Molecular systematics of six Calanus and three Metridia species (Calanoida: Copepoda)

The discrimination of species of the copepod genus, Calanus (Copepoda; Calanoida), is problematical-especially in regions of sympatry. Although the species of Calanus exhibit exceptional morphological similarity, they are quite distinct in genetic character. The DNA base sequences of the mitochondrial large subunit (16S) ribosomal RNA (rRNA) gene unambiguously discriminated C. finmarchicus (Gunnerus 1765), C. glacialis (Jaschnov 1955), C. marshallae (Frost 1974), C. helgolandicus (Claus 1863), C. pacificus (Brodsky 1948), C. sinicus (Brodsky 1965), and C. hyperboreus (Kroyer 1838). Sequence differences among Calanus species for this gene portion range from 7.3% (between C. glacialis and C. marshallae) to 23.9% (between C. glacialis and C. sinicus). Differences among conspecific individuals were approximately 1 to 2%. [These sequence data were determined between April and November 1993; the sequenced domain is similar to that published previously in Bucklin et al. (1992) but are derived from analysis of additional individuals.] Statistical analysis of the sequence data using a variety of tree-building algorithms separated the taxa into one group of species corresponding to the C. finmarchicus group (C. finmarchicus, C. marshallae, and C. glacialis) and another ungrouped set of species corresponding to the C. helgolandicus group (C. helgolandicus, C. pacificus, and C. sinicus). The C. helgolandicus group may be older than the C. finmarchicus group, making the tree topology less reliable in this area. Calanus hyperboreus was an outlier; Nannocalanus minor (Claus 1863) was the outgroup. Similar analysis of Metridia species confirmed that M. lucens (Boeck 1864) and M. pacifica (Brodsky 1948) are distinct species; M. longa (Lubbock 1854) was still more divergent. These sequence data will allow the design of simple, molecular tools for taxonomic identifications. Diagnostic characters, assayed by rapid molecular protocols, will enable biological oceanographers to answer important questions about the distribution and abundance of all life stages (as well as patterns of reproduction) of morphologically similar species, such as those of Calanus.     

Simple molecular method to distinguish the identity of Calanus species (Copepoda: Calanoida) at any developmental stage

Diagnostic morphological characteristics of copepods of the genus Calanus are restricted largely to minor variations in secondary sex characteristics. This presents a persistent problem in the identification of individuals to species level, especially for immature stages. We have developed a simple molecular technique to distinguish between the North Atlantic Calanus species (C. helgolandicus, C. finmarchicus, C. glacialis and C. hyperboreus) at any life stage. Using the polymerase chain-reaction (PCR), the mitochodrial large subunit (16S) ribosomal RNA (rRNA) gene was amplified from individual copepods preserved in ethanol. Subsequent digestion of the amplified products with the restriction enzymes DdeI and VspI, followed by electrophoretic separation in 2% agarose (Metaphor, FMC Ltd), produced a characteristic pattern for each species. The versatility of the method is demonstrated by the unambiguous identification to species of any life stage, from egg to adult, and of individual body parts. Received: 11 May 1998 / Accepted: 5 August 1998     

Molecular systematic and phylogenetic assessment of 34 calanoid copepod species of the Calanidae and Clausocalanidae

DNA sequences for a 639 bp region of mitochondrial cytochrome oxidase I (mtCOI) were determined for 34 species of ten genera in two families of calanoid copepods, including: Calanoides, Cosmocalanus, Meoscalanus, Nannocalanus, Neocalanus, and Undinula (family Calanidae); and Clausocalanus, Ctenocalanus, Drepanopus, and Pseudocalanus (family Clausocalanidae). MtCOI gene sequences proved to be diagnostic molecular systematic characters for accurate identification and discrimination of the species. Levels of mtCOI variation within species (range: 1-4%) were significantly less than those between species (9-25%). Higher levels of intraspecific variation (>2%) usually resulted from comparisons between ecologically distinct or geographically isolated populations. MtCOI sequence variation resolved evolutionary relationships among species of Clausocalanus, Neocalanus, and Pseudocalanus, although there was evidence of saturation at some variable sites. Phylogenetic relationships among 11 copepod genera (adding Calanus to the list above) were reconstructed using a 660 bp region of nuclear small-subunit 18S rRNA, a slowly evolving gene that showed no variability within a species and differed by <1-6% among the genera. The 18S rRNA molecular phylogeny was consistent with the accepted limits of the Calanidae and Clausocalanidae and clearly resolved relationships among genera within each family. This molecular systematic and phylogenetic study was part of the ZooGene project, an international partnership to create a DNA sequence database as a tool for uniform, molecularly based species identification of planktonic calanoid copepods and euphausiids.     

