首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 62 毫秒
1.
Pronounced seasonality is a characteristic feature of polar ecosystems, but seasonal studies in the high-Arctic pack-ice zone are still scarce because of logistical constraints. During six expeditions (1994–2003) to the Fram Strait area between Greenland and Svalbard in winter, spring, early summer, late summer and autumn, the sub-ice habitat and fauna below the pack ice (0–1 m depth) were analyzed for seasonal patterns. Both environmental variables such as ice cover, temperature, salinity and chlorophyll a (chl a), as well as species composition, abundance and biomass of the sub-ice fauna showed distinct seasonal dynamics. Most species of the sub-ice fauna were found in early summer, followed by autumn, spring and late summer; the lowest number occurred in winter. The sub-ice fauna was dominated by copepod nauplii during all seasons. Next numerous was the small pelagic copepod Oithona similis, followed by occassional swarms of Pseudocalanus minutus and Calanus spp. Abundances of the sympagic fauna in the sub-ice water layer were much lower, with ectinosomatid copepods being usually the most numerous sympagic group. In the course of the year, total abundances of the sub-ice fauna showed a steep increase from the earliest sampling dates towards the end of winter/beginning of spring reaching maximum numbers then, and a decrease to minimum numbers in early summer. A second peak occurred in late summer, followed by a decrease towards autumn. This significant trend was due to the abundances of copepod nauplii and Oithona similis. Sympagic species were virtually absent during winter, and increased significantly in spring and early and late summer. A factor analysis revealed the variables ice cover and thickness, water temperature and salinity, as well as chl a as the major controlling factors for the seasonal patterns in different groups and species of the sub-ice fauna. Because of the special environmental conditions in the sub-ice habitat, and the unique species composition characterized by small taxa, young stages, and sympagic species, the seasonal dynamics of the Arctic sub-ice fauna differ substantially from those of the epipelagic zooplankton community in the Arctic Ocean.  相似文献   

2.
A time series of zooplankton sampling carried out at Station 18 off Concepción (36°S, 73°W) from August 2002 to December 2003 allowed the study of annual life cycles of the copepods Calanus chilensis and Centropages brachiatus in association with environmental variability in the coastal upwelling zone. Changes in the abundance of eggs, nauplii, and copepodids were assessed from samples taken at a mean time interval of ca. 20 days. Upwelling variability in near-surface waters was reflected in seasonal changes in salinity, water column stratification, and oxycline depth, as well as a weak seasonal signal in sea surface temperature (1-2 °C). Both copepods exhibited similar life cycles, characterized by continuous reproduction throughout the year. Estimates of generation times, as a function of temperature, were 25-30 days for C. chilensis and 27-35 days for C. brachiatus, predicting about 12 and 10 generations a year, respectively. These estimates were consistent with reproduction pulses observed in the field. It was thus suggested that copepods may grow under non-limiting food conditions in this upwelling area. However, despite continuous reproduction, there were abrupt changes in population sizes along with the disappearance of early naupliar and copepodid stages taking place even during the upwelling season (spring/summer). These changes were attributed to sudden increases in mortality taking place in spring or early summer, after which the populations remained at low levels through the fall and winter. It is thus suggested that, in addition to variability in the physical environment, biological interactions modulating changes in copepod mortality should be considered for understanding copepod life cycles in highly productive upwelling systems.  相似文献   

3.
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   

4.
The micro- and mesozooplankton communities in surface waters of the Greenland Sea are described based on data from five cruises covering an annual cycle. Special emphasis is given to the summer period (June and August), prior to and after the descent of Calanus spp. Calanus spp. dominated the copepod community during the spring bloom and in the beginning of the summer. However, during the summer, there was a pronounced shift in the zooplankton composition in the euphotic zone. In contrast to what has been observed in other Arctic systems, smaller genera such as Pseudocalanus spp., Oncaea spp. and Oithona spp. became abundant and the total copepod biomass remained high after the Calanus spp. descended for hibernation. The peak protozooplankton biomass in the Greenland Sea (June) co-occurred with the peak in Calanus spp. Protozooplankton biomass then decreased during the summer. Growth of protozooplankton and grazing rates of the two dominating non-Calanus genera, Oithona and Pseudocalanus, were measured. For both copepod genera, protozooplankton constituted 40% or more of the diet, and maximum clearance was on prey items with an equivalent spherical diameter between 15 and 30 μm. The non-Calanus components of the zooplankton community were responsible for 70–99% of the total zooplankton grazing on phytoplankton during summer and were crucial for the recycling and respiration of primary production.  相似文献   

