Effects of rotifers and ciliates on the growth and survival of Daphnia

Daphnia can suppress ciliates and rotifers through predationand interference competition, but it is not known whether thisproduces any direct benefit to Daphnia. We conducted survivorshipand cohort lifetable experiments to determine whether Daphniacan utilize ciliates and rotifers as food. Three species ofoligotrich ciliates (Halteria grandinella, Strobilidium gyransand Strobilidiumvelox) and one rotifer (Keratella cochlearis)were used. Lifetable experiments were conducted with a basallevel of algae (Cryptomonas sp.), plus either ciliates or rotifers,while survivorship experiments had only the rotifers or ciliates.Densities of 30 H.grandinella ml^–1, 50 S.gyrans ml^–1and 15 S.velox ml^–1 enhanced Daphnia pulex's populationgrowth rate 35–50% over controls with only algae. TenS.gyrans ml^–1 did not produce a significant change inDaphnia's growth rate. Densities of 100 and 300 K.cochlearis^–1 increased Daphnia population growth rates by II and10%, respectively. Both 10 and 50 S.gyrans ml^–1 enhancedDaphnia's survivorship compared to starved controls, but neither100 nor 300 K.cochlearis l^–1 enhanced its survivorship.The amount of enhancement of Daphnia growth rates by rotifersand ciliates is roughly proportional to the death rates imposedby Daphnia. The death rate imposed by Daphnia on rotifers isa function of both algal density and Daphnia size. Per unitbiomass, neither ciliates nor Keratella appear to be as nutritiousfor Daphnia as is Cryptomonas.     

Predation by ciliates on a metalimnetic Cryptomonas population: feeding rates, impact and effects of vertical migration

Deep algal maxima are frequently overlayed by dense populationsof ciliates, rotifers and crustaceans. This has been interpretedas evidence of heavy predation on the algae, although the impactof this predation has never been determined experimentally.We determined the vertical and seasonal distribution of thealga Cryptomonas phaseolus and its most relevant predators,the ciliates Coleps sp. and Prorodon sp., forming metalimneticmaxima in Lake Cisó. On several dates, in situ feedingrates of ciliates were determined by three independent methods:(i) epifluorescence counts of ingested algal cells togetherwith estimates of the food turnover time of the ciliates; (ii)in situ incubations with radioactively labeled algae: (iii)HPLC determination of alloxanthine content in the predator sizefraction. Feeding rates varied between 0.07 and 0.64 Cryptomonasciliate^–1 h^–1. We then calculated integrated predationon the algae. using the functional response of the ciliatesand the vertical distribution of each population. We found thateven though the ciliates were always food saturated, their predationimpact on Cryptomonas was not very large: as an average, 5–25%of the biomass of Cryptomonas was removed daily by the ciliates.Finally, we studied the effects of the diel vertical movementsof these populations on predation impact. By migrating intothe sulfide-rich hypolimnion during the night, Cryptomonas couldreduce its predation losses by 38%. Thus, the algae were protectedfrom predation during several hours of each diel cycle and maintaineda very large biomass throughout stratification, although thisresulted in a very slow growth. Slow growth, coupled to largebiomass, seems to be a general feature of metalimnetic accumulationsof organisms.     

Genetic Variation and Clonal Diversity of Psammochloa villosa(Poaceae) Detected by ISSR Markers

Genetic variation and clonal diversity of seven Psammochloavillosa(Poaceae) populations from northwest China were investigatedusing inter simple sequence repeat (ISSR) markers. Of the 84primers screened, 12 produced highly reproducible ISSR bands.Using these primers, 173 discernible DNA fragments were generatedwith 122 (70.5%) being polymorphic, indicating considerablegenetic variation at the species level. In contrast, there wererelatively low levels of polymorphism at the population levelwith the percentage of polymorphic bands (PPB) ranging from6.1 to 26.8. Analysis of molecular variance (AMOVA) showed thata large proportion of genetic variation (87.46%) resided amongpopulations, while only 12.54% resided among individuals withinpopulations. Clonal diversity was also high with 98 genets beingdetected from among 157 individuals using 12 ISSR primers. Theevenness of distribution of genotypes in P. villosa populationsvaried greatly, with all of the genotypes being local ones.No significant differences in genetic or clonal diversity werefound between populations in mobile or fixed dunes. The mainfactor responsible for the high level of differentiation amongpopulations and the low level of diversity within populationsis probably the clonal nature of this species, although selfingmay also affect the population genetic structure to some extent.The efficiency of ISSRs in identifying genetic individuals wasmuch higher than that of allozymes. An approximately asymptoticcorrelation was found between the number of genets detectedand the number of polymorphic loci used, suggesting that useof a high number of polymorphic bands is critical in genet identification.Copyright 2001 Annals of Botany Company Psammochloa villosa, ISSRs, genetic variation, clonal diversity     

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.     

