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1.
Neocalanus flemingeri, Neocalanus plumchrus, Neocalanus cristatus and Eucalanus bungii are large and dominant mesozooplankton occurring throughout the subarctic Pacific. They are an important trophic link and transporter of organic matter to the mesopelagic zone. Vertical distributions of these copepods were investigated from March to October 2000 in the Oyashio region of the western subarctic Pacific. Neocalanus plumchrus and N. flemingeri were distributed in the surface layer (0–50 m) and N. cristatus and E. bungii in the subsurface layer (50–100 m). However, when examined in detail, clear seasonal and vertical differences were observed. Neocalanus plumchrus was concentrated in the top 20 m from late April to the end of July, and N. flemingeri showed a little deeper distribution from May to July. Neocalanus cristatus showed a deeper distribution than that of grazing individuals of E. bungii from April to early July, but grazing individuals of E. bungii (C3–C6) showed a deeper distribution than that of N. cristatus from the end of July to October. Early copepodites of E. bungii were distributed much shallower than late copepodite stages and overlapped with copepodites of N. plumchrus and N. flemingeri. These results suggest that the four species of large copepods have established habitat segregation by season, vertical distribution and food resource partitioning in the Oyashio region as well as other regions of the North Pacific.  相似文献   

2.
Grazing experiments and production estimation based on life-history analysis of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were carried out in the Oyashio region to understand the carbon flows associated with the interzonal migrating copepods. These copepods, and also Eucalanus bungii, fed on nano- and micro-sized organisms non-selectively throughout the season. However, diatoms were the dominant food resource until May and organisms, such as ciliates were the major resource after May. Daily growth rate was estimated from the Ikeda–Motoda, Huntley–Lopez and Hirst–Sheader models. Since the growth rates were considered to be overestimates for the Huntley–Lopez model and underestimates for the other two models, we applied the weight-specific growth rates previously reported for these species in the Bering Shelf. Surface biomass of Neocalanus increased rapidly in June during the appearance of C5, and a successive increase of overwintering stock was evident in the deeper layer. The deep biomass decreased gradually from September to May during the dormant and reproduction period. N. cristatus has the largest annual mean biomass (2.3 gC m−2), followed by N. plumchrus (1.1) and N. flemingeri (0.4). Daily production rate of Neocalanus varied from 0.4 to 363.4 mgC m−2 day−1, to which N. cristatus was the largest contributor. Annual production was estimated as 11.5 gC m−2 year−1 for N. cristatus, 5.7 for N. plumchrus and 2.1 for N. flemingeri, yielding annual P/B ratio of 5 for each species. The annual production of Neocalanus accounted for 13.2% of the primary production in the Oyashio region. Their fecal pellets were estimated to account for 14.9% (0.7 gC m−2 year−1) of sinking flux of organic carbon at 1000-m depth. Moreover, their export flux by ontogenetic vertical migration, which is not measured by sediment trap observations, is estimated to be 91.5% (4.3 gC m−2 year−1) of carbon flux of sinking particles at 1000-m depth. These results suggest the important role of interzonal migrating copepods in the export flux of carbon.  相似文献   

3.
A mesoscale iron-fertilization experiment was carried out in the western subarctic Pacific during summer 2001. The iron-patch was traced for 14 days after the fertilization, and the abundance and behavior of mesozooplankton were compared with those outside of the patch. The phytoplankton biomass in the patch rapidly increased to over 15 times the initial level by the later half of the observation period, and was composed of large-sized (>10 mm), centric diatoms. Dominant zooplankton species in the upper 200-m depth were large copepods: Neocalanus plumchrus, Neocalanus cristatus, Eucalanus bungii and Metridia pacifica. Mesozoplankton biomass as well as species composition did not change significantly in the patch over the observation period. Furthermore, no changes of vertical distribution or diel vertical migration were observed for any species or stages of mesozooplankton throughout the observation period. However, the abundance of the first copepodite stages of N. plumchrus and E. bungii increased several fold in the patch after the diatom bloom formation compared to the densities outside the patch. The increases of both species are considered to be due to lowered mortality during the egg and nauplius stages. Spawning of N. plumchrus takes place at depth using lipid storage, while spawning of E. bungii takes place in the surface layer supported by grazing. These facts suggest that the relative importance of nauplii in the diets of the large copepods was decreased in the patch by the diatom bloom. Gut-pigment contents of dominant copepods in the patch increased 4–18 times, and the maximum values were observed during the bloom peak. However, the grazing impact on phytoplankton was low throughout the experiment, especially during the bloom period (<6% of the primary production).  相似文献   

