Remote prey detection in Oithona similis: hydromechanical versus chemical cues

We quantified prey encounter rates and prey reaction distancesin the ambush-feeding cyclopoid copepod Oithona similis by videorecording freely swimming copepods at different concentrationsof prey, the dinoflagellate Gymnodinium dominans. Prey encounterrate increased with prey concentration, and a maximal clearancerate of 0.42 ± 0.10 ml h^–1 was estimated. The averagedistance (from the antennules) at which O.similis reacts toprey is 0.014 ± 0.007 cm. A simple prey encounter modelwas used to combine observed predator and prey velocities andprey reaction distance, and yielded a clearance rate similarto that estimated directly from prey encounter rates. The observedprey reaction distance was consistent with that estimated froma published model of hydromechanical prey perception. The possibilityof remote chemodetection was examined by modeling the distributionof solutes leaking out of a swimming cell. The cell leaves along slender chemical trail in its wake. However, since theambush-feeding O.similis is essentially stationary when perceivingprey, it is the width rather than the length of the trail thatmatters. Owing to advection, the chemical signal vanishes almostinstantaneously off the sides of the swimming flagellate, andsolute concentrations are below any likely detection thresholdwithin 40–50 µm from the flagellate. Our observationsare thus inconsistent with remote chemodetection in O.similis.The considerations are generalized, and it is concluded thatambush-feeding copepods, unlike cruisers and suspension feeders,cannot utilize chemical signals for the detection of individualprey, but rely on either hydromechanical detection or directinterception of prey.     

Sublethal effects of the toxic dinoflagellate Karenia brevis on marine copepod behavior

Apart from grazing interactions, little is known regarding thesublethal effects of Karenia brevis cells on copepod behavior.We conducted grazing and mortality experiments with K. breviscells and brevetoxins (PbTx-2), establishing routes of toxicityfor the copepods Acartia tonsa, Temora turbinata and Centropagestypicus. Subsequent behavioral experiments determined whethercopepod swimming and photobehavior, both behaviors involvedin predator avoidance, were impaired at sublethal K. brevisand PbTx-2 levels. Copepods variably grazed toxic K. brevisand non-toxic Prorocentrum minimum at bloom concentrations.Although copepods accumulated brevetoxins, significant mortalitywas only observed in T. turbinata at the highest test concentration(1 x 10⁷ K. brevis cells L^–1). Acartia tonsa exhibitedminimal sublethal behavioral effects. However, there were significanteffects on the swimming and photobehavior of T. turbinata andC. typicus at the lowest sublethal concentrations tested (0.15µg PbTx-2 L^–1, 1 x 10⁵ K. brevis cells L^–1).Although physiological incapacitation may have altered copepodbehavior, starvation likely played a major role as well. Thesedata suggest that sublethal effects of K. brevis and brevetoxinon copepod behavior occur and predicting the role of zooplanktongrazers in trophic transfer of algal toxins requires knowledgeof species-specific sublethal effects.     

Response of ciliates and Cryptomonas to the spring cohort of a cyclopoid copepod in a shallow hypereutrophic lake

The impact of a cyclopoid copepod population on the protozoacommunity (two ciliate categories and Cryptomonas) was assessedweekly during the spring cohort of Cyclops vicinus (one monthduration) in hypereutrophic Lake Søbygård by insitu gradient experiments with manipulation of ambient zooplanktonabundance. As C.vicinus always made up >92% of the zooplanktonbiomass, the response of protozoa is assumed to be a resultof predation by the copepod. Significant effects of copepodbiomass on protozoa net population growth rates were obtainedin the four experiments. Copepod clearance rates were significantlyhigher on oligotrichs than on prostomatids and Cryptomonas butdeclined for all three protozoa categories during the firstthree weeks of the copepod cohort, probably because of the changein developmental instar composition of the copepod population.Grazing impact on protozoa at ambient copepod abundance wasconsiderable (range, 0.05–0.87 day^–1) and could,together with the estimated reproductive potential of protozoans(range, –0.20–0.87 day^–1), account for thedecline in abundance and biomass of protozoa during the cohortdevelopment. Carbon flow from the protozoa to C.vicinus (range,2.8–23.5 µg C l^–1 day^–1) documents thepresence of a trophic link between protozoa and the spring cohortof C.vicinus in Lake Søbygård.     

