition, biomass (standing stock) and the total and copepod numeric abundance; these characteristics
are discussed with reference to the different monsoon periods. Cruises carried out during March 1993 and May 1994, categorized
as pre-southwest monsoon periods, and a cruise in December 1994, categorized as a northeast monsoon period, are discussed
in detail. The biomass of January 1992 versus August 1992 and August 1992 versus March 1993 differed significantly (F = 6.44, P≤ 0.05). Ranges of highest and lowest biomass from each cruise are also given. Distinct “high” and “low” production areas
of statistically significant difference (F = 12.67, P≤ 0.05) were observed. The “high” and “low” production areas were mobile and followed the surface wind circulation patterns
(wind reversal pattern) during the northeast and southwest monsoon periods. Overall zooplankton showed a patchy distribution.
The overall zooplankton abundance and total copepod counts differed significantly between the Cruises 3 versus 4 and 4 versus
5 (F = 15.67, P≤ 0.05 and F = 34.39, P≤ 0.05, respectively). There was no significant difference (P≥ 0.05) in biomass, between eutrophic and oligotrophic stations, suggesting no difference between near shore and offshore
waters. Thirty-eight taxonomic groups were identified from the samples, with copepods being the most dominant group, followed
by chaetognaths and siphonophores. Copepods constitute an average of 52.50 to 74.93% of the total zooplankton count and reach
maxima of 92.14% of the total zooplankton count at the outset of the southwest monsoon (March 1993) and 91.39% at the outset
of the active northeast monsoon (December 1994).
Received: 27 February 1998 / Accepted: 8 October 1999 相似文献
19.
Black-capped chickadees Poecile atricapillus alter the number of D notes of their chick-a-dee call to reflect urgency and threat. Here, I tested whether heterospecific
responses of an allopatric species to these mobbing calls occur. Heterospecific chickadee mobbing calls and songs from North
America were broadcast to European great tits (Parus major) and compared with conspecific mobbing calls. During conspecific mobbing playbacks, all great tits approached the speaker,
during the heterospecific “chick-a-dee” playbacks, 63.3% individuals approached the speaker, while during the song playback,
only 31.3% of the great tits approached the speaker. Minimum distances of great tits were lower during conspecific mobbing
calls compared to allopatric chick-a-dee calls and to allopatric chickadee song. Also, minimum distances were lower when comparing
allopatric chick-a-dee calls and chickadee song. Great tits approached the speaker on average down to (mean ± SE) 20.0 ± 1.8 m
during playbacks of 1–4 D elements, to 17.7 ± 2.0 m during playbacks of 5–7 D elements and down to 11.5 ± 2.0 m during playbacks
of 8–11 D elements. The number of D notes was inversely related to minimum distance. Thus, the urgency message encoded in
the D notes was perceived also by an allopatric but phylogenetically related European species, suggesting that the heterospecific
response is possibly phylogenetically conserved. 相似文献
20.
The blue mussels Mytilus edulis L. and M. galloprovincialis Lmk. hybridize in western Europe. Within hybrid populations nuclear alleles specific to M. galloprovincialis increase in frequency with age and size. This relationship changes with tidal height; alleles from M. galloprovincialis occur more frequently high in the intertidal zone, while M. edulis alleles predominate in the low intertidal zone. We tested the hypotheses that larvae with M. galloprovincialis alleles tend to settle higher in the intertidal zone, or that mussels redistribute themselves with respect to tidal height
after initial larval settlement. We sampled recently metamorphosed mussels every 2 weeks in a hybrid mussel population at
Whitsand Bay in southwest England throughout the summer of 1996. We observed four cohorts of newly settled mussels. There
was no evidence of differential settlement of mussels with different genotypes in connection with tidal height, or into shaded
versus unshaded microsites. Therefore, we rejected the preferential settlement hypothesis. There was substantial movement
of juvenile mussels in the first 4 weeks following initial settlement, but this “secondary settlement” did not result in genetic
differentiation with respect to tidal height. Further, significant differences in allele frequencies were found between primary
and secondary spat. This allele frequency change was in the opposite direction of that seen in the adult population, suggesting
newly settled larvae may be experiencing different selective pressures than adults. We propose that the genetic structure
of hybrid mussel populations with respect to tidal height is the consequence of differences in selection intensity.
Received: 30 April 1999 / Accepted: 5 May 2000 相似文献