Feeding of planktonic rotifers on ciliates: a method using natural ciliate assemblages labelled with fluorescent microparticles

A method was developed to allow direct measurements of predationexerted by metazooplankton on ciliates. The method relied onthe use of ciliates labelled with fluorescent microparticles(FMP). Optimal labelling conditions were determined with ciliatesfrom cultures (Tetrahymena pyriformis) and with natural ciliateassemblages sampled in a river. Labelled T. pyriformis wereused as tracer food to determine gut passage time (GPT) andingestion rates of the rotifer Brachionus calyciflorus in thelaboratory. Predation of metazooplankton from the lowland riverMeuse (Belgium) was determined by labelling natural assemblagesof ciliates and using them as tracer food for metazooplankterssampled in the river. Optimal labels of ciliates, i.e. sharpdistribution of FMP in cells, were obtained with short incubations(10 min) and low FMP concentrations (1 x 10⁵ mL^–1). GPTvaried between 30 and 45 min for B. calyciflorus and from 25up to >35 min for rotifers from the river. The ingestionrate of B. calyciflorus fed with T. pyriformis was 3.3 ±0.6 ciliate rot^–1 h^–1, i.e. 1.4 ± 0.3 ngCrot^–1 h^–1. Metazooplankton species for which theingestion of ciliates could be measured were the rotifers Keratellacochlearis, Euchlanis dilatata and Synchaeta spp. Ingestionrates measured ranged from 0.4 to 12.5 ngC rot^–1 h^–1.The method proposed proved to be useful in estimating the predationof microplankton on ciliates in semi- in situ conditions; infurther developments, labelled natural assemblages of ciliatescould be used for in situ incubations with the Haney chamber.     

Laboratory-measured grazing and ingestion rates of the salp, Thalia democratica Forskal, and the doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

Grazing and ingestion rates of laboratory-born Thalia democraticaaggregates and Dolioletta gegenbauri gonozooids, phorozooidsand oozooids were determined while fed Isochrysis galbana (4–5µm diameter) alone or in combination with Peridinium trochoideum(16–18 µm diameter) at concentrations of 0.15–0.70mm³ x 1^–1. Grazing rates (ml x zooid^–1 x 24 h ^–1)ranged from 10 to 355, and at zooid weights greater than 5 µgcarbon were in order oozooid > gonozooid > aggregate.Grazing rates increased exponentially with increasing zooidweight. Weight-specific grazing rates (ml x µgC^–1x 24 h^–1) were independent of the four-fold initial foodconcentration. Mean weight-specific grazing rates increasedlinearly with increasing zooid weight for the aggregates andoozooids, but gonozooid mean rates were independent of zooidweight. Aggregate and gonozooid ingestion rates (10⁶ µm³x zooid^–1 x 24 h^–1) ranged from 4 to 134 while oozooidrates ranged from 3 to 67. All ingestion rates were independentof the initial food concentration but increased linearly withincreasing zooid weight at similar rates. All mean weight-specificingestion rates (ml x µgC^–1 x 24 h^–1) wereindependent of zooid weight. The mean aggregate daily ration(µgC ingested x µg body C^–1) was 59% and themean doliolid ration was 132%. Field studies indicate that normalconcentrations of D. gegenbauri in the Georgia Bight clear theirresident water volume (1 m³) in about 4 months, but that highlyconcentrated, swarm populations which occur along thermohalinefronts clear their resident water volume in less than 1 day. ¹Current address: MacLaren Plansearch Ltd., P.O.Box 13250, sta.A.,St.John's, Nfld. A1B 4A5     

Predation impact of Cyclops vicinus on the rotifer community in Lake Constance in spring

The predation impact of Cyclops vicinus on rotifers was studiedunder near-natural conditions in small enclosures to evaluatewhether copepod predation is responsible for the decline ofrotifers in Lake Constance in spring. Cyclops vicinus fed selectivelyon Synchaeta spp.; Keratella and Polyarthra spp. were not selectedfor. Predation rates increased with prey density up to a maximumof 37 Synchueta day^–1 at a density of 1.6 x 10⁶ Synchaetam^–2, i.e. at -1200 Synchaeta l^–1. Calculation ofcropping rates suggests that Cyclops alone can control the abundanceof Synchaeta in spring, i.e. that mainly Cyclops is responsiblefor the decline of Synchaeta species in Lake Constance in May.     

