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.     

WIDESPREAD PHAGOCYTOSIS OF CILIATES AND OTHER PROTISTS BY MARINE MIXOTROPHIC AND HETEROTROPHIC THECATE DINOFLAGELLATES1

An electron microscopic examination of large amorphous inclusions located in a variety of photosynthetic thecate dinoflagellates (Alexandrium ostenfeldii (Paulsen) Balech et Tangen, Gonyaulax diegensis Kofoid, Scrippsiella sp., Ceratium longipes (Bailey) Gran, and Prorocentrum micans Ehrenberg) and a nonphotosynthetic thecate species (Amylax sp.) revealed each inclusion to be a food vacuole, the majority of which were ingested ciliate prey. Recognizable features of these ciliates included linear arrays of basal bodies and cilia consistent with oligotrich polykinetid structure, characteristic macronuclei, chloroplasts (evidently kleptoplastids), cup-shaped starch plates, and cylindrical extrusomes. Three species contained (apparent) nonciliate prey: Scrippsiella sp., whose food vacuoles consistently contained unusual and complex extrusome-like cylindrical bodies having a distinctive six-lobed, multilayered structure; P. micans, which contained an unidentified encysted cell; and a single A. ostenfeldii cell, containing a Dinophysis sp. dinoflagellate cell. Several food vacuoles of ciliate origin had a red hue. This, together with the resemblance of A. ostenfeldii cells to planozygotes, suggests that similar structures previously identified as accumulation bodies may in fact be food vacuoles and that feeding may in some cases be associated with sexual processes.     

The importance of protozooplankton as prey for copepods in the coastal areas of the central Irish Sea

This study evaluates food supply for copepods, highlighting the trophic relationship between copepods and protozooplankton. To test the hypotheses that protozooplankton prey are capable of sustaining the copepod standing stock in the western Irish Sea, the taxonomic and size composition of these two groups and the size-specific predation of copepods on protozooplankton were investigated. Protozooplankton and copepod samples were collected off the southwest coast of the Isle of Man using 1.7 l Niskin water bottles and two nets (64 and 280 μm meshes), respectively. Copepod predation on protozooplankton was calculated using weight-specific clearance rates from the literature, considering the availability of prey that was accessible to a given size of copepod. Low protozooplankton biomass was dominated by small cells (<60 μm), and high copepod biomass was dominated by small species, which were more efficiently collected by a 64-μm mesh net. However, large copepods were only collected by a 280-μm mesh net, suggesting that the combination of the two nets provided a better estimate of copepod biomass. Predation by the copepod assemblage in the Irish Sea removed 1–47% and 0.5–22% of ciliates and dinoflagellates standing stock, respectively, resulting in 1–40% of the copepod feeding requirement per day. Contrary to our hypothesis, copepods could not meet their feeding requirements by grazing only on the microzooplankton prey (15–200 μm), and other food sources (i.e. nanoplankton) must be important additional dietary components to copepods in the Irish Sea. Handling editor: S. M. Thomaz     

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.     

Size-selective feeding by Cyclidium sp. on bacterioplankton and various sizes of cultured bacteria

Abstract Size-selective grazing by Cyclidium sp., isolated as a dominant ciliate bacterivore from the Římov Reservoir (South Bohemia), was examined using fluorescent labelled bacteria (FLB) produced from natural bacterioplankton or pure bacterial cultures. Sizes of ingested bacteria in food vacuoles were measured directly. Three experimental arrangements were used: (1) Ciliates were grown on the pure culture of Alcaligenes xylosoxidans and fed with various proportions of ‘large’ and ‘small’ FLB (mean biovolume, 0.377 and 0.202 μm³, respectively) prepared from the same bacterial species. Results clearly showed significant selection of larger bacteria. (2) Ciliates were grown on natural bacterioplankton from the reservoir and subsequently fed on FLB prepared from the reservoir bacterioplankton (mean biovolume, 0.065 μm³). Independent of either prey or predator abundance, larger FLB (> 0.100 μ m³, and especially those > 0.200 μ m³) were ingested with much higher frequency than their occurrence i the natural assemblage. (3) Ciliates were grown on the reservoir baterioplankton and fed by FLB prepared from the culture of Pseudomonas sp. In contrast with previous results, no size selection of the ciliate was found when FLB were different from the bacterial food used to grow the ciliate. Ecological impacts of size-selective bacterivory are suggested.     