The effects of food deprivation, prey density and volume on clearance rates and ingestion rates of Diacyclops thomasi

The ingestion rates of the copepod, Diacyclops thomasi, on thesoft-bodied rotifer, Synchaeta pectinata, increased 10-fold(0.07–0.77 Synchaeta h^–1) over the range 50–250prey l^–1. The saturating functional response curve appearedsigmoid but was statistically indistinguishable from a parabola.The response curve was more linear and 10 times lower over thesame range of density when Diacyclops was offered Kerarellacochleans, a species having a stiffened lorica. Diacyclops maximizedits ingestion rate on Synchaeta as a function of the availablegut space. Predation effort, measured as clearance rates, waslinked tentatively to changes in swimming speed of Diacyclopsand was a function of hunger level. Diacyclops, which were starvedfor varying periods of time, increased their ingestion rateson Synchaeta up to a maximum (-3.0 h^–1) after 7–10h of food deprivation. The gut passage time of Diacyclops wasestimated to be 7–8 h. Therefore, ingestion rates (andclearance rates) appeared to be strongly correlated to the volumeof food in the gut.     

Neocalanus scattering layers near the western Aleutian Islands

Dense copepod scattering layers were detected in the upper 50m of the water column in the Bering Sea north of the westernAleutian Islands during June 1992. Acoustic data were collectedat frequencies of 200 and 420 kHz, and compared with simultaneousestimates of wet weight biomass from net tows. Regression ofnet and acousticdata produced a scaling factor of –69.6dB g^–1 to convert volume scattering to biomass. Applicationof the fluid sphere scattering model produced an average equivalentspherical radius for the targets of 0.54 mm. The major sound-scatteringorganism, Neocalanus cristatus copepodid stage V, dominatedthe biomass in the pycnocline between the upper mixed layerand the underlying cold intermediate layer. Populations weredominated by Neocalanus plumchrus and Neocalanus flemingeri,withgreatest abundance above the pycnocline.     

Hydrodynamic disturbances produced by small zooplankton: case study for the veliger larva of a bivalve mollusc

Zooplankton produce hydrodynamic disturbances during swimmingand feeding that enlarge their perceptive volume. From the standpointof both prey and predators, fluid disturbances increase theprobability that an organism is detected, identified and reactedto within appropriate time and space scales. Morphology andkinematics dictate the magnitude, symmetry and attenuation ofdisturbances in the fluid medium. Therefore, fluid disturbancesmay be species and age (size) specific. Normal and high-speedvideo microscopy was used to study flow-field generation byfree-swimming and tethered bivalve larvae. These organisms swimand feed using many highly coordinated and symmetrically distributedappendages (i.e. cilia). Larvae tethered in flow at variousfree stream velocities (U₀), simulating swimming activity, inducedparticle trajectories approximately parallel to the organism'sdorso-ventral axis. Velocity (v) and acceleration (a) were symmetricalin the transverse plane and asymmetrical in the vertical plane.Greatest velocity magnitudes ({small tilde}7, 3 and 6 mm s^–)occurred dorsal to the velum and attenuated with source distance(r) as 1/r, 1/r^1.9 and 1/r^2.9 at 10 s^– U₀ =, 3.1 and 6.4mm s^–1, respectively. For a larva in flow, but with velumretracted, simulating sinking, velocity attenuated at Mr towardsthe organism. Mean velocity gradients were on the order of 3,8 and 10 s^–1 for swimming, sinking and hovering larvae,respectively. The high-frequency (22 Hz) component of particlevelocity past free-swimming larvae was due to beat frequencyof the velar cilia. This attenuated rapidly with r leaving onlylow-frequency (1–3 Hz) disturbances 0.1 mm beyond thetips of the cilia. Comparisons of the kinetic energy dissipationrate for turbulence in coastal waters with the kinetic energyof laminar flow fields implied possible dominance of the flowfield of hovering, but not swimming, larvae to at least threebody diameters from the organism (–1 mm). These differencesin flow fields have important implications for larval survival.The perceptive volume of a hovering larva will be 40-fold greaterthan that of a swimming or sinking larva. However, a hoveringlarva U also more likely to be detected by a potential predatorthat uses mechanosensory organs to locate prey.     

