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1.
During late winter and spring of 2002 and 2003, 24 two- to three-day cruises were conducted to Dabob Bay, Washington State, USA, to examine the grazing, egg production, and hatching success rates of adult female Calanus pacificus and Pseudocalanus newmani. Here, we discuss the results of our grazing experiments for P. newmani. Each week, we conducted traditional microzooplankton dilution experiments and “copepod dilution” experiments, each from two different layers. Grazing was measured by changes in chlorophyll concentration and direct cell counts. Clearance rates on individual prey species, as calculated by cell counts, showed that Pseudocalanus are highly selective in their feeding, and may have much higher grazing rates on individual taxa than calculated from bulk chlorophyll disappearance. The grazing rates of the copepods, however, are typically an order of magnitude lower than the grazing rates of the microzooplankton community, or the growth rates of the phytoplankton. P. newmani ingested diatoms, but, at certain times fed preferentially on microzooplankton, such as ciliates, tintinnids, and larger dinoflagellates. Removal of the microzooplankton may have released the other phytoplankton species from grazing pressure, allowing those species’ abundance to increase, which was measured as an apparent “negative” grazing on those phytoplankton species. The net result of grazing on some phytoplankton species, while simultaneously releasing others from grazing pressure resulted in bulk chlorophyll-derived estimates of grazing which were essentially zero or slightly negative; thus bulk chlorophyll disappearance is a poor indicator of copepod grazing. Whether copepods can significantly release phytoplankton from the grazing pressure by microzooplankton in situ, thus causing a trophic cascade, remains to be verified, but is suggested by our study.  相似文献   

2.
The dynamics, composition and grazing impact of microzooplankton were studied during the in situ iron fertilisation experiment EisenEx in the Antarctic Polar Frontal Zone in austral spring (November 2000). During the 21 day experiment, protozooplankton and small metazooplankton were sampled from the mixed layer inside and outside the patch using Niskin bottles. Aplastidic dinoflagellates increased threefold in abundance and biomass in the first 10 days of the experiment, but decreased thereafter to values twofold higher than pre-fertilisation values. The decline after day 10 is attributed to increasing grazing pressure by copepods. They also constrained ciliate abundances and biomass which were higher inside the fertilised patch than outside but highly variable. Copepod nauplii abundance remained stable whereas biomass doubled. Numbers of copepodites and adults of small copepod species (<1.5 mm) increased threefold inside the patch, but doubled in surrounding waters. Grazing rates estimated using the dilution method suggest that microzooplankton grazing constrained pico- and nanoplankton populations, but species capable of feeding on large diatoms (dinoflagellates and small copepods including possibly nauplii) were selectively predated by the metazoan community. Thus, iron fertilisation of a developing spring phytoplankton assemblage resulted in a trophic cascade which favoured dominance of the bloom by large diatoms.  相似文献   

3.
The trophic efficiency of the planktonic food web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major metabolic activities of auto- and heterotrophic planktonic communities (primary production, bacterial production, nanoproto-, micro- and mesozooplankton feeding activities) were determined in nine field assemblages collected during spring at reference station 330. In 1998, the phytoplankton spring flowering was characterised by a moderate diatom bloom followed by a massive Phaeocystis colony bloom. Phaeocystis colonies, contributing 70% to the net primary production, escaped the linear food chain while the early spring diatom production supplied 74% of the mesozooplankton carbon uptake. The rest of mesozooplankton food requirement was, at the time of the Phaeocystis colony bloom, partially fulfilled by microzooplankton. Only one-third of the microzooplankton production, however, was controlled by mesozooplankton grazing pressure. Ungrazed Phaeocystis colonies were stimulating the establishment of a very active microbial network. On the one hand, the release of free-living cells from ungrazed colonies has been shown to stimulate the growth of microzooplankton, which was controlling 97% of the nanophytoplankton production. On the other hand, the disruption of ungrazed Phaeocystis colonies supplied the water column with large amounts of dissolved organic matter available for planktonic bacteria. The budget calculation suggests that ungrazed colonies contributed up to 60% to the bacterial carbon demand, while alternative sources (exudation, zooplankton egestion and lysis of other organisms) provided some 30% of bacterial carbon requirements. This suggests that the spring carbon demand of planktonic bacteria was satisfied largely by autogenic production. The trophic efficiency was defined as the ratio between mesozooplankton grazing on a given source and food production. In spite of its major contribution to mesozooplankton feeding, the trophic efficiency of the linear food chain, restricted to the grazing on diatoms, represented only 5.6% of the available net primary production. The trophic efficiency of the microbial food chain, the ratio between mesozooplankton grazing on microzooplankton and the resource inflow (the bacterial carbon demand plus the nanophytoplankton production) amounted to only 1.6%. These low trophic efficiencies together with the potential contribution of ungrazed Phaeocystis-derived production to the bacterial carbon demand suggest that during spring 1998 most of the Phaeocystis-derived production in the Belgian coastal area was remineralised in the water column.  相似文献   