5.
根据2013年8月(夏季)和2014年5月(春季)在曹妃甸邻近海域的调查资料,研究了浮游动物群落的种类组成、丰度、生物量、优势种和多样性的时空变化特征,分析了其与环境因子的关系,并结合2004年调查资料对比分析了浮游动物丰度和优势种的变化特征及围填海的影响。结果表明,研究海域浮游动物共鉴定得到31种(类),以桡足类和浮游幼体为主,优势种主要包括双刺纺锤水蚤(Acartia bifilosa)、小拟哲水蚤(Paracalanus parvus)、拟长腹剑水蚤(Oithona similis)和桡足类幼体(Copepodid larva)等。春季的浮游动物丰度和生物量均高于夏季,多样性和均匀度指数均低于夏季。浮游动物丰度的空间分布主要受温度、叶绿素a(Chl-a)等环境因子影响,春季基本为近岸高、远岸低的空间分布规律,夏季则相反,基本为近岸低、远岸高的空间分布规律。与2004年相比,本次调查春季和夏季的浮游动物丰度明显下降,可能与浮游植物丰度及DIP浓度降低有关。春季,西侧、东侧海域的浮游动物丰度分别明显降低、升高,与围填海后营养盐重新分布促进了东侧海域浮游植物增殖有关。夏季则主要受河流输入影响,浮游动物丰度的变化不具有空间差异。  相似文献   

6.
Plankton samples collected in November 2002, February, May and August 2003 were used to examine seasonal variation in tidal exchange of zooplankton biomass, abundance and species composition between Lough Hyne Marine Nature Reserve and the adjacent Atlantic coast. Micro- to mesozooplankton were collected by pump over 24-h sampling periods during spring and neap tides from the narrow channel connecting the semi-enclosed water body to the Atlantic. Sample biomass (dry weight) and total zooplankton abundance peaked in the summer and were lowest in winter, showing a positive relationship with temperature. Zooplankton biomass, total abundance and numbers of holo- and meroplankton revealed import during some diel cycles and export in others. However, the tidal import of these planktonic components was generally dominant, especially during May. The greatest import of numbers of holoplankters and meroplanktonic larvae occurred during May and August, respectively. There was no significant variation in sample biomass between periods of light and dark, but some variation in zooplankton abundance could be explained by this diel periodicity. Significant differences in sample assemblage composition between flood and ebb tide samples were always observed, except during winter neap tides. There was a net import of the copepods Temora longicornis and Oithona helgolandica and the larval stages of Mytilus edulis during spring and summer. Proceraea cornuta and Capitellid trochophores were imported during winter, and a hydrozoan of the genus Obelia during the spring spring tides. Seasonal export from the lough was shown by Pseudopolydora pulchra larvae (autumn and spring), Serpulid trochophores (autumn) and veligers of the bivalve Anomia ephippium (summer). It is suggested that the direction of tidal exchange of meroplanktonic taxa is related to the distribution of the adult populations. Copepod naupliar stages dominated the assemblages except during May spring tides when the copepod Pseudocalanus elongatus made up over 22% of the abundance. The general import of micro- to mesozooplankton may, in part, explain the higher densities of this size-class of zooplankton within the semi-enclosed system of Lough Hyne.  相似文献   

7.
Zooplankton biomass and distribution in the KwaZulu-Natal Bight were investigated in relation to environmental parameters during summer (January–February 2010) and winter (July–August 2010). Mean zooplankton biomass was significantly higher in winter (17.1 mg dry weight [DW] m–3) than in summer (9.5 mg DW m?3). In summer, total biomass was evenly distributed within the central bight, low off the Thukela River mouth and peaked near Durban. In winter, highest biomass was found offshore between Richards Bay and Cape St Lucia. Zooplankton biomass in each size class was significantly, negatively related to sea surface temperature and integrated nitrate, but positively related to surface chlorophyll a and dissolved oxygen. Zooplankton biomass was significantly related to bottom depth, with greatest total biomass located inshore (<50 m). Distribution across the shelf varied with zooplankton size. Seasonal differences in copepod size composition suggest that a smaller, younger community occupied the cool, chlorophyll-rich waters offshore from the St Lucia upwelling cell in winter, and a larger, older community occurred within the relatively warm and chlorophyll-poor central bight in summer. Nutrient enrichment from quasi-permanent upwelling off Durban and Richards Bay appears to have a greater influence on zooplankton biomass and distribution in the bight than the strongly seasonal nutrient input from the Thukela River.  相似文献   

