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1.
Pond David W.; Leakey Raymond J. G.; Fallick Anthony E. 《Journal of plankton research》2006,28(4):419-427
Naturally occurring microbial communities are complex, withautotrophs and heterotrophs often similarly sized and impossibleto separate by conventional size fractionation approaches. However,if it was possible to identify specific compounds that are characteristicof particular groups of microbes and determine the stable isotopecomposition of these biomarkers, the requirement for size fractionationcould potentially be negated. This work considered the usefulnessof such an approach by analysis of a simple laboratory predatorpreysystem comprising Nanochloropsis oculata, an autotrophic flagellateprey and Oxyrrhis marina, a heterotrophic flagellate predator.In growth-grazing experiments the fatty acids 20:5(n3)and 22:6(n3) were used as biomarkers for N. oculata andO. marina respectively. Interpretation of 13C values of thesepredator and prey fatty acid biomarkers was not straightforwardsince although isotopic signature of the O. marina biomarkerwas consistently enriched compared to that of its N. oculataprey, the magnitude of enrichment in 13C increased with ageof culture (1.05.4 %). Given the variability we observedin our experimental cultures, it will be difficult to applythis approach to complex field situations without a comprehensiveunderstanding of the factors determining the 13C values of specificbiomarker molecules. 相似文献
2.
In a series of batch experiments in the dark the heterotrophicdinoflagellate Oxyrrhis marina grazed three phytoplankton prey(Phaeodactylun tricornutum, Isochrysis galbana and Dunaliellateriolecta) with equal efficiency. Growth rates of the dinoflagellateranged between 0.8 and 1.3 day1 Maximum observed ingestionrates on a cell basis varied according to the size of the preyfrom about 50 cells flagellate1 day1 when D.tertiolectawas the prey to 250350 cells fiagellate1 day1when the other species were eaten. However, when compared ona nitrogen basis, ingestion rates were independent of prey type.Both ingestion and growth ceased when prey cell concentrationsfell below a threshold concentration of about 105 cells ml1.Maximum specific clearance rates were 0.8x1040ndash;5.7x104it day which is considerably lower than that found for heterotrophicdinoflagellates in oceanic waters and may explain why O.marinagenerally thrives only in productive waters. The timing of NHregeneration was linked to the C:N ratio of the prey at thestart of grazing. Regeneration efficiencies for NH4. never exceeded7%; during the exponential phase and were 45% well into thestationary phase. These results are comparable to those obtainedwith heterotrophic flagellates and demonstrate that the bioenergeticpatterns of grazing and nutrient cycling by different protozoaare very similar. Moreover, they support the notion that toachieve 90+% nutrient regeneration in the open ocean, as iscurrently believed, the microbial food loop must consist ofmultiple feeding steps. Alternatively, nutrient regenerationefficiencies may be considerably lower than 90%. 相似文献
3.
During the growth of Isochrysis galbana, several non-proteinamines may be detected in the growth medium. Of these, one (termedTTl) accumulates in proportion to the numbersof cells present. The concentrations of TTl, andof another (termed TA), are 35 times higherin cultures in which Isochrysis is predated by Oxyrrhis marina.The lowest estimates of the concentration of extracellular TTlare an order of magnitude higher than those of any protein aminoacid. Of the protein amino acids, some like glycine are utilizedduring predation while others, like histidine, accumulate inthe medium Because of the unknown N-content and reactivity ofthe non-protein amines during HPLC, it is not possible to sayif these compounds (together with other components of dissolvedorganic N) form a significant proportion of the unaccountedfor N in the system after predatory activity. During predationin the absence of detectable free ammonium (when Isochrysismay be expected to be N-deprived), particles accumulate in themedium. Most of these are <2.5 µ.m in diameter andare suggested to be remains of digested prey. There is evidenceof a reassimilation of these particles by prey-deplete Oxyrrhis. 相似文献
4.