4.
During late winter and spring of 2002 and 2003, 24, 2–3 day cruises were conducted to Dabob Bay, Washington State, USA, to examine the grazing, egg production, and hatching success rates of adult female Calanus pacificus and Pseudocalanus newmani. The results of the copepod grazing experiments for C. pacificus are discussed here. Each week, copepod grazing incubation experiments from two different depth layers were conducted. Grazing was measured by both changes in chlorophyll concentration and cell counts. In 2002, there was one moderate bloom consisting mainly of Thalassiosira spp. in early February, and a larger bloom in April comprised of two Chaetoceros species and Phaeocystis sp. Similarly, in 2003, there were two blooms, an early one dominated by Thalassiosira spp., and a later one consisting of Chaetoceros spp. and Thalassiosira spp. Clearance rates on individual prey species, as calculated by cell counts, showed that C. pacificus are highly selective in their feeding, and may have much higher clearance rates on individual taxa than rates calculated from bulk chlorophyll disappearance. During weeks of high phytoplankton concentration, the copepods generally ate phytoplankton. However, they often rejected the most abundant phytoplankton species, particularly certain Thalassiosira spp., even though the rejected prey were often of the same genus and similar size to the preferred prey. It is speculated that this avoidance may be related to the possible deleterious effects that certain of these diatom species have on the reproductive success of these copepods. During weeks of medium to low phytoplankton concentration, the copepods selectively ate certain species of phytoplankton, and often had high electivity for microzooplankton. The selection mechanism must consist of active particle rejection most likely based on detection of surface chemical properties, since the diatoms that were selected were of the same genus, nearly the same size, and at lower numerical abundance than those cells that were avoided. The grazing choices made by these copepods may have important consequences for the overall ecosystem function within coastal and estuarine systems through changes in the transfer efficiency of energy to higher trophic levels.  相似文献   

5.
Incubation experiments were carried out daily during a Lagrangian experiment within an upwelled filament off the Galician coast to determine the importance of microzooplankton in the diet of calanoid copepods. Despite low chlorophyll concentrations the microzooplankton formed the minor component of the diet of the copepod community (7 to 15% of carbon ingested through autotrophic and heterotrophic prey). Ingestion of ciliates was greater than that of heterotrophic dinoflagellates, which reflected a higher abundance of ciliates in the water column. Heterotrophic nanoflagellates appeared also to be consumed by the copepods, although the very small size fraction (2–5μm) was probably not grazed by the larger copepods of Calanus spp. Grazing pressure by the copepods enumerated in the net samples was not sufficient to impact significantly the microzooplankton populations (2 to 51% of daily microzooplankton production was removed). Allometric relationships of grazing on microzooplankton for a range of numerically dominant copepod species are developed from the experimental results. The grazing pressure of the whole copepod community is estimated from these relationships. By considering the total mesozooplankton community we suggest that microzooplankton growth was probably restricted by metazoan grazers.  相似文献   