Feeding by larval and post-larval ctenophores on microzooplankton

Feeding by the coastal ctenophorc, Mnemiopsis leidyi, on microplanktonwas investigated. Larval ctenophores (tentaculate stage) grewbest and had the highest survival rates when offered a mixtureof ciliates and copepod nauplii. Larvae did not survive whenoffered phytoplankton alone. Clearing of planktonjc ciliatesby post-larval ctenophores was a function of the ciliate speciesand the size of the predator. Removal of small ciliates (<20µm in size) and phytoplankton was negligible. Small post-larvalctenophores (volume <4 cm³) had higher biovolume-specificclearing rates (0.5–1.5 1 cm^–3 day^–1) thandid larger ctenophores fed the same ciliate species. Duringin situ incubations, adult M. leidyi removed ciliates, rotifersand copepod nauplii from natural microplankton assemblages.The data indicate that non-crustacean microzooplanlctoo arean important component of the diet of larval and post-larvallocate cteoophores, particularly when copepod standing stocksare low.     

Predation and respiration by the small cyclopoid copepod Oithona similisr: How important is feeding on ciliates and heterotrophic flagellates?

Feeding on natural plankton populations and respiration of thesmall cyclopoid copepod Oithona similis were measured duringthe warm season in Buzzards Bay, Massachusetts, USA. AlthoughO.similis did not significantly ingest small autotrophic andheterotrophic flagellates (2–8 µn), this copepodactively fed on >10 µm particles, including autotrophic/heterotrophic(dino)flagel-lates and ciliates, with clearance rates of 0.03–0.38ml animal^–1 h^–1. The clearance rates increased withthe prey size. O.similis also fed on copepod nauplii (mainlycomposed of the N1 stage of Acartia tonsa with a clearance rateof 0.16 ml animal^–1 h^–1. Daily carbon ration fromthe combination of these food items averaged 148 ng C animal^–1day^–1 (41% of body C day^–1), with ciliates and heterotrophicdino-flagellates being the main food source ({small tilde}69%of total carbon ration). Respiration rates were 020–0.23µl O₂ animal^–1 day^–1. Assuming a respiratoryquotient of 0.8 and digestion efficiency of 0.7, the carbonrequirement for respiration was calculated to be 125–143ng C animal^–1 day^–1, close to the daily carbon rationestimated above. We conclude that predation on ciliates andheterotrophic dinoflagellates was important for O.similis tosustain its population in our study area during the warm season.     

Effects of diffusion and upwelling on the formation of red tides

In this paper, records on the timing and location of specificred tides monitored once or twice a week in Mikawa Bay, Japan,are related to horizontal and vertical mixing rates determinedfrom a numerical model. Horizontal (K_h) and vertical (K_z) diffusioncoefficients, and upwelling velocities, were estimated usinga box model analysis. In the wind-mixed period and in the upperlayer during the stratified period, K_h was estimated to be ofthe order of 10² m² s^–1. During the stratified period,K_z was estimated to be of the order of 10^–5 m² s^–1.The upwelling velocity was calculated to be in the range 0.35–5.1m day^–1 with an average of 1.5 m day^–1. Comparisonbetween the literature values of the specific growth rate (µ)of the red tide-forming diatoms and calculated K_h values duringthe red tides show that diatoms which have a low µ cannotform red tides in a strongly diffusive environment, while specieshaving a high µ can form red tides even in a strong diffusiveenvironment. On the other hand, no clear relationship was foundbetween µ of the flagellate group and K_h, although theflagellate group formed red tides even in severe diffusive conditions.From the comparison between the literature values of sinkingrate and swimming speed and the physical parameters associatedwith vertical processes, it was concluded that flagellates willform red tides, even in severe diffusive conditions, by usingtheir swimming ability, while diatoms form red tides by theirhigh growth rates with the aid of vertical diffusion and theupwelling movement of water.     