Changes in salinity are known to alter the morphology of protists, and we hypothesized that these changes subsequently alter also the predatory behavior of the dinoflagellate Oxyrrhis marina. Oxyrrhis was grown in media of 33, 25, 20, and 10% of the regular salinity of f/2 medium (31–32‰). In all cases, the cells discharged trichocysts and swelled. Cell surfaces and volumes increased with decreasing salinity, such that cell surface area at least doubled at 10% and the cell volume increased approximately fourfold. After 1 h, the cells started to regain their regular shape, which was almost completed after 24 h. Oxyrrhis immediately regained its regular shape when culture medium was added 5–10 min after the osmotic stress. When incubated with Pyramimonas grossii as prey, those short-term stressed cells showed no significant different prey uptake in comparison to non-stressed cells. In contrast, 24 h after the addition of prey, short-term stressed Oxyrrhis cells had, with weak statistical significance, more Pyramimonas cells engulfed than non-stressed cells. These results indicated that (1) trichocysts were most likely not involved in prey capture and (2) salinity-stressed Oxyrrhis either enhanced its capability to capture more prey, or its digestion apparatus was hampered. 相似文献
5.
Prey location, recognition and ingestion by the phagotrophic marine dinoflagellate Oxyrrhis marina 总被引:1,自引:0,他引:1
Claire M. Martel 《Journal of experimental marine biology and ecology》2006,335(2):210-220
The initial ingestion rates of Isochrysis galbana and Dunaliella primolecta by Oxyrrhis populations precultured separately on these phytoplanktonic prey were quantified and related to the chemosensory responses elicited in Oxyrrhis by the filtrate from live and heat killed prey cells. Despite evidence to suggest that Oxyrrhis shows specific distaste towards Isochrysis (but not Dunaliella) such that consumption of N-deplete Isochrysis halted in grazing experiments, positive chemotaxis was observed towards the cell-free filtrate from both species. These results suggest that while tactile cues encountered upon contact with Isochrysis and Dunaliella may enable Oxyrrhis to recognise differences between the two species, the chemosensory responses observed towards dissolved chemical cues derived from potential prey items are non-specific. That chemosensory and ingestion behaviours do not appear to be tightly coupled raises important questions concerning the ecological implications of chemotaxis in Oxyrrhis. Chemotaxis may enhance the overall efficiency of prey detection; however, when confronted with a variety of chemical stimuli (i.e. from a mixed-prey assemblage) Oxyrrhis may be unable to discern the difference between cues that originate from high quality, poor quality (or even toxic) prey items. The positive chemosensory responses observed towards a range of synthetic amino acid, amino sugar and ammonium solutions suggest that chemotaxis could facilitate the detection of solute gradients in prey deplete environments for direct exploitation via osmotrophy. Furthermore, the positive chemotaxis elicited by regenerated ammonium and compounds derived from heat killed conspecifics suggests that Oxyrrhis may release chemical cues which induce cannibalistic behaviour as a ‘life boat mechanism’ when no other suitable (non-self) prey items are available. Further work is required to explore the nature of the chemosensory apparatus and signal transduction pathways that mediate responses to dissolved chemical stimuli in Oxyrrhis and to investigate other sensory mechanisms that enable cells to recognise and differentiate between potential prey items. 相似文献
6.
Cannibalistic feeding behavior of the brackish-water copepodSinocalanus tenellus was examined in the laboratory using CI-II,CIII-IV and CVI female as predators and NI-II, NIII-IV, NV-VIand CI-II as prey. In each prey-predator combination, the ingestionrate increased with increasing prey density to an asymptoticvalue. Cannibalism took place even when phytoplankton was availableas an alternative food supply. Based on a daily ration, theoptimal prey stages for CVI females, CIII-IV and CI-II are NI-VI,NI-IV and NI-II respectively. Under average, natural prey density(10 nauplii l1), S tenellus can achieve only a smallfraction (max 9%) of the daily minimum food requirement by cannibalisticfeeding. However, the impact of cannibalism on naupliar survivorshipcan be significant. When adult females occur at a density of10 l1, the mortality due to cannibalism attains 99.2%during the naupliar stages. 相似文献
7.
