Raptorial Feeding Research Articles

Cyanobacterial chemical warfare affects zooplankton community composition

Summary1. Toxic algal blooms widely affect our use of water resources both with respect to drinking water and recreation. However, it is not only humans, but also organisms living in freshwater and marine ecosystems that may be affected by algal toxins.2. In order to assess if cyanobacterial toxins affect the composition of natural zooplankton communities, we quantified the temporal fluctuations in microcystin concentration and zooplankton community composition in six lakes.3. Microcystin concentrations generally showed a bimodal pattern with peaks in early summer and in autumn, and total zooplankton biomass was negatively correlated with microcystin concentrations. Separating the zooplankton assemblages into finer taxonomic groups revealed that high microcystin concentrations were negatively correlated with Daphnia and calanoid copepods, but positively correlated with small, relatively inefficient phytoplankton feeders, such as cyclopoid copepods, Bosmina and rotifers.4. In a complementary, mechanistic laboratory experiment using the natural phytoplankton communities from the six lakes, we showed that changes in in situ levels of microcystin were coupled with reduced adult size and diminished juvenile biomass in Daphnia.5. We argue that in eutrophic lakes, large unselective herbivores, such as Daphnia, are ‘sandwiched’ between high fish predation and toxic food (cyanobacteria). In combination, these two mechanisms may explain why the zooplankton community in eutrophic lakes generally comprise small forms (e.g. rotifers and Bosmina) and selective raptorial feeders, such as cyclopoid copepods, whereas large, unselective herbivores, such as Daphnia, are rare. Hence, this cyanobacterial chemical warfare against herbivores may add to our knowledge on population and community dynamics among zooplankton in eutrophic systems.

Structure of subtidal and intertidal communities of psammophilous ciliates of the Pechora Sea

A rich and diverse bottom ciliate fauna (168 species) was observed in the course of the studies of the subtidal and intertidal zones of the Pechora Sea; 81 of them were encountered for the first time in the Barents Sea region. As compared to the intertidal fauna, the sublittoral ciliofauna featured a higher species diversity but a lower total abundance (32.6 and 20.7 species per station and 10–100 and 2.4–443 ind./cm2 in the subtidal and intertidal zones, respectively). With respect to trophic strategies, raptorial feeders were most abundant in the sublittoral zone (up to 77% of the total biomass), while both raptorial feeders (45%) and upstream filter feeders (36%) dominated in the littoral sediments. In the subtidal zone, two different types of ciliate communities were distinguished according to their total abundance and species composition. The first type is represented by abundant and species-rich communities mainly dominated by large specific interstitial ciliates developed over fine-grained well-sorted sands. The second type of communities joins mainly nonspecific eurybiotic ciliates dwelling over heterogeneous silty sediments; they feature lower abundance and species richness values. The high species diversity, the low abundance or absolute absence of meso-and polysaprobic groups indicating organic pollution, and the high values of the ABC size structure index suggested a good condition of the sediments and biota in the region studied.

Fate of copepod faecal pellets and the role of Oithona spp.

Because the downward flux of zooplankton faecal pellets (FP) measured in sediment traps is typically lower than FP production in overlaying waters, it is inferred that FP are recycled. One suggested explanation for low export fluxes of FP is retention through processes such as FP ingestion (coprophagy) and FP fragmentation (coprorhexy). It has become accepted that the globally important cyclopoid copepod Oithona spp. are one of the main organisms causing high retention of copepod FP, however, the experimental evidence supporting this hypothesis is limited. We conducted 3 experiments to test whether the raptorial feeding Oithona spp. removed sinking FP material pro- duced by Calanus finmarchicus either by grazing or fragmentation. No such evidence was found. We therefore suggest that alternative explanations for pellet recycling should be sought. We believe that Oithona spp. may be indicator species for a 'retention ecosystem', but they are probably not the single factor explaining FP retention in the world oceans.