Growth and grazing rates of Protoperidinium hirobis Abe, a thecate heterotrophic dinoflagellate

Growth and feeding rates of a laboratory-reared small thecateheterotrophic dinoflagellate, Protoperidinium hirobis Abè,grown on the diatom Leptocylindrus danicus, were measured inbatch cultures. Ingestion rates were determined directly bythe enumeration of empty diatom frustules produced by dinoflagellatefeeding. Both growth and feeding rates saturated at diatom concentrationsof {small tilde} 10⁴ cells ml^–1, and reached maximum valuesof 1.7 divisions day^–1 and 23 diatoms grazer^–1 day^–1,respectively. This rate of cell division is notably high comparedto photosynthetic dinoflagellates, which seldom grow fasterthan 1 division day^–1. A maximal clearance rate of 0.5µl h^–1 was measured. Mean cell size varied proportionallywith food abundance, with food-saturated cells having doublethe mean volume of food-depleted cells. Tuning of cell divisionand grazing rate patterns were also examined; while mitosisoccurred chiefly during the dark period, no diel variationsin feeding rate were detected. These rates represent the firstdirect growth and ingestion measurements to be made for a thecateheterotrophic dinoflagellate. They serve to underscore one functionthese dinoflagellates perform within the microzooplanktonicfood web: that of transforming large diatoms into particlesmore easily ingested by microzooplankters.     

Diel variations in gut pigment content, diel vertical migration and estimates of grazing impact for copepods in the southern Benguela upwelling region in October 1987

The gut fluorescence technique was used to estimate ingestionand filtration rates of the adult female copepods Paracalanusparvus, Cenlropages brachiatus and Calanus austrails, and copepoditestages 3, 4 and 5 of C.australis in the southern Benguela upwellingregion. During the study period chlorophyll concentrations withinthe upper 20 m of the water column were high, 5 µg I^–1in mid-shelf waters and 15–30 µg I^–1 in innershelf waters. Copepod gut pigment content was low and constantduring the day then increased sharply during the first 2 h aftersunset. Gut pigment content was 2–6 times higher duringthe night compared with daytime values. Small non-migratingcopepods (Paracalanus parvus) showed the smallest diel differencein gut pigment content and large migrating copepods (Centropagesbrachiatus and Calanus australis) the largest difference. Eggproduction rates were 20 and 50% of maximum at the mid-shelfand inner shelf stations respectively, suggesting food-limitation.Comparison of ingestion rates calculated from egg productiondata with ingestion rates calculated from gut pigment data suggestedthat the copepods were feeding omnivorously at the inner shelfstations but herbivorously at the mid-shelf stations. Assumingthat all of the phytoplankton was available as food, the nearshorecopepod assemblage grazed {small tilde}1% of the standing cropeach day, and the mid-shelf assemblage grazed 5% day^–1.Because of errors and uncertainties associated with the gutfluorescence technique, the feeding impact could be underestimatedby 2–4-fold. We discuss several approaches which couldlead to more precise estimates of feeding rates. ³Present address: Marine Sciences, SUNY, Stony Brook, NY, 11794-5000,USA     

Reproduction rates and secondary production of three species of the rotifer genus Synchaeta in the estuarine Potomac River