Feeding, prey selection and prey encounter mechanisms in the heterotrophic dinoflagellate Noctiluca scintillans 总被引:1,自引:0,他引:1
The heterotrophic dinoflagellate Noctiluca scintillans has anegligible swimming ability and feeds predominantly on immobileprey. How, then, does it encounter prey? Noctiluca scintillansis positively buoyant and, therefore, we hypothesized that itintercepts prey particles during ascent and/or that microscaleshear brings it into contact with prey. Noctiluca scintillanshas a specific carbon content 12 orders of magnitudeless than that typical for protists and, thus, an inflated volume.It also has a density slightly less than that of the ambientwater and therefore ascends at high velocities (-1 m h1).In stagnant water, clearance rates of latex spheres (580µm) increased approximately with prey particle size squared.This scaling is consistent with N.scintillans being an interceptionfeeder. However, absolute clearance rates were substantiallylower than those predicted by modeling N.scintillans both asa spherical and as a cylindrical collector. The latter modelassumes that prey particles are collected on the string of mucusthat may form at the tip of the tentacle. Feeding, growth andprey selection experiments all demonstrated that diatoms arecleared at substantially higher rates than latex beads and otherphytoplankters, particularly dinoflagellates. We propose thatdiatoms stick more efficiently than latex beads to the mucusof N.scintillans and that dinoflagellates reduce fatal contactbehaviorally. We conclude that N.scintillans is an interceptionfeeder and that the high ascent velocity accounts for encounterswith prey. However, the flow field around the cell-mucus complexis too complicated to be described accurately by simple geometricmodels. Fluid shear (0.71.8 s1 had a negativeimpact on feeding rates, which were much less than predictedby models. Noctiluca scintillans can survive starvation forlong periods (>3 weeks), it can grow at low concentrationsof prey (-15 µg C l1), but growth saturates onlyat very high prey concentrations of 5001000 µgC l1 or more. We demonstrate how the functional biologyof N.scintillans is consistent with its spatial and seasonaldistribution, which is characterized by persistence in the plankton,blooms in association with high concentrations of diatoms, andsurface accumulation during quiescent periods or exponentialdecline in abundance with depth during periods of turbulentmixing. 相似文献
8.
Deleterious effect of Chattonella marina on short-necked clam (Ruditapes philippinarum); possible involvement of reactive oxygen species 总被引:1,自引:0,他引:1
Kim Daekyung; Kumamoto Osamu; Lee Kyoung-Seon; Kuroda Aiko; Fujii Akihiko; Ishimatus Atsushi; Oda Tatsuya 《Journal of plankton research》2004,26(8):967-971
In laboratory exposure experiments, Chattonella marina showeda deleterious effect on short-necked clams (Ruditapes philippinarum).Accumulated C. marina cells were observed in gill tissues ofthe clams exposed to C. marina. Immunohistochemical analysisusing antiserum against the crude glycocalyx of C. marina suggestedthat the glycocalyx was present on the gill surface. Mucus substancesprepared from gill tissue of the clams stimulated C. marinato generate increased amounts of O2 in a concentration-dependentmanner. These results suggest that reactive oxygen species (ROS)-mediatedgill tissue damage is one of the causative factors responsiblefor the harmful effect of C. marina on shellfish. 相似文献
9.
Kim Daekyung; Nakashima Takuji; Matsuyama Yukihiko; Niwano Yoshimi; Yamaguchi Kenichi; Oda Tatsuya 《Journal of plankton research》2007,29(3):241-247
Raphidophycean flagellates, Chattonella marina and C. ovata,are harmful red tide phytoplankters; blooms of these phytoplanktersoften cause severe damage to fish farming. Previous studieshave demonstrated that C. marina and C. ovata continuously producereactive oxygen species (ROS) such as superoxide anion (O2)hydrogen peroxide (H2O2) under normal growth conditions, andan ROS-mediated toxic mechanism against fish and other marineorganisms has been proposed. Although the exact mechanism ofROS generation in these phytoplankters still remains to be clarified,our previous study suggested that NADPH oxidase-like enzymelocated on the cell surface of C. marina may be involved inO2 generation. To investigate the localization of O2and H2O2 generation in C. marina and C. ovata, we employed 2-methyl-6(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-oneand 5-(and-6)-carboxy-2',7'-dichlorodihydrodihydrofluoresceindictate, acetyl ester, which are specific fluorescent probefor detecting O2 and H2O2, respectively. Observationby fluorescence microscopy of live phytoplankters incubatedwith each probe revealed that O2 is mainly generatedon the cell surface, whereas H2O2 is generated in the intracellularcompartment in these phytoplankters. When the cells were rupturedby ultrasonic treatment, O2 levels of C. marina and C.ovata decreased significantly, whereas a few times higher levelsof H2O2 were detected in the ruptured cell suspensions whencompared with the levels of the live cell suspension. In immunoblottinganalysis, the protein recognized by anti-human gp91 phox wasdetected in both species. These results suggest that, in bothphytoplankters, the underlying mechanisms of O2 and H2O2generation may be distinct and such systems are independentlyoperating in the cells. 相似文献
10.