Annual population development and production by Calanus finmarchicus, C. glacialis and C. hyperboreus in Disko Bay, western Greenland

The populations of the copepod species Calanus finmarchicus, C. glacialis and C. hyperboreus were investigated in Disko Bay during a 14-month period in 1996-1997. The three species were predominant in the copepod community. The biomass reached a maximum at the beginning of June (127 mg C m^-3). From the end of July until the end of April the following year, the biomass was <1-6 mg C m^-3. All three species showed seasonal ontogenetic migration. The spring ascent for all three species was just prior to or in association with the break-up of sea ice and the development of the spring bloom, whereas descent occurred over a larger time span during summer. The main overwintering stages were CV for C. finmarchicus, CIV and CV for C. glacialis and C. hyperboreus. Peak abundance of juvenile copepodites, representing the new generation, was in August for C. finmarchicus, in July for C. glacialis and in May/June for C. hyperboreus. From the timing of reproduction and the population development, the life cycles were deduced to be 1 year for C. finmarchicus and at least 2 years for C. glacialis and C. hyperboreus. Secondary production and potential grazing impact of the Calanus community were estimated by two methods based on specific egg-production rates and temperature-dependent production. The Calanus community was not able to control the primary producers during the spring bloom but probably did during post-bloom. The estimates also indicated that grazing on ciliates and heterotrophic dinoflagellates contributes as an essential food source in the post-bloom period.     

Reproductive cycles of three dominant Calanus species in Disko Bay, West Greenland

This study describes the annual reproductive cycles of the three dominant Calanus species, C. finmarchicus, C. glacialis and C. hyperboreus, in Disko Bay (West Greenland) in relation to seasonal phytoplankton development. Relative abundance of females, copepodite stage V (CV) and males, and the developmental stage of the female gonad were examined from plankton samples collected at weekly to monthly intervals from May 1996 to June 1997 with a WP2 net or a pump. During spring and summer, egg production rates were determined. Females of all three species were present year round. Maximum relative abundance was reached by C. hyperboreus females at the beginning of February, by C. glacialis in mid-February, and by C. finmarchicus in April. All three species reproduced successfully in Disko Bay. Their reproductive cycles were considerably different with respect to the timing of final gonad maturation and spawning, and hence in their relation to seasonal phytoplankton development. In all three species, early gonad development took place during winter, before living food became plentiful, suggesting that these processes were largely food independent. Final gonad maturation and spawning in C. finmarchicus was related to the phytoplankton concentration, reflecting that final gonad maturation processes are food dependent in this species. C. glacialis females matured and spawned prior to the spring bloom. Our results indicate that first internal lipid stores and later ice alga grazing supplied final gonad maturation and egg production. Maximum egg production rates of C. glacialis were found in spring and summer, when the chlorophyll a concentration was high. Mature female C. hyperboreus were found from February until mid-April, when the chlorophyll a concentration was still low. In this species, reproductive activity was decoupled from phytoplankton development, and final maturation processes and spawning were solely fuelled by internal energy stores.     

Calanus marshallae,a new species of calanoid copepod closely allied to the sibling species C. finmarchicus and C. glacialis

Species of the copepod genus Calanus frequently dominate the marine zooplankton in boreal and arctic waters. Up to now there have been no operational means of identifying several species closely related to Calanus finmarchicus. Reanalysis of these taxa, using material from plankton samples collected throughout Northern Hemisphere polar and coreal waters, shows that there are 3 sibling species which have been previously combined under the names C. finmarchicus and C. glacialis. Several new taxonomic characters permit unequivocal identification of C. finmarchicus, C. glacialis, and a new species, C. marshallae. Claims that C. finmarchicus and C. glacialis are subspecies are refuted; there is no evidence that the two species continuously intergrade either where they co-occur or where they are allopatric, nor is there evidence that the two species hybridize. C. finmarchicus is basically restricted to the North Atlantic Ocean and C. marshallae to the North Pacific Ocean and Bering Sea; C. glacialis is primarily an Arctic species, but its geographical distribution slightly overlaps those of the other two species. Taxa closely related to C. finmarchicus and C. helgolandicus probably represent two separate, but closely linked evolutionary lineage; species of these two lineages are placed in one of two species groups, the finmarchicus group and the helgolandicus group.     