6.
The role of mesozooplankton as consumers and transformers of primary and secondary production in the Beaufort and Chukchi Seas was examined during four cruises in spring and summer of both 2002 and 2004 as part of the western Arctic Shelf–Basin Interactions (SBI) program. Forty-seven grazing experiments using dominant mesozooplankton species and life stages were conducted at locations across the shelf, slope, and basin of the Chukchi and Beaufort Seas to measure feeding rates on both chlorophyll and microzooplankton and to determine mesozooplankton prey preferences.Mesozooplankton biomass was at all times dominated by life stages of four copepod taxa: Calanus glacialis, Calanus hyperboreus, Metridia longa, and Pseudocalanus spp. Significant interannual, seasonal, regional, between species and within species differences in grazing rates were observed. Overall, the dominant zooplankton exhibited typical feeding behavior in response to chlorophyll concentration that could be modeled using species and life-stage specific Ivlev functions. Microzooplankton were preferred prey at almost all times, with the strength of the preference positively related to the proportion of microzooplankton prey availability. Average mesozooplankton grazing impacts on both chlorophyll standing stock (0.6±0.5% d−1 in spring, 5.1±6.3% d−1 in summer) and primary production (12.8±11.8% d−1 in spring, 27.6±24.5% d−1 in summer) were quite low and varied between shelf, slope, and basin. Coincident microzooplankton grazing experiments [Sherr, E.B., Sherr, B.F., Hartz, A.J., 2009. Microzooplankton grazing impact in the Western Arctic Ocean. Deep-Sea Research II] were conducted at most stations. Together, microzooplankton–mesozooplankton grazing consumed only 44% of the total water-column primary production, leaving more than half directly available for local export to the benthos or for offshore transport into the adjacent basin.  相似文献   

7.
We adapted the dilution technique to study microzooplankton grazing of algal dimethylsulfoniopropionate (DMSP) vs. Chl a, and to estimate the impact of microzooplankton grazing on dimethyl sulfide (DMS) production in the Labrador Sea. Phytoplankton numbers were dominated by autotrophic nanoflagellates in the Labrador basin, but diatoms and colonial Phaeocystis pouchetii contributed significantly to phytomass at several high chlorophyll stations and on the Newfoundland and Greenland shelfs. Throughout the region, growth of algal Chl a and DMSP was generally high (0.2–1 d−1), but grazing rates were lower and more variable, characteristic of the early spring bloom period. Production and consumption of Chl a vs. DMSP followed no clear pattern, and sometimes diverged greatly, likely because of their differing distributions among algal prey taxa and size class. In several experiments where Phaeocystis was abundant, we observed DMS production proportional to grazing rate, and we found clear evidence of DMS production by this haptophyte following physical stress such as sparging or filtration. It is possible that grazing-activated DMSP cleavage by Phaeocystis contributes to grazer deterrence: protozoa and copepods apparently avoided healthy colonies (as judged by relative growth and grazing rates of Chl a and DMSP), and grazing of Phaeocystis was significant only at one station where cells were in poor condition. Although we hoped to examine selective grazing on or against DMSP-containing algal prey, the dilution technique cannot differentiate selective ingestion and varying digestion rates of Chl a and DMSP. We also found that the dilution method alone was poorly suited for assessing the impact of grazing on dissolved sulfur pools, because of rapid microbial consumption and the artifactual release of DMSP and DMS during filtration. Measuring and understanding the many processes affecting organosulfur cycling by the microbial food web in natural populations remain a technical challenge that will likely require a combination of techniques to address.  相似文献   

8.
A combined empirical and modelling study was conducted to further examine the potential importance of grazing by zooplankton in pelagic food webs in which Phaeocystis is a significant or dominant component. Laboratory experiments were designed to measure ingestion of Phaeocystis and other potential prey items which co-occur with Phaeocystis. Grazers included copepods and ciliates, and prey included Phaeocystis colonies and solitary cells, diatoms, ciliates, bacteria, and detritus. These data were expressed in the model currency of nitrogen units, and fit to hyperbolic tangent equations which included minimum prey thresholds. These equations and literature data were used to constrain a food web model whose purpose was to investigate trophic interactions rather than to mimic actual events. Nevertheless, the model output was similar to the general pattern and magnitude of development of Phaeocystis–diatom communities in some environments where they occur, e.g. north Norwegian waters. The model included three forms of nitrogen, three phytoplankton groups, bacteria, two zooplankton groups, and detritus, with detailed flows between compartments. An important component of the model was inclusion of variable prey preferences for zooplankton. The experiments and model simulations suggest several salient conclusions. Phaeocystis globosa colonies were eaten by a medium-sized copepod species, but ingestion appeared to be strongly dependent upon a proper size match between grazer and prey. If not, colonies were eaten little if at all. Phaeocystis solitary cells were ingested rapidly by ciliate microzooplankton, in agreement with prior literature observations. In contrast, detritus was eaten comparatively slowly by both ciliates and copepods. Both types of zooplankton exhibited apparent minimum prey thresholds below which grazing did not occur or was inconsequential. Model simulations implied that transitions between life cycle stages of Phaeocystis may potentially be important to phytoplankton–zooplankton interactions, and that relative rates of ingestion of Phaeocystis by various zooplankton may have significant impacts upon material fluxes through and out of Phaeocystis–diatom ecosystems. Indirect effects of trophic interactions appear to be equally significant as direct effects.  相似文献   

