Maximum Ingestion Rate Research Articles

Ingestion kinetics of mixotrophic and heterotrophic flagellates

AbstractIn sunlit waters, significant predation is performed by unicellular, phagotrophic mixotrophs, that is, predators that also possess plastids. The success of a mixotrophic lifestyle will depend in part on how well mixotrophs acquire prey relative to specialized heterotrophs. Likewise, consequences of mixotrophy for productivity and element cycling will depend on the rate and efficiency at which mixotrophs consume prey biomass relative to heterotrophs. However, trait differences between mixotrophs and heterotrophs are not well characterized. In addition, cell size of mixotrophs varies widely, and constitutive mixotrophs include small flagellates deriving from diverse taxa, while larger species are primarily dinoflagellates. To determine whether similar constraints apply to phagotrophs across this broad range of size and taxa, we compiled 83 measurements of flagellate functional responses and compared maximum clearance rates (Cmax) and maximum ingestion rates (Imax) between trophic modes. We found that the average mixotroph has a 3.7‐fold lower Cmax and 7.8‐fold lower Imax than the average heterotroph, after controlling for cell size. The smaller penalty for Cmax suggests that relative fitness of mixotrophs will be enhanced under dilute prey concentrations that are common in pelagic ecosystems. We also find that growth efficiency is greater for mixotrophs and for flagellates with lower Cmax, indicating a spectrum of trophic strategies that may be driven by phototrophy vs. phagotrophy allocation as well as fast vs. slow metabolic variation. Allometric scaling shows that Imax is constrained by a common relationship among dinoflagellates and other taxa, but dinoflagellates achieve a greater volume‐specific Cmax. These results should aid in interpreting protistan communities and modeling mixotrophy.

Higher ingestion rates and importance of ciliates in the diet of a large, subarctic copepod revealed by larger volume incubations

AbstractDespite ecological importance, the feeding ecology of the large calanoid copepod, Neocalanus cristatus is little known, as its ingestion rate under experimental conditions consistently falls short of its metabolic demand. The conventional incubation bottle size (~ 2 liters) used in previous studies may have affected its feeding behavior. Here, we examined the effect of bottle size (2.4 vs. 13liters) and copepod density on the feeding of N. cristatus Stage C5. Under similar copepod density (0.4 ind. L−1) ingestion rates decreased significantly for tests conducted in small bottles and thus, small bottles inhibited copepod feeding. In experiments with large bottles, ingestion rates were highest in the single‐individual treatments (1 ind. 13 L−1), decreasing exponentially to < 1% of the maximum ingestion rate with increasing copepod densities (up to 20 ind. 13 L−1). Considerable food limitation occurred in the higher copepod density treatments with lower initial prey allocation per individual. Moreover, in the single‐individual treatments, clearance rates on naked ciliates (11–20 L ind.−1 d−1) were remarkably higher than in multiple‐individual treatments. Grazer–grazer interaction, thus, interfered with copepod feeding on microzooplankton in multiple‐individual treatments. The ingestion rate in the single‐individual treatments (62–102 μgC ind.−1 d−1) exceeded the daily metabolic requirement; feeding rates noted in previous studies were, thus, underestimations, affected by bottle size and copepod mutual interference. Efficient feeding by N. cristatus on naked ciliates emphasizes the importance of the ciliate‐copepod link in the grazing food chain in the subarctic Pacific.

