Omnivory in the calanoid copepod Temora longicornis: feeding, egg production and egg hatching rates

We measured in laboratory experiments the ingestion, egg production and egg hatching rates of female Temora longicornis as a function of diet. The diets consisted of a diatom (Thalassiosira weissflogii), an autotrophic dinoflagellate (Heterocapsa triquetra), and a bacterivorous ciliate (Uronema sp.) given as sole foods, or combinations of these single-food items: diatom+dinoflagellate, diatom+ciliate, dinoflagellate+ciliate, and diatom+ciliate+dinoflagellate. For the three single-item diets, the functional response was similar; i.e., ingestion rate increased linearly with food concentration (food range: ∼25 to ∼600 μg C l⁻¹). When all diets were considered, maximum daily carbon ration (∼70% of body weight) was independent of food type. However, the maximum daily egg production rate (12% of body carbon) was obtained with the diatom diet. For all diets, both ingestion and egg production rates increased with food concentration. Ingestion and egg production rates were affected differently by the interaction of food concentration and food type: at low food concentrations, ingestion rates were highest on diets containing the diatom. At high food concentrations, egg production rates were highest on the two phytoplankter diets and their combination. The presence of the ciliate in the diet did not enhance ingestion rate or egg production. Mixed-food diets did not enhance egg production relative to single-food diets. Hence, dietary diversity did not appear to be particularly advantageous for reproduction. Carbon-specific egg production efficiency (EPE; egg production/ingestion) was independent of food concentration and type, and equaled 9%. Egg hatching success was low (mean<30%) and independent of food concentration and type, and egg production rates. Our results are consistent with previous observations that egg production in T. longicornis is enhanced during diatom blooms. However, the relatively low EPE and egg hatching success suggest that reproduction and recruitment in this study were severely constrained by the biochemical composition of the diet, or the physiological condition of the females towards the end of their season of growth in Long Island Sound.     

Toxin content and toxic effects of the dinoflagellate Gyrodinium corsicum (Paulmier) on the ingestion and survival rates of the copepods Acartia grani and Euterpina acutifrons

Short-term experiments showed that ingestion rates of the copepods Acartia grani and Euterpina acutifrons on different concentrations of the dinoflagellate Gyrodinium corsicum were not usually different from those obtained with the non-toxic and similar sized Prorocentrum triestinum. Long-term experiments showed that no A. grani survived for more than 288 h on concentrated cultures (1500 μg C l⁻¹) of G. corsicum compared with survival rates of 86.7% on the non-toxic P. triestinum. In contrast high and similar survival rates were found for E. acutifrons exposed for the same time to similar concentrations of both dinoflagellates. These results demonstrated that G. corsicum produce toxins which have significant adverse effects on the long-term survival rates of some copepods like A. grani but not on other copepods like E. acutifrons. The possibility of PSP-toxin production by G. corsicum was analysed by chromatographic analysis (HPLC-FD) and mouse bioassay of extracts obtained from cultures maintained in exponential growth phase in f/2-Si and L1 culture mediums. These analyses and the bioassay ruled out the presence of PSP toxins in this dinoflagellate. However, mouse tests provided the first evidence for the presence of some type of NSP toxin in G. corsicum. Haemolytic assays also gave the first positive results for the methanol extract of this dinoflagellate species.     

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.     

Differential interactions between the nematocyst-bearing mixotrophic dinoflagellate Paragymnodinium shiwhaense and common heterotrophic protists and copepods: Killer or prey

To investigate interactions between the nematocyst-bearing mixotrophic dinoflagellate Paragymnodinium shiwhaense and different heterotrophic protist and copepod species, feeding by common heterotrophic dinoflagellates (Oxyrrhis marina and Gyrodinium dominans), naked ciliates (Strobilidium sp. approximately 35 μm in cell length and Strombidinopsis sp. approximately 100 μm in cell length), and calanoid copepods Acartia spp. (A. hongi and A. omorii) on P. shiwhaense was explored. In addition, the feeding activities of P. shiwhaense on these heterotrophic protists were investigated. Furthermore, the growth and ingestion rates of O. marina, G. dominans, Strobilidium sp., Strombidinopsis sp., and Acartia spp. as a function of P. shiwhaense concentration were measured. O. marina, G. dominans, and Strombidinopsis sp. were able to feed on P. shiwhaense, but Strobilidium sp. was not. However, the growth rates of O. marina, G. dominans, Strobilidium sp., and Strombidinopsis sp. feeding on P. shiwhaense were very low or negative at almost all concentrations of P. shiwhaense. P. shiwhaense frequently fed on O. marina and Strobilidium sp., but did not feed on Strombidinopsis sp. and G. dominans. G. dominans cells swelled and became dead when incubated with filtrate from the experimental bottles (G. dominans + P. shiwhaense) that had been incubated for one day. The ingestion rates of O. marina, G. dominans, and Strobilidium sp. on P. shiwhaense were almost zero at all P. shiwhaense concentrations, while those of Strombidinopsis sp. increased with prey concentration. The maximum ingestion rate of Strombidinopsis sp. on P. shiwhaense was 5.3 ng C predator⁻¹d⁻¹ (41 cells predator⁻¹d⁻¹), which was much lower than ingestion rates reported in the literature for other mixotrophic dinoflagellate prey species. With increasing prey concentrations, the ingestion rates of Acartia spp. on P. shiwhaense increased up to 930 ng C ml⁻¹ (7180 cells ml⁻¹) at the highest prey concentration. The highest ingestion rate of Acartia spp. on P. shiwhaense was 4240 ng C predator⁻¹d⁻¹ (32,610 cells predator⁻¹d⁻¹), which is comparable to ingestion rates from previous studies on other dinoflagellate prey species calculated at similar prey concentrations. Thus, P. shiwhaense might play diverse ecological roles in marine planktonic communities by having an advantage over competing phytoplankton in anti-predation against potential protistan grazers.     