Rotifers are a relatively well-studied component of lacustrinesystems but their role is only poorly understood in estuaries.Three species of the genus Synchaeta—S. baltica, S. triophthalmaand S.cecilia—dominate the cold-water assemblage of rotifersin Chesapeake Bay. Laboratory experiments were conducted todetermine the temperature dependence of egg development time(EDT) for each species; EDT varied over an approximate rangeof 90–9 h as temperature (T) varied from 2 to 22°C.The EDT/temperature relationships could be closely fitted bya simple polynomial equation of the form log(EDT) = a + b(logT) + c(log T)² for each species. Natural populations of thesethree rotifers were sampled during a cruise in the Potomac River(7–11 March 1983). Estimates of specific reproductiverates (b) were calculated based on the previously defined EDT/temperaturerelationship and the observed ratio of eggs/rotifers for eachspecies. The two most abundant species, S.triophthalma and S.cecilia,showed a clear dependence of b on the observed chlorophyll aconcentrations. Maximum reproductive rates ({small tilde}0.015h^–1) were attained only at relatively high phytoplanktondensities within a bloom of Heterocapsa triquetra where thechlorophyll a concentrations exceeded 10 µg l^–1.Estimates of secondary production suggest that Synchaeta spp.may contribute to the trophic flow of carbon in this systemwith a significance at least similar to that of the planktoniccopepods.     

Gut clearance and pigment destruction in a herbivorous copepod, Acartia tonsa, and the determination of in situ grazing rates

Gut clearance rates of starving and continuously feeding Acartiatonsa were estimated. During the initial 30 min the rates weresimilar (0.045 and 0.048 min^–1, respectively; 14°C)but thereafter starving animals expelled the remains of theirgut contents at half the rate (0.019 min^–1) of fed ones(0.048). Pigment destruction was estimated by (i) incubationexperiments over 3–4 days, (ii) silica to pigment ratioin algae and faeces and (iii) by gut filling experiments. Theincubations showed that 8% of the ingested pigments were destroyedto nonfluorescent residues during gut passage. The silica topigment ratio method gave an average of 11 % (1 –24) destructionand gut-filling experiments showed no systematic differencebetween ingestion measured as gut filling rate (fluorescence)and particle reduction. ¹Present address: Kristineberg Marine Biological Station, S-45034 Fiskebäckskil, Sweden     

Experimental studies into the feeding biology of rotifers in brackish water

Mass developments of rotifers of the genus Brachionus, and especiallyof B.quadridentatus, occur regularly in the largely hypertrophicchain of shallow waters (‘boddens’) south of theDarss-Zingst peninsula (Southern Baltic). Interest in the autecologyof the species is, therefore, considerable. Various food sourceswere used in laboratory experiments to ascertain the food requirementsof B.quadridentatus, determine its filtration and ingestionrates, and assess its food particle size-selection ability.Growth experiments showed that the chlorophyceans Nannochlorissp. and Chlorella vulgaris possess considerable nutritionalvalue for the species, whereas abundances declined when Microcystisfirma, detritus from Enteromorpha sp. and only bacteria (Pseudomonas),respectively, were provided as food sources. Filtration ratesvaried between 0.02 and 1.73 µl ind.^–1 h^–1,and ingestion rates between 121 and 5560 cells ind.^–1h^–1, depending on the filtration rate and algal concentration.Investigations into food particle size selection using fluorescentlatex particles revealed that particle size influences foodparticle intake. When particles of different sizes were mixed,the animals showed a preference for the larger particles andingested the smaller ones with a diameter of 1–2 µmless efficiently. The brackish water species Brachionus plicatiliswas studied besides B.quadridentatus in all experiments. Theformer species proved to be superior both in its range of utilizableparticle sizes and its growth rate. The experiments with laboratorycultures were backed up by studies performed with various rotiferspecies taken from natural populations.     

Feeding and growth rates of the doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

The goal of this research is to enhance our knowledge of thecontributions of doliolids to the planktonic community as consumersand secondary producers. The objectives are to quantify feedingand growth rates of Dolioletta gegenbauri gonozooids at fourfood concentrations and four temperatures in order to determinetheir impact as grazers throughout the water column. Althoughdoliolids are abundant in numerous regions of the coastal ocean,and are considered to be major planktonic grazers, data on ratesof feeding and growth are scarce. Laboratory experiments wereconducted at 16.5, 20, 23.5 and 26.5°C to quantify removalof a 50:50 volumetric concentration of Thalassiosira weissflogiiand Rhodomonas sp. at four different food concentrations of20, 60, 160 and 390 µg C l^–1. Results from theseexperiments suggest that clearance rates are similar at concentrationsfrom 20 to 60 µg C l ^–1, and decrease as the foodconcentrations increase to 160 and 390 µg C l ^–1.The ingestion rates increase over a range of phytoplankton concentrationsfrom 20 to 160 µg C l ^–1, then decrease when abnormallyhigh concentrations of 390 µg C l ^–1 are offered.Clearance and ingestion rates increase as temperature increasesfrom 16.5 to 26.5°C. The exponential growth rates rangefrom k = 0.2–0.7, with the lowest rates occurring at thehighest food concentration. Growth rates increase with increasingtemperature from K = 0.1–0.3 at 16.5°C to 0.45–0.7at 26.5°C. In each case, the small- and medium-sized zooidshad higher growth rates than the larger gonozooids. These resultssuggest that doliolid feeding and growth rates are a functionof environmental food concentrations and temperatures, and implythat they can be important consumers in a changing neritic environment.     