Top-down effects of crustacean zooplankton on pelagic microorganisms in a mesotrophic lake

A series of single-factor in situ experiments was conductedin a mesotrophic lake in Brandenburg, North Germany, to studythe predatory impact of Eudiaptomus graciloides (adults, copepodites,nauplii), cyclopoid copepods (adult Diacyclops bicuspidatus,Thermocyclops oithonoides) and daphnids (adult Daphnia hyalina,Daphnia cucullata) on the microbial community (bacteria, autotrophicpicoplankton, flagellates, ciliates). All zooplankton speciestested reduced the ciliate community significantly and ingestionrates were always higher for ciliates in the 20–55 µmsize category as compared to smaller ciliates (10–20 µm).Adult E.graciloides, which exhibited the highest predatory impacton ciliates, differed from cyclopoids and daphnids by theirability to decimate ciliates to very low abundances. Ingestionrates of ciliates by the crustacean zooplankton followed thesequence E.graciloides > daphnids = cyclopoids = copepodites.While top-down control was evident for ciliates, top-down effectsdown to the autotrophic picoplankton and flagellates were mostlyrestricted to Daphnia-dominated treatments. Top-down effectswere never strong enough to produce negative bacterial growthrates. For all zooplankton tested, clearance rates for ciliatesexceeded those for phytoplankton. Besides the potential of thecrustacean zooplankton to influence the structure of ciliatecommunities, ciliates may contribute to the energy demands ofcopepods and daphnids, especially when phytoplankton resourcesare limited.     

Cyclops predation on ciliates: species.specific differences and functional responses

Experiments were conducted to measure to what extent cyclopoidcopepods ingest ciliated protists. Five freshwater ciliate species,ranging in size from 22 to 120 µm diameter, were testedwith two species of cyclopoids: Cyclops abyssorum and Cyclopskolensis. Ingestion rates were measured by radiolabeling ciliateswith ¹⁴C, and from these, functional response curves (the changein ingestion rate with changing cell densities) were constructed.Cyclopoids ingest ciliates with very high estimated maximalrates of >200 cells cyclopoid^–1 h^–1 However,there are large differences in ingestion rates that are notpredictable by the size of predator or prey. One ciliate speciesof intermediate size, Coleps hirtus, is nearly immune from cyclopoidpredation at all measured ciliate densities. Three other smallciliate species that move in rapid jumps elicit Honing type3 functional responses, with very little change in ingestionrates at low ciliate densities. Thus, while cyclopoids are capableof having a very considerable impact on ciliate populations,some ciliate species appear to have behavioral, morphologicalor chemical defenses to reduce their vulnerability. This callsinto question the practice of considering ciliates a homogeneousgroup when constructing food web models.     

Ecological Implications of Clonal Diversity in Parthenogenetic Morphospecies

Most parthenogenetic animal taxa which have been investigatedelectrophoretically, cytologically, or with tissue graftingtechniques are clonally diverse. I have examined data on multiclonalparthenogenetic populations using ecological diversity measuresto elucidate patterns of clonal coexistence. Analysis of a discretepopulation cage experiment on clones of Drosophila mercatorumrevealed monotonic decay of clonal diversity and evenness; however,in a continuous generation cage, clonal diversity appeared tostabilize. Clonal diversity and evenness fluctuated widely overtime in several multiclonal populations of Daphnia magna althoughno clonal extinction was observed. There were few spatial trendsin clonal diversity and evenness within parthenogenetic taxa.It is suggested that the degree of clonal differentiation, determinedby the mode of clonal origin, is important in determining whetheror not selection occurs among sympatric clones     

Experimental Approach to the Role of Protozoa in Aquatic Ecosystems

In enrichment batch experiments, samples from three water bodieswere alternatively supplemented by various amounts of organicmaterial and incubated at 20 C. Colpidium campylum reached itshighest total cell volumes in cultures with the highest initialtotal cell volumes in cultures with the highest initial concentrationsof organics; Cyclidium glaucoma preferred lower concentrations;and Glaucoma chattoni occupied the intermediate position. Noneof the species preferred any special type of organic material.In two-stage continuous-flow units, a mixed culture of bacteriawas kept in stage I and the clones of ciliates were maintainedin stage II. The interrelations between the total cell volumesof ciliates at various concentrations of bactopeptone were inaccordance with the results from the enrichment experiments.Since the growth of bacteria continued in the presence of ciliates,a four-stage apparatus was constructed in which a bacterialculture was raised and diluted in three stages before enteringthe culture ofColpidium. The bacterial growth in the presenceof Colpidium was not eliminated even by this arrangement, asdemonstrated by dosing antibiotics along with bacteria. An effectof ciliate metabolites on bacterial growth rate is suggested,completing a metabolic cycle in the bacteria-protozoa system.     