The colonial cyanobacterium Trichodesmium as a physical and nutritional substrate for the harpacticoid copepod Macrosetella gracilis

The pelagic harpacticoid copepod Macrosetella gracilis usesthe colonial cyanobacterium Trichodesmium not only as a physicalsubstrate for juvenile development, but also as a food source.By associating itself with a buoyant colonial cyanobacterium,M.gracilis has developed a successful mode of life for existencein the plankton. Further evidence of M.gracills' dependenceon Trichodesmium as a physical substrate is demonstrated bypreviously undescribed microscopic observations of a gravidM.gracilis female attaching eggs to a Trichodesmium colony.Shipboard experiments investigating the ingestion and assimilationof Trichodesmium carbon (C) were conducted in September 1991and January/February 1992 in waters of the Bahamas and the Caribbean,respectively. Macrosetella gracilis not only ingested, but rapidlyincorporated, cyanobacterial organic matter into its own cellularmaterial. Utilization of ingested Trichodesmium by M.graciliswas investigated by assessing the metabolic partitioning andincorporation of ¹⁴C-labelled Trichodesmium into copepod lipids,proteins, polysaccharides and low-molecular-weight (LMW) compoundsusing sequential biochemical fractionation techniques. Despitevariations in grazing rates between the two sites and times(September 1991,0.017 µg C^* µg^–1 C h^–1;January 1992, 0.134 µg C ^* µg^–1 C h^–1,the partitioning of incorporated C into the different biochemicalfractions was relatively consistent. There was rapid assimilationof ingested C into the LMW ({small tilde}60%) and polysaccharidefractions ({small tilde}30%) in the first few hours, with asubsequent increase in the percent C incorporated into protein.On average, {small tilde}21% of the Trichodesmium C ingestedby M.gracilis was assimilated. Therefore, M.gracilis is an importantsecondary link in the food web of oligotrophic waters whereTrichodesmium is abundant.     

Copepod abundance in the western Irish Sea: relationship to physical regime, phytoplankton production and standing stock

The distinct patterns of stratification in the North Channeland stratified region of the western Irish Sea influence theseasonal abundance of phytoplankton. The 3–4 month productionseason in the stratified region was characterized by productionand biomass peaks in the spring (up to 2378 mg C m² day^–1and 178.4 mg chlorophyll m^–2) and autumn (up to 1280 mgC m^–2 day^–1 and 101.9 mg chlorophyll m^–2).Phytoplankton in the North Channel exhibited a short, late productionseason with a single summer (June/July) peak in production (4483mg Cm^–2 day^–1) and biomass (–160.6 mg chlorophyllm^–2). These differences have little influence on copepoddynamics. Both regions supported recurrent annual cycles ofcopepod abundance with similar seasonal maxima (182.8–241.810³ind. m^–2) and dominant species (Pseudocalanus elongatusand Acartia clausi). Specific rates of population increase inthe spring were 0.071 and 0.048 day¹ for the North Channel andstratified region, respectively. Increased copepod abundancein the stratified region coincided with the spring bloom, andwas significantly correlated with chlorophyll standing stock.Increased copepod abundance preceded the summer production peakin the North Channel. This increase was not correlated withchlorophyll standing crop, suggesting that a food resource otherthan phytoplankton may be responsible for the onset of copepodproduction prior to the spring bloom. Hetero-trophic microplanktonas an alternative food source, and advection of copepods fromthe stratified region, are proposed as possible explanationsfor copepod abundance increasing in advance of the summer peakin primary production.     

