Mixotrophy in the phototrophic harmful alga Cochlodinium polykrikoides (Dinophycean): prey species, the effects of prey concentration, and grazing impact

We first reported here that the harmful alga Cochlodinium polykrikoides, which had been previously known as an autotrophic dinoflagellate, was a mixotrophic species. We investigated the kinds of prey species and the effects of the prey concentration on the growth and ingestion rates of C. polykrikoides when feeding on an unidentified cryptophyte species (Equivalent Spherical Diameter, ESD = 5.6 microm). We also calculated grazing coefficients by combining field data on abundances of C. polykrikoides and co-occurring cryptophytes with laboratory data on ingestion rates obtained in the present study. Cocholdinium polykrikoides fed on prey cells by engulfing the prey through the sulcus. Among the phytoplankton prey offered, C. polykrikoides ingested small phytoplankton species that had ESD's < or = 11 microm (e.g. the prymnesiophyte Isochrysis galbana, an unidentified cryptophyte, the cryptophyte Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellate Amphidinium carterae). It did not feed on larger phytoplankton species that had ESD's > or = 12 microm (e.g. the dinoflagellates Heterocapsa triquetra, Prorocentrum minimum, Scrippsiella sp., Alexandrium tamarense, Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum). Specific growth rates of C. polykrikoides on a cryptophyte increased with increasing mean prey concentration, with saturation at a mean prey concentration of approximately 270 ng C ml(-1) (i.e. 15,900 cells ml(-1)). The maximum specific growth rate (mixotrophic growth) of C. polykrikoides on a cryptophyte was 0.324 d(-1), under a 14:10 h light-dark cycle of 50 microE m(-2) s(-1), while its growth rate (phototrophic growth) under the same light conditions without added prey was 0.166 d(-1). Maximum ingestion and clearance rates of C. polykrikoides on a cryptophyte were 0.16 ng C grazer(-1)d(-1) (9.4 cells grazer(-1)d(-1)) and 0.33 microl grazer(-1)h(-1), respectively. Calculated grazing coefficients by C. polykrikoides on cryptophytes were 0.001-0.745 h(-1) (i.e. 0.1-53% of cryptophyte populations were removed by a C. polykrikoides population in 1 h). The results of the present study suggest that C. polykrikoides sometimes has a considerable grazing impact on populations of cryptophytes.     

Feeding by the newly described, nematocyst-bearing heterotrophic dinoflagellate Gyrodiniellum shiwhaense

We explored the feeding ecology of the newly described, nematocyst-bearing heterotrophic dinoflagellate Gyrodiniellum shiwhaense (GenBank accession number=FR720082). Using several different types of microscopes and high-resolution video-microscopy, we investigated feeding behavior and types of prey species that G. shiwhaense feeds upon. Additionally, we measured its growth and ingestion rates on its optimal algal prey, the cryptophyte Teleaulax sp. and the dinoflagellate Amphidinium carterae, as a function of prey concentration. These rates were measured for other edible prey at single prey concentrations at which the growth and ingestion rates of G. shiwhaense were saturated. After anchoring the prey with a tow filament, G. shiwhaense fed using a peduncle, ingesting small algal species with equivalent spherical diameters (ESDs) of <13 μm. However, it did not feed on larger algal species that had ESDs≥13 μm or the small diatom Skeletonema costatum. The specific growth rates for G. shiwhaense feeding upon Teleaulax sp. and A. carterae increased rapidly with increasing mean prey concentration before saturating at concentrations of ca. 180-430 ng C/ml. The maximum specific growth rate of G. shiwhaense on Teleaulax sp. and A. carterae were 1.05 and 0.82/d, respectively. However, Heterosigma akashiwo did not support positive growth of G. shiwhaense. The maximum ingestion rates of G. shiwhaense on Teleaulax sp. and A. carterae were 0.35 and 0.54 ng C/grazer/d, respectively. The calculated grazing coefficients attributable to G. shiwhaense on co-occurring cryptophytes and Amphidinium spp. were 0.01-1.87/d and 0.08-2.60/d, respectively. Our results suggest that G. shiwhaense can have a considerable grazing impact on algal populations.     