8.
Abstract. Seasonal changes in zooplankton biomass, abundance and species composition were studied at a neritic station in the Balearic Sea between April 1993 and May 1994. Sampling was carried out every 10 days in a zone influenced by the main current circulating through the Mallorca channel. Three main peaks of zooplankton biomass and abundance were observed: (1) at the beginning of summer when the thermocline developed, (2) in autumn when the thermocline broke down, and (3) in early spring. The smaller zooplankton fraction (100–250 μm) comprised on average 32 % of the total biomass and 73 % of total abundance. Copepods were the predominant group (64 % of the total abundance) with Clausocalanus, Oithona and Paracalanus being the most abundant genera. Paracalanus parvus, Clausocalanus furcatus, Acartia clausi, Oithona plumifera, Temora stylifera, Centropages typicus and Oncaea mediterranea were found to be the most important species in the area. Other abundant groups were cladocerans (15 %) and meroplankton larvae (12 %), both of which were particularly numerous during the stratified period. The copepod community was characterized by the above‐cited perennial species, which were abundant during the cycle studied. However, the influence of the hydrological conditions of the Balearic Sea, such as the Atlantic water influx and the physical structure of the water column (stratification and mixing), promoted the observed variability in zooplankton as well as the appearance of characteristic species during the annual cycle.  相似文献   

9.
Zooplankton in the coastal upwelling region off northern Chile may play a significant biogeochemical role by promoting carbon flux into the subsurface OMZ (oxygen minimum zone). This work identifies the dominant zooplankton species inhabiting the area influenced by the OMZ in March 2000 off Iquique (20°S, northern Chile). Abundance and vertical distribution studies revealed 17 copepod and 9 euphausiid species distributed between the surface and 600 m at four stations sampled both by day and by night. Some abundant species remained in the well-oxygenated upper layer (30 m), with no evidence of diel vertical migration, apparently restricted by a shallow (40–60 m) oxycline. Other species, however, were found closely associated with the OMZ. The large-sized copepod Eucalanus inermis was found below the oxycline and performed diel vertical migrations into the OMZ, whereas the very abundant Euphausia mucronata performed extensive diel vertical migrations between the surface waters and the core of the OMZ (200 m), even crossing it. A complete assessment of copepods and euphausiids revealed that the whole sampled water column (0–600 m) is occupied by distinct species having well-defined habitats, some of them within the OMZ. Ontogenetic migrations were evident in Eucalanidae and E. mucronata. Estimates of species biomass showed a substantial (>75% of total zooplankton biomass) daily exchange of C between the photic layer and the OMZ. Both E. inermis and E. mucronata can actively exchange about 37.8 g C m−2 d−1 between the upper well-oxygenated (0–60 m) layer and the deeper (60–600 m) OMZ layer. This migrant biomass may contribute about 7.2 g C m−2 d−1 to the OMZ system through respiration, mortality, and production of fecal pellets within the OMZ. This movement of zooplankton in and out of the OMZ, mainly as a result of the migratory behavior of E. mucronata, suggests a very efficient mechanism for introducing large amounts of freshly produced carbon into the OMZ system and should, therefore, be considered when establishing C budgets for coastal upwelling systems.  相似文献   