Feeding by heterotrophic flagellates on marine archaea

Archaea live in diverse habitats including extreme environments. Although they are sometimes the dominant heterotrophic organisms in microbial communities, relatively little is known about their ecological roles in microbial food webs. To explore predator–prey relationships between archaea and heterotrophic protists, we determined feeding occurrence by the heterotrophic nanoflagellates Bodo sp., Goniomonas sp., and Pedospumella sp. the common heterotrophic dinoflagellates Cryptoperidiniopsis brodyi, Gyrodinium dominans, Oblea rotunda, Oxyrrhis marina, and Polykrikos kofoidii on ammonia-oxidizing archaea (AOA) by examining the food vacuoles of these heterotrophic flagellates under an epifluorescence microscope using fluorescently labeled AOA. In addition, we measured the ingestion rates of Goniomonas sp., C. brodyi, G.dominans, and O. marina on AOA as a function of prey concentration. Cells of Bodo sp., Goniomonas sp., Pedospumella sp., C. brodyi, G.dominans, and O. marina were able to feed on AOA, whereas O. rotunda and P. kofoidii were not. With increasing initial prey concentration up to 1.7 × 106 – 9.3 × 106 cells mL−1, the ingestion rates of Goniomonas sp., C. brodyi, G.dominans, and O. marina on AOA increased rapidly but increased slowly or became saturated at higher concentrations. Although the maximum ingestion rates of the smaller flagellate Goniomonas sp. (23.1 cells predator−1 h−1) on AOA was much lower than that of the larger flagellate O. marina (296.4 cells predator−1 h−1), AOA supported the positive growth of only Goniomonas sp. The results of the present study suggest that these small heterotrophic flagellates could be effective heterotrophic protist grazers of AOA in marine ecosystems.

Mixotrophy in the bloom-forming genus Phaeocystis and other haptophytes

Phaeocystis is a globally widespread marine phytoplankton genus, best known for its colony-forming species that can form large blooms and odorous foam during bloom decline. In the North Sea, Phaeocystis globosa typically becomes abundant towards the end of the spring bloom, when nutrients are depleted and the share of mixotrophic protists increases. Although mixotrophy is widespread across the eukaryotic tree of life and is also found amongst haptophytes, a mixotrophic nutrition has not yet been demonstrated in Phaeocystis. Here, we sampled two consecutive Phaeocystis globosa spring blooms in the coastal North Sea. In both years, bacterial cells were observed inside 0.6 – 2% of P. globosa cells using double CARD-FISH hybridizations in combination with laser scanning confocal microscopy. Incubation experiments manipulating light and nutrient availability showed a trend towards higher occurrence of intracellular bacteria under P-deplete conditions. Based on counts of bacteria inside P. globosa cells in combination with theoretical values of prey digestion times, maximum ingestion rates of up to 0.08 bacteria cell−1 h−1 were estimated. In addition, a gene-based predictive model was applied to the transcriptome assemblies of seven Phaeocystis strains and 24 other haptophytes to assess their trophic mode. This model predicted a phago-mixotrophic feeding strategy in several (but not all) strains of P. globosa, P. antarctica and other haptophytes that were previously assumed to be autotrophic. The observation of bacterial cells inside P. globosa and the gene-based model predictions strongly suggest that the phago-mixotrophic feeding strategy is widespread among members of the Phaeocystis genus and other haptophytes, and might contribute to their remarkable success to form nuisance blooms under nutrient-limiting conditions.

Mechanisms and fluid dynamics of foraging in heterotrophic nanoflagellates

AbstractHeterotrophic nanoflagellates are the main consumers of bacteria and picophytoplankton in the ocean. In their microscale world, viscosity impedes predator–prey contact, and the mechanisms that allow flagellates to daily clear a volume of water for prey corresponding to 106 times their own volume is unclear. It is also unclear what limits observed maximum ingestion rates of about 104 bacterial preys per day. We used high‐speed video microscopy to describe feeding flows, flagellum kinematics, and prey searching, capture, and handling in four species with different foraging strategies. In three species, prey handling times limit ingestion rates and account well for their reported maximum values. Similarly, observed feeding flows match reported clearance rates. Simple point force models allowed us to estimate the forces required to generate the feeding flows, between 4 and 13 pN, and consistent with the force produced by the hairy (hispid) flagellum, as estimated using resistive force theory. Hispid flagella can produce a force that is much higher than the force produced by a naked (smooth) flagellum with similar kinematics, and the hairy flagellum is therefore key to foraging in most nanoflagellates. Our findings provide a mechanistic underpinning of observed functional responses of prey ingestion rates in nanoflagellates.