4.
Reproduction and early development of the large subarctic copepods Neocalanus cristatus, N. plumchrus and N. flemingeri were investigated in the laboratory. All three species produced eggs at intervals of 5.0 to 14.7 days, depending on species and temperature. The females of N. flemingeri released the fewest clutches of the three species, but with the largest clutch size. Clutch size of N. cristatus was smallest with longest intervals between clutches. Mean±1 S.E. of total fecundities were 386±116 eggs for N. cristatus, 840±214 eggs for N. plumchrus, and 924±346 eggs for N. flemingeri. The egg laying period of a female at 2°C was estimated to be 91 days for N. cristatus, 60 days for N. plumchrus and 47 days for N. flemingeri. The color and outer characteristics of eggs and nauplii of these species were quite different. C : N ratios of the eggs were 9.3–10.5, which were slightly higher than that of females or CV. Egg hatching times for each species were 4.6–5.7 days at 2°C and decreased with increasing temperature at a Q10 of 2.8–3.0. N. cristatus nauplii developed to copepodid stage I (CI) without feeding, and the developmental time in days from hatching to CI was expressed as a Bělehrádek equation, DCI=17068×(T+14.7)−2.05. Reproduction strategies of the three species of Neocalanus are discussed with reference to their life history strategies.  相似文献   

5.
The open subarctic Pacific Ocean is a high nitrate low chlorophyll (HNLC) system characterized by low concentrations of phytoplankton, a community dominated by small cells, and iron-limited growth of, especially, the larger phytoplankton. In such systems the main energy and material flow is through the microbial web, with large copepods considered primarily to be grazers on the larger microzooplankton occupying the top of this web. Consistent with this is the recognition that much of the nutrition of the dominant copepods in this system, Neocalanus flemingeri, N. plumchrus and N. cristatus, is derived from microzooplankton. Also, these copepods consume only a small fraction of the total phytoplankton production. In this paper, we show that the contribution made by N. flemingeri and N. plumchrus to establishing and maintaining the community structure of this ecosystem should be re-evaluated. Our experiments indicate these grazers have high clearance rates on large particles, including both large phytoplankton and microzooplankton, and this selective removal contributes to establishment and maintenance of the observed foodweb structure in the Gulf of Alaska. These high feeding rates combined with large populations of these two Neocalanus species concentrated in the upper layer of the ocean, result in population-based feeding rates approximately equal to the growth rates of large phytoplankton under iron-limited conditions. We conclude that N. flemingeri and N. plumchrus populations (a) directly prevent the accumulation of large phytoplankton cells by selectively feeding on them at high rates, and (b) indirectly stimulate the accumulation of the smaller phytoplankton by consumption of their major grazers, the microzooplankton.  相似文献   