Mixotrophy in the newly described phototrophic dinoflagellate Woloszynskia cincta from western Korean waters: feeding mechanism, prey species and effect of prey concentration

Woloszynskia species are dinoflagellates in the order Suessiales inhabiting marine or freshwater environments; their ecophysiology has not been well investigated, in particular, their trophic modes have yet to be elucidated. Previous studies have reported that all Woloszynskia species are photosynthetic, although their mixotrophic abilities have not been explored. We isolated a dinoflagellate from coastal waters in western Korea and established clonal cultures of this dinoflagellate. On the basis of morphology and analyses of the small/large subunit rRNA gene (GenBank accession number=FR690459), we identified this dinoflagellate as Woloszynskia cincta. We further established that this dinoflagellate is a mixotrophic species. We found that W. cincta fed on algal prey using a peduncle. Among the diverse prey provided, W. cincta ingested those algal species that had equivalent spherical diameters (ESDs) ≤12.6 μm, exceptions being the diatom Skeletonema costatum and the dinoflagellate Prorocentrum minimum. However, W. cincta did not feed on larger algal species that had ESDs≥15 μm. The specific growth rates for W. cincta increased continuously with increasing mean prey concentration before saturating at a concentration of ca. 134 ng C/ml (1,340 cells/ml) when Heterosigma akashiwo was used as food. The maximum specific growth rate (i.e. mixotrophic growth) of W. cincta feeding on H. akashiwo was 0.499 d(-1) at 20 °C under illumination of 20 μE/m(2) /s on a 14:10 h light-dark cycle, whereas its growth rate (i.e. phototrophic growth) under the same light conditions without added prey was 0.040 d(-1). The maximum ingestion and clearance rates of W. cincta feeding on H. akashiwo were 0.49 ng C/grazer/d (4.9 cells/grazer/d) and 1.9 μl/grazer/h, respectively. The calculated grazing coefficients for W. cincta on co-occurring H. akashiwo were up to 1.1 d(-1). The results of the present study suggest that grazing by W. cincta can have a potentially considerable impact on prey algal populations.     

Prey-dependent retention of dimethylsulfoniopropionate (DMSP) by mixotrophic dinoflagellates

We investigated the retention of dimethylsulfoniopropionate (DMSP) in phototrophic dinoflagellates arising from mixotrophy by estimating the cellular content of DMSP in Karlodinium veneficum (mixotrophic growth) fed for 7-10 days on either DMSP-rich Amphidinium carterae (phototrophic growth only) or DMSP-poor Teleaulax sp. (phototrophic growth only). In K. veneficum fed on DMSP-poor prey, the cellular content of DMSP remained almost unchanged regardless of the rate of feeding, whereas the cellular content of DMSP in cells of K. veneficum fed on DMSP-rich prey increased by as much as 21 times the cellular concentration derived exclusively from phototrophic growth. In both cases, significant fractions (10-32% in the former case and 55-65% in the latter) of the total DMSP ingested by K. veneficum were transformed into dimethylsulfide and other biochemical compounds. The results may indicate that the DMSP content of prey species affects temporal variations in the cellular DMSP content of mixotrophic dinoflagellates, and that mixotrophic dinoflagellates produce DMS through grazing on DMSP-rich preys. Additional studies should be performed to examine the universality of our finding in other mixotrophic dinoflagellates feeding on diverse prey species.     

KLEPTOPLASTIDY IN THE TOXIC DINOFLAGELLATE PFIESTERIA PISCICIDA (DINOPHYCEAE)

The ichthyotoxic dinoflagellate Pfiesteria piscicida Steidinger et Burkholder has a complex life cycle with several heterotrophic flagellated and amoeboid stages. A prevalent flagellated form, the nontoxic zoospore stage, has a proficient grazing ability, especially on cryptophyte prey. Although P. piscicida zoospores lack the genetic capability to synthesize chloroplasts, they can obtain functional chloroplasts from algal prey (i.e. kleptoplastidy), as demonstrated here with a cryptophyte prey. Zoospores grown with Rhodomonas sp. Karsten CCMP757 (Cryptophyceae) grazed the cryptophyte population to minimal densities. After placing the cultures in near darkness where cryptophyte recovery was restricted and further prey ingestion did not occur, the time-course patterns in growth, prey chloroplast content·zoospore⁻¹, and prey nucleus content·zoospore⁻¹ were followed. Ingested chloroplasts were selectively retained in the dinoflagellate, as indicated by the decline and, ultimately, near absence of cryptophyte nuclei in plastid-containing zoospores. Chloroplasts retained inside P. piscicida cells for at least a week were photosynthetically active, as indicated by starch accumulation and microscope-autoradiographic measurements of bicarbonate uptake. Recognition that P. piscicida can function as a phototroph broadens our perspective of the physiological ecology of the dinoflagellate because it suggests that, at least during part of its life cycle, P. piscicida 's growth and survival might be affected by photoregulation and nutritional control of photosynthesis.     