Comparative growth rates and yields of ciliates and heterotrophic dinoflagellates

Growth rates, ingestion rates and grazer yields (grazer volumeproduced/prey volume consumed) were measured for six protozoanspecies (ciliates: Favella sp., Strombidinopsis acuminatum,Uronema sp.; heterotrophic dinoflagellates: Amphidinium sp.,Gymnodinium sp., Noctiluca scintillans) in laboratory batchculture experiments. Comparative growth data indicate that theprymnesiophyte Isochrysis galbana, the prasinophyte Mantoniellasquamata, two cryptophyte species and several autotrophic dinoflagellatespecies were suitable foods for these grazers. When grown onoptimized diets at 13C, maximum ciliate growth rates (range0.77–1.01 day^–1 uniformly exceeded maximum heterotrophicdioflagellate growth rates (range 0.41–0.48 day^–1).A compilation of published data demonstrates that this growthrate difference persists across a range of ciliate and dinoflagellatetaxa and cell sizes. Comparison of volume-specific ingestionrates and yields for the six species studied here showed thatthere was no single explanation for this growth rate disparity.Heterotrophic dinoflagellates exhibited both low ingestion ratesand, in one case, low yields; ciliates were able to achievehigher growth rates via either higher ingestion rates or higheryields, depending on ciliate species. Volume yield increasedover time throughout the exponential growth phase in nearlyall experiments, suggesting variation in response to changingfood concentrations or long-term acclimation to culture conditions.Higher maximum ciliate growth rates mean that these grazershave the potential to exercise tighter control over incipientblooms of their prey than do heterotrophic dinoflagellates.     

Trophodynamics of the scyphomedusae Aurelia aurita. Predation rate in relation to abundance, size and type of prey organism

Ephyra larvae and small medusae (1.7–95 mm diameter, 0.01–350mg ash-free dry wt, AFDW) of the scyphozoan jellyfish Aureliaaurita were used in predation experiments with phytoplankton(the flagellate Isochrysis galbana, 4 µm diameter, {smalltilde}6 x 10^–6 µg AFDW cell^–1), ciliates (theoligotrich Strombidium sulcatum, 28 µm diameter, {smalltilde}2 x 10^–3 µg AFDW), rotifers (Synchaeta sp.,0.5 µg AFDW individual^–1) and mixed zooplankton(mainly copepods and cladocerans, 2.1–3.1 µg AFDWindividual^–1). Phytoplankton in natural concentrations(50–200 µg C I^–1) were not utilized by largemedusae (44–95 mm diameter). Ciliates in concentrationsfrom 0.5 to 50 individuals ml^"1 were consumed by ephyra larvaeand small medusae (3–14 mm diameter) at a maximum predationrate of 171 prey day^–1, corresponding to a daily rationof 0.42%. The rotifer Synchaeta sp., offered in concentrationsof 100–600 prey I^–1, resulted in daily rations ofephyra larvae (2–5 mm diameter) between 1 and 13%. Mixedzooplankton allowed the highest daily rations, usually in therange 5–40%. Large medusae (>45 mm diameter) consumedbetween 2000 and 3500 prey organisms day^"1 in prey concentrationsexceeding 100 I^–1. Predation rate and daily ration werepositively correlated with prey abundance. Seen over a broadsize spectrum, the daily ration decreased with increased medusasize. The daily rations observed in high abundance of mixedzooplankton suggest a potential ‘scope for growth’that exceeds the growth rate observed in field populations,and this, in turn, suggests that the natural populations areusually food limited. The predicted predation rate at averageprey concentrations that are characteristic of neritic environmentscannot explain the maximum growth rates observed in field populations.It is therefore suggested that exploitation of patches of preyin high abundance is an important component in the trophodynamicsof this species. ¹Present address: University of Bergen, Department of MarineBiology, N-5065 Blomsterdalen, Norway     