Ecology of the red-tide dinoflagellate Ceratium furca: distribution, mixotrophy, and grazing impact on ciliate populations of Chesapeake Bay

Ceratium furca is a primarily photosynthetic dinoflagellate also capable of ingesting other protists. During 1995 and 1996, we documented the abundance of C. furca in Chesapeake Bay and determined grazing rates on prey labeled with fluorescent microspheres. Abundance usually remained below 20 cells ml(-1), although the species was capable of localized late-summer blooms (< or = 478 cells ml(-1)) in the more saline lower to mid-Bay region. Feeding rates ranged from 0 to 0.11 prey dinoflagellate(-1) h(-1) or from 0 to 37 pg C dinoflagellate(-1) h(-1) and were highest at lower salinities. Clearance rates averaged 2.5 +/- 0.35 microl dinoflagellate(-1) h(-1). Impact of C. furca feeding on prey populations was higher in the lower Bay, averaging 67% of Strobilidium spp. removed d(-1). Ingestion rates were positively correlated with prey abundance and dissolved inorganic nitrogen, but negatively with salinity, depth, dissolved inorganic phosphorus, and inorganic P:N ratio. Daily consumption of prey biomass by C. furca averaged 4.6% of body carbon, 6.5% of body nitrogen, and 4.0% of body phosphorus. with maximal values of 36, 51, and 32%, respectively. Thus, the ability to exploit an organic nutrient source when inorganic nutrients are limiting may give C. furca a competitive advantage over purely photosynthetic species.     

Evidence of phagotrophy in Dinophysis fortii (Dinophysiales, Dinophyceae), a dinoflagellate that causes diarrhetic shellfish poisoning (DSP)

Food vacuoles were found in one species of pho‐totrophic Dinophysis, Dinophysis fortii Pavillard, collected in Okkirai Bay. Under transmission electron microscopy, almost 70% of observed food vacuoles were characterized by membranous profiles and contained large numbers of mitochondria. The mitochondria in the food vacuole had different morphologies from those in the D. fortii cytoplasm. This indicates that these vacuoles are not autolytic accumulation bodies, but ‘true’ food vacuoles. Identification of the origin of the contents failed, but the existence of large amounts of foreign mitochondria implies that the contents in the vacuoles were derived from eukaryotic prey. Other than the observation of the food vacuoles, bacterial cells were observed in the flagellar canal. Because the flagellar canal and connecting pusule sacs had been reported to relate to macromolecule uptake, the prey organisms of D. fortii were assumed to be both eukaryotic and prokaryotic organisms.     

Significance of predation by protists in aquatic microbial food webs

Predation in aquatic microbial food webs is dominated by phagotrophic protists, yet these microorganisms are still understudied compared to bacteria and phytoplankton. In pelagic ecosystems, predaceous protists are ubiquitous, range in size from 2 μm flagellates to >100 μm ciliates and dinoflagellates, and exhibit a wide array of feeding strategies. Their trophic states run the gamut from strictly phagotrophic, to mixotrophic: partly autotrophic and partly phagotrophic, to primarily autotrophic but capable of phagotrophy. Protists are a major source of mortality for both heterotrophic and autotrophic bacteria. They compete with herbivorous meso- and macro-zooplankton for all size classes of phytoplankton. Protist grazing may affect the rate of organic sinking flux from the euphotic zone. Protist excretions are an important source of remineralized nutrients, and of colloidal and dissolved trace metals such as iron, in aquatic systems. Work on predation by protists is being facilitated by methodological advances, e.g., molecular genetic analysis of protistan diversity and application of flow cytometry to study population growth and feeding rates. Examples of new research areas are studies of impact of protistan predation on the community structure of prey assemblages and of chemical communication between predator and prey in microbial food webs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fine scale spatial correlations between planktonic ciliates and dinoflagellates