Interactions Between the Kleptoplastidic Dinoflagellate Shimiella gracilenta and Several Common Heterotrophic Protists

The newly described dinoflagellate, Shimiella gracilenta, is known to survive for approximately 1 month on the plastids of ingested prey cells during starvation, indicating kleptoplastidy. To understand the population dynamics of this dinoflagellate in marine planktonic food webs, its growth and mortality rate due to predation should be assessed. Thus, we investigated the feeding occurrence of eight common heterotrophic protists on S. gracilenta. We also determined the growth and ingestion rates of Oxyrrhis marina and the naked ciliate, Rimostrombidium sp. on S. gracilenta as a function of the prey concentration. The common heterotrophic dinoflagellates (HTDs) Gyrodinium dominans, O. marina, and Pfiesteria piscicida and a naked ciliate Rimostrombidium sp. were able to feed on S. gracilenta; whereas the HTDs Aduncodinium glandula, Gyrodinium jinhaense, Oblea rotunda, and Polykrikos kofoidii were not. Shimiella gracilenta supported positive growth of O. marina and Rimostrombidium sp. but did not support that of G. dominans and P. piscicida. With increasing prey concentrations, the growth and ingestion rates of O. marina and Rimostrombidium sp. on S. gracilenta increased and became saturated. The maximum growth rates of O. marina and Rimostrombidium sp. on S. gracilenta were 0.645 and 0.903 day−1, respectively. Furthermore, the maximum ingestion rates of O. marina and Rimostrombidium sp. on S. gracilenta were 0.11 ng C predator day−1 (1.6 cells predator−1 day−1) and 35 ng C predator day−1 (500 cells predator−1 day−1), respectively. The maximum ingestion rate of O. marina on S. gracilenta was lower than that on any other algal prey reported to date, although its maximum growth rate was moderate. In conclusion, S. gracilenta had only a few common heterotrophic protist predators but could support moderate growth rates of the predators. Thus, S. gracilenta may not be a common prey species for diverse heterotrophic protists but may be a suitable prey for a few heterotrophic protists.

Ratio-dependent functional response of two common Cladocera present in farmland ponds to Batrachochytrium dendrobatidis

Batrachochytrium dendrobatidis is responsible for amphibian declines worldwide. Decreasing the aquatic density of this chytrid through consumption of its infectious zoospores by Cladocera (water fleas) may mitigate the impact of chytridiomycosis. Understanding this predator-prey relationship requires insights in the zoospore ingestion rate of an average water flea, but such data are almost non-existent. We investigated the functional response of Simocephalus vetulus and Chydorus sphaericus feeding on B. dendrobatidis zoospores. These Cladocera commonly occur in farmland ponds, which may represent a major habitat for disease control. Both water fleas actively ingested zoospores and their per capita ingestion rate was best modelled in function of zoospore-to-Cladocera ratio, implying mutual interference among water fleas during zoospore feeding. The larger S. vetulus substantially consumed more zoospores, characterised by a maximum ingestion rate of 2.5 × 10 5 zoospores.Cladocera −1 .h −1 .mL −1 , which is about 12 times higher than for C. sphaericus . These findings are useful to support model-based management of chytridiomycosis. • Simocephalus vetulus and Chydorus sphaericus are common Cladocera in farmland ponds. • S. vetulus and C. sphaericus consume zoospores of B. dendrobatidis . • Zoospore ingestion rate for both Cladocera depends on zoospore-to-Cladocera ratio. • The larger S. vetulus has a significant larger per capita ingestion rate than C. sphaericus .