Assessing feeding of a carnivorous copepod using species-specific PCR

The polymerase chain reaction (PCR) offers a sensitive and selective way to detect trace amounts of biological remnants. Here, we show that this simple molecular technique can be applied to identify prey copepods in the fecal pellets of carnivorous zooplankton. Using variation in the mitochondrial cytochrome C oxidase subunit I (mtCOI) sequence, we developed a species-specific oligonucleotide PCR primer (COI-2026) for Calanus helgolandicus. In a touch-down PCR, Calanus DNA was amplified from pellets collected from freshly incubated individuals of the carnivorous copepod Pareuchaeta norvegica. Positive results could easily be detected by agarose gel electrophoresis.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by M. Kühl, Helsingør     

Vertical distributions of Calanus finmarchicus and C. helgolandicus (Crustacea: Copepoda)

The vertical distributions of the spring populations of Calanus finmarchicus (Gunnerus) and C. helgolandicus Claus are described and compared. The differences we observed between the two species have probably confused the understanding of the vertical distribution and development of the populations of Calanus spp. in the shelf seas around the United Kingdom where the species occur together. The results imply that these two congeneric species have different behaviour patterns which minimise interspecific competition where the species have sympatric distributions. C. finmarchicus has its younger development stages overlying the older stages in the water column. In C. helgolandicus the converse is true; i. e., the majority of the populations of Stage I and II copepodites of the first spring generations are found below the thermocline. It is also suggested that the different behaviour patterns lead to different feeding regimes and strategies.JONSDAP Contribution No. 52     

Mesozooplankton community structure, abundance and biomass in the central Arctic Ocean

During the "International Arctic Ocean Expedition 1991" (20 August-21 September 1991) mesozooplankton was sampled at six stations in the Nansen, Amundsen and Makarov Basins of the central Arctic Ocean from 1,500 m depth to the surface by multiple opening/closing net hauls. Total mesozooplankton abundance decreased from 268 ind. m^-3 in the surface layer (0-50 m) to <25 ind. m^-3 below 200 m depth. The small copepods Oithona similis and Microcalanus pygmaeus, as well as copepod nauplii, were most abundant close to the surface, while Oncaea borealis and Spinocalanus spp. frequently occurred at greater depth. Mesozooplankton dry mass (DM) integrated over the upper 1,500 m of the water column was surprisingly stable throughout the investigation area and measured 2.0ǂ.3 g DM m^-2. Dry mass in the upper 50 m measured 20.9 mg m^-3 and was dominated by Calanus hyperboreus (57.4%) and C. glacialis (21.1%). C. finmarchicus was very abundant only in the Nansen Basin. Below 200 m the calanoid copepods Metridia longa, Microcalanus pygmaeus and Pareuchaeta spp., the decapod Hymenodora glacialis and chaetognaths of the genus Eukrohnia were the principal contributors to biomass values of <1 mg DM m^-3. Hence, vertical changes in abundance, biomass and species composition were much more pronounced than regional differences between the basins. Three different mesozooplankton communities were differentiated according to their faunistic composition and are discussed in context with the major water masses: Polar Surface Water, Atlantic Layer and Arctic Deep Water.     

Geographical range and taxonomic divergence in North Atlantic Calanus (C. helgolandicus,C. finmarchicus and C. glacialis)

The known distribution of Calanus helgolandicus in the North Atlantic Drift is difficult to explain in the absence of a reproductively active population inhabiting continental waters off eastern North America. New evidece indicates that this population, overlooked in the past, does in fact exist. The species has been found in a study of zooplankton samples from a number of MARMAP (Marine Resource Monitoring, Assessment, and Prediction Program) cruises surveying ichthyoplankton between Cape Hatteras and the New York Bight. Sexual activity in these stocks of C. helgolandicus was indicated by the ripeness of ovaries, the frequency of males, the presence of sperm in the females' seminal receptacles and the appearance of a female bearing a Calanus spermatophore. The new records provide a likely origin for the presence of the species in the vicinity of the Labrador Grand Banks as well as further east in the North Atlantic Drift. C. finmarchicus, similarly sexually active, was found to be sympatric with C. helgolandicus in the MARMAP collections which were taken from a region contiguous with the southernmost, known distribution, of C. glacialis. The distribution of integumental organs (i.e., pore signature patterns) was examined in the three species to determine whether they would be taxonomically useful. Strikingly different patterns were found on the female urosome. Pore signature differences between the polar species C. glacialis and the temperate C. helgolandicus proved to be as pronounced as those between the boreal C. finmarchicus and its two neighboring species. The successively overlapping ranges and the distinctive differences in pore signature patterns suggest that divergence from the generic pattern of integumental organ distribution has been a product of selection against hybridizing among the three species. If this is in fact the case, the reproductive range of C. helgolandicus has overlapped with those of C. finmarchicus and C. glacialis for appreciable periods in the history of the three species.     