Fine scale spatial distributions of planktonic ciliates whichprey on dinoflagellates were investigated in a small estuary.The horizontal distributions of Favella sp., Balanion sp. andStrobilidium sp. were positively correlated with the patchydistribution of dinoflagellates. The vertical distribution ofFavella was positively corrdated with the distribution of dinoflagellates.Throughout the diel cycle, the vertical distribution of Faveilawas similar to the vertical distribution of dinoflagellates.We speculate that behavioral responses are responsible for theassociation of diliates with their prey in the water column.Vertically coincident ciliate and algal populations should respondsimilarly to turbulent mixing and water displacement causedby wind stress, bathymetry, or frontal convergences. This wouldresult in horizontal patches in which the ciliates and algaeremain associated. This fine scale spatial coupling betweenciliates and their prey should result in higher ciliate growthrates and greater impact of ciliate grazing on phytoplanktonpopulations than would be predicted from average ciliate oralgal densities. Coincident patches of algae and ciliates mayalso provide higher food concentrations for larger grazers whichcan use both resources. ^{Contribution No. 5532, W.H.O.I.}     

Winter Ciliates in a British Columbian Fjord: Six New Species and an Analysis of Ciliate Putative Prey

ABSTRACT. This work provides the first study of North Pacific planktonic ciliates by quantitative protargol staining. Triplicate water bottle samples were collected at a depth of 2 m (above the shallow pycnocline) at six stations in Indian Arm, British Columbia, on February 15, 1990, and February 26, 1991. Thirty-six ciliate species were observed. Six new species are described from protargolstained specimens: Strombidium lynni n. sp., Strombidium taylori n. sp., Strombidium basimorphum n. sp., Slrombidiurn ventropinnum n. sp., Strobilidium undinum n. sp., and Urotricha cyrtonucleata n. sp.
Ciliate abundance varied significantly (ANOVA, α= 0.05) between sampling sites, ranging from 550 to 6,800 cells/liter in 1990 and from 1,800 to 7,900 cells/liter in 1991. Biomass also varied significantly (ANOVA, α= 0.05) ranging from 3.7 × 10⁵ to 3.3 × 10⁶ pg carbon/liter in 1990 and 3.04 × 10⁶− 6.97 × 10⁶ pg carbon/liter in 1991. Putative prey were enumerated in three size fractions (1.5–5 μm, 5–10 μm and 10–25 μm). The source of variation in ciliate abundance and biomass was not identified. Parameters of salinity, temperature, putative prey, chlorophyll a and pycnocline depth did not significantly correlate with ciliate biomass or abundance (α= 0.05).     

Indirectly fluorescently labelled flagellates (IFLF): a tool to estimate the predation on free-living heterotrophic flagellates

A procedure was developed to estimate the direct grazing impacton free-living heterotrophic nanoflagellates (HNF). Culturedflagellates were labelled by feeding on brightly fluorescingbacteria (FLB) and then offered as indirectly fluorescentlylabelled flagellates (IFLF) to potential predators of HNF. Thenumber of FLB in the predators' food vacuoles could be convertedinto IFLF uptake and consumption of HNF. This new techniquewas used to study the HNF-ciliate relationship in the pelagiczone of Lake Constance. Three groups of ciliates were detectedas HNF grazers: small representatives of the genus Strobilidium.a small Haltena-like ciliate (probably Halteria grandinella)and a Codonella sp. Tintinnidium sp. group The ingestion ofHNF by these groups of ciliates ranged between 3 and 15, 3 and39, and 3 and 7 HNF ciliate^–1 h^–1; respectively.The IFLF method allows the direct determination of ingestedflagellate prey in the food vacuoles of their predators. Becauseindigenous living prey organisms were used, tracer discriminationcan be reduced.     