Growth and Grazing Rates of the Heterotrophic Dinoflagellate Polykrikos kofoidii on Red-Tide and Toxic Dinoflagellates

We investigated growth rates, grazing rates, and prey selection of Polykrikos kofoidii when feeding on several species of red-tide and/or toxic dinoflagellates. Polykrikos kofoidii ingested all prey species used in this study, exhibiting positive growth on Lingulodinium polyedrum, Scrippsiella trochoidea, Ceratium furca, Gymnodinium catenatum, Gyrodinium impudicum, Prorocentrum micans, and the toxic dinoflagellate Amphidinium carterae, but not on P. minimum. Specific growth rates of P. kofoidii increased rapidly with increasing density of L. polyedrum, S. trochoidea, C. furca, and G. catenatum before saturating between 500-2,000 ng C ml(-1). Specific growth rates increased continuously when P. kofoidii was fed the other prey species. Maximum specific growth rates of P. kofoidii on G. catenatum (1.12 d(-1)), S. trochoidea (0.97 d(-1)), and L. polyedrum (0.83 d(-1)) were higher than those on C. furca (0.35 d(-1)), A. carterae (0.10 d(-1)), P. micans (0.06 d(-1)), G. impudicum (0.06 d(-1)), and P. minimum (-0.03 d(-1)). Threshold prey concentrations (where net growth = 0) were 54-288 ng C ml(-1). Maximum ingestion and clearance rates of P. kofoidii on these dinoflagellates were 5-24 ng C pseudocolony(-1) d(-1) and 1.0-5.9 microl pseudocolony(-1) h(-1), respectively. Polykrikos kofoidii strongly selected L. polyedrum over S. trochoidea in prey mixtures. Polykrikos kofoidii exhibited higher maximum growth, ingestion, and clearance rates than previously reported for the mixotrophic dinoflagellate Fragilidium cf. mexicanum or the heterotrophic dinoflagellates Protoperidinium cf. divergens and P. crassipes, when grown on the same prey species. Grazing coefficients calculated by combining field data on abundances of Polykrikos spp. and co-occurring red-tide dinoflagellate prey with laboratory data on ingestion rates obtained in the present study suggest that Polykrikos spp. sometimes have a considerable grazing impact on prey populations.     

ESTUARINE HETEROTROPHIC CRYPTOPERIDINIOPSOIDS (DINOPHYCEAE): LIFE CYCLE AND CULTURE STUDIES1

Cryptoperidiniopsoids are an unclassified group of delicately thecate heterotrophic dinoflagellates known to be common in eastern U.S. estuarine waters. Over the past 10 years cryptoperidiniopsoids were isolated from different geographical regions and cultured with cryptophyte algal prey. In the seven clonal isolates examined, reproduction was strongly linked to the availability of prey cells. The dinoflagellates phagocytized the contents of prey cells through a tube‐like peduncle, similarly as close relatives of Pfiesteria spp. and several other heterotrophic species. Cell division occurred while encysted, most commonly yielding two biflagellated offspring. Abundant fusing gametes, phagotrophic planozygotes, and cysts with a pronounced nuclear cyclosis characterized persistent sexuality. Cysts with nuclear cyclosis produced two flagellated offspring cells. The resistance of reproductive cysts to antimicrobial treatments was examined, and a simple high‐yield technique was developed for population synchronization while ridding the dinoflagellates of most contaminating vacuolar prey DNA and external contaminants. The DNA content and population DNA profiles of synchronously excysted cryptoperidiniopsoids from different isolates were measured using flow cytometry and were related to the life history of these and other dinoflagellates. Cryptophyte‐fed cultures with versus without extracellular bacteria were compared, and bacteria apparently promoted cryptoperidiniopsoid feeding and growth. Externally bacteria‐free dinoflagellates were cultured in media enriched with dissolved organic nutrients, and nutritional benefit may have occurred in some treatments. The potential for mixotrophic nutrition from maintenance of cryptophyte chloroplasts was examined using flow cytometrically sorted cells, but evidence of kleptoplastidy was not found in these isolates under the conditions imposed.     

Feeding by the heterotrophic dinoflagellate Oxyrrhis marina on the red-tide raphidophyte Heterosigma akashiwo: a potential biological method to control red tides using mass-cultured grazers