Growth and grazing of the chlorarachniophyte Bigelowiella natans (Chlorarachniophyceae) on the marine cyanobacterium Synechococcus

ABSTRACT Chlorarachniophytes are cosmopolitan, typically unicellular marine phototrophic protists with green plastids of secondary endosymbiotic origin. However, there are few studies of their eco-physiology. Bigelowiella natans feeds mixotrophically on diverse strains of Synechococcus. We investigated feeding by B. natans (Chlorarachniophyceae) on diverse strains of the marine cyanobacterium Synechococcus and quantified the ingestion and clearance rates of B. natans on Synechococcus strains CC9311 and CC9605 as a function of prey concentration, as well as the growth rates of B. natans feeding on these Synechococcus strains. The maximum ingestion rates of B. natans on Synechococcus strains CC9311 and CC9605 were 2.77 and 2.18 cells predator–1 h–1, respectively. The maximum clearance rates of B. natans on Synechococcus CC9311 and CC9605 were 197.2 and 331.5 nl predator–1 h–1, respectively. The maximum mixotrophic growth rates of B. natans on Synechococcus CC9311 and CC9605 were 0.38 d–1 and 0.28 d–1, respectively, while its autotrophic growth rates were 0.174 ± 0.019 d–1. The results of the present study suggest that B. natans is an effective protistan grazer of Synechococcus and that it obtains a significant ecological advantage from a mixotrophic strategy in marine planktonic food webs.

Vitamin B12 auxotrophy of the red tide dinoflagellate Heterocapsa rotundata and the effects of feeding on Synechococcus and vitamin B12 availability upon phagotrophic activity

ABSTRACT Vitamins are an important growth factor for the majority of microalgae. Although the effects of light and prey availability on the growth and feeding of mixotrophic dinoflagellates are relatively well understood, the effects of vitamins are currently poorly understood. We investigated the effects of vitamin conditions on feeding by the red tide-forming dinoflagellate Heterocapsa rotundata SIOHR01 on the cyanobacterium Synechococcus sp. CC9311. Furthermore, we explored the growth rates of H. rotundata with and without added prey under different vitamin conditions and found that H. rotundata is auxotrophic for vitamin B12. Heterocapsa rotundata SIOHR01 was able to ingest Synechococcus sp. CC9311 with maximum ingestion and clearance rates, in f/2–Si seawater media, of 0.72 cells predator–1 h–1 and 28.08 nl predator–1 h–1, respectively; these were considerably higher than those in f/2–Si seawater media without B vitamins, which showed a maximum of 0.15 cells predator–1 h–1 and 2.91 nl predator–1 h–1, respectively. However, the mixotrophic growth rate of H. rotundata on Synechococcus sp. under each vitamin condition was similar to that of its autotrophic growth rates without added prey under the same vitamin condition. Therefore, this study suggests that while the availability of prey did not enhance the growth of H. rotundata, the concentration of vitamin in the medium affected growth, apparently due to the auxotrophic requirement of the dinoflagellate for vitamin B12.

Intraspecific trait variation alters the outcome of competition in freshwater ciliates.

Trait variation among heterospecific and conspecific organisms may substantially affect community and food web dynamics. While the relevance of competition and feeding traits have been widely studied for different consumer species, studies on intraspecific differences are more scarce, partly owing to difficulties in distinguishing different clones of the same species. Here, we investigate how intraspecific trait variation affects the competition between the freshwater ciliates Euplotes octocarinatus and Coleps hirtus in a nitrogen‐limited chemostat system. The ciliates competed for the microalgae Cryptomonas sp. (Cry) and Navicula pelliculosa (Nav), and the bacteria present in the cultures over a period of 33 days. We used monoclonal Euplotes and three different Coleps clones (Col 1, Col 2, and Col 3) in the experiment that could be distinguished by a newly developed rDNA‐based molecular assay based on the internal transcribed spacer (ITS) regions. While Euplotes feeds on Cry and on bacteria, the Coleps clones cannot survive on bacteria alone but feed on both Cry and Nav with clone‐specific rates. Experimental treatments comprised two‐species mixtures of Euplotes and one or all of the three different Coleps clones, respectively. We found intraspecific variation in the traits “selectivity” and “maximum ingestion rate” for the different algae to significantly affect the competitive outcome between the two ciliate species. As Nav quickly escaped top‐down control and likely reached a state of low food quality, ciliate competition was strongly determined by the preference of different Coleps clones for Cry as opposed to feeding on Nav. In addition, the ability of Euplotes to use bacteria as an alternative food source strengthened its persistence once Cry was depleted. Hence, trait variation at both trophic levels codetermined the population dynamics and the outcome of species competition.