Variations in the abundance of Centropages typicus and Calanus helgolandicus in the North Sea: deviations from close relationships with temperature

The interannual variations in abundance of the calanoid copepod Centropages typicus (Krøyer) in the North Sea are significantly positively correlated with sea-surface temperature. The same is true of Calanus helgolandicus Claus. In both cases there was a deviation from the close relationship with temperature for several years in the early to mid-1980s. Centropages typicus was less abundant than expected from 1981 to 1984, but Calanus helgolandicus recovered from a period of lower than expected abundance from 1980 to 1982, to become more abundant than expected from 1983 to 1987. The difference between the responses of the two species to climate-driven changes in seasonal cycles of phytoplankton is interpreted in relation to their biology. Geographical variations of the interannual variability and seasonal cycles of Centropages typicus in the North Sea are analysed. The centre of the population of this species in the North Sea is in the German and Southern Bights, but the variations in abundance may be partly influenced by advection from areas to the west of Britain.     

Vertical distribution of Calanus finmarchicus and C. helgolandicus in relation to the development of the seasonal thermocline in the Celtic Sea

The geographical distribution and annual mean abundance of Calanus finmarchicus (Gunnerus) and C. helgolandicus (Claus) in the northern North Atlantic Ocean were shown in relation to the seasonal and annual fluctuations of abundance of the species in the Celtic Sea from 1960 to 1981. These congeneric copepods, although showing allopatric distributions over most of their geographical range, have sympatric distributions in the Celtic Sea where they dominate the dry weight biomass of the plankton throughout the year. The two species respond differently to the development of the seasonal thermocline and halocline by taking up different vertical distributions in the water column. C. finmarchicus occurred in the colder, more saline water below the thermocline, while C. helgolandicus occurred in the warmer, less saline water above the thermocline. This behaviour is postulated as a mechanism by which these morphologically similar copepods more fully exploit the resources of their temporally and spatially heterogeneous environment and also minimise interspecific competition. The species have the same foraging techniques and are able to exploit the same size spectrum of particulates. The vertical depth strata in which the populations are found for most of the year in the Celtic Sea means that both species exploit the diatom bloom in early spring but, thereafter, C. helgolandicus grazes on the daily production of the autotrophs in the euphotic zone while C. finmarchicus, below the thermocline, has to rely for its food on sedimenting particulates (whole cells, detritus and faecal material). The isolating mechanisms whereby these two populations partition the habitat in the Celtic Sea are discussed.     

Acoustical identification of the concentration layer of a copepod species,Calanus euxinus

Swimming trajectories of Calanus euxinus Hulsemann in the Black Sea were studied using an echosounder at 120 and 200 kHz. C. euxinus were acoustically discriminated with respect to vertical migration and swimming speed, according to dissolved oxygen (DO) concentration and the timing of migrations. Species became torpid in water with DO values <0.5 mg l^у. The time spent swimming under DO conditions between 2 and 5 mg l^у was insignificant, and varied greatly from the 10% to 25% of total time spent swimming under normoxic conditions (5-10 mg l^у). C. euxinus formed a concentration layer in the water of 1-3 m thickness. Upward migration was completed in about 3.5 h, starting 2.5 h before and ending 1 h after sunset (average rate: 0.95 cm s^у) in summer. Species ascended discretely from the suboxic to the lower boundry of the cold intermediate layer (CIL) at 0.82 cm s^у, and passed up the CIL and thermocline fast (2.3 cm s^у). Downward migration took less time (2 h), starting ~1 h before and ending ~1 h after sunrise. Swimming speed within the thermocline and CIL was 2.7 cm s^у; copepods subsequently returned to daylight depth at a sinking speed of 0.57 cm s^у. Total time for C. euxinus to settle to their nocturnal depth layer was about 5 h.     