Effect of temperature on growth and ingestion rates of Favella sp

This study describes the effect of temperature on the growthand ingestion rates of the tintinnid, Favella sp. cultured withthe dinoflagellate Heterocapsa triquetra. In vivo fluorescencewas used to monitor the change in density of the H. triquetrapopulation over 4- to 5-day periods in control tubes containingonly algae, and in experimental tubes containing algae and tintinnids.A ‘switchover point’ occurred in the temperaturedependency of the growth rate such that below 11.4°C, H.triquetra grew more quickly than Favella sp. and above thistemperature the situation was reversed. Ingestion rates of Favellaon H. triquetra were found to be temperature dependent in anonlinear fashion. The rate doubled (from 2.5 to 5.3 cells animal^–1h^–1) between 11.4 and 16.4°C whereas there was nochange in ingestion rates between 8.0 and 11.4°C, or between16.4 and 21.1°C.     

Feeding and metabolism of the siphonophore Sphaeronectes gracilis

The in situ predation rate of the siphonophore Sphaeronectesgracilis was estimated from gut content analysis of hand-collectedsiphonophores and from laboratory data on digestion rates ofprey organisms. At daytime prey densities of 0.25 copepods 1^–1,S. gracilis was estimated to consume 8.1 – 15.4 prey day^–1siphonophore^–1. From data on abundances of siphonophoresand copepods, S. gracilis was estimated to consume 2–4%of the copepods daily. In laboratory experiments, ingestionrates averaged 13.8 prey day^–1 siphonophore^–1 atprey densities of 5 copepods 1^–1 and 36.9 at 20 copeods1^–1. This was equivalent to a specific ingestion rate(for both carbon and nitrogen) of –17% day^–1 and45% day^–1, respectively, while specific ingestion in situwas only 2% day^–1. Ammonium excretion averaged 0.095 µg-atsiphonophore^–1 day^–1 at 5 prey 1^–1, and 0.162at 20 prey 1^–1. The specific respiration (carbon) andspecific excretion (nitrogen as ammonium) were calculated tobe 3% day^–1 at the lower experimental food level, and5% day^–1 at the higher food level. ¹Contribution from the Catalina Marine Science Center No. 66. ²Present address: Dept. of Biology, University of Victoria,Victoria, B.C., Canada V8W 2Y2.     

Nitrogen regeneration by the subtropical marine copepod Eucalanus pileatus

Ammonium release rates by individual marine copepods (Eucalanuspileatus) were examined kinetically over successive 10-min intervalsafter the animals were exposed to three concentrations of thediatom Thalassiosira fluviatilis as food. Food concentrationsspanned those expected in the natural environment. "Well-fed"(3 mm³ T. fluviatilis l^–1) copepods released ammoniumsignificantly (p<0.05) faster than those fed zero or lowconcentrations of food, but differences were not dramatic. Meanexcretion rates (± SE) for animals removed from foodfor 18 –22 h [30 ± 6 nmol NH₄(mg ash free dry weight)^–1h ^–1] were 60% of those for "well-fed" animals [49 ±8 nmol NH₄ (mg ash free dry weight)^–1 h^–1]. Continuedhigh release rates after extended periods without food suggestthat E. pileatus must feed frequently in nature to maintainan adequate nitrogen balance. Depending on food concentration,animals released ammonium at rates ranging from 40 to > 100%of their N ingestion rates over the previous 18–22 h.Long-term (4–6 h) kinetic excretion experiments with "well-fed"animals indicated that, on average, release rates decreasedwith time after food removal, but patterns varied among individualcopepods. In addition to ammonium release, o-phthalaldehydereactive amino acid nitrogen was occasionally released by E.pileatus in large "spurt events" lasting from 20 to 60 min. ¹GLERL Contribution No. 283     