Effects of prey motility and concentration on feeding in Acartia tonsa and Temora longicornis: the importance of feeding modes

Feeding experiments were conducted with the ambush-feeding copepodAcartia tonsa and the feeding-current-generating copepod Temoralongicornis. The copepods were offered a mixed diet of the dinoflagellateHeterocapsa triquetra and the ciliate Balanion comatum of similarcell size. The dinoflagellate was offered at a constant concentrationof 10–15 cells mL^–1, whereas the ciliate was offeredat a variety of concentrations, ranging from 7 to 57 cells mL^–1.Copepods with different feeding modes possess different mechanismsfor prey detection, suggesting that the two copepods would responddifferently to the two prey types. Both copepods had significantlyhigher clearance rates on the highly motile ciliate than onthe less motile dinoflagellate. In encounters between A. tonsaand its prey, we argue that this is due to the higher hydromechanicalsignal generated by the ciliate. The advection feeding copepodT. longicornis fed on the two prey according to their relativeconcentrations; in this case, we suggest that although B. comatumis capable of detecting feeding-current-generating predators,the feeding current velocity generated by T. longicornis isgreater than the escape velocity of this ciliate.     

Light, temperature and nitrogen as interacting factors affecting diel vertical migrations of dinoflagellates in culture

Diel vertical migrations of the marine dinoflagellates Gonyaulaxpolyedra Stein and Ceratium furca (Ehr.) Clap, et Lachm. werefollowed in a laboratory tube (2.02 m x 0.25 m) under a 12:12hlight:dark cycle. The effects of temperature stratification,two levels of surface irradiance and nitrogen depletion on patternsof vertical migrations were examined. At temperatures between22–26°C with small temperature gradients, both speciesmigrated at a rate of 0.7 –1.0 m h^–1. Steeper thermoclines(ca. 0.8°C 0.1 m^–1) with temperatures below ca. 20°Ccaused a marked decrease in swimming speed which resulted inaccumulations of cells in these thermocline regions. Under conditionsof nutrient sufficiency both algae migrated into the surfacelayers at irradiance values of over 1000 µE m^–2s^–1. Increasing nitrogen depletion caused the downwardmigration of both algae to commence progressively earlier inthe day and before the end of the light period. The earlierdownward migrations enabled a more complete descent throughthe thermocline. Nitrogen depleted cells of Gonyaulax continuedto undertake vertical migrations but avoided high irradiancesthus forming subsurface maxima at irradiance levels close to150 µE m^–2 s^–1. Ceratium cells which exhaustedboth inorganic nitrogen and phosphorus ceased to migrate accompaniedby a large change in cellular fluorescence.     

In situ egg production rate of the planktonic copepod Acartia steueri in Ilkwang Bay, southeastern coast of Korea

Egg production rate (EPR) of the copepod Acartia steueri wasinvestigated by in situ incubation in Ilkwang Bay, Korea. EPRranged from 3.8 to 10.1 eggs female^–1 d^–1, and weight-specificgrowth rate decreased with increasing body weight of the adultfemale.     

Ammonium release by juveniles and adult females of the subtropical marine copepod Eucalanus pileatus

Release rates of ammonium by nauplii, copepodid stages (CIIand CIV) and adult females of the marine copepod Eucalanus pileatusat 0.1 and 3.0 mm³ 1^–1 of the diatom Thalassiosira weissflogiiwere determined at 20°C. When food was abundant, animalsof all stages released ammonium at similar rates per unit ash-freedry weight [24–35 nmol NH₄(mg AFDW)^–1 h^–1on average]. At low food levels, CIVs and adult females releasedammonium significantly more slowly than did the naupliior CIIs[28 and 24 versus 51 and 50 nmoles(mg AFDW)^–1h^–1].Because they weighed less (50%), low-food nauplii and CIIs hadhigher calculated weight-specific excretion rates, than high-foodones of the same stage but release rates per copepod were similarin the two food regimens. In contrast to the early life stages,the CIVs and adult females released less ammonium per copepodin the low-food than in the high-food environment. ¹GLERL - Contribution No. 380     