甲藻的异养营养型

综述了甲藻的异养类型。目前已知异养营养型在甲藻中广泛存在,只有很少几种甲藻营严格自养营养方式。有近一半的甲藻物种是没有色素体的,还有很多甲藻即使具有色素体也会有异养营养需求,称为兼养营养类型。这些兼养类群不一定主要以有机物作为其获取碳的来源,而仅仅是补充一些生长必需的有机物如维生素、生物素等。兼养类群以渗透营养和腐食营养方式进行,同时也可以寄生方式和共生方式进行兼养生活。无色素体的甲藻以有机物作为碳的唯一来源,仅仅依靠异养方式生存,属于严格异养营养方式,又称有机营养型。它们是甲藻异养营养型的主体,其主要类型有寄生、渗透营养和吞噬营养。由于吞噬营养是甲藻异养的主要类型,因此论述了3种吞噬营养型:吞噬营养方式、捕食茎营养方式和捕食笼营养方式。吞噬营养方式在无甲类和具甲类甲藻中都有存在,主要通过甲藻细胞的纵沟或底部对猎物进行吞噬,也有研究发现吞噬部位为顶孔或片间带。捕食茎营养方式是通过捕食茎刺穿猎物细胞膜并吸食其细胞质来获取营养,在异养甲藻中也较常见。捕食笼营养方式只在原多甲藻属(Protoperidinium)和翼藻属(Diplopsalis)里发现,是甲藻通过鞭毛孔分泌细胞质到胞外形成捕食笼将猎物包裹并进行消化来摄食的。甲藻摄食对象尺寸范围变化较大,小至几微米,大至几百微米。有些甲藻具有摄食选择性,通过感应猎物释放的化学物质来判断猎物的位置并进行摄食,摄食完成后由于体积的增加经常会发生细胞分裂和蜕鞘。对于甲藻异养的其他形式如拦截摄食营养方式、伪足摄食营养方式、口足摄食营养方式、触手摄食营养方式等只作简单介绍。还就甲藻异养的研究方法、其生态学意义和进化学意义进行简要论述,并对相关研究进行展望。     

THE COMPOSITION AND TOXICITY OF DINOFLAGELLATE BLOOMS IN THE SALTON SEA, CALIFORNIA

Phytoplankton blooms have been implicated in mortality events of diverse groups of organisms including fish, birds and humans. About 300 species have been reported to form "red tides," or surface discolorations due to high densities, but only 60–80 of these species produce harmful blooms. In marine systems, dinoflagellates account for 75% of all harmful algal bloom species. The Salton Sea is a large saline lake located in southeastern California, USA. The lake is eutrophic largely because it is in a closed basin and receives most of its input from agricultural and municipal wastewaters. Dinoflagellates comprise a significant portion of the phytoplankton biomass, particularly in winter, often resulting in "red" or "brown" tides. To date, 16 species of dinoflagellates have been identified from the Salton Sea, and many other unidentified forms have also been documented. In 1992, 150,000 eared grebes were found dead over a period of several months at the Salton Sea. This mortality event was among the largest of any bird species. The principal cause remains unknown, but algal toxins were suspected. A survey of the composition and toxicity of algal blooms was undertaken in 1999, and we report results from blooms where dinoflagellates dominated. Dominant species included Gonyaulax grindleyi , Gymnodinium spp., Gyrodinium uncatenum , Heterocapsa niei , and an unidentified scrippsielloid. Although most samples showed activity in a brine shrimp lethality assay, all were negative in a mouse bioassay. This evidence suggests that toxins from dinoflagellate blooms in the Salton Sea are not responsible for eared grebe mortality events.     

Two New Species of Hartmannella Amebae Infecting Freshwater Mollusks

SYNOPSIS. Two new species of small amebae, Hartmannella biparia n. sp. and Hartmannella quadriparia n. sp., were 1st observed in the freshwater mollusks Bulinus globosus and Biomphalaria pallida, respectively. The amebae multiplied in cytoplasmic vacuoles in host cells, particularly in foci in the mantle collar, foot, and intestinal wall. Both amebae had functional contractile vacuoles while within host cells. H. biparia emerged from intracytoplasmic vacuoles in pairs, H. quadriparia in fours, suggesting characteristic reproductive stages.
H. biparia had limax-type motility by smooth lobopodia, was 22 μ long; with vesicular nucleus 3 μ and central endosome 1.5 μ, multiplied by binary fission and formed spherical, smooth-walled cysts 11 μ in diameter. H. quadriparia had limax-type motility by lobopodia with fine, acute projections; was 10 μ long, with vesicular nucleus 2 μ and central endosome 0.75 μ, multiplied and formed spherical, smooth-walled cysts 5 μ in diameter. Neither species multiplied in cysts outside the host.
H. biparia was found infecting 12 species and experimentally transferred to 4 more species of freshwater snails; H. quadriparia was found in one species and experimentally transferred to 6 other species.     