Growth and ingestion rates of larval fish populations in the coastal waters of Israel

Clupeoid larvae were collected on eight cruises between February1984 and February 1985 in the coastal waters of Israel. Fromanalysis of daily growth increments of otoliths, growth ratesof the abundant clupeoids, Engraulis encrasicolus, Sardina pilchardusand Sardinella aurita were found to be 0.55 mm day^–1,0.67 mm day^–1 and 0.60 mm day^–1, respectively, duringthe first month after hatching. Ingestion rates were estimatedusing an equation from the literature relating ingestion andgrowth of larval fish. Ingestion calculated for populationsof fish larvae in pelagic waters ranged from 0 to >23 mgC m^–2 day^–1 with maximum rates observed in April.Annual ingestion by larval fish at a pelagic station near Haifawas calculated to be 2.2 g C m^–2 year^–1, 10–20%of annual primary production estimated from ¹⁴C uptake.     

Ontogeny of growth, respiration and feeding rate of the freshwater calanoid copepod Eudiaptomus graciloides

The calanoid copepod, Eudiaplomus graciloides, was reared fromegg to adult on uni-algal diets (0.1. 0.5 and 2.5 mg dry wt1^–1) using the green alga, Chlamydomonas reinhardtii,as food, or on a mixed diet consisting of Lake Esrom water filteredthrough a plankton net with pore size 45 µm and supplementedwith C. reinhardtii (2.5 mg dry wt 1^–1). On the mixeddiet at 21.0°C growth in body dry wt (W, µg dry wt)was exponential, and the growth constants were 0.21 day^–1in the early to mid juvenile stage (N1 - C4) and 0.11 day^–1in the late juvenile to early adult stage (C4-A). At 14.5°Cthe corresponding growth rate constants were 0.10 and 0.08 day^–1.Similar growth rates were found at uni-algal concentrationsof 0.5 and 2.5 mg dry wt I^–1, and it was argued that thethreshold concentration for growth in Eudiaptomus was closeto 0.1 mg dry wt I^–1. The clearance (C, ml h^–1)of copepodites was measured on the uni-algal diets. The constantsof the regression (C = aW^b) were: a = 0.125, b = 0.858 (2000C. reinhardtii ml^–1), a = 0.068, b = 0.849 (10 000), a= 0.028, b = 0.875 (50 000). Ingestion rates were calculatedfrom the clearances and the average algal concentrations. Atthe three food levels the average daily rations were 30, 67and 125% of body dry wt. The respiration rate (R, nl O₂ h^–1)was measured in individuals reared on the mixed diet. The constantsof the regression (R = aW^b) were: a = 4.82, b = 1.07 (nauplii,14.5°C), a = 4.17, b = 0.904 (copepodites and adults, 14.5°C),a = 6.87, b = 0.757 (copepodites and adults, 21.0°C). Nosignificant difference in the respiration rate of copepoditesreared on uni-algal diets and the mixed diet could be demonstrated.Energy budgets were calculated. The assimilation efficiencyand the gross growth efficiency of copepodites decreased markedlywith increasing food concentration, the net growth efficiencyvaried from an average of 0.44 at the lowest algal concentrationto 0.60 on the mixed diet. The results are discussed in relationto previous findings with both freshwater and marine copepods.     