The behaviour of an omnivorous protozoan affects the extent of induced morphological defence in a protozoan prey

Summary1. The ciliate Euplotes octocarinatus responds to the presence of Stylonychia mytilus with a morphological transformation rendering its ingestion more difficult. Predation on Euplotes is reduced when an alternative prey, the flagellate Chlorogonium elongatum, is available. Lower predation is accompanied by reduced induction in Euplotes.2. We quantified the motility of both ciliates in the presence and absence of Chlorogonium to test the hypothesis that the differential response in Euplotes is a consequence of behavioural changes affecting the encounter rate of the prey and the predator.3. The results indicate that S. mytilus uses different feeding strategies for each prey. It is a filter feeder when small food particles (Chlorogonium) are abundant, however, it becomes a raptorial feeder when large prey with an escape capability (Euplotes) is available and small alternative prey are absent.4. As the mobility of filter feeding Stylonychia is strongly limited, the presence of the flagellate may indirectly affect the defence level in Euplotes by reducing the frequency of contacts with the predator.5. An experiment with Chaetogaster diastrophus, a more specialised predator not affected by the presence of Chlorogonium, as well as direct manipulation of the encounter rate by changing the surface area available for the crawling ciliates, supported the encounter rate hypothesis.

Feeding selectivities and food niche separation of Acartia clausi, Penilia avirostris (Crustacea) and Doliolum denticulatum (Thaliacea) in Blanes Bay (Catalan Sea, NW Mediterranean)

Selectivity-size spectra, clearance and ingestion rates and assimilation efficiencies of Acartia clausi (Copepoda), Penilia avirostris (Cladocera) and Doliolum denticulatum (Doliolida) from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluated in grazing experiments over a wide range of food concentrations (0.02-8.8 mm 3 L -1 plankton assemblages from Blanes Bay, grown in mesocosms at different nutrient levels). Acartia clausi reached the highest grazing coefficients for large algae >70 μm (longest linear extension), P. avirostris for intermediate food sizes between 15 and 70 μm, and D. denticulatum for small sizes from 2.5 to 15 μm. Penilia avirostris and D. denticulatum acted as passive filler-feeders. Acartia clausi gave some evidence for a supplementary raptorial feeding mode. Effective food concentration (EFC) decreased linearly with increasing nutrient enrichment for D. denticulatum and followed domed curves for A. clausi and for P. avirostris with maximum values at intermediate and high enrichment levels, respectively. Clearance rates of crustacean species showed curvilinear responses with narrow modal ranges to increasing food concentration. Clearance rates of D. denticulatum increased abruptly and levelled into a plateau at low food concentrations. Mean clearance rates were 13.9, 25.5 and 64.1 mL ind. -1 day -1 , respectively. No clearance could be detected for A. clausi at food concentrations <0.1 mm 3 L -1 and for P. avirostris at food concentrations <0.02 mm 3 L -1 . Ingestion rates indicate a rectilinear functional response for A. clausi and for P. avirostris and showed a sigmoidal curve for D. denticulatum. Mean ingestion rates were 1.3, 2.8 and 7.7 μg C μg C ind . -1 day -1 , respectively. Conversion of ingested carbon to tissue was 30-80% for the investigated crustaceans and 20-50% for doliolids. Food niche calculations suggest that food niche separation may explain the coexistence of the three species in summer in Blanes Bay.

Reversed sexual dimorphism in tawny owls, Strix aluco, correlates with duty division in breeding effort

Even though most bird species with a raptorial feeding habit express varying extents of reversed sexual dimorphism (RSD: females bigger than males), the evolutionary basis for its maintenance, as well as its possible secondary consequences for the ecological adaptations of the different sexes, is debated. We studied pairs of tawny owls, Strix aluco (females 20% heavier than males), throughout the year by telemetry to test whether any inter‐sexual differences in movement patterns, resource partitioning and breeding effort correlated with RSD. Females were larger than males in all body size measures and were 16% heavier than would be expected from the difference in wing length alone. In accordance with predictions from flight economics, males moved longer distances per time unit than females, in particular during the post‐fledging season, when they also fed chicks more often than the females. Males had larger home ranges than females during the post‐fledging period, whereas the sexes had home ranges of equal size during the non‐breeding season. Until 10 days after fledging, females foraged much closer to the offspring than males, apparently balancing their distance to offspring between the needs of offspring guarding and foraging. In males, the parent–offspring distance only increased with decreasing brood condition. The sexes did not differ in habitat use or feeding habits, rendering no indications of food niche partitioning. The study provides further evidence that selection for males to be light and energetically efficient foragers is the main evolutionary force behind RSD in raptorial birds, even when the prey base is confined by territoriality.

