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1.
The little-known cladoceran population of the Aegean Sea was studied. One hundred and seventy-six planktonic samples were collected during 8 cruises in the Aegean Sea (4 in the northern part, 4 in the southern part). From these samples, the following 4 species of Cladocera were determined: Evadne spinifera Muller, Evadne tergestina Claus, Penilia avirostris Dana, Podon intermedius Lilljeborg. All species were found both in the north and in the south Aegean Sea, with the exception of P. avirostris, which was found only in the northern Aegean Sea. Its absence from the southern part is attributed to the higher salinities and the pelagic character of the area. With regard to abundance, E. spinifera is by far the commonest in this area; P. avirostris and E. tergestina could be characterised as frequent forms; P. intermedius is scarce. P. avirostris, E. spinifera and E. tergestina are thermophilic; their occurrence is more or less restricted to the warm season; P. intermedius is psychrophilic and appears only in winter. 相似文献
2.
Seasonal fluctuations in the abundance of populations of marine cladocerans and their resting eggs in the Inland Sea of Japan 总被引:1,自引:0,他引:1
T. Onbé 《Marine Biology》1985,87(1):83-88
Seasonal fluctuations in the abundance of resting eggs of four species of marine cladocerans, Penilia avirostris Dana, Podon polyphemoides (Leuckart), Evadne tergestina Claus and Evadne nordmanni Lovén, were investigated in association with their planktonic populations in the central part of the Inland Sea of Japan for a period of over two years. Most numerous were the eggs of P. avirostris, followed by those of the species in the aforementioned order. There was a marked seasonal fluctuation in the number of eggs that was closely correlated with the occurrence of the planktonic population for each species. The egg-number was highest just before the planktonic population disappeared from the water column, and gradually decreased thereafter until a minimum value was reached shortly before the new planktonic population appeared in the next season. The pattern of fluctuation in number was found to be very similar among all four species, indicating strongly that the cladoceran populations in this warm temperate sea may persist either as plankton in warmer seasons or as benthic resting eggs in colder seasons. The possible causes of the decrease in egg density in bottom sediments are discussed. 相似文献
3.
Molecular genetic variation in tarpon (<Emphasis Type="Italic">Megalops atlanticus</Emphasis> Valenciennes) in the northern Atlantic Ocean 总被引:2,自引:0,他引:2
The tarpon (Megalops atlanticus) is a highly valued game fish and occasional food fish in the eastern and western Atlantic Ocean. Tarpon have a high capacity for dispersal, but some regional biological differences have been reported. In this study we used two molecular genetic techniques—protein electrophoresis of nuclear DNA loci, and restriction fragment length polymorphism analysis of the mitochondrial DNA (mtDNA)—to assess this species population genetic structure in the eastern (coastal waters off Gabon and Sierra Leone, Africa) and western (coastal waters off Florida, Caribbean Sea) Atlantic Ocean north of the equator. Genetic differentiation was observed between tarpon from Africa and tarpon from the western Atlantic Ocean. A unique allele and haplotype, significant differences in allozyme allele and mtDNA haplotype frequencies between the African and western Atlantic samples, and significant FST analyses suggest that levels of gene flow between tarpon from these two regions is low. Among the western Atlantic Ocean collections, genetic diversity values and allele and haplotype frequencies were similar. AMOVA analyses also showed a degree of genetic relatedness among most of the western Atlantic Ocean collections: however, some significant population structuring was detected in the allozyme data. A regional jackknifed FST analysis indicated the distinction of the Costa Rica population from the other western Atlantic populations and, in pairwise analyses, FST values tended to be higher (i.e., genetic relatedness was lower) when the Costa Rican sample was paired with any of the other western Atlantic samples. These data suggest that Costa Rican tarpon could be partially isolated from other western Atlantic tarpon populations. Ultimately, international cooperation will be essential in the management of this species in both the eastern and western Atlantic Ocean.Communicated by P.W. Sammarco, Chauvin 相似文献
4.