Rates of ingestion and their variability between individual calanoid copepods: direct observations

The goals of this study were to determine rates of ingestionand fecal pellet release, and their variability, for individualplanktonic copepods over extended periods of time (>20 min).Ingestions and rejections of individual cells of the diatomThalassiosira eccentrica by adult females of the calanoid Paracalanusaculeatus were directly quantified by observing individual copepodscontinuously at cell concentrations ranging from 0.1 toli mm³l^–1.Average ingestion rates increased with increasing food concentration,but were not significantly different between 0.3 and 1.0 mm³l^–1(9.8 and 32.7 µg Cl^–1) of T.eccentrica. Rates ofcell rejections were low and similar at 0.1 and 0.3, but weresignificantly higher at 1.0 mm³ l^–1. The coefficientsof variation for average ingestion rates of individual copepodshardly differed between food concentrations, ranging from 17to 22%, and were close to those for average fecal pellet releaseintervals which ranged from 15 to 21%. A comparison betweenindividuals at each food concentration found no significantdifferences at 1.0; at 0.1 and 0.3 mm³l^–1, respectively,ingestion rates of four out of five females did not differ significantlyfrom each other. Average intervals between fecal pellet releaseswere similar at 0.3 and 1.0 mm³l^–1 of T.eccentrica, butsignificantly longer at 0.1 mm³ l^–1. Fecal pellet releaseintervals between individuals were significantly different ateach food concentration; these significant differences wereattributed to rather narrow ranges of pellet release intervalsof each individual female. Potential sources/causes of variabilityin the sizes and rates of copepods in the ocean are evaluated. ³Present address: Great Lakes Environmental Research Laboratory,2205 Commonwealth Boulevard, Ann Arbor, Ml 48105, USA     

Feeding, growth and food conversion of the marine cladoceran Penilia avirostris

Ingestion and clearance rates, feeding behaviors and life historyvariables of the marine cladoceran Penilia avirostris were evaluatedover a range of food concentrations encountered in nature (0.01–3.0mm³ 1^–1 of Isochrysis galbana). Ingestion rates increasedand clearance rates decreased with increasing food concentration.No maximum feeding thresholds were observed over the range ofalgal concentrations offered. Weight-specific ingestion ratesdecreased with increasing body weight. Feeding behaviors suchas mandibular activity, abdominal claw rejections of cloggedfeeding structures and feeding appendage activity decreasedat a food level of 0.3 mm³ l^–1 of l. galbana. Peniliaavirostris had very poor survivorship at extremely low (0.01mm³ l^–1 and high (3.00 mm³ l^–1) food levels. Mortalitywas hardly affected at food levels of 0.03–1.0 mm³ l^–1Reproduction did not occur at food levels of     

Respiratory rates in the cladoceran Ceriodaphnia dubia in Lake Rotongaio, a monomictic lake

The experimentally measured oxygen consumption rate by the cladoceran,Ceriodaphnia dubia, showed a linear increase between 5 and 20°C.Oxygen consumption rates of C. dubia were estimated in situfrom respiratory electron transport system (ETS) activity inLake Rotongaio during summer stratification and winter mixing.Oxygen consumption was 0.002 µl O₂ animal^–1 h^–1in the hypolimnion and 0.076 µl O₂ animal^–1 h^–1in the epilimnion during stratification. Implications of respiredoxygen for metabolic carbon requirements are discussed.     

Autotrophic and heterotrophic nanoplankton in the diet of the estuarine copepods Eurytemora affinis and Acartia bifilosa

The ingestion of autotrophic and heterotrophic nanoplanktonby two estuarine copepods, Eurytenora affinis and Acarith bifilosa,was measured in various environmental conditions using the incubationmethod and epifluorescence microscopy. Egg production of thespecies was also deter mined in order to estimate their carbonrequirements. Assuming a gross efficiency of egg productionof 0.3, nanoplanktonic carbon ingested always met the carbonrequirements suggesting that, most of the time, other carbonsources could be unnecessaly. Nanoplankton ingestion by A.bifilosa(from 128 to 1693 cells ind.^–1 h^–1) was dominatedby autotrophic forms (60–97%) and was seriously affectedby high (>100 mg l^–1 suspended particulate matter (SPM)concentrations. Nanoplankton ingestion by E.affinis (from 300to 1049 cells ind^–1 h^–1) was relatively stable incomparison, but this latter species seemed to switch its grazingpressure from autotrophic to heterotrophic forms when SPM concentrationsincreased. Thus, two copepod species, living in the same estuary,presented two different feeding behaviours, probably to maximizeenergy input per unit of energy expenditure. Such differencescould contribute to the spatial and seasonal segregation ofthese species which is usually observed.