Grazing of a heterotrophic nanoflagellate on prokaryote and eukaryote prey: ingestion rates and gross growth efficiency

Heterotrophic nanoflagellates (HNANs) play a pivotal role as consumers of picoplankton, remineralizers and carbon vectors, yet knowledge on how prey quantity and quality affect HNAN physiology remains limited. In a series of grazing experiments using an uncharacterized member of the HNAN assemblage, we found that growth (μ) and ingestion rate (IR) varied when offering heterotrophic bacteria (HB), Synechococcus spp. (Syn), Ostreococcus lucimarinus (Ost) or a combination of all 3 prey types. Highest average μ rates (1.8 d-1) were detected on HB at densities of ~106 cells ml-1 and maximum IR on Syn (485 pg C d-1) at ~106 cells ml-1. Independent of prey type, flagellate μ increased with IR up to ~50 pg C d-1. A relatively low P-content in Ost was linked to shifts in C:N:P ratios of the HNAN in the single-prey experiment and when Ost was offered as part of the mixed assemblage. Presented with a mixed diet, the highest contribution to daily C intake came from Ost with 50%, followed by HB with 46% and Syn with only 4%. C-based gross growth efficiencies (GGEs) were higher when feeding on HB and mixed prey, compared to both picophototrophs, while N- and P-based GGEs in mixed prey treatments markedly exceeded those when feeding on any single prey. The findings in this study corroborate the importance of investigating the biogeochemical role of HNANs in relation to prey availability and quality to refine estimates of energy transfer within the microbial loop.

Functional Ecology of Two Contrasting Freshwater Ciliated Protists in Relation to Temperature.

We conducted microcosm experiments with two contrasting freshwater ciliates on functional traits (FTs) related to their growth rate (numerical response, NR) and ingestion rate (functional response, FR) over a range of ecologically relevant temperatures. Histiobalantium bodamicum and Vorticella natans are common planktonic ciliates but their abundance, swimming behavior, and temperature tolerance are different. In contrast to most sessile peritrich species, the motile V. natans is not strictly bacterivorous but also voraciously feeds upon small algae. We observed three main alterations in the shape of NR of both species with temperature, that is, change in the maximum growth rate, in the initial slope and in the threshold food level needed to sustain the population. Similarly, maximum ingestion rate, gross growth efficiency (GGE), and cell size varied with temperature and species. These findings caution against generalizing ciliate performance in relation to the ongoing global warming. Our results suggest that V. natans is the superior competitor to H. bodamicum in terms of temperature tolerance and bottom‐up control. However, the abundance of V. natans is usually low compared to H. bodamicum and other common freshwater ciliates, suggesting that V. natans is more strongly top‐down controlled via predation than H. bodamicum. The taxonomic position of V. natans has been debated. Therefore, to confirm species and genus affiliation of our study objects, we sequenced their small subunit ribosomal RNA (SSU rDNA) gene.

What controls microzooplankton biomass and herbivory rate across marginal seas of China?

AbstractMicrozooplankton are the primary herbivores and nutrient regenerators in the marine food web, but their importance is often underestimated, and the quantitative relationships between environmental factors and the biomass and herbivory rate of microzooplankton remain obscure. To fill this gap, we conducted 224 dilution experiments to measure microzooplankton biomass and herbivory rate across a vast area of the marginal seas of China. To gain the potential mechanisms controlling microzooplankton herbivory, we also use a model that combines the Metabolic Theory of Ecology and the functional responses of grazing to quantify the effects of temperature, phytoplankton biomass, and microzooplankton biomass on microzooplankton grazing rate. We estimate an activation energy of 0.51 eV of microzooplankton and found that the Holling III function best described the functional response of microzooplankton grazing with a maximal ingestion rate of 4.76 d−1 at 15°C and a half‐saturation constant of 0.27 μM N. We also find that microzooplankton biomass scales with phytoplankton biomass with an exponent of 0.77, consistent with the general 3/4 scaling law found in other ecosystems. This scaling relationship is accompanied by a shift from ciliates to heterotrophic dinoflagellates with increasing phytoplankton biomass. Our results provide empirical patterns that will be vital to parameterize and validate marine ecosystem models, particularly in China seas.