Feeding preferences and grazing rates of Pfiesteria piscicida and a cryptoperidiniopsoid preying on fish blood cells and algal prey

The grazing rates and feeding preferences of the dinoflagellates Pfiesteria piscicida and a cryptoperidiniopsoid on the alga Rhodomonas sp. and fish blood cells were calculated at different ratios of the two food types and at different total food densities. Data from 6 h grazing periods within microcosms were used to calculate grazing rates. Grazing rates of both dinoflagellates increased linearly with an increased ratio of blood cells to Rhodomonas, and P. piscicida had a higher maximum grazing rate than the cryptoperidiniopsoid. The grazing rate of P. piscicida on Rhodomonas also increased with increased Rhodomonas densities relative to the blood cells, but increased densities of Rhodomonas did not increase the grazing rate of the cryptoperidiniopsoid, suggesting a lower feeding threshold for this species. Both dinoflagellates demonstrated a preference for fish blood cells over Rhodomonas cells, with no significant difference in the index of preference between the two species. Total food abundance affected the degree of preference differently for each dinoflagellate species. A higher index of feeding preference was attained by P. piscicida when resource levels were high, while the cryptoperidiniopsoid did not show this response. A preference for fish blood cells occurred at all food ratios for both dinoflagellates, including when blood cells were scarce relative to the alternate food type (15% of total available food). These results suggest that these strains of P. piscicida and the cryptoperidiniopsoid share similar feeding preferences for the prey types tested, although cryptoperidiniopsoids have not been associated with fish kills.     

Fine Structure of the Marine Amoeba Vexillifera telmathalassa Collected from a Coastal Site Near Barbados with a Description of Salinity Tolerance, Feeding Behavior and Prey

ABSTRACT. Amoebae cultured from seawater collected at a coastal site near Barbados were largely a lobose amoeba with long tapered subpseudopodia identified as Vexillifera telmathalassa. Vexillifera telmathalassa occurs widely in marine environments and additional information is presented here on its fine structure, salinity tolerance, and feeding behavior toward clarification of its taxonomic characteristics and ecological niche. The amoebae were able to adjust to a gradual decline in salinity from 36‰ to 16‰, but at a salinity of 12‰. They all became immobilized and discoidal. The fine structure showed a centrally located nucleus (2.1 μ m) with a prominent nucleolus. The plasma membrane is coated with glycostyles 17 nm long and 14 nm apart, and may be derived from secretory vesicles with similar glycocalyx lining. Bacteria and occasional eukaryotic remains occur in digestive vacuoles or membrane-enclosed spaces. Some vacuoles (2.0–2.5 μ m) are filled with scattered masses of digested material and resemble the "glanzkörper" previously identified by light microscopy. In addition to bacterial prey, microflagellates were also ingested in laboratory culture as observed by light microscopy. Vexillifera telmathalassa may be more closely linked trophically to the microbial loop than previously recognized.     

Food selection by bacterivorous protists: insight from the analysis of the food vacuole content by means of fluorescence in situ hybridization

A modified fluorescence in situ hybridization (FISH) method was used to analyze bacterial prey composition in protistan food vacuoles in both laboratory and natural populations. Under laboratory conditions, we exposed two bacterial strains (affiliated with beta- and gamma-Proteobacteria -- Aeromonas hydrophila and Pseudomonas fluorescens, respectively) to grazing by three protists: the flagellates Bodo saltans and Goniomonas sp., and the ciliate Cyclidium glaucoma. Both flagellate species preferably ingested A. hydrophila over P. fluorescens, while C. glaucoma showed no clear preferences. Differences were found in the digestion of bacterial prey with B. saltans digesting significantly faster P. fluorescens compared to two other protists. The field study was conducted in a reservoir as part of a larger experiment. We monitored changes in the bacterial prey composition available compared to the bacteria ingested in flagellate food vacuoles. Bacteria detected by probe HGC69a (Actinobacteria) and R-BT065 were negatively selected by flagellates. Bacteria detected by probe CF319a were initially positively selected but along with a temporal shift in bacterial cell size, this trend changed to negative selection during the experiment. Overall, our analysis of protistan food vacuole content indicated marked effects of flagellate prey selectivity on bacterioplankton community composition.     