10.
After a prolonged summer dry period, the effects of a distinctive and continuing rainfall on the nutrients and plankton of an urban coastal lagoon were investigated over 2 months. The lagoon filled up over 5 weeks from <10% of its maximum volume until it broke open to the sea. Nutrients (ammonia and oxidised nitrogen) significantly increased the day after initial rainfall, before returning to pre-rainfall conditions within 5 days. Phytoplankton biomass grew 10 fold within a week after initial rainfall in the 25–30 °C water and declined to near initial levels 2 weeks later. The assemblage of phytoplankton and zooplankton changed dramatically after 1 day and again by 6 days later, gradually returning to the original community by 2 weeks after the initial rainfall. Zooplankton responded within a day with a two fold increase in the adult stages of the calanoid copepod Oithona sp., followed a week later by nauplii and adult Acartia bispinosa. The influx of adult Oithona indicates resting populations that were previously under sampled by our plankton net. The plankton community returned to the initial state by 2 weeks, to being dominated by a centric diatom and A. bispinosa after 5 weeks. Dilution of the lagoon reached a maximum of 0.25 d−1, while growth rates of the phytoplankton population reached a maximum of 1 d−1, and A. bispinosa nauplii growth of 2.5 d−1. Declines in chlorophyll biomass from the maximum 10 μg l−1, at a rate of approximately 10% d−1 are consistent with the modelled uptake by zooplankton. The nutrients from runoff, growth and the influx of new zooplankton into the water column, resulted in a depleted δ13C and δ15N stable isotope signature of A. bispinosa by 2–4 ppt within 1–2 weeks, consistent with diatom growth and the terrestrial supply of depleted nutrients. δ34S of A. bispinosa was enriched by 2 ppt for 1–2 weeks after rainfall, but unlike C and N, returned to pre-rainfall levels by the end of the study period. We suggest that plankton studies in coastal lakes with variable water levels that are not tidally driven, should account for the influence of changes in water levels to help explain data variability.  相似文献   

11.
《Oceanologica Acta》2002,25(1):13-22
This paper is the first to describe the spatio-temporal changes of mesozooplankton in the Seine estuary. Monthly samples were collected along the estuary in 1996 in order to analyse the seasonal changes of the mesozooplankton community and to identify the major environmental parameters that may influence the spatial distribution of zooplankton in this megatidal estuary. Statistical analysis (canonical correspondence analysis) showed that salinity was the main factor correlated with the longitudinal distribution of zooplankton. Marine species (Temora longicornis, barnacle larvae…) were located in the outer part of the estuary, while more oligohaline species (Eurytemora affinis) were recorded in the inner part of the estuary. A mixed zone was characterised by the presence of the neritic copepods Acartia spp. and Eurytemora affinis. The marine species (e.g. T. longicornis, Oikopleura dioica, Barnacle larvae) showed maximum abundance at the end of spring (June) while the most abundant estuarine species, E. affinis, peaked in late winter-spring and declined with the onset of summer. This copepod dominated the estuarine zooplankton throughout the year, and found in the Seine estuary very high favourable conditions to exhibit ultimate abundances (> 190 000 ind m–3) which is one order of magnitude higher than those found in other European estuaries. It represented the main prey for major planktonivorous species such as suprabenthic and fish species located living in the upstream zone of the Seine estuary.  相似文献   

12.
Recurrent coastal upwelling is recognized as one of the main factors promoting the exceptionally high productivity of the Humboldt Current System. Herein, we study time series data of gross primary production (2003-2006) and its fluctuation in relation to seasonal changes in the light and nutrient field of the Concepción upwelling ecosystem. Concurrent measurements of gross primary production, community respiration, bacterial secondary production, and sedimentation rates allowed a characterization of the main carbon fluxes and pathways in the study area. The integrated values of gross primary production were higher during the upwelling period (>1 g C m−2 d−1; October-April; that is, early spring to early austral fall). Seasonal changes in the system were also reflected in community respiration, organic matter sedimentation, and bacterial production rates, which varied along with the gross primary production. The significant correlation between gross primary production and community respiration (Spearman, r = 0.7; p < 0.05; n = 18) reflected an important degree of coupling between organic matter formation and its usage by the microplanktonic community during periods when gross primary production/community respiration were highly similar. Higher gross primary production values (>6 g C m−2 d−1) were consistently associated with maximum biomass levels of Skeletonema costatum and Thalassiosira subtilis. We observed a positive correlation between gross primary production and the sedimentation of intact diatom cells (Spearman, r = 0.5, p < 0.05, n = 17). Our data suggest that, in the Concepción upwelling ecosystem, bacteria utilize an important fraction of the gross primary production. If our interpretations are correct, they leave unanswered the question of how the system supports the extremely high fish biomass levels, therein pointing out the system’s limited capacity to buffer the evasion of CO2 following upwelling.  相似文献   