Klein Bert; Gieskes Winfried W. C.; Krray Gijsbert G. 《Journal of plankton research》1986,8(5):827-836
Algal pigments were measured, by reverse-phase h.p.l.c., duringgrazing experiments with the protozoan Oxyrrhis marina Dujardinon Rhodomonas sp. Chlorophylls and carotenoids were degradedto colourless residues; the rate of degradation of pigmentswas highest in the light. Very little chlorophyll a (5%) wasdegraded to phaeophytin and none to phaeophorbide during grazing.This suggests that phaeopigment concentrations cannot be usedas a measure of algal mortality due to grazing when heterotrophicProtozoa are a component of the grazer community. 相似文献
11.
The effects of a population of the boring gastropod Natica tectaon the bivalve Choromytilus meridionalis were investigated atBailey's Cottage, False Bay, South Africa. In July 1979 theN. tecta density on the mussel bed averaged 69 m2 andthe population consisted mainly of reproductively mature individualsbetween 2033 mm shell width. Laboratory experiments on N. tecta showed that prey size selectionis an increasing function of predator size. The prey size rangetaken by large N. tecta is also greater than that taken by smallindividuals. The position of the borehole on the mussel shellis a function of the way in which the shell is held by the footduring the boring process. Consumption rates measured in thelaboratory showed an increase from approximately 1 kJ per weekin 18 mm N. tecta to 4.5 kJ per week in 28 mm individuals. Populationconsumption in the field was calculated as 663 kJ m2month1. It was estimated that at this rate the standingcrop of mussels in the pool would be eliminated within 10 months.Field measurements showed significant depletion after 6 months. New spat settlement of mussels occur every 46 years.The growth curve shows that after one year the population meansize exceeds 30 mm shell length, which is beyond the prey selectionsize range of small N. tecta. It was concluded that at the timeof a new mussel settlement a niche is provided for the simultaneoussettlement and growth of juvenile N. tecta in high densities.However, within one year the increase in prey size, togetherwith depletion due to over-exploitation, limits population growthand density in N. tecta. (Received 14 March 1980; 相似文献
12.