Shakil Visram Ming-Che Yang Ruby Moothien Pillay Sadri Said Oskar Henriksson Mats Grahn Chaolun Allen Chen 《Marine Biology》2010,157(7):1475-1487
Studies on genetic connectivity are essential for the design of management strategies for coral reef fisheries. In this study
we used a mitochondrial DNA marker to investigate population structure of the reef-associated parrotfish, Scarus ghobban, from four countries, Kenya, Mauritius, Seychelles and Tanzania, in the western Indian Ocean. We obtained nucleotide sequences
of the mitochondrial control region for 117 individuals. Measures of haplotype diversity were relatively high. Pairwise population
differentiation (F
ST) was low, but not always non-significant. Analysis of molecular variance (AMOVA) showed genetic differentiation between groups,
when the data was partitioned into two groups consisting of samples from Mauritius and Tanzania in one group, and samples
from Kenya and Seychelles in another group. Direction of gene flow was estimated using a Bayesian approach. Migration was
sometimes asymmetric or directional, coinciding with the flow of major oceanic and coastal currents in the region. Mismatch
distributions, based on the observed number of differences among haplotype pairs, produced a unimodal distribution, indicative
of recent demographic expansion. Phylogenetic analyses revealed three clades without any geographic structure, suggesting
recent migration between historically isolated lineages. We reconstructed the historical demography of S. ghobban and examined it in the context of Pleistocene climate stages and changes in relative sea level. Overall, these results showed
that populations of S. ghobban are genetically diverse and have relatively high gene flow, with some genetic structuring in the western Indian Ocean. 相似文献
5.
Thomas A. Jefferson Dagmar Fertl Jaime Bolaños-Jiménez Alexandre N. Zerbini 《Marine Biology》2009,156(6):1109-1124
Due to indications that misidentification (largely confusion among dolphins of the genera Delphinus and Stenella) in the past had led to erroneous assumptions of distribution of the two species of common dolphins (Delphinus delphis and D. capensis) in the western Atlantic Ocean, we conducted a critical re-examination of records of the genus Delphinus from this region. We compiled 460 ‘plottable’ records, required support for confirmation of genus and species identifications,
and found many records lacking (and some clearly misidentified). When we plotted only the valid records (n = 364), we found evidence of populations in only three areas, and apparent absence throughout much of the tropical/subtropical
regions. Off the east coast of the US and Canada, D. delphis is found from the Georgia/South Carolina border (32°N) north to about 47–50°N off Newfoundland. Since the 1960s, they have
apparently been absent from Florida waters. There is no evidence that dolphins of the genus occur in the Gulf of Mexico. Reports
of common dolphins from most of the Caribbean Basin are also rejected, and the only place in that region where they are confirmed
to occur is off central-eastern Venezuela (a coastal D. capensis population). Off eastern South America, common dolphins appear to be restricted to south of 20°S. There is a coastal long-beaked
population found in the South Brazil Bight, and one or more short-beaked populations south and offshore of this (ranging south
to at least northern Argentina). The results are very different from commonly-accepted patterns of distribution for the genus
in the Atlantic. Most areas of distribution coincide with moderate to strong upwelling and common dolphins appear to avoid
warm, tropical waters. This study shows that great care must be taken in identification of similar-appearing long-beaked delphinids,
and that uncritical acceptance of records at face value can lead to incorrect assumptions about the ranges of the species
involved. 相似文献
6.
Comparative phylogeography of marine cladocerans 总被引:1,自引:0,他引:1
We examined the population genetics of six species of marine cladocerans, using a ~600 bp fragment of the cytochrome oxidase
subunit I gene sequence. Phylogenetic analysis revealed significant intraspecific, semi-allopatric phylogenetic breaks in
four out of five species belonging to the Podonidae, supporting an ancient radiation and oceanic expansion for this group.