Detection of infrasonic water oscillations by copepodids of Lepeophtheirus salmonis (Copepoda Caligida)

The cues that trigger infection of fish by parasitic copepodsare largely unknown. We show that copepodids of the parasiticcopepod Lepeophtheirus salmonus respond to uniform, linear accelerations,which are similar to those found in front of a swimming fish.Copepodid responses to vibrations at 1, 3, 5 and 10 Hz frequencywere filmed and analysed. The animals were stimulated in a completelywater-filled, clear perspex chamber, which was suspended likea swing in four wires from a steel frame. The chamber was movedby a vibrator which was fed amplified signals from a sine waveoscillator. On stimulation, copepodids responded by executingswimming bursts of 1–3 s duration. There was no apparentpreferred swimming direction. Sensitivity was highest at 3 Hz,with a threshold value of 5 x 10^–3 m s^–2 (rms).At 1 Hz the threshold was <6 dB higher, and sensitivity wasmarkedly reduced at 10 Hz, where the threshold was 1.8 x 10^–1m s^–2 rms. These results indicate that the copepodidsmay react to the near-field accelerations produced within centimetresof a swimming fish. Acceleration sensitivity may therefore bea cue that triggers high-speed swimming and subsequent infestationof the host. If this ability is present in holoplanktonic copepods,it may facilitate detection and escape from predatory fish.     

Infection of Coscinodiscus spp. by the parasitoid nanoflagellate Pirsonla diadema: I. Behavioural studies on the infection process

The investigation of successive steps involved in the infectionprocess of the marine diatoms Coscinodiscus granii and Coscuwdiscuswailesii by the host-specific parasitoid nanoflagellate (PNF)Pirsonia diadenw showed that flagellates reacted chemokJinokineticallywith changes of swimming pattern to the presence of a host diatom.Chemosensory stimulation appeared to induce readiness for infection,whereas attachment and penetration of the diatom cell wall wasinduced by a mechanosensory response to morphological featureson the diatom frustules. The mean swimming speed of P.diademaflagellates decreased during their infective lifetime of 3 daysfrom an average of 78 µm s^–1 to 51 µm s^–1while the frequency of small loops in the swimming pattern increasedfrom 0.8 to 6.3 loops min^–1. At high Cgranii densities,an epidemic was delayed. It is suggested that this could becaused by overlapping gradients of extracellular material releasedby the diatoms which impaired the sensing of spatial gradientsby PNF and, therefore, the location of hosts.     

Trophodynamics of the plankton community at Dogger Bank: predatory impact by larval fish

The trophodynamics of a coastal plankton community were studied,focusing on fish larvae and their copepod prey. The major objectiveswere to describe distributional overlap and evaluate the predatoryimpact by larval fish. The study was carried out across DoggerBank in the North Sea, August-September 1991. Sampling transectscrossed tidal fronts off the Bank and plankton at all trophiclevels showed peak abundance within frontal zones. Also Verticallythere was a significant overlap in distributional patterns ofthe plankton. Seven species of fish larvae were abundant, ofthese sprat (Sprattus sprattus) dominated. The abundance ofone group of fish larvae peaked in the shallow water close tothe Bank, whereas other species, including sprat, were foundin deeper water. Prey preference and predation pressure of fishlarvae were assessed using information on prey sizes and growthrates of larvae and the copepod prey. We estimated larval removalof preferred prey sizes to 3–4% day^–1, counterbalancedby a 3–7% day^–1' replenishment from copepod productionand growth. Additional predation pressure on copepods by aninvertebrate predator was estimated to 1–3%day^–1.In conclusion, the dynamics of fish larvae and other zooplankterswere closely linked. At peak abundances of fish larvae (>35mg dry weight m^–2), the accumulated predation on specificsize ranges of copepods, exerted by larvae and other predators,could exceed the ability of copepod replenishment and intra-/interspecificcompetition among predators might take place.     