6.
The role of copepod grazing on the ecosystem dynamics in the Oyashio region, western subarctic Pacific was investigated during six cruises from June 2001 to June 2002. In situ grazing rates of the copepod community (CGR) were measured by the gut fluorescence method in respect to developmental stages of dominant species. In terms of biomass, more than 80% of the copepod community was dominated by six large calanoid species (Neocalanus cristatus, Neocalanus flemingeri, Neocalanus plumchrus, Eucalanus bungii, Metridia pacifica and Metridia okhotensis) throughout the year. Resulting from the observed pattern of the interzonal migrating copepods, the CGR in the Oyashio region was divided into three phases, i.e. spring (bloom), summer (post-bloom) and autumn-winter phase. During the spring bloom, late copepodites of the interzonal migrating species, N. cristatus, N. flemingeri and E. bungii appeared in the surface layer (0-50 m) to consume the production of the bloom, resulting in a high grazing rate of the copepod community (7.9 mg Chl m−2 d−1), though its impact on phytoplankton community was low due to the high primary productivity. During the post-bloom period, although the copepod community which was dominated by N. cristatus, N. plumchrus, M. pacifica and newly recruited E. bungii still maintained a high biomass, the CGR was generally lower (1.8-2.6 mg Chl m−2 d−1 for June and August 2001), probably due to the lower availability of phytoplankton. Nevertheless, the highest CGR was also observed during this period (10.5 mg Chl m−2 d−1 in June 2002). The high CGR on autotrophic carbon accounted for 69% of the primary production, suggesting that the copepod community in the Oyashio region potentially terminates the phytoplankton bloom. Abundant occurrence of young E. bungii, which is a characteristic phenomenon in the Oyashio region, was largely responsible for the high grazing pressure in June 2002 suggesting that success of reproduction, growth, and survival in E. bungii during the spring bloom is an important factor in controlling phytoplankton abundance during the post-bloom season. During autumn and winter, CGR was the lowest in the year (0.29-0.38 mg Chl. m−2 d−1) due to the disappearance of the interzonal migrating copepods from the surface layer. Diel migrant M. pacifica was the most important grazer during this period. The annual ingestion of the copepod community is estimated as 37.7 gC m−2 on autotrophic carbon (converted using C:Chl ratio of 30) or 137.9 gC m−2 on suspended particles (using C:Chl ratio of in situ value, 58-191), accounting for 13% and 46% of annual primary production, respectively. This study confirms that copepod grazing is an important pathway in carbon flow in the Oyashio region and in particular their role in the phytoplankton dynamics is significant for the termination of the spring bloom.  相似文献   

7.
Size distributions of Neocalanus cristatus, N. flemingeri and N. plumchrus were investigated in the eastern and the western subarctic gyres and three marginal seas of the North Pacific during the diapause period to examine the geographical variation in body size of Neocalanus species and to clarify the origin of the large biennial N. flemingeri which has been observed in the Oyashio region. There were significant among region variations in body sizes for all three species of Neocalanus. Generally, the body sizes of the copepods were larger in the marginal seas and marginal areas of the open ocean. In the open ocean, the body sizes increased westward. These patterns of variation in the body sizes roughly correlated with local food availability. Distribution of biennial N. flemingeri was restricted to the Sea of Japan, the Okhotsk Sea and the Oyashio region. The large-sized biennial N. flemingeri were abundantly observed in the Okhotsk Sea, and the medium-sized biennial individuals were observed in the Sea of Japan. These facts strongly suggest that the large biennial N. flemingeri in the Oyashio region are advected from the Okhotsk Sea.  相似文献   

8.
Geographical variations in prosome length and body weight of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were investigated on samples from North-South and East-West transects in the North Pacific during spring to early summer in 1998 and 1999. Southward and eastward increasing patterns were pronounced for water temperature, although no significant pattern was observed for chlorophyll a concentrations. All Neocalanus species showed large geographical variations in prosome length and body weight, being smaller in the southern and eastern waters. Comparing the relationship between prosome length and body weight, large deviations (lower body weight at a given prosome length) were evident for the eastern specimens of N. cristatus and N. plumchrus. In stepwise regression analysis, the geographical variations of prosome length and body weight revealed a significantly negative correlation with temperature variations. These results suggest that temperature is a more important environmental factor than chlorophyll a concentration in its effect on geographical variations in prosome length and body weight of Neocalanus copepods in the North Pacific. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

9.
Discovery that the subarctic Pacific copepods previously grouped as Neocalanus plumchrus belong to two species required reanalysis of the life histories of both. After correction of the abundance estimates for N. plumchrus s.str., our concept of its life history remains much as previously described, because it makes up about 90% of the summed populations. Fifth copepodites of the new species, Neocalanus flemingeri, descend from the surface layer in late May to early June and mature immediately. Males are only present for about two months, and females carrying spermatophores are found during that period. Throughout the summer and autumn the entire population is constituted of females with small, dormant ovaries. This appears to be a diapause phase. Ovarian development begins in November, and spawning occurs at the end of January. Copepodite stages develop in surface layers from February through May.  相似文献   