13.
We collected mesozooplankton samples in the upper 100 m in spring or early summer each year between 1995 and 2000 along a section from Hamilton Bank (Labrador) to Cape Desolation (Greenland), and along additional sections in spring 1997 and early summer 1995. The North Atlantic waters of the central basin were characterised by the presence of the copepods Calanus finmarchicus, Euchaeta norvegica and Scolecithrocella minor and euphausiids. Calanus glacialis, Calanus hyperboreus and Pseudocalanus spp. were associated with the Arctic waters over the shelves. Amongst the other enumerated groups larvaceans were concentrated over the shelves and around the margins. Amphipods, pteropods and the copepods Oithona spp. and Oncaea spp. showed no definable relationships with water masses or bathymetry, while the diel migrant ostracods and chaetognaths were confined to deep water. Metrida longa, also a strong diel migrant, and Microcalanus spp., a mainly deep water species and possible diel migrant, were both sometimes quite abundant on the shelves as well as in the central basin, consistent with their likely Arctic origins.Analysis of community structure along the section across the Labrador Sea indicated that stations could be grouped into five different zones corresponding to: the Labrador Shelf; the Labrador Slope; the western and central Labrador Sea; the eastern Labrador Sea and Greenland Slope; and, the Greenland Shelf. The boundaries between zones varied spatially between years, but community composition was relatively consistent within a given zone and a given season (spring versus early summer). The relationship between community composition and water masses was not entirely straightforward. For example, Labrador Shelf water was generally confined to the shelf, but in spring 2000 when it also dominated the adjacent slope zone, the community in the Labrador Slope zone was similar to those found in other years. Conversely, in spring 1997, when Arctic organisms were unusually abundant in the Labrador Slope zone, there was no increased contribution of shelf water. In addition, North Atlantic organisms were often found on the shelves when no slope or central basin water was present.Although other organisms were sometimes very abundant, the mesozooplankton preserved dry weight biomass was dominated everywhere by the three species of Calanus, which together always accounted for ≥70%. One species, C. finmarchicus, comprised >60% of the total mesozooplankton biomass and >80% of the abundance of large copepods in spring and summer throughout the central Labrador Sea. In western and central regions of the central basin average C. finmarchicus biomass was ca 4 g dry weight m−2 and average abundance, ca 17?000 m−2 over both seasons. Highest levels (ca 7 g dry weight m−2, >100?000 m−2) occurred in the northern Labrador Sea in spring and in eastern and southwest regions in early summer. C. hyperboreus contributed ca 20% of the total mesozooplankton biomass in the central basin in spring and <5% in early summer, while C. glacialis accounted for <1%. Over the shelves, C. hyperboreus contributed a maximum of 54% and 3.6 g dry weight m−2, and C. glacialis, a maximum of 29% and 1 g dry weight m−2, to the total mesozooplankton biomass.  相似文献   