As part of the development of a method to control the outbreak and persistence of red tides using mass-cultured heterotrophic protist grazers, we measured the growth and ingestion rates of cultured Oxyrrhis marina (a heterotrophic dinoflagellate) on cultured Heterosigma akashiwo (a raphidophyte) in bottles in the laboratory and in mesocosms (ca. 60 liter) in nature, and those of the cultured grazer on natural populations of the red-tide organism in mesocosms set up in nature. In the bottle incubation, specific growth rates of O. marina increased rapidly with increasing concentration of cultured prey up to ca. 950 ng C ml(-1) (equivalent to 9,500 cells ml(-1)), but were saturated at higher concentrations. Maximum specific growth rate (mumax), KGR (prey concentration sustaining 0.5 mumax) and threshold prey concentration of O. marina on H. akashiwo were 1.43 d(-1), 104 ng C ml(-1), and 8.0 ng C ml(-1), respectively. Maximum ingestion and clearance rates of O. marina were 1.27 ng C grazer(-1) d(-1) and 0.3 microl grazer(-1) h(-1), respectively. Cultured O. marina grew well effectively reducing cultured and natural populations of H. akashiwo down to a very low concentration within 3 d in the mesocosms. The growth and ingestion rates of cultured O. marina on natural populations of H. akashiwo in the mesocosms were 39% and 40%, respectively, of those calculated based on the results from the bottle incubation in the laboratory, while growth and ingestion rates of cultured O. marina on cultured H. akashiwo in the mesocosms were 55% and 36%, respectively. Calculated grazing impact by O. marina on natural populations of H. akashiwo suggests that O. marina cultured on a large scale could be used for controlling red tides by H. akashiwo near aquaculture farms that are located in small ponds, lagoons, semi-enclosed bays, and large land-aqua tanks to which fresh seawater should be frequently supplied.     

The Newly Described Heterotrophic Dinoflagellate Gyrodinium moestrupii,an Effective Protistan Grazer of Toxic Dinoflagellates

Few protistan grazers feed on toxic dinoflagellates, and low grazing pressure on toxic dinoflagellates allows these dinoflagellates to form red‐tide patches. We explored the feeding ecology of the newly described heterotrophic dinoflagellate Gyrodinium moestrupii when it fed on toxic strains of Alexandrium minutum, Alexandrium tamarense, and Karenia brevis and on nontoxic strains of A. tamarense, Prorocentrum minimum, and Scrippsiella trochoidea. Specific growth rates of G. moestrupii feeding on each of these dinoflagellates either increased continuously or became saturated with increasing mean prey concentration. The maximum specific growth rate of G. moestrupii feeding on toxic A. minutum (1.60/d) was higher than that when feeding on nontoxic S. trochoidea (1.50/d) or P. minimum (1.07/d). In addition, the maximum growth rate of G. moestrupii feeding on the toxic strain of A. tamarense (0.68/d) was similar to that when feeding on the nontoxic strain of A. tamarense (0.71/d). Furthermore, the maximum ingestion rate of G. moestrupii on A. minutum (2.6 ng C/grazer/d) was comparable to that of S. trochoidea (3.0 ng C/grazer/d). Additionally, the maximum ingestion rate of G. moestrupii on the toxic strain of A. tamarense (2.1 ng C/grazer/d) was higher than that when feeding on the nontoxic strain of A. tamarense (1.3 ng C/grazer/d). Thus, feeding by G. moestrupii is not suppressed by toxic dinoflagellate prey, suggesting that it is an effective protistan grazer of toxic dinoflagellates.     

Feeding by Phototrophic Red-Tide Dinoflagellates on the Ubiquitous Marine Diatom Skeletonema costatum

ABSTRACT We investigated feeding by phototrophic red‐tide dinoflagellates on the ubiquitous diatom Skeletonema costatum to explore whether dinoflagellates are able to feed on S. costatum, inside the protoplasm of target dinoflagellate cells observed under compound microscope, confocal microscope, epifluorescence microscope, and transmission electron microscope (TEM) after adding living and fluorescently labeled S. costatum (FLSc). To explore effects of dinoflagellate predator size on ingestion rates of S. costatum, we measured ingestion rates of seven dinoflagellates at a single prey concentration. In addition, we measured ingestion rates of the common phototrophic dinoflagellates Prorocentrum micans and Gonyaulax polygramma on S. costatum as a function of prey concentration. We calculated grazing coefficients by combining field data on abundances of P. micans and G. polygramma on co‐occurring S. costatum with laboratory data on ingestion rates obtained in the present study. All phototrophic dinoflagellate predators tested (i.e. Akashiwo sanguinea, Amphidinium carterae, Alexandrium catenella, Alexandrium tamarense, Cochlodinium polykrikoides, G. polygramma, Gymnodinium catenatum, Gymnodinium impudicum, Heterocapsa rotundata, Heterocapsa triquetra, Lingulodinium polyedrum, Prorocentrum donghaiense, P. micans, Prorocentrum minimum, Prorocentrum triestinum, and Scrippsiella trochoidea) were able to ingest S. costatum. When mean prey concentrations were 170–260 ng C/ml (i.e. 6,500–10,000 cells/ml), the ingestion rates of G. polygramma, H. rotundata, H. triquetra, L. polyedrum, P. donghaiense, P. micans, and P. triestinum on S. costatum (0.007–0.081 ng C/dinoflagellate/d [0.2–3.0 cells/dinoflagellate/d]) were positively correlated with predator size. With increasing mean prey concentration of ca 1–3,440 ng C/ml (40–132,200 cells/ml), the ingestion rates of P. micans and G. polygramma on S. costatum continuously increased. At the given prey concentrations, the maximum ingestion rates of P. micans and G. polygramma on S. costatum (0.344–0.345 ng C/grazer/d; 13 cells/grazer/d) were almost the same. The maximum clearance rates of P. micans and G. polygramma on S. costatum were 0.165 and 0.020 μl/grazer/h, respectively. The calculated grazing coefficients of P. micans and G. polygramma on co‐occurring S. costatum were up to 0.100 and 0.222 h, respectively (i.e. up to 10% and 20% of S. costatum populations were removed by P. micans and G. polygramma populations in 1 h, respectively). Our results suggest that P. micans and G. polygramma sometimes have a considerable grazing impact on populations of S. costatum.     