10.
To identify seasonal patterns of change in zooplankton communities, an optical plankton counter (OPC) and microscopic analysis were utilised to characterise zooplankton samples collected from 0 to 150 m and 0 to 500 m in the Oyashio region every one to three months from 2002 to 2007. Based on the OPC measurements, the abundance and biomass of zooplankton peaked in June (0–150 m) or August (150–500 m), depending on the depth stratum. The peak periods of the copepod species that were dominant in terms of abundance and biomass indicated species-specific patterns. Three Neocalanus species (Neocalanus cristatus, Neocalanus flemingeri and Neocalanus plumchrus) exhibited abundance peaks that occurred before their biomass peaks, whereas Eucalanus bungii and Metridia pacifica experienced biomass peaks before their abundance peaks. The abundance peaks corresponded to the recruitment periods of early copepodid stages, whereas the biomass peaks corresponded to the periods when the dominant populations reached the late copepodid stages (C5 or C6). Because the reproduction of Neocalanus spp. occurred in the deep layer (>500 m), their biomass peaks were observed when the major populations reached stage C5 after the abundance peaks of the early copepodid stages. The reproduction of E. bungii and M. pacifica occurred near the surface layer. These species first formed biomass peaks of C6 and later developed abundance peaks of newly recruited early copepodid stages. From the comparison between OPC measurements and microscopic analyses, seasonal changes in zooplankton biomass at depths of 0–150 m were governed primarily by E. bungii and M. pacifica, whereas those at depths of 150–500 m were primarily caused by the three Neocalanus species.  相似文献   

11.
The copepods Neocalanus flemingeri and N. plumchrus are major components of the mesozooplankton on the shelf of the Gulf of Alaska, where they feed, grow and develop during April–June, the period encompassing the spring phytoplankton bloom. Satellite imagery indicates high mesoscale variability in phytoplankton concentration during this time. Because copepod ingestion is related to food concentration, we hypothesized that phytoplankton ingestion by N. flemingeri and N. plumchrus would vary in response to mesoscale variability of phytoplankton. We proposed that copepods on the inner shelf, where the phytoplankton bloom is most pronounced, would be larger and have more lipid stores than animals collected from the outer shelf, where phytoplankton concentrations are typically low. Shipboard feeding experiments with both copepods were done in spring of 2001 and 2003 using natural water as food medium. Chlorophyll concentration ranged widely, between 0.32 and 11.44 μg l−1 and ingestion rates varied accordingly, between 6.0 and 627.0 ng chl cop−1 d−1. At chlorophyll concentrations<0.50 μg l−1, ingestion is always low, <40 ng cop−1 d−1. Intermediate ingestion rates were observed at chlorophyll concentrations between 0.5 and 1.5 μg l−1, and maximum rates at chlorophyll concentrations>1.5 μg l−1. Application of these feeding rates to the phytoplankton distribution on the shelf allowed locations and time periods of low, intermediate and high daily feeding to be calculated for 2001 and 2003. A detailed cross-shelf survey of body size and lipid store in these copepods, however, indicated they were indistinguishable regardless of collection site. Although the daily ingestion of phytoplankton by N. flemingeri and N. plumchrus varied widely because of mesoscale variability in phytoplankton, these daily differences did not result in differences in final body size or lipid storage of these copepods. These copepods efficiently dealt with small and mesoscale variations in their food environment such that mesoscale structure in phytoplankton did not affect their final body size.  相似文献   