Okazaki Noriko; Imai Kazuhide; Kikuno Reiko F.; Misawa Kazuharu; Kawai Makoto; Inamoto Susumu; Ohara Reiko; Nagase Takahiro; Ohara Osamu; Koga Hisashi 《DNA research》2005,12(3):181-189
We have previously described the sequence features of 1500 mouseKIAA (mKIAA) genes in comparison with those of human KIAA genes(Okazaki, N., Kikuno, R., Inamoto, S., Hara, Y., Nagase, T.,Ohara, O., and Koga, H. 2002, DNA Res., 9, 179188; Okazaki,N., Kikuno, R., Ohara, R., Inamoto, S., Aizawa, H., Yuasa, S.,Nakajima, D., Nagase, T., Ohara, O., and Koga, H. 2003, DNARes., 10, 3548; Okazaki, N., Kikuno, R., Ohara, R., Inamoto,S., Koseki, H., Hiraoka, S., Saga, Y., Nagase, T., Ohara, O.,and Koga, H. 2003, DNA Res., 10, 167180; and Okazaki,N., F-Kikuno, R., Ohara, R., Inamoto, S., Koseki, H., Hiraoka,S., Saga, Y., Seino, S., Nishimura, M., Kaisho, T., Hoshino,K., Kitamura, H., Nagase, T., Ohara, O., and Koga, H. 2004,DNA Res., 11, 205218). To validate the orthologous relationshipbetween mKIAA and KIAA genes in detail, we examined their chromosomalpositions and evolutionary rate of synonymous substitutionsand confirmed that >93% of the mKIAA/KIAA gene pairs areorthologous. During the sequence analysis of mKIAA genes, wefound that 3'-untranslated region (3'-UTR) lengths of mKIAAand KIAA genes are extremely long. In the meanwhile, we havealso examined the tissue-specific expression of 1700 mKIAA genesusing cDNA microarray and verified predominantly their expressionin adult brain (Koga, H., Yuasa, S., Nagase, T., Shimada, K.,Nagano, M., Imai, K., Ohara, R., Nakajima, D., Murakami, M.,Kawai, M., Miki, F., Magae, J., Inamoto, S., Okazaki, N., Ohara,O. 2004, DNA Res., 11, 293304). To connect these twoevidences, we statistically analysed the relationship betweenthem by using the mKIAA genes. Consequently, a positive correlationwas observed between the 3'-UTR lengths and the relative expressionintensities in adult brain. Furthermore, we searched sequenceelements in the 3'-UTR possibly related with their expressionand found some candidates regarding the brain-specific expression. 相似文献
13.
Martel CM 《Microbial ecology》2009,57(4):589-597
It is suspected that phagotrophic marine protozoa might possess feeding receptors that enable them to discern the nutritional
quality of individual prey items (during prey-handling) on the basis of their cell-surface biochemistry. This article reviews
advances in our understanding of the molecular mechanisms that mediate the biorecognition and selection of nonself (microalgal)
prey items by the microplanktonic marine phagotroph Oxyrrhis marina. The potential importance of lectin–glycan interactions is first considered in view of findings which demonstrate that O. marina possesses lectin-like feeding receptors specific for prey-surface (mannose) glycoconjugates. Secondly, some conceptual bases
for indirect or ‘opsonic’ modes of prey biorecognition mediated by soluble prey-labelling proteins are presented. Finally,
the possibility that some accounts of selective feeding in O. marina might result from the noxious effects of prey-associated chemicals rather than active ‘distaste’ by phagotrophic cells is
discussed. Recent evidence for toxic superoxide (O2
−) production by marine microalgae is afforded particular attention given that release of O2
− anions can be exacerbated by the binding of mannose-specific lectins to the microalgal cell wall; a novel model for grazing-activated
chemical defence is proposed. 相似文献
14.
Nitric oxide synthase-like enzyme mediated nitric oxide generation by harmful red tide phytoplankton, Chattonella marina 总被引:1,自引:0,他引:1
The unicellular marine phytoplankton Chattonella marina is knownto exhibit potent fish-killing activity. Previous studies havedemonstrated that C. marina produces reactive oxygen species(ROS), and ROS-mediated ichthyotoxic mechanism has been postulated.However, the exact toxic mechanism is still controversial. Inthis study, we obtained evidence that C. marina produces nitricoxide (NO) under normal growth conditions. We utilized chemiluminescence(CL) reaction between NO and luminolH2O2 to detect NOin C. marina cell suspensions. In this assay, significant CLwas observed in C. marina in a cell-number-dependent manner,and this was diminished by the addition of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide(carboxy-PTIO), a specific NO scavenger. The NO generation byC. marina was also confirmed by a spectrophotometric assay basedon the measurement of the diazo-reaction-positive substances(NOx) and by fluorometric assay using highly specific fluorescentindicator of NO. The NO level in C. marina was significantlydecreased by NG-nitro-L-arginine methyl ester (L-NAME), a specificNO synthase (NOS) inhibitor. The addition of L-arginine resultedin the increased NO level, whereas NaNO2 had no effect. Theseresults suggest that a NOS-like enzyme is mainly responsiblefor NO generation in C. marina. 相似文献
15.