By contrast, Penilia
avirostris (Sididae) displayed no phylogeographic structure across a global sampling, suggesting a recent worldwide expansion. Our results
also show a transoceanic distribution of identical or very similar haplotypes in several species of marine Cladocera, which
may be interpreted as either natural transport or evidence of recent anthropogenic transport. If the latter is the case, marine
cladocerans represent one of the first genetically documented cases of exotic or invasive marine zooplankton, likely an underreported
group.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Sequence data from this article have been deposited with the EMBL/GenBank Data Libraries under accession nos. EU675871–EU675924. 相似文献
7.
S. Eriksson 《Marine Biology》1974,26(4):319-327
The present paper is based on a 3-year field study of marine Cladocera in the waters off Gothenburg on the Swedish west coast. The group mainly occurred from May to September, when there was a temperature stratification of the waters. The dominant species, Evadne nordmanni Lovén, may occur in large numbers during the entire warm period, both in offshore and inshore waters. The species Podon leuckarti G.O. Sars, P. intermedius Lilljeborg, and Pleopis (=Podon) polyphemoides (Leuckart) occurred separately both in time and space. The occurrence of different species may primarily be regulated by abiotic factors, e.g. temperature and currents, but may also be modified by competition for food between closely related species. During the early summer, the populations of E. nordmanni and Podon leuckarti seem to be comprised of specimens brought in by the sea, while the estuarine species Pleopis polyphemoides seems to be more indigenous within the area. 相似文献
8.
Leonardo K. Miyashita Mayza Pompeu Salvador A. Gaeta Rubens M. Lopes 《Marine Biology》2010,157(11):2511-2519
We studied the population dynamics and the reproductive biology of Penilia avirostris during three consecutive years on the inner shelf off Ubatuba, Brazil. Penilia avirostris individuals and its eggs and embryos were counted, measured, and classified into stages. The species occurred throughout
the studied period, in a wide temperature range (14.8–28.2°C). Cladoceran densities were usually higher (>2,000 ind m−3) in warm seasons, when the water column was stratified as a consequence of bottom intrusions of the cold- and nutrient-rich
South Atlantic Central Water. Juveniles, non-reproducing females, and parthenogenic females were the dominant developmental
stages. Males and gamogenic females were rare and only occurred when females reached peak abundances. This suggests that in
tropical and subtropical coastal seas gamogenesis in P. avirostris is not as common as in temperate seas, but may play a significant role in the density-dependent control of the population
preceding unfavourable periods. 相似文献
9.
The genetic structure of Patagonian toothfish populations in the Atlantic and western Indian Ocean Sectors of the Southern Ocean (SO) were analysed using partial sequences of the mitochondrial 12S rRNA gene and seven microsatellite loci. Both haplotype frequency data (F
ST>0.906, P<0.01) and microsatellite genotype frequency data (F
ST=0.0141–0.0338, P<0.05) indicated that populations of toothfish from around the Falkland Islands were genetically distinct from those at South Georgia (eastern Atlantic Sector SO), around Bouvet Island (western Atlantic Sector SO) and the Ob Seamount (western Indian Ocean Sector of the SO). Genetic differentiation between these populations is thought to result from hydrographic isolation, as the sites are separated by two, full-depth, ocean-fronts and topographic isolation, as samples are separated by deep water. The South Georgia, Bouvet and Ob Seamount samples were characterised by an identical haplotype. However, microsatellite genotype frequencies showed genetic differentiation between South Georgia samples and those obtained from around Bouvet Island and nearby seamounts (F
ST=0.0037, P<0.05). These areas are separated by large geographic distance and water in excess of 3,000 m deep, below the distributional range of toothfish (<2,200 m). No significant genetic differentiation was detected between samples around Bouvet Island and the Ob Seamount although comparisons may have been influenced by low sample size. These localities are linked by topographic features, including both ridges and seamounts, that may act as oceanic “stepping stones” for migration between these populations. As for other species of deep-sea fish, Patagonian toothfish populations are genetically structured at the regional and sub-regional scales. 相似文献
10.