Plasticity in the grazing ecophysiology of Florenciella (Dichtyochophyceae), a mixotrophic nanoflagellate that consumes Prochlorococcus and other bacteria

AbstractMixotrophic nanoflagellates can account for more than half of the bacterivory in the sunlit ocean, yet very little is known about their ecophysiology. Here, we characterize the grazing ecology of an open‐ocean mixotroph in the genus Florenciella (class Dictyochophyceae). Members of this class were indirectly implicated as major consumers of Prochlorococcus and Synechococcus in the oligotrophic North Pacific Subtropical Gyre, but their phagotrophic capabilities have never been investigated. Our studies showed that Florenciella readily consumed Prochlorococcus, Synechococcus, and heterotrophic bacteria, and that the ingested prey relieved nutrient limitations on growth. Florenciella grew faster (3 d−1) in nitrogen‐deplete medium given sufficient live Synechococcus, than in nitrogen‐replete K medium (2 d−1), but it did not grow in continuous darkness. Grazing rates were substantially higher under nutrient limitation and showed a hint of diel variability, with rates tending to be highest near the end of the light period. An apparent trade‐off between the maximum clearance rate (5 nL Florenciella−1 h−1) and the maximum ingestion rate (up to ∼ 10 prey cells Florenciella−1 h−1) across experiments suggests that grazing behavior may also vary in response to prey concentration. If the observed grazing rates are representative of other open‐ocean mixotrophs, their collective activity could account for a significant fraction of the daily cyanobacterial mortality. This study provides essential parameters for understanding the grazing ecology of a common marine mixotroph and the first characterization of mixotrophic nanoflagellate functional responses when feeding on unicellular cyanobacteria, the dominant marine primary producers in the oligotrophic ocean.

Contrasting stoichiometric dynamics in terrestrial and aquatic grazer–producer systems

The turnover rate of producer biomass in aquatic ecosystems is generally faster than in terrestrial. That is, aquatic producer biomass grows, is consumed, and is replaced considerably faster than terrestrial. The WKL model describes the flow of phosphorus and carbon through a grazer–producer system, hence varying the model parameters allows for analysis of different ecosystems of this type. Here we explore the impacts of the intrinsic growth rate of the producer and the maximal ingestion rate of the grazer on these dynamics because these parameters determine turnover rate. Simulations show that for low intrinsic growth rate and maximal ingestion rate, the grazer goes extinct; for higher values of these parameters, coexistence occurs in oscillations. Sensitivity analysis reveals the relative importance of all parameters on asymptotic dynamics. Lastly, the impacts of changing these two parameters in the LKE model appears to be quantitatively similar to the impacts in the WKL model.

Effects of irradiance and temperature on the growth and feeding of the obligate mixotrophic dinoflagellate Gymnodinium smaydae

Gymnodinium smaydae is a fast-growing mixotrophic dinoflagellate. This study investigated whether light intensity (0–346 µmol photons m−2 s−1) and temperature (5–35 °C) affect the autotrophic or mixotrophic growth rate or ingestion rate of Gymnodinium smaydae GSSH1005. At all light intensities tested, G. smaydae GSSH1005 showed negative autotrophic growth rates, but positive mixotrophic growth rates when feeding on Heterocapsa rotundata. However, both autotrophic and mixotrophic growth rates were significantly affected by light intensity. The mixotrophic growth rates at 0–6 µmol photons m−2 s−1 were 0.67–0.72 day−1; they increased up to 1.28 day−1 at 58 µmol photons m−2 s−1, but became saturated at higher light intensities. The ingestion rates were also significantly affected by light intensity. The maximum ingestion rate of 2.3 ng C predator−1 day−1 was achieved at 58 µmol photons m−2 s−1. Although the autotrophic growth rates were negative at all temperatures tested, the mixotrophic growth rates were positive at 10–32 °C. Both autotrophic and mixotrophic growth rates were significantly affected by temperature. The maximum mixotrophic growth rate of 1.55 day−1 was noted at 25 °C. The ingestion rates were also significantly affected by temperature. The maximum ingestion rate of 4.2 ng C predator−1 day−1 was noted at 32 °C. Therefore, both light intensity and temperature can affect the population dynamics of G. smaydae GSSH1005.