Ephyra larvae and small medusae (1.795 mm diameter, 0.01350mg ash-free dry wt, AFDW) of the scyphozoan jellyfish Aureliaaurita were used in predation experiments with phytoplankton(the flagellate Isochrysis galbana, 4 µm diameter, {smalltilde}6 x 106 µg AFDW cell1), ciliates (theoligotrich Strombidium sulcatum, 28 µm diameter, {smalltilde}2 x 103 µg AFDW), rotifers (Synchaeta sp.,0.5 µg AFDW individual1) and mixed zooplankton(mainly copepods and cladocerans, 2.13.1 µg AFDWindividual1). Phytoplankton in natural concentrations(50200 µg C I1) were not utilized by largemedusae (4495 mm diameter). Ciliates in concentrationsfrom 0.5 to 50 individuals ml"1 were consumed by ephyra larvaeand small medusae (314 mm diameter) at a maximum predationrate of 171 prey day1, corresponding to a daily rationof 0.42%. The rotifer Synchaeta sp., offered in concentrationsof 100600 prey I1, resulted in daily rations ofephyra larvae (25 mm diameter) between 1 and 13%. Mixedzooplankton allowed the highest daily rations, usually in therange 540%. Large medusae (>45 mm diameter) consumedbetween 2000 and 3500 prey organisms day"1 in prey concentrationsexceeding 100 I1. Predation rate and daily ration werepositively correlated with prey abundance. Seen over a broadsize spectrum, the daily ration decreased with increased medusasize. The daily rations observed in high abundance of mixedzooplankton suggest a potential scope for growththat exceeds the growth rate observed in field populations,and this, in turn, suggests that the natural populations areusually food limited. The predicted predation rate at averageprey concentrations that are characteristic of neritic environmentscannot explain the maximum growth rates observed in field populations.It is therefore suggested that exploitation of patches of preyin high abundance is an important component in the trophodynamicsof this species.
1Present address: University of Bergen, Department of MarineBiology, N-5065 Blomsterdalen, Norway 相似文献
16.
The ingestion preferences of planktonic protozoa influence the structure and succession of microbial communities and thus biogeochemical cycling within aquatic environments. Some predatory ciliates and flagellates are reported to switch to cannibalism when no suitable non-self prey items are available for consumption. However, the importance of cannibalism as a survival strategy, and its ubiquity within the planktonic protozoa is not known. We report the first attempt to quantify cannibalism in a phagotrophic marine dinoflagellate (Oxyrrhis marina). Cannibalistic Oxyrrhis cells seldom comprised >2% of any experimental population, including those in which all non-self prey items had been grazed to extinction. Such 'prey-deplete' cultures became dominated by homogeneous populations of highly motile Oxyrrhis that were morphologically unable (too similar in size) to cannibalise. That cannibalism can only occur when 'victim' and 'cannibal' cell size-classes of sufficient difference collide, suggests that cannibalism may be of limited use as a long-term survival strategy in phagotrophic protozoa. 相似文献
17.
The in situ predation rate of the siphonophore Sphaeronectesgracilis was estimated from gut content analysis of hand-collectedsiphonophores and from laboratory data on digestion rates ofprey organisms. At daytime prey densities of 0.25 copepods 11,S. gracilis was estimated to consume 8.1 15.4 prey day1siphonophore1. From data on abundances of siphonophoresand copepods, S. gracilis was estimated to consume 24%of the copepods daily. In laboratory experiments, ingestionrates averaged 13.8 prey day1 siphonophore1 atprey densities of 5 copepods 11 and 36.9 at 20 copeods11. This was equivalent to a specific ingestion rate(for both carbon and nitrogen) of 17% day1 and45% day1, respectively, while specific ingestion in situwas only 2% day1. Ammonium excretion averaged 0.095 µg-atsiphonophore1 day1 at 5 prey 11, and 0.162at 20 prey 11. The specific respiration (carbon) andspecific excretion (nitrogen as ammonium) were calculated tobe 3% day1 at the lower experimental food level, and5% day1 at the higher food level.
1Contribution from the Catalina Marine Science Center No. 66.
2Present address: Dept. of Biology, University of Victoria,Victoria, B.C., Canada V8W 2Y2. 相似文献
18.