S. Isari S. Psarra P. Pitta P. Mara M. O. Tomprou A. Ramfos S. Somarakis A. Tselepides C. Koutsikopoulos N. Fragopoulu 《Marine Biology》2007,151(3):1035-1050
Mesozooplankton group composition was examined in the Northeastern Aegean Sea (NEA) over a grid of 30 stations sampled during
July 2004. The surface water layer influenced by the low salinity Black Sea waters (BSW) is considered in this paper. We attempted
to study horizontal distribution patterns of major mesozooplankters within a more comprehensive framework, taking into account
not only hydrology but also available, concurrently collected data on lower trophic levels (autotrophic and microbial heterotrophic
communities). BSW was mainly restricted in the eastern part of the surveyed area where it was entrapped in a ca. 50-km wide
anticyclone (the “Samothraki” gyre). High Chlα concentrations, autotrophic biomass as well as abundance and biomass of mesozooplankton were associated with the BSW, with
the highest values recorded inside the gyre as well as at its coastal northern periphery and the lowest values towards the
western and offshore part of the surveyed area characterized by high salinity waters of Levantine origin. Among mesozooplankters,
cladocerans (mainly Penilia avirostris) showed a high abundance within the gyre in contrast to the very low abundance of copepods and appendicularians. Low salinity-high
temperature gyre waters were characterized by the dominance of cyanobacteria of the genus Synechococcus in autotrophic biomass and the significant contribution of heterotrophic nanoflagellates in microbial heterotrophic biomass.
Based on existing knowledge on ecophysiological traits and prey size-spectra selectivity, we discuss the observed distribution
patterns of major mesozooplankton groups in terms of ambient abiotic parameters and the possible biological interactions among
these groups as well as with lower or upper trophic levels. 相似文献
11.
Genetic stock structure of the swordfish (Xiphias gladius ) inferred by PCR-RFLP analysis of the mitochondrial DNA control region 总被引:2,自引:0,他引:2
Restriction fragment length polymorphism (RFLP) analysis was performed on PCR amplified DNA fragments containing the control
region of the swordfish (Xiphias gladius Linnaeus, 1758) mitochondrial DNA. A total of 456 individuals comprising 13 local samples (six Pacific, three Atlantic, the
Mediterranean Sea, two Indian Ocean and the Cape of Good Hope) were surveyed with four endonucleases (Alu I, Dde I, Hha I and Rsa I), yielding a total of 52 composite genotypes. Within-sample genotypic diversity (H) was high ranging from 0.702 to 0.962 with a value of 0.922 for the pooled sample. Significant geographic variation in the
frequencies of genotypes and restriction patterns was revealed. The Mediterranean sample was highly distinct from all other
samples. Further, Rsa I digestion revealed high levels of polymorphism in all but the Mediterranean samples, indicating that exogenous swordfishes
rarely enter that body of water. Heterogeneity between the North and South Atlantic samples was significant, both of which
differed from those of the Pacific. In contrast, the Indian Ocean samples were not significantly different from the samples
of South Atlantic and Pacific. Genetic differentiation among the Pacific samples was low. The results indicate that the world-wide
swordfish population is genetically structured not only among, but also within ocean basins and suggest that gene flow is
restricted despite the absence of geographic barriers.
Received: 28 August 1996 / Accepted: 2 October 1996 相似文献
12.