Characterization of Porphyrobacter sanguineus sp. nov., an aerobic bacteriochlorophyll-containing bacterium capable of degrading biphenyl and dibenzofuran

Three strains of " Agrobacterium sanguineum", an aerobic marine bacterial species described previously, were re-characterized from phylogenetic and taxonomic viewpoints. 16S rDNA sequence comparisons showed that the " A. sanguineum" strains belong to the alpha-4 subgroup of alpha-Proteobacteria, with members of the genera Erythromicrobium and Porphyrobacter as their closest relatives. DNA-DNA hybridization studies indicated that the " A. sanguineum" strains were distinguishable from any previously known species of these genera. Bacteriochlorophyll a, monosaccharide-type glycosphingolipids, 2-OH fatty acids of C14:0, C15:0, C16:0, and C16:1, and ubiquinone-10 were detected in the " A. sanguineum" strains. The G+C of the DNA was 63.8-64.0 mol%. Two of the " A. sanguineum" strains, IAM 12620 (=ATCC 25659) and ATCC 25661, were able to grow with biphenyl and dibenzofuran as sole carbon source in the presence of 0.05% yeast extract. The medium in these cultures turned yellowish-orange at the exponential phase of growth due to the release of soluble chromogenic metabolites. The remaining " A. sanguineum" strain, ATCC 25660, and all test strains of Erythromicrobium and Porphyrobacter neither grew nor produced yellow-orange pigment with biphenyl or dibenzofuran. In PCR experiments, bphA1 gene, coding for the large subunit protein of biphenyl dioxygenase, was detected in " A. sanguineum" IAM 12620 and ATCC 25661. Based on these results, we propose classifying " A. sanguineum" IAM 12620 and ATCC 25661 as a new species of the genus Porphyrobacter with the name Porphyrobacter sanguineus sp. nov.     

Feeding behaviour of the rotifer Ascomorpha ovalis: functional response, handling time and exploitation of individual Ceratium cells

The planktonic rotifer Ascomorpha ovalis feeds on large dinoflagellates(e.g. Ceratium sp., Peridinium sp.) and is able to extract theircell contents by means of its virgate mastax. This paper presentsthe results of experiments on the feeding behaviour of laboratory-culturedAscomorpha with Cerarium furcoides as food algae. Ascomorphaare three times larger than their prey Ceratium (by volume),but with regard to total length, their prey was even 20% larger.Ascomorpha showed a hyperbolic functional response curve witha plateau of the feeding rate at 8 Ceratium cells animal^–1dar^–1 when concentrations of Ceratium were >100 cellsml^–1. The mean handling time (time for capturing and extractingone Ceratium cell) was 3 min. The shape of the functional responsewas better described by a curvilinear model than by a rectilinearmodel. However, handling times cannot be responsible for this,since they were too short to set limits on ingestion rates.At low food concentrations, encounter rates with prey seemedto limit the feeding rates of Ascomorpha, whereas at mediumto high food concentrations, Satiation effects (lower attackrates) seemed to set limits on the feeding rates. Ascomorphashowed a significant decrease in the exploitation of singleCeratium cells at high prey concentrations. This decrease couldbe explained by a saturation effect in which the partly filledguts of Ascomorpha did not permit the total extraction of thecontents of a Ceratium cell.     

The role of picoplankton (cyanobacteria and plastidic picoflagellates) in the diet of tintinnids

Food vacuole contents in naturally occurring populations oftintinnids in surface waters at the mouth of the Bay of Villefranchewere examined from November 1988 to December 1989. Three typesof prey were considered: cyanobactena (Synechococcus spp.),plastidic pico- and nanoflagel lates. The relative frequency(%) of these were observed in the diet of 18 tintinnid species.Results confirm that nanoflagellates constitute the dominantfraction in the diet of most of the tintinnids examined. Theyare preferentially ingested by some species, such as Amphoridesquadrilineata and Favella sp. Nevertheless, picoplankton isingested throughout the year by all the tintinnids, and canreach up to 100% of the ration mainly during winter and summer.Cyanobacteria are the prey most ingested by Rhabdonella spiralisand the only prey observed in food vacuoles of Salpingella acuminaia.As indicated by the Strauss linearity index values, picoflagellatesare actively grazed by some species (e.g. Dictyocysta elegans,Eutintinnus spp.). The implications of the ingestion of picoplanktonby tintinnids in the food webs are discussed.