Feeding by the newly described heterotrophic dinoflagellate Stoeckeria changwonensis: A comparison with other species in the family Pfiesteriaceae

The feeding ecology of the newly described heterotrophic dinoflagellate Stoeckeria changwonensis was explored. The feeding behavior of S. changwonensis, and the kinds of prey species that it feeds on were investigated with several different types of microscopes and high-resolution video-microscopy. Additionally, the growth and ingestion rates of S. changwonensis as a function of prey concentration for perch (Lateolabrax japonicus) blood cells, the raphidophyte Heterosigma akashiwo, the cryptophytes Rhodomonas salina and Teleaulax sp., and the phototrophic dinoflagellate Amphidinium carterae prey were measured. S. changwonensis feeds on prey through a peduncle, after anchoring the prey by using a tow filament. This type of feeding behavior is similar to that of Stoeckeria algicida, Pfiesteria piscicida, and Luciella masanensis in the family Pfiesteriaceae; however, S. changwonensis feeds on various kinds of prey species different from those of the other heterotrophic dinoflagellates. S. changwonensis ingested perch blood cells and diverse algal species, in particular, the large thecate dinoflagellate Lingulodinium polyedrum which are not eaten by the other peduncle feeders. H. akashiwo and the perch blood cells supported positive growth of S. changwonensis, but R. salina, Teleaulax sp., and A. carterae which support positive growth of P. piscicida and L. masanensis did not support positive growth of S. changwonensis. With increasing mean prey concentration the growth rates for S. changwonensis on H. akashiwo and the perch blood cells increased rapidly and then slowly or became saturated. The maximum growth rates of S. changwonensis on H. akashiwo and the perch blood cells were 0.376 and 0.354 d⁻¹, respectively. Further, the maximum ingestion rates of S. changwonensis on H. akashiwo and the perch blood cells were 0.35 ng C predator⁻¹ d⁻¹ (3.5 cells predator⁻¹ d⁻¹) and 0.27 ng C predator⁻¹ d⁻¹ (29 cells predator⁻¹ d⁻¹), respectively. These maximum growth and ingestion rates of S. changwonensis on H. akashiwo, the perch blood cells, R. salina, Teleaulax sp., and A. carterae differed considerably from those of S. algicida, P. piscicida, and L. masanensis on the same prey species. Thus, the feeding behavior of S. changwonensis may differ from that of other species in the family Pfiesteriaceae.     

Growth and Grazing Rates of the Marine Planktonic Ciliate Strombidinopsis sp. on Red-Tide and Toxic Dinoflagellates

ABSTRACT We investigated growth and grazing rates of Strombidinopsis sp. when feeding on several species of red-tide and/or toxic dinoflagellates. Strombidinopsis sp. one of the largest aloricate choreotrichs so far reported, grew well on Lingulodinium polyedrum, Gymnodinium sanguineum, Scrippsiella trochoidea, Cochlodinium polykrikoides , and Prorocentrum minimum , but failed to grow on Amphidinium carterae. Specific growth rates of Strombidinopsis sp. increased rapidly with increasing prey density up to ca. 100 ng C ml^-1, but were saturated or increased slightly at higher concentrations. Maximum specific growth rates of Strombidinopsis sp. on various prey species were 1.38 day^-1 for C. polykrikoides , 1.27 for G. sanguineum , 1.06 for P. minimum , 0.83 for L. polyedrum , and 0.67 for S. trochoidea. Threshold prey concentrations (where net growth = 0) were 12–38 ng C ml^-1. Maximum ingestion and clearance rates of Strombidinopsis sp. were 353 ng C grazer^-1 day^-1 and 110 μ, l grazer^-1 h^-1, respectively. Strombidinopsis sp. exhibited higher maximum growth, ingestion, and clearance rates than the mixotrophic dinoflagellate Fragilidium cf. mexicanum or the heterotrophic dinoflagellates Protoperidinium cf. divergens and P. crassipes , when grown on the same prey species. In addition, the sequence of prey species arranged according to growth response of Strombidinopsis sp. differed considerably from those of Fragilidium cf. mexicanum, Protoperidinium cf. divergens , and P. crassipes.     