High abundance of picoplankton-ingesting ciliates during late fall in Lake Kinneret, Israel

Small, aloricate ciliates dominated the biomass of heterotrophicprotists throughout the water column at the end of the periodof stratification in Lake Kinneret, Israel The integrated biomassof cilates was 5–20 times that of heterotrophic flagellatesDuring incubation experiments, ciliate growth rates in cpilimneticwater corresponded to population doubling times of 9.6–19.4h, while flagellate populations showed no growth. Most of thealiates were small forms (10–30 µm long), includingscuticocihates, choreotnchs, Coleps spp. and Colpoda spp., andappeared to be consuming bacteria, coccoid cyanobacteria, and<5 µm eukaryotic algae. Grazing rates of cihate assemblageson picoplankton in the epilimnion, as determined by the uptakeof fluorescently labeled bacteria and cyanobactena, ranged from62 to 86 nl cell^–1 h^–1 Colpoda steini, isolatedfrom lakewater, grew on a cultured freshwater Synechococcussp with a doubling time of 4.5 h, and a gross growth efficiencyof 48% The estimated daily requirements of ciliates for growthapproximately equalled total phytoplankton production. We calculatedthat ciliates in the epilimnion were clearing 4–10% ofthe bacterioplankton and cyanobactenal standing stocks per daySince this would not be sufficient food consumption to meetdaily carbon requirements of the aliates, it is likely thatthese organisms were also grazing a significant amount of autotrophicand heterotrophic eukaryotic cells in Lake Kinneret.     

Fission in sea anemones: integrative studies of life cycle evolution

Sea anemones (Phylum Cnidaria; Class Anthozoa, Order Actiniaria)exhibit a diversity of developmental patterns that include cloningby fission. Because natural histories of clonal and aclonalsea anemones are quite different, the gain and loss of fissionis an important feature of actiniarian lineages. We have usedmitochondrial DNA and nuclear intron DNA phylogenies to investigatethe evolution of longitudinal fission in sixteen species inthe genus Anthopleura, and reconstructed an aclonal ancestorthat has given rise at least four times to clonal descendents.For A. elegantissima from the northeastern Pacific Ocean, atransition to clonality by fission was associated with an up-shorehabitat shift, supporting prior hypotheses that clonal growthis an adaptation to the upper shore. Fission in Actiniaria likelyprecedes its advent in Anthopleura, and its repeated loss andgain is perplexing. Field studies of the acontiate sea anemoneAiptasia californica provided insight to the mechanisms thatregulate fission: subtidal Aiptasia responded to experimentallydestabilized substrata by increasing rates of pedal laceration.We put forth a general hypothesis for actiniarian fission inwhich sustained tissue stretch (a consequence of substratuminstability or intrinsic behavior) induces tissue degradation,which in turn induces regeneration. The gain and loss of fissionin Anthopleura lineages may only require the gain and loss ofsome form of stretching behavior. In this view, tissue stretchinitiates a cascade of developmental events without requiringcomplex gene regulatory linkages.     

GENOTYPE‐BY‐TEMPERATURE INTERACTIONS MAY HELP TO MAINTAIN CLONAL DIVERSITY IN ASTERIONELLA FORMOSA (BACILLARIOPHYCEAE)

Marine and freshwater phytoplankton populations often show large clonal diversity, which is in disagreement with clonal selection of the most vigorous genotype(s). Temporal fluctuation in selection pressures in variable environments is a leading explanation for maintenance of such genetic diversity. To test the influence of temperature as a selection force in continually (seasonally) changing aquatic systems we carried out reaction norms experiments on co‐occurring clonal genotypes of a ubiquitous diatom species, Asterionella formosa Hassall, across an environmentally relevant range of temperatures. We report within population genetic diversity and extensive diversity in genotype‐specific reaction norms in growth rates and cell size traits. Our results showed genotype by environment interactions, indicating that no genotype could outgrow all others across all temperature environments. Subsequently, we constructed a model to simulate the relative proportion of each genotype in a hypothetical population based on genotype and temperature‐specific population growth rates. This model was run with different seasonal temperature patterns. Our modeling exercise showed a succession of two to several genotypes becoming numerically dominant depending on the underlying temperature pattern. The results suggest that (temperature) context dependent fitness may contribute to the maintenance of genetic diversity in isolated populations of clonally reproducing microorganisms in temporally variable environments.     