9.
Dilution experiments were conducted to investigate microzooplankton grazing impact on phytoplankton of different taxonomic groups and size fractions (< 5, 5–20, 20–200 μm) during spring and summer bloom periods at two different sites (inner Tolo Harbour and Tolo Channel) in the Tolo Harbour area, the northeastern coastal area of Hong Kong. Experiments combined with HPLC pigment analysis in three phytoplankton size fractions measured pigment and size specific phytoplankton growth rates and microzooplankton grazing rates. Pigment-specific phytoplankton growth rates ranged between 0.08 and 3.53 d− 1, while specific grazing rates of microzooplankton ranged between 0.07 and 2.82 d− 1. Highest specific rates of phytoplankton growth and microzooplankton grazing were both measured in fucoxanthin in 5–20 μm size fraction in inner Tolo Harbour in summer, which coincided with the occurrence of diatom bloom. Results showed significant correlations between phytoplankton growth and microzooplankton grazing rates. Microzooplankton placed high grazing pressure on phytoplankton community. High microzooplankton grazing impact on alloxanthin (2.63–5.13) suggested strong selection toward cryptophytes. Our results provided no evidence for size selective grazing on phytoplankton by microzooplankton.  相似文献   

10.
In order to investigate the parameters controlling the heterotrophic protists (nano-microzooplankton) on the continental shelf of the southern Bay of Biscay, plankton communities and their physico-chemical environment were studied 4 times in February, April, June and September–October 2004 at three stations in the euphotic zone in the Bay of Biscay. The abundance and carbon biomass of heterotrophic protists (ciliates, heterotrophic dinoflagellates and nanoflagellates) as well as all the others groups of plankton (picoplankton, nanophytoplankton, diatoms, autotrophic dinoflagellates, metazoan microzooplankton and mesozooplankton), the environmental parameters and the primary and bacteria production were evaluated at each sampling period. Microzooplankton grazing experiments were undertaken at the same time. Ciliates and heterotrophic dinoflagellates accounted for the main major component of nano- and microzooplankton communities in term of biomass. The total carbon biomass of heterotrophic protists was highest in spring and lowest at the end of summer. The development of heterotrophic protists started after a winter microphytoplankton bloom (principally large diatoms), the biomass was lower in June and was low in September (through inappropriate prey). The carbon requirement of microzooplankton ranged from 50 to more than 100% of daily primary, bacterial and nanoflagellate production. The heterotrophic protist community was predominantly constrained by bottom-up control in spring and at the end of summer via food availability and quality.  相似文献   

11.
The objectives of this study were to (1) investigate whether the availability of suitable zooplankton prey limits the distribution of the coastal larval areas of pike (Esox lucius) in two archipelago areas of the northern Baltic Sea and (2) compare the availability of zooplankton prey in spring between different types of coastal littoral habitat. According to the results, reed belt habitats formed by Phragmites australis constitute hot spots for zooplankton prey in the coastal ecosystem. During the spring, reed-covered shores of the inner archipelago maintained more than 10 times higher densities of copepods and cladocerans, the preferred prey for larval pike, compared to the other studied shores. Temperature conditions were also most favourable in the reed belt habitat. Thus, the reed belts of the inner and middle archipelago were shown to form the best habitat for larval pike in the coastal area of the northern Baltic Sea, and this was also the only habitat where pike larvae were found. Our results suggest that the poor survival and recruitment of pike in the outer archipelago, however, cannot exclusively be explained by sub-optimal feeding conditions of the larvae. There are also other important factors, presumably connected to the exposure to the open sea, that affect the distribution of the pike larvae. Our results, however, highlight the importance of sheltered coastal reed belt shores as reproduction habitat for spring-spawning fish in the northern Baltic Sea. Further, this study disproves the assumption that the seaweed bladder wrack (Fucus vesiculosus) forms a reproduction habitat for pike in the coastal area.  相似文献   