Eva Friis Møller Christian Marc Andersen Borg Sigrún H. Jónasdóttir Suree Satapoomin Cornelia Jaspers Torkel Gissel Nielsen 《Marine Biology》2011,158(3):677-688
The vertical distribution of copepods, fecal pellets and the fecal pellet production of copepods were measured at seven stations
across the Southern Indian Ocean from productive areas off South Africa to oligotrophic waters off Northern Australia during
October/November 2006. We quantified export of copepod fecal pellet from surface waters and how much was retained. Furthermore,
the potential impact of Oncaea spp. and harpacticoid copepods on fecal pellets degradation was evaluated and found to be regional substantial. The highest
copepod abundance and fecal pellet production was found in the western nutrient-rich stations close to South Africa and the
lowest at the central oligotrophic stations. The in situ copepod fecal pellet production varied between 1 and 1,000 μg C m−3 day−1. At all stations, the retention of fecal pellets in the upper 400 m of the water column was more than 99% and the vertical
export of fecal pellets was low (<0.02 mg m−2 day−1). 相似文献
13.
Surface “swarms” of the swimming crabs Charybdis smithii are still considered as an unusual phenomenon in the open Indian Ocean, although their dense pelagic aggregations were already
reported in waters off the Indian coast and in the northern Arabian Sea. Based on an extensive large-scale data series taken
over 45 years, we demonstrate that C. smithii is common in the pelagic provinces of the western Indian Ocean driven by the wind monsoon regime. Swimming crabs are dispersed
by the monsoon currents throughout the equatorial Indian Ocean. They aggregate at night in the upper 150-m layer, where their
estimated biomass derived from pelagic trawling data can exceed 130 kg km−2. Abundance of C. smithii can reach >15,000 ind. km−2 in July (i.e. the peak of the south-west monsoon), declines by 50-fold in March and is negligible in May. C. smithii is an important prey for more than 30 species of abundant epipelagic top predators. In turn, it feeds on mesopelagic species.
This swimming crab is a major species of the intermediate trophic levels and represents a crucial seasonal trophic link in
the open ocean ecosystem of the western Indian Ocean. Outbursts in pelagic waters of huge biomasses of ordinarily benthic
crustaceans (C. smithii and Natosquilla investigatoris) are a remarkable feature of the Indian Ocean, although similar, but smaller, events are reported in the Pacific and Atlantic
Oceans.
相似文献
Evgeny RomanovEmail: |
14.
A cryptic lineage of hammerhead shark closely related to but evolutionarily distinct from the scalloped hammerhead (Sphyrna lewini) was recently documented in the western North Atlantic Ocean. Here, we demonstrate using nuclear and mitochondrial DNA sequences
that this cryptic lineage also occurs in the western South Atlantic Ocean, extending its distribution >7,000 km from its only
previously reported location. Our results also further validate the existence of this evolutionarily distinct hammerhead shark
lineage. The southern hemisphere cryptic individuals were 1.6 and 5.8% divergent from S. lewini (sensu stricto) for the nuclear internal transcribed spacer 2 (ITS2) and mitochondrial control region loci, respectively, and formed a strongly
supported, reciprocally monophyletic sister group to sympatric S. lewini. Coalescent analysis (ITS2 locus) yielded a divergence estimate of ~4.5 million years between S. lewini and the cryptic lineage. Given expanding concerns about overfishing of the large-bodied hammerhead sharks, this cryptic lineage
needs to be formally recognized and incorporated into shark management and conservation planning to avoid the inadvertent,
potential extirpation of a unique hammerhead lineage. 相似文献
15.
K. Ohwada 《Marine Biology》1972,14(1):10-17
A simple, rapid and sensitive method of microbiological assay for the determination of biotin in seawater has been developed by using a marine bacterium, Achromobacter sp. (Strain yH-51) as an assay organism. When the organism was incubated at 25°C for 48 h in a synthetic medium with constant shaking, a standard reference curve of bioassay was obtained. The organism is sensitive in the range 0.1 to 8.0 ng/l biotin. The distribution of biotin has been determined in the East China Sea, the North Pacific Ocean, and the bays and inlets along the Pacific coast of Japan. Biotin concentrations in surface waters were in the range from less than 0.1 ng/l up to 57.9 ng/l; generally high in coastal waters and low in deep open waters. The concentrations were generally high in surface waters, and rapidly decreased with depth down to 50 m, below which values were generally low. The vertical distribution of biotin followed closely the concentration of chlorophyll a, with high concentrations of biotin restricted to the euphotic layer of high chlorophyll a contents at most stations observed. Biotin concentrations in surface waters were generally high during summer, but in autumn and winter the concentrations decreased markedly. 相似文献
16.