Metabolic Interrelations Underlying the Physiological and Evolutionary Advantages of Genetic Diversity

Past findings have established how the faster growth, greaterreproductive output and/or longer survival that are associatedwith heterosis and genomic diversity measured as multi-locusheterozygosity stem from slower intensities with which proteinsare renewed and replaced (=protein turnover). Slower turnoverresults in lower energy requirements and reduced metabolic sensitivityto environmental change, representing a mechanistic basis forevolutionary consequences of genetic polymorphism. To determinethe genetic and functional basis of differences in whole-bodyprotein turnover, we have begun to resolve different proteolyticpathways, searching for genetic polymorphisms with a directeffect upon proteolysis, and assessing the metabolic and physiologicalconsequences of those genetic influences in the mussel Mytilusedulis. Our recent work has established the physiological importanceof lysosomal enzymes under normal conditions of basal proteolysis,and shown that associated effects on energy flux may vary accordingto functional differences between separate enzymes. Data arepresented here which compare metabolic consequences of polymorphismin the lysosomal aminopeptidases Lap-1 and Lap-2. Findings establishthat metabolic and phenotypic effects of genetic polymorphismresult directly from genetic variation at the loci coding forthese peptidases, rather than from linked loci. They also illustratethe complexity of interrelations that ultimately influence theevolutionary consequences of genomic diversity, including associatedinfluences of both Lap-1 and Lap-2 on energy requirements andanimal condition. We impress that energy requirements for proteinturnover may represent a functional basis for epistasis, includingassociations whereby advantages of genetic polymorphism aregreatest at loci that code for enzymes acting in both proteincatabolism and energy provision.     

Species-specific interactions between small planktonic ciliates (Urotricha spp.) and rotifers (Keratella spp.)

We investigated the potential impact of four isolates of smallciliates of the genus Urotricha on the common rotifer speciesKeratella cochlearis and Keratella quadrata in laboratory batchculture experiments. Two small Cryptomonas species served asfood for the ciliates and the rotifers in the experiments. Populationgrowth rates of the rotifers were measured when they grew aloneand when they were paired with one of their potential ciliatecompetitors. Growth rates of K. cochlearis were enhanced andtheir mortality rates reduced in the presence of Urotricha furcata,most likely because the rotifers preyed upon the ciliates. Thelarger rotifer species, K. quadrata, also feeds upon small Urotricha,yet their population growth rates were negatively affected byUrotricha. This was because the mortality rate of K. quadrataincreased in the presence of all three isolates of U. furcataand the one isolate of Urotricha farcta. It needs to be investigatedwhether this effect is chemically mediated and ecologicallyrelevant.     

A study of feeding in predacious ciliates using prey ciliates labeled with fluorescent microspheres

Feeding in predacious estuarine ciliates was investigated ina series of laboratory experiments using a new method of preylabeling which facilitates microscopic indentification of ingestedprey items. Ingestion rates of Mesodinium pulex, Euplotes vannusand E.woodruffi were estimated using the appearance, insidethe predator, of bacteriovorous ciliates (Metanophrys sp., Cyclidiumsp.and Pleuronema sp ) labeled with fluorescent microspheres. Preyremain motile and have presumably unaltered surface characteristics.Ingestion rates of log-growth phase predators increased withprey density. Mesodinium pulex ingested 0 15–0.32 cellsh^–1 over a prey concentration of 60–2300 ml^–1.Maximum ingestion rates of E. woodruffi and E. vannus were 4.5and 3.4 cells h^–1 respectively, estimated at prey abundancesof 75 and 172 cells ml^–1 respectively. Comparisons offeeding rates on prey of different sizes, and the effects ofstarvation, indicated that ingestion is likely limited by differentfactors in ‘raptorial’ (M pulex) and ‘filterfeeding’ (Euplotes spp.) predators.     