Three new genera of the Ridgewayiidae (Copepoda, Calanoida) from anchialine caves in the Bahamas

Stargatia palmeri gen. et sp. nov. was obtained in great numbers in plankton from very low dissolved oxygen waters of Stargate Blue Hole, South Andros at 44 r m depth. The species shows similarities to Exumellina bucculenta Fosshagen in the modifications of the endopod of both mandible and maxillule, and by the presence of only two outer spines on the third exopod segment of legs 3 and 4. The rostrum comprises two rounded lobes without filaments. The right antennule of the male is modified in proximal part with extra geniculations. It differs from other ridgewayiids by not having the typical offset third exopod segment in the female leg 5. Robpalmeria asymmetrica gen. et sp. nov. was also recorded from Stargate Blue Hole. In the female the last somite of the prosome is asymmetrical. The rostrum is narrow with two filaments at the tip. The maxilliped is strongly developed, reflexed and with a condensed endopod bearing several modified setae; suggesting raptorial feeding. Leg 5 in the male has complex exopo...

Alternative feeding mechanisms in megalopae of the blue crab Callinectes sapidus

The apparent mismatch between the energy requirements for planktotrophic growth and prey availability has long been paradoxical. One hypothesis to explain this paradox is that planktotrophic larvae display plasticity in feeding mechanisms in response to variable prey types and concentrations. This hypothesis was tested by videotaping megalopae of the brachyuran crab Callinectessapidus Rathbun feeding on various-sized prey. Frame-by-frame analysis of the videotapes indicated that C. sapidus megalopae used both raptorial and suspension feeding to capture prey while in the water column. Raptorial feeding was used to capture macro-zooplankton, including copepods. The swimming form of suspension feeding was based on a modified fling-and-clap mechanism using the chelipeds. Suspension feeding while at rest utilized a weak current generated by the mouthparts to direct prey to the mouth. Both suspension-feeding mechanisms resulted in the efficient capture of rotifer-sized particles. The energy/handling time ratios for all three feeding mechanisms are very similar (E/H range 0.016–0.019 µg C s–1) for the natural prey tested. These results support the hypothesis that feeding in brachyuran larvae is plastic and includes mechanisms of both raptorial and suspension feeding. The ability to suspension feed at rest is adaptive, since megalopae use selective tidal transport to re-invade an estuary and may spend up to 18 h day–1 clinging to a benthic substrate. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00227-002-0781-1.

Phagotrophic Mechanisms and Prey Selection in Free‐living Dinoflagellates1

Three types of feeding mechanisms are known in dinoflagellates: pallium feeding, tube feeding, and direct engulfment. Pallium feeding has only been described for heterotrophic thecate species (Protoperidinium, Diplopsalis group). Tube feeding is commonly found among both naked and thecate species of mixotrophic and heterotrophic dinoflagellates (e.g. Amphidinium, Dinophysis, Gyrodinium, Peridiniopsis). Direct engulfment is mainly found among naked species (e.g. Gymnodinium, Gyrodinium, Noctiluca): recently, however, some thecate species have been shown to use this feeding mechanism as well. Feeding behavior in dinoflagellates involves several steps prior to actual ingestion, including precapture, capture, and prey manipulation. As feeding mechanisms allow the ingestion of relatively large prey or parts thereof, dinoflagellates are regarded as raptorial feeders. While prey size plays an important role in the ability of dinoflagellates to ingest food, this alone cannot explain observed prey preferences. Some dinoflagellate species can be very selective in their choice of prey, while others show a remarkable versatility.