12.
A mesoscale iron fertilization experiment was carried out in the western subarctic Pacific during summer 2004. The iron-patch was traced for 26 days after the enrichment, and the abundance and behavior of meso- and microzooplankton was compared with those outside of the patch. The surface chlorophyll-a concentration in the patch was high between days 10 and 13 (2.5 mg m−3) and decreased to the initial level after day 20. Microzooplankton grazing rates, estimated by a dilution method, was mostly balanced with phytoplankton growth rates throughout the observed period. Dominant mesozooplankton species in the upper 200 m were copepods: dominated by Eucalanus bungii, Neocalanus plumchrus and Metridia pacifica. Species composition did not change in the patch over the observation period. The copepod biomass was 3–5 times higher than in Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study (SEEDS), the previous iron-enrichment experiment in the same area, before the bloom, and exponentially increased both inside and outside the patch, which was mainly brought by the development of N. plumchrus. The development rates of N. plumchrus were not significantly different between inside and outside the patch. Estimated grazing rate suggest that the copepod grazing was main cause of the low accumulation of phytoplankton biomass, and dominance of grazing-resistant organisms such as large ciliates, large diatoms and diatoms with extremely long setae. “Arrested migration” for M. pacifica and upward shift of vertical distribution by E. bungii were observed during the bloom period, even if the accumulation of phytoplankton biomass was very low compared to other iron-enrichment experiments. These results indicate that the copepod grazing shaped the food-web structure of the lower trophic levels (biomass and species composition) in SEEDS II.  相似文献   

13.
The horizontal transport of calanoid copepod Neocalanus flemingeri, N. plumchrus and N. cristatus in the subarctic North Pacific has been investigated by particle tracking experiments using an ocean circulation model. In our physical numerical model, the current and frontal systems in the subarctic Pacific are reproduced realistically, and fine-resolved (not smoothed) and vertically sheared western boundary currents in the model enable us to assess the differences in horizontal transports among Neocalanus species. In the experiments, seasonal vertical migration and life cycle of Neocalanus species is included, and this attempt is a novel approach in examining the transports of the zooplanktons. The maximal depths of the vertical migrations and the lengths of the surface and mesopelagic dwelling duration are the essential factors in characterizing the trajectory of the horizontal transport. Both small and large forms of N. flemingeri (hereafter NF-SF and NF-LF) whose mesopelagic-inhabited depths are the shallowest among the three Neocalanus species are transported to more distant regions from initial positions compared with the others. The longest transport distance is over 5000 km for NF-SF. On the other hand, the transport distance of the deepest inhabitant N. cristatus (hereafter NC) is the shortest. The differences in the transport distance are due to the current speed of the western boundary currents at the inhabited depth at which they spend most of their lifetime (ca. 3/4 of their lifetime). More than 82% of NF-LF that originated from the Okhotsk Sea completes its life cycle in the Okhotsk Sea, and all the animals out to the Pacific are transported to the south of the subarctic front where their survivals are unexpected due to high temperatures. This is consistent with the observed limited distribution of NF-LF in the Okhotsk Sea and its surrounding waters. Geographical genetic variations of Neocalanus species are reported as very low. This implies frequent genetic exchange all over the Pacific and its adjacent seas. Being consistent with the above, the present study suggests that the trans-Pacific transport of Neocalanus species can be accomplished within a few generations.  相似文献   