14.
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   

15.
Zooplankton was sampled through eight depth intervals above about 500 m along a transect of the eastern tropical Pacific (ETP), 23°N to 3°S, encompassing four environments. (1) The California Current—ETP transition off Baja California and the mouth of the Gulf of California is inhabited by California Current species at their southern limits, and by the galatheid ‘red crab’ Pleuroncodes planipes together with euphausiids (e.g. Euphausia eximia) of an abundance-based recurrent group of species, distinguished using the criterion of > x abundance (Numbers under unit area of sea surface) at common localities, adapted to productive zones marginal to the O2-deficient part of the ETP. Tropical species appear here where water with surface temperature > 26°C and [O2] of < 0.1 ml l?1 beneath a shoaling thermocline replaces the upwelling environment off Baja California. (1) The zone 22° to 10°N harbors euphausiids of two groups: the vertically migrating tropical species (e.g. Euphausia diomedeae) which tolerate intense O2-deficiency at their daytime depths and enter the oxygenated mixed layer at night, and non-migrating Stylocheiron species which have vertical ranges extending up into the mixed layer. Nevertheless, most of these ‘ETP-adapted’ species are denser farther south, in the north equatorial countercurrent, but three ETP endemics (e.g. E. distinguenda), all vertical migrators belonging in one subgeneric division of Euphausia, are densest in the O2-deficient regions. (3) The zone of the North Equatorial Countercurrent maintains high densities of three groups: the widely-ranging, ETP-adapted tropical species, the four common Stylocheiron species which, while recurring in abundance at the same localities, differ in depth and the mesopelagic tropical-subtropical species, not tolerant of O2-deficiency, which occur here in easterly tongues of range. (4) At the equator (93°W), easterly ranging species (e.g. E. paragibba) and westerly Nyctiphanes simplex appear to migrate between equatorial currents which differ in direction with depth, thereby maintaining their narrow ranges along the equator. The ‘marginal proliferators’ such as E. eximia, prominent off Baja California, are again abundant here, availing of the equatorial divergence for high productivity and of the oppositely-directed currents for geographical stability.A second recurrent grouping of species, based on presence of their larvae at common localities, yielded groups also distinguishable by whether the larvae lived within or beneath the mixed layer.Ontogenetic strengthening of vertical migration capability is demonstrated by many species, with older larvae, juveniles and adults showing ranges, respectively, increasing from a few meters to up to 400 m. The pattern is the same in O2-deficient regions as elsewhere.Regional distribution of euphausiid volume (wet displacement biomass) tended to agree with zooplankton volume, with maxima at the equator, 8°N, and at some localities off Baja California and the Gulf of California where red crab volume peaked. The depth at which euphausiid volume is equal in amount day and night, across which vertical migration takes place, is designated the equilibrium depth (EqD) for euphausiid volume. EqD for euphausiids generally agreed with EqD for zooplankton volume, indicating that euphausiids play a role in determining depth of EqD for zooplankton volume. Euphausiids comprised 13% (x) of zooplankton volume. 80% (x) of euphausiid volume migrated across EqD, the value showing no significant regional differences. 37% (x) of zooplankton volume engaged in such migration, but in the region south of 14°N encompassing the broad O2-deficient zone, the value was 26%, which compares with 18% previously determined for biomass transferring in a comparable way between epiplankton and planktostad in the same region.  相似文献   

16.
The inner shelf waters off Southeastern Brazil are periodically enriched by bottom intrusions of the cold and nutrient‐rich South Atlantic Central Water (SACW), which is transported offshore by the Brazil Current. This study examined the temporal contrasts in abundance and structure of pelagic copepod assemblages in a neritic station off Ubatuba, in relation to hydrography and phytoplankton biomass, to investigate the effects of SACW bottom intrusions on copepod population dynamics during three consecutive years. The water‐column characteristics shifted from a well‐mixed, more turbid and phytoplankton‐poor scenario during subsidence conditions to a stratified, less turbid and high Chl‐a concentration scenario during SACW bottom intrusions, leading to increased copepod diversity, abundance, and biomass. The rise in copepod diversity during SACW intrusions was related to the contribution of oceanic species in addition to coastal water species. The copepod community was numerically dominated by small‐sized species, such as Oncaea waldemari, Oithona plumifera, and clausocalanid and paracalanid copepodids, regardless of seasonality and SACW intrusions. Some large calanoid species contributed considerably to the total copepod biomass during intrusions. In addition to confirming that SACW seasonal intrusions play a key role in pelagic processes off Southeast Brazil, this study showed that the multiannual variability of SACW seasonal intrusions is important in regulating the structure and dynamics of copepod communities in this subtropical area.  相似文献   

17.
The results of multiyear observations of the seasonal and inter-annual variability of the population structure, abundance, and biomass of the arctic calanoids copepod Calanus glacialis in the White Sea are presented. The spring season represents the most crucial period for the population’s seasonal dynamics. During the spring, the maximal abundance, biomass, and contribution of C. glacialis to the total zooplankton biomass is observed. The interannual variability of the abundance is closely related to the timing of the spring warming of the upper water column and the respective shifts of the onset of reproduction and the offspring development. The development of a new generation to the overwintering copepodite stage IV is usually completed three to four weeks later in the cold years compared to the warm ones. Our multiyear observations suggest that C. glacialis could be more tolerant of Arctic warming than it is usually believed. The high abundance of the C. glacialis population in the White Sea indicates that this arctic species is able to cope with the seasonal surface warming and should continue to do so, being provided with the cold water “refuge” in the deep sea.  相似文献   