Tseng LC Kumar R Dahms HU Chen CT Chen QC Hwang JS 《Journal of environmental biology / Academy of Environmental Biology, India》2008,29(3):275-280
This study analyses distribution and abundance patterns of mesozooplankton communities at 13 stations in the coastal waters over a marine outfall area in the northeastern South China Sea. Cruises were conducted in March, June and September 2002, and plankton samples were collected with a 333 microm North Pacific net. The Mesozooplankton was dominated by calanoid Copepods, Cladocera, Chaetognatha and Pteropoda. Stations located near the entrance of the harbor provided a relatively higher abundance of Noctilucales and Radiolarians. In total, 20 zooplankton groups were identified in which, Calanoida, Cladocera, Chaetognatha, Pteropoda, Poecilostomatoida and Appendicularia comprised 92.77% of the total zooplankton abundance. Copepoda dominated in all three cruises, comprising 65.32% of the total mesozooplankton abundance. Samples collected in June recorded higher mesozooplankton abundance than March and September samples. Onshore stations recorded higher BOD values, higher abundance of Noctilucales and Radiolarians and a relativelylower abundance of the overall mesozooplankton. Total mesozooplankton abundance did not correlate significantly with temperature, pH, or dissolved oxygen, but correlated negatively with BOD. 相似文献
17.
Dacha Atienza Albert Calbet Enric Saiz Miquel Alcaraz Isabel Trepat 《Marine Biology》2006,150(2):221-235
In this work we studied the trophic ecology and feeding impact of the cladoceran Penilia avirostris and the cyclopoid copepod Oithona nana, the two dominant zooplankters in the summer communities of the coastal NW Mediterranean, on the naturally occurring microbial communities. In order to ascertain carbon surplus for growth and reproduction and the contribution to carbon and nitrogen recycling of these two species, we also determined their basal metabolism and excretion rates. The experiments conducted during summers 2002, 2003, and 2004 indicate that P. avirostris grazed mostly upon small flagellates, dinoflagellates, and diatoms, whereas O. nana had a narrower prey range, selecting motile organisms such as ciliates and occasionally dinoflagellates. The grazing impact of both species accounted, on average, for <10% of the standing stock of the microbial groups considered. In spite of the oligotrophic conditions, the feeding activity of P. avirostris is in general sufficient to compensate basal metabolism and allows a surplus for growth and reproduction. This was not the case for O. nana, its daily rations being often lower than the carbon basal demands. Regarding excretion rates, both species presented different N:P excretion ratios, the ones of O. nana falling within values typical for copepods, whereas the absence of detectable phosphorus excretion by P. avirostris implied an unbalance recycling with respect to typical Redfield ratio composition of marine seston. 相似文献
18.
Marine cladocerans are important contributors to the zooplankton community of tropical and temperate coastal ecosystems during the warmer months, when they show explosive population growth. Despite this fact, little information is available on their ecology compared with the extensive studies on their freshwater relatives. The main objective of this study was to determine the in situ feeding and growth rates, and life history parameters of Penilia avirostris in São Sebastião Bay (Brazil) during austral summer 2004, as a premise to understand the advantages of this cladoceran in oligotrophic waters. Culture development experiments, monitored for a period of 12 days, showed that maximum juvenile release occurred after 2 days, and that the development duration of a complete cohort was around 9 days. From bottle incubation grazing experiments, significant ingestion rates upon flagellates, ciliates, dinoflagellates and diatoms were detected. Flagellates were the most important contributors to P. avirostris diet (ca. 80%). P. avirostris ingested between 28 and 97% of its own carbon biomass per day (daily ration) and individual growth rates of this marine cladoceran (0.10–0.24 d?1) increased with prey availability. The combination of ingestion rates of natural prey and growth rates provided gross growth efficiencies (GGE) of 15–53%, on a carbon basis. Our results suggest that P. avirostris has similar GGE to copepods, although at low food conditions the values for the marine cladocerans seems slightly higher. However, this characteristic alone does not explain the explosive growth and community dominance shown by P. avirostris. Therefore, other traits related to the reproductive biology of the species, such as short generation time, parthenogenetic reproduction, and continuous somatic growth, seems to be mostly responsible for the success of P. avirostris in many marine ecosystems during their seasonal occurrence. 相似文献
19.