14.
Life histories for the dominant, larger copepods of the subartic Pacific have been constructed by sampling from weatherships patrolling Ocean Station P (50°N, 145°W) during 1980 and 1981. Neocalanus plumchrus reproduced at depths below 250 m from July through February. Copepodite stages were present in surface layers from October through August with a large peak in numbers and biomass in spring. Fifth copepodites prepared for diapuse in 38 days during spring and descended to depths below 250 m. They commenced immediately to mature, and the females reproduced without renewed feeding. This schedule contrasts with that of the population in the Strait of Georgia, which remains in diapause from July to January and matures exclusively in January and February. There appears to be a difference between the coastal and oceanic habitats in preparing the diapausing individuals for maturation.Maturation of the diapausing stock of N. plumchrus maintained constant adult populations, averaging 714 males m?2 from June through October and 1,434 females m?2 from August through January. This constancy, together with the exponential pattern of decline in the diapause stock from September through February, suggests that density of adults may regulate maturation of fifth copepodites. Offspring of individuals delaying maturation and, thus, reproduction would benefit from the resulting moderation of intraspecific competition, probably that among copepodites.Reproduction of Neocalanus cristatus also occurred below 250 m, and, while spawning was continuous through the year, there was a substantial peak in November. That resulted in a peak of abundance for early copepodite stages in mid-winter, and a peak for the fifth copepodite stage in June. Stocking of the population of fifth copepodites in diapause below 250 m occurred from July through October. Some fifth copepodites were present in surface layers through the entire summer, and some younger copepodites persisted through the summer in progressively declining abundance just below the mixed layer. In autumn 1980 resurgence of early copepodite populations was rapid, occurring during the course of a prolonged October storm. The storm may have improved the habitat either by cooling the mixed layer or by resupplying nutrients to the euphotic zone.Eucalanus bungii reproduced in the mixed layer in early May and in early July. The first event was a spawning by females that had previously spawned in 1979 and then had returned to diapause. The second, heavier spawning (more females, more eggs per female) was by newly matured females from stocks that had overwintered as fifth copepodites. Nauplii peaked sharply in abundance on 19 July, one week after the peak in spawning. First and second copepodites peaked on 1 August, and all had advanced to the third copepodite stage by September. The diapause stock was established by September, principally between 250 and 500 m, and consisted of copepodite stages from third to sixth. Duration of the E. bungii life cycle appears to be typically two years. New nauplii develop as far as the third or fourth copepodite stage during their first summer, then enter diapause. The second summer they advance to the fifth copepodite stage and reenter diapause. Fifth copepodites mature in their third summer at two years of age. The males remain at depth and mate without subsequent feeding. Females migrate at night to the mixed layer where spawning occurs. About 20% of females that had already spawned in 1980 reentered diapause. They would reproduce again in their fourth summer at three years of age. All aspects of the life cycle suggest low mortality rates for copepodite stages, particularly at depth in the habitat occupied during diapuse. There can be no premium on rapid reproduction for E. bungii in the subartic Pacific, and there must even be benefit from spreading reproduction between years. This iteroparity may amount to a “bet-hedging” tactic, the young from a given mother having more than one chance to find sustaining conditions. It also produces gene flow between the year classes of the biennial life cycle.  相似文献   

15.
Copepodites of Neocalanus plumchrus dominate the macrozooplankton biomass of the subarctic Pacific during spring. Living specimens have patches of bright red-orange pigment. During May of 1984 it was found sharing dominance with another, related species with differently placed patches of more distinctly red pigment. This is an undescribed species, which is designated here as Neocalanus flemingeri sp. nov. In the Gulf of Alaska it is smaller than N. plumchrus, but in the Bering Sea where food supplies are greater it reaches dimensions as large or larger. The morphologies of the two species are distinct, and previous confusion in the taxonomy of these forms was caused by differences in their life histories.  相似文献   

16.
Mesozooplankton biomass, species composition, abundance, and vertical distribution were determined along a transect from the continental slope off the west coast of Canada to Ocean Station Papa (OSP) in the open-ocean waters of the NE subarctic Pacific as part of the Canadian Joint Global Ocean Flux Study of this area. All of these measurements had distinct seasonal patterns. At OSP biomass peaked in spring, coincident with the annual biomass maximum of large copepods of the genus Neocalanus. Early copepodites of these copepods were present in surface waters at all stations along the transect in winter, but N. plumchrus and N. flemingeri copepodites were only at the offshore stations in spring. This indicated that these large copepods had completed the growth phase of their life cycle slower in the open ocean than closer to shore where they had already descended to deep water by May or June. Summer biomass was low compared to the spring peak. The summer mesozooplankton abundance was similar to the springtime abundance, but the composition had changed from large-bodied copepods in the spring to small copepods and fewer non-copepod taxa in the summer, which accounts for the reduction in total biomass. Winter biomass was the lowest of the year. Winter species composition was similar to summer except for the appearance of juvenile stages of the genera Neocalanus and Calanus. Diel changes in biomass in the upper 150 m were found in summer but not in winter or spring. Vertical distributions of copepods were often distinct, with closely related species occupying different depth strata. Measurements of wet weight at OSP were higher than the long-term mean wet weight during winter and spring, and lower during summer.  相似文献   