Cyclopoids feed selectively on free‐living stages of parasites

Abstract Many aquatic organisms can consume parasite larvae, thus hampering parasite transmission; however, information about feeding on them in the presence of an alternative prey remains scarce. When having a food choice, predators may decrease parasite consumption, therefore, it is important to assess the role of parasites in the diet of predators in natural communities with different types of prey available. Our study aims to test whether common freshwater cyclopoids feed on trematode free‐living stages (cercariae) when an alternative food source is present. We experimentally studied ingestion rates of cyclopoids Macrocyclops distinctus fed with cercariae of trematode Diplostomum pseudospathaceum, a common and harmful parasite of freshwater fishes, and ciliates Paramecium caudatum (an alternative prey, known as suitable food for copepods). First, the feeding response of cyclopoids to different densities of each prey was studied. Then, feeding selectivity in the mixtures of cercariae and ciliates was tested. Feeding rates of cyclopoids increased with prey densities (both ciliates and cercariae) but almost stopped growing at high prey densities, which indicated saturation (Holling type II functional response). In most cases, cyclopoids consumed cercariae at higher rates than ciliates. Maximum ingestion rates estimated from the obtained curves were 37 cercariae ind−1 hr−1 and 17 ciliate ind−1 hr−1. When exposed to prey mixtures, cyclopoids fed on cercariae selectively. When cercariae were offered to cyclopoids at concentrations exceeding the saturation level, the ingestion of ciliates remained constantly low at all ciliate densities. In contrast, the ingestion of cercariae increased with rising cercariae densities even when ciliates were presented ad libitum, decreasing only at very high prey densities. Possible reasons of such feeding preferences are discussed. Our study demonstrated that cyclopoids may prefer to feed on cercariae when there is an alternative food choice and can ingest cercariae at high rates. These experimental results could be extended to natural communities, suggesting that cyclopoids can reduce the transmission of parasites and contribute to the incorporation of parasite production in food webs of lentic ecosystems.

The missing piece of the upper mesopelagic carbon budget? Biomass, vertical distribution and feeding of aggregate-associated copepods at the PAP site

Although zooplankton are recognized as important consumers of marine snow, our knowledge of the contribution of the small (<1 mm) zooplankton to the degradation of sinking particles, and therefore on the efficiency of the biological pump, is limited. To estimate the marine snow consumption by small aggregate-feeding copepods, we measured the daily changes in biomass and vertical distribution of the harpacticoid Microsetella norvegica and the poecilostomatoid Oncaea spp. over a period of 10 days and combined these with estimates of their feeding and respiration rates. We estimated copepod feeding rates in multiple ways, using: gut chlorophyll content, maximum ingestion rates from functional responses on two types of aggregates, carbon demand based on the respiration measurements, and egg production rates. Microsetella norvegica and Oncaea spp. biomass levels varied > 2-fold between sampling dates for geographically-close sampling stations. Microsetella norvegica resided mainly in the surface layer, at or immediately below the fluorescence peak, while Oncaea spp. was typically deeper. Microsetella norvegica fed actively on Trichodesmium filaments, with a maximum ingestion rate of ca. 0.11 µg C ind.−1 d−1, while their ingestion of detritus aggregates was low. Feeding on Trichodesmium was reflected in their gut chl-a content, which was high for M. norvegica at all but one sampling time. In contrast, Oncaea spp. had significantly lower gut chl-a content and may have been feeding on other types of aggregates. Respiration of both copepods was variable and as much as 0.08 µL ind.−1 h−1 for M. norvegica and 0.04 µL ind.−1 h−1 for Oncaea spp. Based on individual biomass, vertical distribution, and carbon demand, aggregate-associated copepods could degrade up to 79 ± 33 mg C m−2 d−1, a value similar to the surplus in the epipelagic carbon budget of the area. This large degradation rate demonstrates that zooplankton < 1 mm can have a large influence on the vertical flux and that the factors controlling their abundances and feeding rates should be high in the priority list of future zooplankton studies.