Copepod daily egg production and growth rates in Bahia Magdalena, Mexico

The hydrography, chlorophyll (Chl) a and egg production of thecopepods Paracalanus parvus (Claus), Acartia lilljeborgii Giesbrecht,Acartia clausi Giesbrecht and Centropages furcatus were estimateddaily between 7 February and 5 March 1998 in Bahía Magdalena,Baja California Sur, México. Temperature was homogeneousthroughout the water column during the study (20°C). Positiveanomalies of the sea surface temperature were recorded 10 monthsbefore and during the sampling period compared with a temperature–timeseries, 1982–1989. Chlorophyll a concentration indicatedoligotrophic conditions with <10 Chl a mg m^–2 from15 m depth to the surface during the first half of the study,with a pulse of moderate concentration in the second part. Theegg production of these copepod species was usually suboptimal,and not correlated with Chl concentration or temperature. Eachgenus responded differently to Chl a and to environmental variables.The rate of input of turbulent kinetic energy to the ocean bythe winds, indicated by the cube of the wind speed, was negativelycorrelated to copepod egg production, suggesting that turbulencecan disperse phytoplankton patches and may affect the carboninput to these copepod populations. Turbulence and a previouslong warming event observed several months before the winterseason were probably the most important factors in limitingcopepod production and growth rates.     

The relative importance of food and temperature to copepod egg production and somatic growth in the southern Benguela upwelling system

The fecundity and somatic growth rates of Calanus agulhensisand Calanoides carinatus, the dominant large calanoid copepodsin the southern Benguela upwelling system, as well as the fecundityof several other common copepods, were measured between Septemberand March of 1993/94 and 1994/95. Mean egg production of mostcopepods was low at >30 eggs female^-1 day^-1 {Calanoides carinatus23.7, Calanus agulhensis 19.0, Neocalanus tonsus 16.1 and Rhincalanusnasutus 26.1), whereas the mean fecundity of Centropages brachiatuswas significantly greater (83.6 eggs female^–1 day^-1).This study also presents the first comprehensive field estimatesof the fecundity of Nanno-calanus minor (mean: 26.1 eggs female^–1day^–1, range: 0.0–96.2 eggs female^–1 day^–1)and of somatic growth of N6 and all copepodite stages of Calanoidescarinatus (decreasing from 0.58 day^–1 for N6 to 0.04 day^–1for C5). Somatic growth rates of Calanus agulhensis also declinedwith age: from 0.57 day1 for N6 to 0.09 day1 for C5. Data ongrowth rates were used to assess the relative importance offood [as measured by total chlorophyll (Chi) a concentration],phytoplankton cell size (proportion of cells >10 µm)and temperature to the growth of copepods. Multiple regressionresults suggested that fecundity and somatic growth rates werepositively related to both Chi a concentration and phytoplanktoncell size, but not to temperature. Although it was not possibleto separate the effects of Chi a concentration and phytoplanktoncell size, data from previous laboratory experiments suggestthat copepod growth is not limited by small cells per se, butby the low Chi a concentrations that are associated with theseparticles in the field. Despite growth not being directly relatedto temperature, a dome-shaped relationship was evident in somespecies, with slower growth rates at cool (<13°C) andwarm (>18°C) temperatures. The shape of this relationshipmirrors that of Chi a versus temperature, where poor Chi a concentrationsare associated with cool and warm temperatures. It is concludedthat the effect of food limitation on growth of copepods outweighsthat of temperature in the southern Benguela region. Sourcesof variability in relationships between growth and Chi a concentrationare discussed.