12.
As part of a broader field study examining the potentially deleterious effects of diatoms on planktonic food webs, we examined the abundance, stage composition, diet, and feeding success of the chaetognath, Sagitta elegans, and the abundance and morphometric condition of larval Pacific hake, Merluccius productus. Our objective was to look for a relationship between spring phytoplankton blooms and planktonic predators, as mediated by their copepod prey, with special reference to possible deleterious effects of diatoms. Zooplankton were collected weekly during February–May and in mid-summer of 2002 and 2003 in Dabob Bay, Washington State, USA. S. elegans abundance was high in summer of both years and was higher in spring 2003 than spring 2002. Larval chaetognaths dominated the population in early spring and remained present throughout sampling. S. elegans consumed mostly copepods. The abundance of larval S. elegans was correlated with the abundance of copepodites, although no relationship between chaetognath feeding success and prey abundance was found. Larval Pacific hake abundance was high (1200 larvae per square meter) in late February and early March of 2002 and 2003 and decreased rapidly in late spring. The morphometric condition of M. productus was not significantly related to copepod abundance. These results indicate that any deleterious effects of diatoms on copepod abundance, at the scale seen during spring 2002 and 2003 in Dabob Bay, did not greatly affect the next higher trophic level.  相似文献   

13.
Reduced ice extent within coastal regions of the Southern Ocean may lead to deeper surface mixed layers (SML), as prevail in offshore areas. A future decline of ice melt-induced stability of the water column may be associated with a shift in dominant food webs, from larger, sun-adapted diatoms grazed by euphausiids to smaller, shade-adapted flagellates consumed by salps. A basically one-dimensional numerical model of three dominant groups of the Antarctic phytoplankton community (diatoms, cryptophytes, and colonial prymnesiophytes) and four types of herbivore (protozoans, salps, copepods, and euphausiids) is used to explore the seasonal importance of both light limitation and grazing pressure on the amount of annual carbon sequestration and larval krill survival within contrasting oceanic and neritic waters, where respective validation data have been gathered during austral spring by the European JGOFS and RACER programs. With imposition of moderate and large grazing stresses, thought to be typical of offshore waters, we were able to replicate the European JGOFS 1992 observations of light penetration, phytoplankton biomass, primary production, pCO2, bacterial biomass, labile DOC, ammonium, and total particle effluxes at 100 m within the deep SML of our model. The fidelity of such a large set of simulated state variables suggests that multiple limiting factors are indeed operating on different components of the oceanic phytoplankton community — selective grazing losses on the flagellates, but light limitation of diatoms. Release of protozoan grazing pressure in our model instead leads to unobserved spring blooms of cryptophytes, found only in laboratory enclosures. On an annual basis, weak sequestration of atmospheric CO2 is simulated in a habitat typical of the Polar Front, while evasion of carbon dioxide occurs under biophysical conditions of the Antarctic Circumpolar Current. Stratification in shallow SML and the same absolute grazing demands by krill and copepods allows sun-adapted diatoms of our model to bloom at the expense of shade-adapted cryptophytes and prymnesiophytes, eaten by salps and protozoans. We were also able to replicate RACER-I observations of the same suite of variables in 1986–1987, as well as the observed 10-fold range of detrital fluxes caught by other sediment trap deployments during 1980 and 1983 along the Antarctic Peninsula. In western Bransfield Strait, coastal waters are a strong sink for atmospheric CO2 within parcels of Bellingshausen Sea origin, but not perhaps in those from the Weddell Sea, which resemble the oceanic regime of deep SML. We conclude that even in shallow neritic SML, some protozoan rivals of larval krill must still crop flagellates to ensure sufficient abundance of diatom food for both euphausiid survival and possible clogging of the mucous nets of other salp rivals.  相似文献   

14.
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   

15.
To improve our understanding of the trophic link between micro-zooplankton and copepods in Gyeonggi Bay, Yellow Sea, the diet composition, ingestion rates, and prey selectivity of Acartia hongi, known as the most abundant and widespread copepod species, was estimated by conducting in situ bottle incubation throughout the different seasons. The results showed that A. hongi preferentially grazed on ciliate and heterotrophic dinoflagellate of a size ranging from 20 to 100 μm rather than phytoplankton. Although micro-zooplankton comprised only an average 13.7% of the total carbon available in the natural prey pool, micro-zooplankton accounted for >70% of the total carbon ration ingested by A. hongi throughout the year, except for winter diatom blooming periods when A. hongi obtained about 60% of its carbon ration from phytoplankton. Our results demonstrated that A. hongi modified their diet composition and feeding rates in response to change in composition and size of prey available to them, and that A. hongi preferentially ingested micro-zooplankton over phytoplankton. Feeding activity of A. hongi could therefore affect the species composition and size structure of natural plankton communities in this study area, particularly the micro-zooplankton. Strongly selective feeding and high grazing pressure by A. hongi on micro-zooplankton shows the role of trophic coupling between copepods and the microbial food web in the pelagic ecosystem of Gyeonggi Bay.  相似文献   