Feeding currents facilitate a mixotrophic way of life

Mixotrophy is common, if not dominant, among eukaryotic flagellates, and these organisms have to both acquire inorganic nutrients and capture particulate food. Diffusion limitation favors small cell size for nutrient acquisition, whereas large cell size facilitates prey interception because of viscosity, and hence intermediately sized mixotrophic dinoflagellates are simultaneously constrained by diffusion and viscosity. Advection may help relax both constraints. We use high-speed video microscopy to describe prey interception and capture, and micro particle image velocimetry (micro-PIV) to quantify the flow fields produced by free-swimming dinoflagellates. We provide the first complete flow fields of free-swimming interception feeders, and demonstrate the use of feeding currents. These are directed toward the prey capture area, the position varying between the seven dinoflagellate species studied, and we argue that this efficiently allows the grazer to approach small-sized prey despite viscosity. Measured flow fields predict the magnitude of observed clearance rates. The fluid deformation created by swimming dinoflagellates may be detected by evasive prey, but the magnitude of flow deformation in the feeding current varies widely between species and depends on the position of the transverse flagellum. We also use the near-cell flow fields to calculate nutrient transport to swimming cells and find that feeding currents may enhance nutrient uptake by ≈75% compared with that by diffusion alone. We argue that all phagotrophic microorganisms must have developed adaptations to counter viscosity in order to allow prey interception, and conclude that the flow fields created by the beating flagella in dinoflagellates are key to the success of these mixotrophic organisms.     

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.     

Feeding characteristics of two tintinnid ciliate species on phytoplankton including harmful species: effects of prey size on ingestion rates and selectivity

The feeding abilities of two tintinnid ciliates, Favella ehrenbergii and Favella taraikaensis, on 10 species of flagellates including harmful marine algae were examined under single prey conditions, and selective feeding of F. taraikaensis on two species of algae of different sizes was investigated under mixed prey conditions. Ingestion rates calculated from the rate of increases of auto-fluorescent particles inside food vacuoles in individuals ranged from 0.5 to 22.1 cells ind(-1) h(-1) for F. ehrenbergii and from 0.8 to 44.9 cells ind(-1) h(-1) for F. taraikaensis on nine species of prey algae. Significant ingestion rates of both Favella species could not be detected on Heterosigma akashiwo, although some individuals of both species were observed ingesting H. akashiwo in the initial incubation period. The relationship between prey cell volume and ingestion rate could be expressed mathematically for both Favella species, indicating that it is possible to estimate the potential feeding activity of each Favella species on specific algae using an equation, and may be applicable to evaluate the food value of prey alga for both Favella species. When F. taraikensis was fed mixtures of H. circularisquama and Pavlova lutheri, significant ingestion rates of H. circularisquama by F. taraikaensis could not be measured when H. circularisquama accounted for less than 20% of the other prey biomass. However, clear selectivity for H. circularisquama was observed when H. circularisquama reached and exceeded 34% of the other prey biomass. Under mixed prey conditions, it is likely that the selectivity of F. taraikaensis is stronger for larger prey compared to prey algae with a size near the lower limit on which F. taraikaensis can feed.     