Effects of Food Availability and Predation on a Marine Zooplankton Community — a Study on Copepods in the Baltic Sea

AbstractThe importance of food resources versus predatory effects in determining the abundance pattern of zooplankton varies over time and space. Here, we evaluate the population dynamics of dominant calanoid copepods (Acartia spp. bifilosa/A. longiremis and Eurytemora affinis) in a reference area and a eutrophied area in the northern Baltic Sea Proper. We base the paper on a combination of statistical analyses of a long term (12 years) data set on population biomass dynamics, laboratory experiments on the feeding biology of these species and literature data of their susceptibility to predation. Overall, copepods were equally abundant at both sites, but Eurytemora was more abundant in the eutrophied area while Acartia spp. dominated in the non‐eutrophied reference area. There was, however, no significant difference between the two areas in biomass dynamics (biomass specific rate of change) of the two groups of copepods. However, in spring and early summer the population biomass increased faster for Eurytemora as compared to Acartia spp. This is consistent with our findings from feeding and respiration experiments. Eurytemora exhibited generally higher ingestion rates and had a higher growth efficiency (ratio of ingestion to respiration rates), which suggests an advantage over Acartia spp. when food availability increases. Both species generally showed a rapid population decline starting in late summer, most likely caused by intensive predation by fish and mysid shrimps. In late autumn and winter, biomasses of both genera continued to decrease, but the decline was fastest for Eurytemora. During this period of the year, when the food availability is sparse, Acartia spp. may have an advantage over Eurytemora, as we found that the former ingests a broader size range of food particles and it has also been reported to be able to switch from filter feeding to raptorial feeding. This study shows that dominant copepods in the net‐zooplankton community in our study area were structured both by food availability and predation. The relative importance of these effects varied seasonally.

Kinetid architecture and bicosoecid affinities of the marine heterotrophic nanoflagellate Caecitellus parvulus (Griessmann, 1913) Patterson et al., 1993

Summary The kinetid of the common marine heterotrophic nanoflagellate Caecitellus parvulus ( Griessmann, 1913 ) Patterson et al., 1993 is essentially identical to those found in members of the stramenopile protist order Bicosoecida (= Bicosoecales) in absolute configuration, microtubular root characters, especially those of root R3, and the structure and arrangement of bands connecting the basal bodies to each other and to the microtubular roots. Caecitellus parvulus , originally assigned to the bodonids (as Bodo parvulus ), is therefore considered to be allied with the Bicosoecida. The characters distinguishing the genus Caecitellus from other bicosoecids include the presence of gliding motility and a raptorial feeding mechanism, as well as the absence of flagellar hairs, a filter feeding mechanism, and the ability to adhere to substrate by the tip of the posterior flagellum. These results suggest that the stramenopile clade that includes bicosoecids and Caecitellus is likely to contain much additional taxonomic, morphological and ecological diversity.

Benefits and costs of predator-induced morphological changes in the ciliate Colpidium kleini (Protozoa, Ciliophora)

Summary Phenotypic transformation of C. kleini occurred when the prey coexisted with the predatory ciliate Lembadion bullinum for at least 24 hours, and was completed after 36–48 h. Net-separated predator medium caused visible shape changes in the prey. The induced phenotype was about 60% wider and 20% shorter than the typical one and had an almost spherical shape. The results showed that the induced morphological changes are a defense against L. bullinum, which is a raptorial feeder. In the presence of 100 predators, on an average 132 of 150 induced phenotypes survived for 2 h, but in the same conditions only 33 of 150 normal phenotypes did. The predator needed significantly more time and had to repeat attacks many times to catch and engulf the morphologically transformed prey. Only 16% of the attacks ended in ingestion of the transformed prey in less than 15 min, while in 54% of the cases the typical C. kleini form was ingested during the first predator attack, which occurred in the first 2 min. The growth rate of induced C. kleini phenotypes was on an average about 25% less than that of typical ones, indicating the substantial cost of the defense mechanism. Other predacious ciliates such as Dileptus margaritifer, Homalozoon vermiculare and Stylonychia mytilus did not cause any morphological changes in C. kleini.