A note on the feeding of Calanus helgolandicus on detritus

Experiments on the feeding of Calanus helgolandicus females on detrital material were carried out. Natural detritus from the ocean was never ingested, whereas dead diatoms were readily eaten. Furthermore, it was shown that C. helgolandicus females ingested large amounts of fecal material produced by the same species in other vessels. These results indicate that the copepod C. helgolandicus feeds not only on living organisms, but also on dead particles.     

Short-term effects of sucralose on Calanus finmarchicus and Calanus glacialis in Disko Bay,Greenland

The potential effects of sucralose on the Arctic copepods Calanus finmarchicus and Calanus glacialis were studied in Disko Bay, Greenland. Sucralose is a non-calorie sweetener and chlorine derivate of sucrose containing three chlorine atoms. Scandinavian screening studies of sucralose in 2007, revealed sucralose in all effluent samples. To investigate whether sucralose is harmful to the Arctic aquatic ecosystems, possible short-term effects were investigated on egg production, hatching rate, food intake and mortality of two species of Arctic copepods. The copepods were exposed to six different concentrations (0–50,000 ng · L^?1) of sucralose, which spans the range of concentrations found in the screening studies. Exposure led to no mortality among the copepods. Food intake by C. glacialis increased with increasing concentrations of sucralose. In C. finmarchicus, food intake did not differ with increasing concentrations. No effect of sucralose was observed on egg production of C. finmarchicus. Despite increased food intake with increasing concentrations of sucralose, C. glacialis did not increase its egg production. The results show that both species responded weakly to sucralose, but with C. glacialis being possibly slightly more sensitive to sucralose than C. finmarchicus.     

Reproductive strategy of<Emphasis Type="Italic"> Calanoides carinatus</Emphasis> and<Emphasis Type="Italic"> Calanus helgolandicus</Emphasis> during a summer upwelling event off NW Spain

Reproductive activity and production of the calanoid copepods Calanus helgolandicus and Calanoides carinatus were measured during a summer upwelling event off the coast of NW Spain. The upwelling pattern affected the distribution and fecundity of both species in the study area. The demographic composition of both populations and the stage of gonad maturation (e.g. the high abundance of fertilised females with mature ova) indicated active reproduction. C. carinatus, a highly fecund species associated with the African upwelling zones and considered as an upwelling specialist, showed low production rates (overall means of 15 eggs female^–1 day^–1 and 3% body C day^–1), despite the fact that the food conditions (high phytoplankton biomass dominated by diatoms) seemed to be optimal for this species. By contrast, C. helgolandicus, a temperate species that shows a strong link between spring phytoplankton blooms and reproduction time, seems to be flexible enough to take full advantage of shorter-term, enhanced feeding conditions associated with the pulsed nature of the summer coastal upwelling. Both the egg and carbon-specific production rates attained by this species (overall means of 26 eggs female^–1 day^–1 and 12% body C day^–1) were similar to values reported for a spring bloom situation. This high production would imply a long spring–summer recruitment event of C. helgolandicus in these waters. For both species the stage of gonad maturation was significantly correlated with their egg production rates and likely influenced by the food conditions; a species-specific nutritional requirement for final oogenesis is suggested. The carbon condition factor (carbon weight/prosome volume) of C. carinatus females was higher than that of C. helgolandicus, suggesting differential use of the carbon ingested; C. helgolandicus seems to use all ingested carbon to produce eggs at a high rates, whereas C. carinatus seems to store part of the ingested carbon as lipid reserves to ensure female survival and to support production during subsequent unfavourable food conditions.Communicated by S.A. Poulet, Roscoff     

Zooplankton grazing on the coccolithophore Emiliania huxleyi and its role in inorganic carbon flux

Grazing and faecal pellet production by the copepods Calanus helgolandicus and Pseudocalanus elongatus, feeding on the coccolithophore Emiliania huxleyi, were measured under defined laboratory conditions, together with the chemical characteristics and sinking rates of the faecal pellets produced. Ingestion rates of both copepods were equivalent at comparable cell concentrations, the relationship between ingestion rate (I, cells copepod^-1 h^-1) and food concentration (C, cells ml^-1), being I=0.558C for both species. P. elongatus produced a larger number of smaller faecal pellets than C. helgolandicus, but egested a larger volume of material per individual. Only between 27 and 50% of the ingested coccolith calcite was egested in the faecal pellets, and it is possible that acid digestion in the copepod gut is responsible for these considerable losses. Average sinking rates of faecal pellets containing E. huxleyi coccoliths, produced by both species, were >100 m d^-1. The implications of the quantitative laboratory estimates for the vertical flux of inorganic carbon are considered using recently studied shelf-break and oceanic E. huxleyi blooms in the N. E. Atlantic as examples.     