16.
Phytoplankton group-specific growth and microzooplankton grazing were determined seasonally using the dilution technique with high-performance liquid chromatography （HPLC） in the Xiamen Bay, a subtropical bay in southeast China, between May 2003 and February 2004. The results showed that growth rates of phytoplankton ranged from 0.71 to 2.2 d^-1 with the highest value occurred in the inner bay in May. Mierozooplankton grazing rates ranged from 0.5 to 3.1 d^-1 with the highest value occurred in the inner bay in August. Microzooplankton grazing impact ranged from 39% to 95% on total phytoplankton Chl a biomass, and 65% to 181% on primary production. The growth and grazing rates of each phytoplankton group varied, the highest growth rate （up to 3.3 d^-1 ） was recorded for diatoms in August, while the maximum grazing rate （ up to 2.1 d ^-1 ） was recorded for chlorophytes in February in the inner bay. Among main phytoplankton groups, grazing pressure of microzooplankton ranged from 10% to 83% on Chl a biomass, and from 14% to 151% on primary production. The highest grazing pressure on biomass was observed for cryptophytes （83%） in August, while the maximum grazing pressure on primary production was observed for eyanobacteria （up to 151% ） in December in the inner bay. Net growth rates of larger phytoplanktons （diatoms and dinoflagellates） were higher than those of smaller groups （ prasinophytes, chlorophytes and cyanobacteria）. Relative preference index showed that microzooplankton grazed preferentially on prasinophytes and avoided to harvest diatoms in cold seasons （December and February）.  相似文献   

17.
This study examined monthly feeding rates and grazing impact on phytoplankton biomass, as well as diel feeding rhythms of four key copepod species in a tidally well mixed estuary (Asan Bay, Korean Peninsula). Monthly ingestion rates estimated based on gut pigment analysis were closely associated with their peak densities, but not with phytoplankton biomass, implying high ingestion may be related to reproductive output for population growth. The three smaller copepods, Acartia hongi, Acartia pacifica and Paracalanus parvus, showed feeding preference for smaller phytoplankton (<20 μm) with higher clearance rates, whereas the larger Calanus sinicus preferred larger phytoplankton. Acartia pacifica and P. parvus showed distinct increased nocturnal feeding rates as measured with gut fluorescence, whereas A. hongi showed no significant day–night differences. Copepod diel feeding patterns were not associated with food quantity, and endogenous physiological rhythm might be hypothesized as responsible for the observed diel feeding patterns. Grazing impact on phytoplankton biomass by the four copepods in the estuary was on average 8% (range 0.2–29.8%) of the phytoplankton standing stock, similar to values reported in other coastal waters. Very high copepod abundances but low daily carbon ration (<20% for all copepods) provided by feeding on phytoplankton indicate that copepods also grazed on other non‐phytoplankton foods in Asan Bay.  相似文献   

18.
While numerous laboratory studies in the last decade have shown that diatoms can induce reproductive failure in copepods, field evidence for a negative diatom effect is equivocal. To unambiguously elucidate the effects diatoms have on copepod reproduction in situ, we undertook a study of the abundance, distribution, grazing rates, and reproductive success of Calanus pacificus in Dabob Bay, Washington, USA, during two spring bloom periods. We simultaneously measured the phytoplankton composition, abundance, and distribution. Here we present results for the reproductive success of C. pacificus using four measurements: egg production rate, clutch size, egg hatching success, and naupliar survival (to the first feeding stage). Egg production rate was positively correlated with chlorophyll a concentration, and egg hatching success and naupliar survival were usually greater than 80%. However, in February 2002 and 2003 – during blooms of diatoms of the genus Thalassiosira – either egg hatching success, naupliar survival, or both were significantly depressed compared to other times in spring and summer. These effects, combined with evidence that C. pacificus was grazing aldehyde-producing Thalassiosira at the time of their blooms, indicate that diatoms can negatively affect copepod reproduction in the field, albeit only under specific circumstances and for brief periods.  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.
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