A Cautionary Note on Measuring Protistan Bacterivory by Acid Lysozyme

A Cautionary Note on Measuring Protistan Bacterivory by Acid Lysozyme

Digestive process of the raptorial feeder ciliate Litonotus lamella (Rabdophora, Litostomatea) visualized by fluorescence microscopy

In this paper we present a fluorescence microscopy investigation of the digestive process of Litonotus lamella, which we used as a prototype of the raptorial feeding behaviour. The sequence of its digestive processes, from the capture of the prey ( Euplotes crassus) to the formation of digestive vacuoles was evidenced using Acridine Orange, a high quantum yield fluorescent vital probe which has a great affinity with the acid vesicle compartments. Acid vesicle localization and displacement during digestion consisted of the following phases: in starved Litonotus vesicles were localized in the neck of the ciliate; after the capture, they were displaced around the vacoule containing the prey in early digestiion, whereas in advanced digestion tens of digestive vacuoles containing Euplotes fragments were spread over the body of the predator; 1 h after capture, the digestive process was complete, and acid vesicles reorganized in the neck of the predator. The most important feature we observed was that the digestive process occurred not in the single phagosome as in filter feeder ciliates, such as Paramecium, but in many digestive vacuoles scattered all over the predator cytoplasm, which asynchronously digest prey fragments.

FILAMENTOUS ALGAE AN ADDITIONAL FOOD FOR THE PREDATORY ANOSTRACAN BRANCHINECTA GIGAS

We observed Branchinecta gigas Lynch of a size known to feed by raptorial predation feeding on a clump of filamentous algae in the genus Spirogyra. A review of feeding in the Anostraca points to great diversity and suggests there is much yet to be learned.

Growth rates of dominant planktonic ciliates in two freshwater bodies of different trophic degree

The in situ growth rates of dominant ciliate species were studied during and shortly after phytoplankton peaks in two water bodies: the eutrophic Ri'mov Reservoir (South Bohemia, Czech Republic) and the oligo-mesotrophic Piburger See (Tyrol, Austria). Growth rate estimates based on changes in ciliate abundances in incubated pre-screened samples (EN) were compared with those derived from the ciliate cell volume and ambient temperatures (£T). The values of EN were always rather lower than those of £T. During the studies, the food supply limited the ciliate growth depending on the ciliate feeding mode. An ecological grouping into filter feeding versus raptorial feeding ('hunt- ing') species, on the one hand, and attached/crawling (browsing) versus free swimming species, on the other hand, clearly affected experimental estimation. Both fine filter feeders (namely attached) and browsers exhibited a calculated £N closer to the theoretical (maximum) £T than did hunters and coarse filter feeders. It was apparent, for example, comparing £N and £T (day1) of the following species: filter feeders Halieria grandinella (£N = 0.42; £T >1.4), Strobilidium hexakinetum (0.34; >1.9), Pelagohalte- ria viridis (0.27; >0.9), Vorticella aquadulcis complex (0.75; >1.0); raptorial Balamon planctonicum (0.65; >1.5), Urotricha furcata (in Ri'mov Reservoir 0.65; >2.1; in Piburger See 0.20; >1.5), Rhab- doaskenasia minima (0.22; >1.0), Askenasia acrostomia (0.12; >0.6); opportunistic Cyrtolophosis mucicola (0.42; >1.6) and Cinetochilum margaritaceum (0.86; >1.4). Predation by rotifers apparently affected measurements in several samples containing —400 rotifers I1; however, it seemed to be of little importance in the water column.

Impact of Aurelia aurita medusae (Cnidaria, Scyphozoa) on the standing stock and community composition of mesozooplankton in the Kiel Bight (western Baltic Sea)

During 5 consecutive summer seasons (1990 to 1994) both Aureliaaurita medusa and mesozooplankton abundances were investigated at 2 stations in the Kiel Bight (western Baltic Sea). Stocks of medusae varied considerably between the years, with median abundance of 1 and 0.3 ind. 100 m-3 in 1990 and 1991, 3 and 4 ind. 100 m-3 in 1992 and 1994, but 9 ind. 100 m-3 in 1993. Significant differences in the mesozooplankton stock and community composition were observed in 1993 when compared with the year of rather low Aurelia abundance (1991). Total zooplankton and copepod numbers both exhibited an inverse relationship with the abundance of medusae and were thus considerably lower in 1993 than in 1991. However, not all copepod species were affected by A. aurita. Pseudo- and Paracalanus spp. and Oithonasimilis showed dramatically reduced stocks in the bloom year when compared with the medusa-poor situation, but no significant changes were found for Centropageshamatus and Acartia spp. Also other zooplankton groups with the exception of bivalve larvae were reduced by the medusae. The differential response of zooplankton to varying abundance of medusae led to a shift in the trophic structure of the zooplankton community. Fine-filter feeders and raptorial feeders were much more important in years when medusae occurred in low densities, whereas coarse-filter feeders dominated in the opposite situation.