Stoecker Diane K.; Gallager Scott M.; Langdon Chris J.; Davis Linda H. 《Journal of plankton research》1995,17(5):1105-1124
Particle capture by the tintinnid ciliate, Favella sp., wasinvestigated with high-speed video microscopy. Experiments withmicrospheres and algal cells indicate that within the size range119 p.m. behavioral responses are partly responsiblefor the differential capture of large over small particles.For example, 4 µm microspheres or Isochrysis [spheiicaldiameter (ESD) - 4.5 µ are only captured if they are encounteredin the inner zones of the encounter area. Ten micrometer microspheresor Heterocapsa(1419 are captured with a greaterefficiency than smaller particles from the inner zones, butcan also be captured from the outer zone of the encounter area.Capture of particles from the outer zone is associated withcilialy reversal. Microsp1ieres and algal cells of similar sizeare captured in a similar manner. 相似文献
19.
Karlodinium veneficum is a common member of temperate, coastal phytoplankton assemblages that occasionally forms blooms associated with fish kills. Here, we tested the hypothesis that the cytotoxic and ichthyotoxic compounds produced by K. veneficum, karlotoxins, can have anti-grazing properties against the heterotrophic dinoflagellate, Oxyrrhis marina. The sterol composition of O. marina (>80% cholesterol) renders it sensitive to karlotoxin, and does not vary substantially when fed different algal diets even for prey that are resistant to karlotoxin. At in situ bloom concentrations (104–105 K. veneficum ml−1), grazing rates (cells ingested per Oxyrrhis h−1) on toxic K. veneficum strain CCMP 2064 were 55% that observed on the non-toxic K. veneficum strain MD5. At lower prey concentrations typical of in situ non-bloom levels (<103 cells ml−1), grazing rates (cells ingested per Oxyrrhis h−1) on toxic K. veneficum strain CCMP 2064 were 70–80% of rates on non-toxic strain MD5. Growth of O. marina was significantly suppressed when fed the toxic strain of K. veneficum. Experiments with mixed prey cultures, where non-toxic strain MD5 was fluorescently stained, showed that the presence of toxic strain CCMP 2064 inhibited grazing of O. marina on the co-occurring non-toxic strain MD5. Exogenous addition of a sub-lethal dose (100 ng ml−1) of purified karlotoxin inhibited grazing of O. marina by approximately 50% on the non-toxic K. veneficum strain MD5 or the cryptophyte S. major. These results identify karlotoxin as an anti-grazing compound for those grazers with appropriate sterol composition (i.e., desmethyl sterols). This strategy is likely to be an important mechanism whereby growth of K. veneficum is uncoupled from losses due to grazing, allowing it to form ichthyotoxic blooms in situ. 相似文献
20.
Our goal was to test our understanding of ingestion, assimilationefficiency and metabolism for Mnemiopsis mccradyi by formulatingand validating a simulation model of growth under differentconditions of food availability. The model was based on a carbonbudget approach using formulations derived from empirical results,including how each process was affected by food availabilityand ctenophore size. An experimentally measured carbon budgetfor pulsed food availability indicated that, relative to totalingestion, growth was high (1748%), respiration plusorganic release was relatively low (2448%) and little(<10%) of the ingested carbon was unaccounted for. New laboratoryinvestigations of feeding and assimilation efficiency were necessaryto refine the formulations so that model predictions comparedfavorably with a variety of laboratory measurements of growth,and growth efficiency, as well as the complete experimentallymeasured carbon budget. The refined model predicted a high ratioof growth to metabolism (>2) and a high gross growth efficiency(>30%) for smaller ctenophores at high food concentrations(>20 prey l1). Both growth rates and growth efficiencieswere predicted to decrease for larger ctenophores. Model predictionswere generally consistent with experimental results, includinginvestigations using pulsed food availability to simulate environmentalpatchiness. Although the model underpredicted ctenophore growthin some experiments at low food densities, the model predictionof a minimum prey concentration of about 8 l1 (24 µgC l1) for sustaining a ctenophore population of reproductivesize agreed with field observations. 相似文献