Selective feeding and foreign plastid retention in an Antarctic dinoflagellate

The peridinin‐containing plastid found in most photosynthetic dinoflagellates is thought to have been replaced in a few lineages by plastids of chlorophyte, diatom, or haptophyte origin. Other distinct lineages of phagotrophic dinoflagellates retain functional plastids obtained from algal prey for different durations and with varying source species specificity. 18S rRNA gene sequence analyses have placed a novel gymnodinoid dinoflagellate isolated from the Ross Sea (RSD) in the Kareniaceae, a family of dinoflagellates with permanent plastids of haptophyte origin. In contrast to other species in this family, the RSD contains kleptoplastids sequestered from its prey, Phaeocystis antarctica. Culture experiments were employed to determine whether the RSD fed selectively on P. antarctica when offered in combination with another polar haptophyte or cryptophyte species, and whether the RSD, isolated from its prey and starved, would take up plastids from P. antarctica or from other polar haptophyte or cryptophyte species. Evidence was obtained for selective feeding on P. antarctica, plastid uptake from P. antarctica, and increased RSD growth in the presence of P. antarctica. The presence of a peduncle‐like structure in the RSD suggests that kleptoplasts are obtained by myzocytosis. RSD cells incubated without P. antarctica were capable of survival for at least 29.5 months. This remarkable longevity of the RSD's kleptoplasts and its species specificity for prey and plastid source is consistent with its prolonged co‐evolution with P. antarctica. It may also reflect the presence of a plastid protein import mechanism and genes transferred to the dinokaryon from a lost permanent haptophyte plastid.     

Feeding by the Newly Described Mixotrophic Dinoflagellate Paragymnodinium shiwhaense: Feeding Mechanism,Prey Species,and Effect of Prey Concentration

ABSTRACT. To investigate the feeding by the newly described mixotrophic dinoflagellate Paragymnodinium shiwhaense (GenBank accession number=AM408889), we explored the feeding process and the kinds of prey species that P. shiwhaense is able to feed on using several different types of microscopes, including a transmission electron microscope and high‐resolution video‐microscopy. In addition, we measured the growth and ingestion rates of P. shiwhaense on its optimal algal prey Amphidinium carterae as a function of prey concentration. We also measured these parameters for edible prey at a single concentration at which the growth and ingestion rates of P. shiwhaense on A. carterae were saturated. Paragymnodinium shiwhaense feed on algal prey using a peduncle after anchoring the prey by a tow filament. Among the algal prey offered, P. shiwhaense ingested small algal species that had equivalent spherical diameters (ESDs) ≤11 μm (e.g. the prymnesiophyte Isochrysis galbana, the cryptophytes Teleaulax sp. and Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellates Heterocapsa rotundata and A. carterae). However, it did not feed on larger algal species that had ESDs ≥12 μm (e.g. the dinoflagellates Prorocentrum minimum, Heterocapsa triquetra, Scrippsiella trochoidea, Alexandrium tamarense, Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum) or the small diatom Skeletonema costatum. The specific growth rates for P. shiwhaense feeding upon A. carterae increased rapidly with increasing mean prey concentration before saturating at concentrations of ca. 350 ng C/ml (5,000 cells/ml). The maximum specific growth rate (i.e. mixotrophic growth) of P. shiwhaense on A. carterae was 1.097/d at 20 °C under a 14:10 h light–dark cycle of 20 μE/m²/s, while its growth rate (i.e. phototrophic growth) under the same light conditions without added prey was ?0.224/d. The maximum ingestion and clearance rates of P. shiwhaense on A. carterae were 0.38 ng C/grazer/d (5.4 cells/grazer/d) and 0.7 μl/grazer/h, respectively. The calculated grazing coefficients for P. shiwhaense on co‐occurring Amphidinium spp. was up to 0.07/h (i.e. 6.7% of the population of Amphidinium spp. was removed by P. shiwhaense populations in 1 h). The results of the present study suggest that P. shiwhaense can have a considerable grazing impact on algal populations.     

Feeding and grazing impact by small marine heterotrophic dinoflagellates on heterotrophic bacteria

ABSTRACT. We investigated the feeding of the small heterotrophic dinoflagellates (HTDs) Oxyrrhis marina , Gyrodinium cf. guttula , Gyrodinium sp., Pfiesteria piscicida , and Protoperidinium bipes on marine heterotrophic bacteria. To investigate whether they are able to feed on bacteria, we observed the protoplasm of target heterotrophic dinoflagellate cells under an epifluorescence microscope and transmission electron microscope. In addition, we measured ingestion rates of the dominant heterotrophic dinoflagellate, Gyrodinium spp., on natural populations of marine bacteria (mostly heterotrophic bacteria) in Masan Bay, Korea in 2006–2007. Furthermore, we measured the ingestion rates of O. marina , G . cf. guttula , and P. piscicida on bacteria as a function of bacterial concentration under laboratory conditions. All HTDs tested were able to feed on a single bacterium. Oxyrrhis marina and Gyrodinium spp. intercepted and then ingested a single bacterial cell in feeding currents that were generated by the flagella of the predators. During the field experiments, the ingestion rates and grazing coefficients of Gyrodinium spp. on natural populations of bacteria were 14–61 bacteria/dinoflagellate/h and 0.003–0.972 day⁻¹, respectively. With increasing prey concentration, the ingestion rates of O. marina , G . cf. guttula , and P. piscicida on bacteria increased rapidly at prey concentrations of ca 0.7–2.2 × 10⁶ cells/ml, but increased only slowly or became saturated at higher prey concentrations. The maximum ingestion rate of O. marina on bacteria was much higher than those of G . cf. guttula and P. piscicida . Bacteria alone supported the growth of O. marina . The results of the present study suggest that some HTDs may sometimes have a considerable grazing impact on populations of marine bacteria, and that bacteria may be important prey.     