Occurrence of cyclopoid copepods and faecal material in the Halley Bay region, Antarctica, during January?February 1991

Faecal material and cyclopoid copepods were collected during the expedition ANT IX/3, in the Halley Bay area (Weddell Sea, Antarctica), between January and February 1991. Faecal material comprised pellets produced by krill, copepods, ostracods and appendicularians. Cyclopoid copepods were represented by two genera, Oithona and Oncaea. In the Halley Bay area, higher concentrations of krill faecal material (420.9 mm3 m−2) and chl.-a (39.3 mg m−2) were found within the upper 200 m of the water column of the polynya than in ice-covered open-ocean areas (58.2 mm3m−2 and 25.5 mg m−2, respectively). At an ice-drift station, high concentrations of krill faecal strings under fest-ice were found. In addition, similarities between diatom assemblages in the pack-ice algae and krill faecal strings contents suggest an active utilization of ice-algae by krill populations. Sedimented material collected at 50 m depth by a sediment trap was dominated by krill faecal strings. Contents of small oval pellets (of probable cyclopoid copepod origin) resemble those of krill faecal pellets suggesting that coprophagy was involved. This suggestion is supported by: (1) The small quantity of food particles (other than krill faecal matter) available in the water column (< 0.3 μg chl.-al−1). (2) The negative in situ correlation between krill faecal strings and cyclopoid copepods. (3) The structure of cyclopoid copepod buccal appendages, which are more adapted for raptorial feeding.

The Possible Origin of Mucus Jets Used for Immobilizing Prey in Species of Euchirella (Copepoda, Calanoida, Aetideidae). I. Theoretical Considerations in Relation To Swimming and Feeding Behaviour

The origin of jets of mucus produced in raptorial feeding by species of Euchirella has previously been related to two distinct types of glandular pores in the oral cavity, viz., to urn-shaped and to tubular pores, respectively. The dimensions of both types of integumental organs present no theoretical clues, however, as to which type would be better suited to extrude masses of mucous secretion with hydrodynamic properties such as required to travel some definite distance through the water on their own.

Identifying ecosystem properties: a case study using plankton biomass size distributions

Abstract Concepts regarding the hierarchical organization of ecosystems postulate the existence of specific properties that emerge at the ecosystem level. As an example, empirically based biomass size distributions of a pelagic ecosystem (Lake Constance) were investigated. The plankton biomass was approximately uniformly distributed over the entire sie-range from bacteria (10−14 gC/cell) to crustaceans (10−4 g C/individual) on a seasonal average. The continuum of organisms with respect to body size may indicate the existence of a continuum of functional guilds in the planktonic food web, owing to the close relationship between body size and physiological and ecological features of planktonic organisms. It is hypothesized that the internal organization of the pelagic food web (mediated by interspecific competition and successful invasion into “empty” size-ranges) promotes an approximately regular distribution of biomass over the range of functional guilds. This process may be an underlying mechanism for the observed regular size distribution of biomass in pelagic ecosystems. Regarding second-order effects, systematic deviations from the overall rule of a uniform biomass size distribution were observed. The plankton community of Lake Constance was divided into two autotrophic and five heterotrophic groups to analyze potential causes for biomass accumulation in certain size ranges. The allocation of organisms into groups was based on the vulnerability of the algae to grazing, and on the feeding modes (raptorial feeders vs. filter feeders) and prey sizes of the heterotrophs. The overlapping size spectra of the different groups were calculated for different time periods during the season. They revealed that specific properties of component organisms influencing the flow of matter from small to larger sized organisms may cause deviations from a regular size distribution of biomass. For example, algae with a low vulnerability to grazing, and daphniids which feed on a broad range of relatively small prey organisms, both formed modes in the size spectrum. The dominance of size-ranges (≈groups of organisms) with respect to biomass changed seasonally. These findings contradict a former conjecture that biomass accumulations in size spectra reflect the action of ecological second-order scaling factors.