稻田节肢动物群落的多样性及对褐飞虱的控制功能

对江苏江浦及安徽安庆两地五种类型稻田的节肢动物群落生物多样性研究表明,以对褐飞虱Nilaparvata lugens具有抗性的粳稻田多样性指数最高。稻田蜘蛛亚群落与褐飞虱种群数量变化间存在明显的相关性,11年中64%的年份表现为显著相关。利用天敌功能指数EF=（E+P）^E/P、数值反应的方法研究了稻田蜘蛛功能团与褐飞虱种群间的生存、繁殖和数量关系,结果表明,初始EF值与褐飞虱对水稻的危害率及褐飞虱种群的未来最大饱和容量K值间呈显著相关。本文讨论了利用初始EF值来预测天敌对害虫的功能作用及生物防治与化学防治协调的可能性。     

Fitness‐consequences of geitonogamous selfing in a clonal marine angiosperm (Zostera marina)

Plant mating systems have received considerable attention because the proportion of selfed vs. outcrossed progeny is an important evolutionary factor. In clonally reproducing plants, geitonogamous selfing between distant ramets belonging to the same genet is expected to be widespread, yet empirical data are sparse. Nothing is known about between‐ramet selfing in aquatic flowering plants with subaqueous pollen transfer, most of which display pronounced clonal reproduction. From two locations in the western Baltic Sea, I present data on the effects of patch isolation and clonal diversity on the outcrossing rate of eelgrass, Zostera marina L., based on the genotypes of maternal plants and recently fertilized ovules scored at eight microsatellite loci. There were no differences in outcrossing rates between vegetation patches and continuous meadow although patches were nearly always composed of single genets. Quantitative effects of clonal diversity were present in the continuous vegetation where a significant positive correlation between genet diversity and the proportion of outcrossed offspring was detected (Kendall’s τ=0.82, P=0.0017). On a population‐scale as well, the genotypic diversity was positively correlated with outcrossing. The relative fitness of selfed offspring was low (ω ± 95% confidence interval=0.56 ± 0.032 and 0.322 ± 0.15) indicating that geitonogamy incurred substantial fitness costs. Selfing rates in Z. marina may not be in evolutionary equilibrium because of spatial and temporal heterogeneity of clonal size and diversity. The high prevalence of dioecy in seagrasses may have evolved to avoid the fitness costs associated with geitonogamy.     

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.     

Contrast Between Solitary and Clonal Lifestyles in the Sea Anemone Anthopleura elegantissima

The common intertidal sea anemone Anthopleura elegantissima(Brandt) occurs in two forms the clonal aggregating form andthe solitary form The obvious differences between the two apparentlyresult from the presence of asexual reproduction in the clonalaggregating form and its absence in the solitary form resultingdifferences in growth form suit the two anemones to differentlifestyles The clonal form is well suited to life higher inthe mid intertidal Asexual reproduction resulting in moderatelysmall individual size and close association with clonematesimproves its resistance to physical stress (drag and desiccation)and makes it a superior competitor in exposed habitats higherin the intertidal where species diversity and predator pressureare low The larger solitary animals live in more protected microhabitatslower in the intertidal and subtidal and are probably more resistantto predation and less able to withstand physical stress or intenseintraspecific competition The two forms also have differentbiogeographic ranges While the clonal aggregations are quitecommon at rocky sites at least as far north as Vancouver Islandin British Columbia populations of solitaries have not beenfound north of Point Reyes California Apparently the two formsare re productively isolated phenotype frequencies are verydifferent for clonals and solitaries living at the same locationswhile the between-sample variation within each form is relativelysmall These differences in phenotype frequencies biogeographicrange and microhabitat suggest that the clonal anemones andthe solitary anemones known as Anthopleura elegantissima areactually a sibling species pair.     

Effects of a storm event on the structure of the pelagic food web with special emphasis on planktonic ciliates

Storm-induced changes in the water column structure and thepelagic food web were investigated by daily sampling duringa 3 week period (October 24 to November 10, 1988) at a permanentstation in the southern Kattegat (Denmark) Subsequent to a stormthe primary production increased and the size-distribution ofthe phytoplankton changed towards larger cells. Some componentsof the zooplankton community responded to the increase in potentialfood, either in terms of a functional response (copepods) orin terms of a numerical response (cladocera), whereas no changesin the populations of mixo- and heterotrophic aliates were evident.The dilates were not food limited since growth rates determinedin situ were comparable to maximum growth rates measured inthe laboratory. Calculations suggest that the total clearancecapacity of planktonic copepods (as fraction of water columncleared per unit time) was of the same magnitude as the measuredinstantaneous growth rates of the ciliates (0.55–0 85day^–1). Ciliate populations were therefore probably limitedby copepod predation. Ciliates, however, contributed only insignificantlyto the diets of copepods. Although the total zooplankton productionincreased by at least 30% subsequent to the storm (and thatof the copepods by 50%), the zooplankton community was unableto assimilate the entire increase in primary production. Therelative zooplankton (copepods, cladoceran and ciliates) grazingrate on the primary production decreased 30%, and the flow ofcarbon to biomass accumulation, other grazers and in particularsedimentation is predicted to have increased by 100% followingthe storm.     

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.