GC-EAG-analysis of volatiles from Brussels sprouts plants damaged by two species of Pieris caterpillars: olfactory receptive range of a specialist and a generalist parasitoid wasp species

Summary. Feeding by Pieris brassicae or P. rapae caterpillars on Brussels sprouts plants induces the emission of synomones that attract natural enemies of the caterpillars, Cotesia glomerata, a generalist parasitoid, and C. rubecula, a specialist on P. rapae. Previous research on this tritrophic system has identified a large number of volatiles in the headspace of herbivore-damaged Brussels sprouts plants, and this paper addresses the question which of these volatiles are perceived by the two parasitoid species. Headspace odors from both P. brassicae- and P. rapae-damaged Brussels sprouts plants were analyzed by coupled gas chromatography electro- antennogram (GC-EAG) detection. Twenty volatiles evoked consistent EAG reactions in the antennae of both species and nineteen of these volatiles could be identified with GC-MS. One component that could not be identified due to its low concentration, evoked EAG responses in antennae of C. rubecula only. Possible consequences for searching behavior of the two parasitoid species are discussed.     

Measurement of copepod predation on nauplii using qPCR of the cytochrome oxidase I gene

A method to directly measure predation rates by older stage copepods upon copepod nauplii using species-specific primers for the mitochondrial cytochrome oxidase subunit one gene (mtCOI) and real-time quantitative PCR (qPCR) was developed. The general approach is to determine the mtCOI gene copy number of an individual prey organism and the copy number of the same gene in the stomachs of predatory copepods collected in the field. From the knowledge of DNA disappearance rates in the stomachs, ingestion rates can be calculated. In October 2006, laboratory experiments were carried out with Acartia tonsa N1 and N2 as prey and adult female Centropages typicus as predator. The copepods were collected in Narragansett Bay, USA. A. tonsa mtCOI copy numbers copepod⁻¹ were determined for stages N1–C1 and for adults. A. tonsa DNA was detectable in the guts of the predators for as long as 3 h. Exponential rates of decline in prey DNA from the stomachs of the predators are similar to those measured for gut pigments. Because of the very small amount of DNA in an individual N1 or N2 nauplius, procedures were developed to maximize the quantitative extraction and recovery of DNA and to increase the sensitivity of the method. Two quite divergent haplotypes of A. tonsa were found in Narragansett Bay, which required separate qPCR primers; one was present in summer (July) and the other in fall and winter (October and February). With modification, the methods in this study can likely be applied to a range of predator–prey systems.     

Significance of food type for growth of ephyrae Aurelia aurita (Scyphozoa)

We studied growth of newly released Aurelia aurita ephyra larvae fed five different food types, including a large-sized copepod, a phytoflagellate, and suspended POM (particulate organic matter) made from bivalve meat. Experiments were run at saturated food concentration in two different temperatures over 10 days. The effect of small differences in temperature was inconsistent and interacted with the effect of food type, which, in turn, was highly significant. A low average growth rate (4-9% day^-1) was shown when feeding on the large-sized copepod Calanus finmarchicus (80 µg AFDW individual^-1), in spite of an extremely high daily ration of up to 1500% of body AFDW. When feeding on the cryptophyte Rhodomonas baltica (ca. 8 µm cell diameter), the ephyrae showed an average growth rate over the 10 day experiment of 7-11%, but with a considerably higher growth rate during the first days. Suspended POM generated an average growth rate of 7-9% day^-1, whereas fresh bivalve meat, manually placed into the stomach of the ephyra, gave an average growth rate of 12-14% day^-1. Artemia nauplii (ca. 3 µg AFDW individual^-1), used as a general reference, resulted in higher growth rates than any of the other food types (17-31% day^-1). We conclude that A. aurita ephyrae can capture and feed on phytoplankton, large copepods, and POM; that phytoplankton might be of nutritive significance early in development; and that the high quantity of large-sized copepods ingested is inefficiently converted to growth during early development. POM is a potential food source because of the ability of the ephyrae to encounter and ingest it, although concentration, size distribution, and nutritional composition of natural POM probably constrain its effect on growth.