Relatively few insects have invaded the marine environment, and only five species of sea skaters, Halobates Eschscholtz (Hemiptera: Gerridae), have successfully colonized the surface of the open ocean. All five species occur in the
Pacific Ocean, H. germanus White also occurs in the Indian Ocean, whereas H. micans Esch- scholtz is the only species found in the Atlantic Ocean. We sequenced a 780 bp long region of the mitochondrial cytochrome
oxidase subunit I gene (COI) for a total of 66 specimens of the five oceanic Halobates species. Our purpose was to investigate the genetic variation within species and estimate the amount of gene flow between
populations. We defined 27 haplotypes for H. micans and found that haplotype lineages from each of the major oceans occupied by this species are significantly different, having
sequences containing five to seven unique base substitutions. We conclude that gene flow between populations of H. micans inhabiting the Atlantic, Pacific, and Indian Ocean is limited and hypothesize that these populations have been separated
for 1 to 3 million years. Similarly, there may be limited gene flow between H. germanus populations found in the Pacific and Indian Ocean and between H. sericeus populations inhabiting the northern and southern parts of the Pacific Ocean. Finally, we discuss our findings in relation
to recent hypotheses about the influence of oceanic diffusion on the distribution and population structure of oceanic Halobates spp.
Received: 29 July 1999 / Accepted: 23 November 1999 相似文献
20.
We conducted grazing experiments with the three marine cladoceran genera Penilia, Podon and Evadne, with Penilia avirostris feeding on plankton communities from Blanes Bay (NW Mediterranean, Spain), covering a wide range of food concentrations (0.02–8.8 mm3 l–1, plankton assemblages grown in mesocosms at different nutrient levels), and with Podon intermedius and Evadne nordmanni feeding on the plankton community found in summer in Hopavågen Fjord (NE Atlantic, Norway, 0.4 mm3 l–1). P. avirostris and P. intermedius showed bell-shaped grazing spectra. Both species reached highest grazing coefficients at similar food sizes, i.e. when the food organisms ranged between 15 and 70 µm and between 7.5 and 70 µm at their longest linear extensions, respectively. E. nordmanni preferred organisms of around 125 µm, but also showed high grazing coefficients for particles of around 10 µm, while grazing coefficients for intermediate food sizes were low. Lower size limits were >2.5 µm, for all cladocerans. P. avirostris showed upper food size limits of 100 µm length (longest linear extension) and of 37.5 µm particle width. Upper size limits for P. intermedius were 135 µm long and 60 µm wide; those for E. nordmanni were 210 µm long and 60 µm wide. Effective food concentration (EFC) followed a domed curve with increasing nutrient enrichment for P. avirostris; maximum values were at intermediate enrichment levels. The EFC was significantly higher for P. intermedius than for E. nordmanni. With increasing food concentrations, the clearance rates of P. avirostris showed a curvilinear response, with a narrow modal range; ingestion rates indicated a rectilinear functional response. Mean clearance rates of P. avirostris, P. intermedius and E. nordmanni were 25.5, 18.0 and 19.3 ml ind.–1 day–1, respectively. Ingestion rates at similar food concentrations (0.4 mm3 l–1) were 0.6, 0.8 and 0.9 g C ind.–1 day–1.Communicated by O. Kinne, Oldendorf/Luhe 相似文献