First feeding and subsequent growth performances in piscivorous larvae of Chinese perch Siniperca chuatsi (Perciforms: Sinipercidae)

The success of first feeding is influenced by many factors, such as prey availability, and is critical to subsequent larval growth performances. To test the advantages of prey exposure before complete yolk absorption in piscivorous larvae, feeding incidence and specific growth rate were longitudinally measured in Chinese perch Siniperca chuatsi larvae first fed at different ages. The results showed that Chinese perch larvae were able to capture live piscine prey at 4 DAH (days after hatching), 1 day before complete yolk absorption. The feeding incidence and specific growth rate were higher in larvae first fed at 4 DAH than in larvae first fed at 5 or 6 DAH. These results indicate that prey exposure experience can facilitate the onset of first feeding, and that successful exogenous feeding, even before complete yolk absorption, is important for growth performances of piscivorous fish larvae.     

Differences in feeding selectivity and efficiency between young-of-the-year European perch (Perca fluviatilis) and roach (Rutilus rutilus) — field observations and laboratory experiments on the importance of prey movement apparency vs. evasiveness

Feeding selectivity and efficiency of young-of-the-year European perch and roach were compared under field and laboratory conditions. In laboratory experiments, the importance of prey evasiveness versus prey movement conspicuousness for fish selectivity was evaluated with respect to changing Cladocera/Copepoda prey ratio. Feeding efficiency was additionally investigated in relation to feeding time (5, 10, 20 min) and prey density (approx. 50, 200, 700 ind. L⁻¹). In Říov Reservoir, the diet of both fish species was nearly exclusively composed of crustacean zooplankton. In roach, diet shifted from rotifers and bosminids in May, towards Daphnia sp. and Leptodora kindtii in June and July. Daphnia contributed almost exclusively to the roach diet since June, composing on average more than 94% of total prey. Cyclopoid copepods, occurred in the roach’s diet only on the first sampling date; later on both cyclopoid and calanoid copepods were completely absent. On the other hand, copepods played an important role in the diet of perch. In early and mid-June when their share in the zooplankton was particularly high, copepods contributed by more than 50% to the diet of perch. Although their contribution dropped with their decline in zooplankton in June/July, by the end of July they again comprised about one third of perch’s diet. In both fish species, the increase in numbers of cladocerans in their diet was related to increase in SL. In roach, the numbers of consumed prey were doubled every twenty days during the investigated period. In perch the increase was not so consistent, but significantly higher efficiency of perch was reported on three out of six sampling dates. In laboratory experiments, roach showed a distinct avoidance for copepods and a preference for cladocerans. Both prey categories were only fed non-selectively when they dominated the prey mixture. Perch selectivity was more diversified. Contrary to roach, perch were fed copepods non-selectively on a balanced prey ratio. Further, with an increasing share of Cladocera, a situation resembling that of roach and Copepoda was avoided. However, when the share of copepods in the prey mixture dropped below ten percent, they were consumed non-selectively and with their ongoing decline in the prey mixture their preference even increased. Feeding efficiency differed significantly between perch and roach when foraging on copepods exclusively or on a prey mixture where copepods predominated. In the short time feeding experiment (5 min) with copepods, perch consumed on average 5.9 times more prey than roach. Although roach increased their success with increasing time it was still 1.7 times greater than for perch in the long time feeding experiment (20 min). Total numbers of prey consumed were positively affected by prey density and feeding time. With increasing feeding time, the consumption rate generally declined. With a fourfold increase in feeding time, the numbers of consumed prey increased on average only two times. Only in roach feeding on copepods did the numbers of prey consumed per minute of feeding increase with increasing feeding time. However, the overall numbers were low. Differences in feeding selectivity and efficiency between perch and roach juveniles were found to be significant both in the field and laboratory experiments. In roach, selectivity was determined solely by prey evasiveness. By contrast, perch’s selectivity was influenced by prey movement conspicuousness; prey escape abilities did not play an important role. Perch were more efficient foragers on evasive prey, but its feeding efficiency for non-evasive prey was not lower than that of roach. According to our observations, we suggest feeding behaviour to be responsible for the roach’s inefficiency in capturing evasive copepods.