18.
The trophic structure of zooplankton was investigated in Fram Strait (north western Svalbard) in spring and autumn of 2003. Depth-stratified zooplankton samples were collected at 12 stations on the shelf (200 m), across the shelf-slope (500 m) and over deep water (>750 m), using a Multiple Plankton Sampler equipped with 0.180-mm mesh size nets.Higher zooplankton abundance and estimated biomass were found in the shelf area. Abundance and biomass were two times higher in August, when sea-surface temperature was higher than in May. Herbivores dominated numerically in May, and omnivores in August, suggesting a seasonal sequence of domination by different trophic groups. Cirripedia nauplii and Fritillaria borealis prevailed in spring, whereas copepod nauplii and Calanus finmarchicus were numerically the most important herbivores in autumn. Small copepods, Oithona similis and Triconia borealis, were the most numerous omnivorous species in both seasons, but their abundances increased in autumn. Chaetognatha (mainly Eukrohnia hamata) accounted for the highest abundance and biomass among predatory taxa at all deep-water stations and during both seasons. Regarding vertical distribution, herbivores dominated numerically in the surface layer (0–20 m), and omnivores were concentrated somewhat deeper (20–50 m) during both seasons. Maximum abundance of predators was found in the surface layer (0–20 m) in spring, and generally in the 20–50 m layer in autumn. This paper presents the first comprehensive summary of the zooplankton trophic structure in the Fram Strait area. Our goals are to improve understanding of energy transfer through this ecosystem, and of potential climate-induced changes in Arctic marine food webs.  相似文献   

19.
The plankton community composition comprising heterotrophic bacteria, pro-/eukaryotes, heterotrophic nanoflagellates, microzooplankton and mesozooplankton was assessed during the spring bloom and at non-bloom stations in the English Channel and Celtic Sea between 6 and 12 April 2002. Non-bloom sites were characterised by a dominance of pro-/eukaryotic phytoplankton <20 μm, higher abundance of heterotrophic nanoflagellates, microzooplankton standing stocks ranging between 60 and 380 mg C m−2, lower mesozooplankton diversity and copepod abundance of between 760 and 2600 ind m−3. Within the bloom, the phytoplankton community was typically dominated by larger cells with low abundance of pro-/eukaryotes. Heterotrophic nanoflagellate cell bio-volume decreased leading to a reduction in biomass whereas microzooplankton biomass increased (360–1500 mg C m−2) due to an increase in cell bio-volume and copepod abundance ranged between 1400 and 3800 ind m−3. Mesozooplankton diversity increased with an increase in productivity. Relationships between the plankton community and environmental data were examined using multivariate statistics and these highlighted significant differences in the abiotic variables, the pro-/eukaryotic phytoplankton communities, heterotrophic nanoflagellate, microzooplankton and total zooplankton communities between the bloom and non-bloom sites. The variables which best described variation in the microzooplankton community were temperature and silicate. The spatial variation in zooplankton diversity was best explained by temperature. This study provides an insight into the changes that occur between trophic levels within the plankton in response to the spring bloom in this area.  相似文献   

20.
Main features of the zooplankton distribution and the ecological characteristics of the dominant species in the northern Benguela during different phases of upwelling are discussed. The composition of the zooplankton between 17 and 27°S was similar each year. Among the 20°30 most abundant species, 3°4 copepods dominated, influencing the distribution of total zooplankton biomass. During quiescent upwelling, zooplankton abundance was low and there were no significant differences in the inshore-offshore distribution of zooplankton biomass, the maximum occurring over the slope. During active upwelling, zooplankton biomass increased significantly, the maximum over the shelf being constituted almost entirely of developmental stages of herbivorous copepods. Over the inner shelf, all stages of the copepod Calanoides carinatus were feeding actively, removing up to 5 per cent per day of the standing stock of phytoplankton. Comparison of daily ration, respiration rate and biochemical composition of C. carinatus revealed active storage of energy inshore. Offshore populations of C. carinatus, found deeper than 200 m, comprised mainly copepodite stage V, which were not feeding and were characterized by decreased mobility and respiration and a high lipid content. It is estimated that the energy stored during active upwelling enables copepods to survive up to six months without any additional source of energy.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号