17.
Copepod species of the genus Neocalanus dominate the zooplankton biomass of the oceanic subarctic Pacific Ocean. Neocalanus spp. populations in the subarctic Pacific environment are successful: they feed, accumulate lipid, and persist from year to year. Prior experimental observations derived from a variety of methods indicated that, although their functional morphology is such that they clear the small phytoplankton cells characteristic of the oceanic subarctic Pacific environment efficiently, Neocalanus spp. do not consume sufficient phytoplankton to meet even basic metabolic requirements in that environment. Hence, their success in the subarctic Pacific must depend on their ability to obtain nutrition from other sources. As part of the SUPER (SUbarctic Pacific Ecosystem Research) program, experiments were performed to test the hypothesis that N. plumchrus and N. cristatus obtain a significant portion of their nutrition from planktonic Protozoa. The experiments demonstrate that Protozoa alone do not provide sufficient nutrition for N. cristatus to meet its basic metabolic needs. Protozoa constitute the major dietary component of N. plumchrus however, in agreement with the predictions of Frost's (1987) model of the subarctic Pacific ecosystem. At a minimum this diet permits N. plumchrus to meet basic metabolic requirements. Copepod grazing activities appear to be sufficient to control protozoan stocks in the oceanic subarctic Pacific during late spring and early summer when Neocalanus spp. inhabit the upper water column.  相似文献   

18.
The food habits of the dominant myctophid Stenobrachius leucopsarus were examined in the central basin of the Bering Sea in relation to oceanographic conditions, in summer 2002 and 2003 and spring 2006. S. leucopsarus exhibited an ontogenetic and seasonal dietary shift. In spring, small fish (≤40 mm) preyed mainly on Neocalanus flemingeri/plumchrus whereas large fish fed mainly on Neocalanus cristatus. In summer, small fish preyed mainly on Metridia pacifica whereas large fish fed mainly on euphausiids (Thysanoessa spp.). In the summer of 2003, when water temperature in the epipelagic layer (≤100 m) was warmer, reflecting the prevalence of the Alaskan Stream, small-sized S. leucopsarus showed a higher stomach content index, perhaps reflecting the greater abundance of M. pacifica. Thus, the present study shows that the physical variability in the epipelagic layer affects not only diets but also feeding performance of micronekton.  相似文献   

19.
Samples collected during four cruises on board R.S. Africana were used to study the trophic ecology and feeding behaviour of Engraulis capensis in the southern Benguela region. Previous work had indicated that this species was a non-selective filter-feeding omnivore, diatoms comprising the bulk of the diet. The results of the present study reveal that anchovies selectively feed on mesozooplankton, especially calanoid copepods and euphausiids. Investigation of the feeding behaviour of the species indicates that raptorial feeding is dominant over filter-feeding and that prey appears to be selected primarily on the basis of size.  相似文献   

20.
An analysis of the time series data sets collected from the 1960s to 1990s in the Oyashio Water revealed signs of alteration in the physical, chemical and biological properties of the water column in the western subarctic North Pacific. Wintertime salinity, phosphate concentration and apparent oxygen utilization (AOU) in the subsurface increased linearly over the 30 years. At the same time, salinity and phosphate in the surface mixed layer decreased. An increase in the density gradient in the surface and subsurface suggested that the water column stratification intensified, reducing the vertical exchange of water properties during the period. The Net Community Production (NCP), estimated from the phosphate consumption from February through August, also declined. Water column Chl a was approximately halved and diatoms decreased by one order of magnitude in spring, consistent with the multi-decadal decreasing trend of NCP. Zooplankton biomass was also nearly halved during the same period. In contrast, wintertime Chl a increased by 63% and diatom abundance doubled. Developmental timing became earlier in Neocalanus flemingeri, and spring occurrence of N. plumchrus increased after the 1980s. Reduced vertical water exchange might have limited nutrient supply to the level, decreasing winter-summer NCP for these three decades. It is speculated that, in the meantime, the earlier stabilization of the surface layer might have enhanced wintertime diatom production in the Oyashio's light-limited environment. This condition could allow zooplankton to effectively utilize diatoms from earlier timing, resulting in the apparent early developmental timing and abundance increase. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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