The Effect of Temperature and Food Concentration On Ingestion Rates of Quinqueloculina Seminula On the Diatom Nitzschia Closterium

Abstract The majority of sediment-dwelling foraminifera are thought to be deposit feeders. They use their reticulopodia to gather sediment with associated algae, organic detritus, and bacteria. Uptake of diatoms by foraminifera have been observed but rarely quantified. We measured the clearance (gathering) rate and ingestion rate of diatoms by the common benthic foraminifer Quinqueloculina seminula using Nitzschia closterium as prey under laboratory culture conditions. Grazing experiments were performed to evaluate the effects of temperature (at 12, 15, 18, 21, and 24°C) and food availability (10 to 800 cells mm−2) on uptake rates of diatoms. The clearance rates, estimated from the disappearance of food items, were variable (0.59–4.4 mm2 foram−1 h−1) and did not show a clear relationship with food availability. The maximum clearance rates increased from 1.80 ± 0.21 to 2.69 ± 0.32 mm2 foram−1 h−1 when temperature increased from 12 to 18°C and decreased to 2.28 ± 0.25 mm2 foram−1 h−1 at 24°C. Ingestion rates varied from 1.0 to 43 × 103 diatoms foram−1 h−1, following a hyperbolic response to food concentrations at all experimental temperatures. The maximum individual ingestion rates increased from 842 ± 180 to 1648 ± 480 (mean ± SE) cells foram−1 h−1 and then decreased to 316 ± 54 cells foram−1 h−1 as temperature increased from 12 to 24°C. Experimental results revealed that 12–18°C was the optimal temperature range for Q. seminula feeding for specimens adapted to local conditions. Our study indicates that Q. seminula plays an ecological role by feeding upon benthic diatoms in marine benthic ecosystems.

Feeding by common heterotrophic protists on the mixotrophic alga Gymnodinium smaydae (Dinophyceae), one of the fastest growing dinoflagellates.

Gymnodinium smaydae is one of the fastest growing dinoflagellates. However, its population dynamics are affected by both growth and mortality due to predation. Thus, feeding by common heterotrophic dinoflagellates Gyrodinium dominans, Gyrodinium moestrupii, Oblea rotunda, Oxyrrhis marina, and Polykrikos kofoidii, and the naked ciliate Pelagostrobilidium sp. on G.smaydae was investigated in the laboratory. Furthermore, growth and ingestion rates of O.marina, G.dominans, and Pelagostrobilidium sp. on G.smaydae in response to prey concentration were also determined. Oxyrrhis marina, G.dominans, G.moestrupii, and Pelagostrobilidium sp. were able to feed on G.smaydae, but P.kofoidii and O.rotunda did not feed on this dinoflagellate. The maximum growth rate of O.marina on G.smaydae was 0.411 per day. However, G.smaydae did not support the positive growth of Pelagostrobilidium sp. The maximum ingestion rates of O.marina and Pelagostrobilidium sp. on G.smaydae were 0.27 and 6.91ng C·predator-1 ·d-1 , respectively. At the given mean prey concentrations, the highest growth and ingestion rates of G.dominans on G.smaydae were 0.114 per day and 0.04ng C·predator-1 ·d-1 , respectively. The maximum growth and ingestion rates of O.marina on G.smaydae are lower than those on most of the other algal prey species. Therefore, O.marina may be an effective predator of G.smaydae, but G.smaydae may not be the preferred prey for supporting high growth of the predator in comparison to other species as inferred from a literature survey.