Zooplankton community composition and copepod grazing on the West Florida Shelf in relation to blooms of Karenia brevis

Blooms of the toxin producing dinoflagellate Karenia brevis occur routinely on the West Florida Shelf of the Gulf of Mexico. Nutrient supplies are thought to play a large role in the formation and maintenance of these blooms. The role of top-down control has been less well studied, but grazing, or the lack thereof, on these toxic species may also enhance the formation of large biomass blooms in this region. Zooplankton community structure and copepod species composition were analyzed from samples collected on the West Florida Shelf (WFS) during a NOAA funded ECOHAB regional Karenia Nutrient Dynamics project during October 2007–2010. In 2008 there was no statistical difference in the abundance of zooplankton at bloom and non-bloom stations, however in 2009 there was a statistically significant difference (p < 0.05) between the abundance of zooplankton at stations with Karenia present. To investigate copepod ingestion rates in relation to K. brevis, shipboard and laboratory experiments of the single label method of ¹⁴C labeled phytoplankton culture, and time course ingestion experiments with isolated copepods were performed. Calculated ingestion rates suggest that the copepod species Centropages velificatus, and Acartia tonsa ingested K. brevis, however rates were variable among collection sites and K. brevis strains. Parvocalanus crassirostris did not ingest K. brevis in any of the experiments.     

Study of selective feeding in the marine cladoceran Penilia avirostris by HPLC pigment analysis

Food selection by the marine cladoceran Penilia avirostris was studied in the field by HPLC analysis of phytoplankton marker pigments and in the laboratory by microscopic measurement of cell removal. Comparison between pigment composition in natural phytoplankton and in P. avirostris showed that P. avirostris preferred diatoms, cryptophytes and chlorophytes, and ignored prymnesiophytes and dinoflagellates. Peridinin, the marker pigment for dinoflagellates was found in P. avirostris only when the dinoflagellate populations were dominated by Prorocentrum. Pigment degradation rates ranged from 13.73% for alloxanthin to 36.62% for chlorophyll a. Clearance rates measured in the laboratory provided further evidence of strong preference for diatoms and cryptophytes, and avoidance of dinoflagellates. Microscopic counts suggested that P. avirostris was feeding on prymnesiophytes, although ingestion of prymnesiophytes could not be confirmed by pigment analysis.     

Importance of copepod faecal pellets to the fate of the DSP toxins produced by Dinophysis spp.

An ingestion experiment was carried out in Rı́a de Pontevedra (Spain) with the copepod Temora longicornis in order to determine ingestion rates of the DSP toxin-producers, Dinophysis spp. (Dinophyceae), and the excretion rate of Dinophysis spp. cells within the faecal pellets. Ingestion rate was a function of dinoflagellate abundance and did not vary with either the amount, or the composition of the co-occurring phytoplankton species in the food suspension. Faecal pellet production increased at higher food concentrations. Intact Dinophysis spp. cells representing 34.4% of the total Dinophysis cells ingested by the copepods were found within the pellets. T. longicornis was the only dominant copepod species in the area that fed on Dinophysis spp., thus the pellets produced by T. longicornis were the main source of copepod “toxic” pellets in the media during blooms of Dinophysis spp. These “toxic” pellets might contribute to the maintenance of the toxic algal blooms, if the cells inside the pellets remain viable, can spread the potential toxicity of the toxic dinoflagellates throughout the pelagic food web due to coprophagy, and/or be an important toxic vector into the benthic food web. However, during a Dinophysis spp. bloom, the percentage of cells excreted daily within the pellets was lower than 1% of the total dinoflagellate population and, moreover, copepod faecal pellets represent a small fraction of the sinking material in this area. Although it was not possible to measure the amount of toxins in the pellets, we concluded that copepod faecal pellets do not have an important role in the transport of DSP toxins through the food web in this area.     

Phagotrophic phytoflagellates in microbial food webs

Phagotrophy by pigmented flagellates is known from the literature but has recently been rediscovered in the context of microbial food webs. Particle ingestion rates were found to be equivalent for pigmented and nonpigmented microflagellates in both field and laboratory studies. Ingestion rates of the chrysophytes Ochromonas danica, O. minuta, and Poterioochromonas malhamensis, the dinoflagellate Peridinium inconspicuum, and the cryptophytes Cryptomonas ovata and C. erosa were compared with those of two nonpigmented Monas species using 0.57 μm polystyrene beads as a food source. Ingestion rates were 0.31 to 3.17 beads/cell/h and filtration rates were 10⁻⁷ to 10⁻⁸ ml/cell/h with no detectable difference between pigmented and nonpigmented forms. Ingestion rates in unpigmented Monas species showed a linear increase with increasing particle concentration from 1.9 × 10⁶ to 1.6 × 10⁷ beads/ml. Light and DOC levels in the range of those encountered by phytoflagellates in the field also influenced laboratory measurements of bead ingestion by Poterioochromonas malhamensis. Ingestion rates decreased and photosynthesis increased over the natural PAR light range from 0 to 1800 microeinsteins/s/m². At 40 microeinsteins/s/m² maximum ingestion rates and high rates of photosynthesis occurred simultaneously. Ingestion rates decreased above 4 mgC/l supplied as glucose. DOC levels commonly occurring in Lake Oglethorpe range from 3.5 to 10.0 mgC/l. These studies suggest that mixotrophy, the trophic utilization of particulate food and dissolved organic matter as well as photosynthetically fixed organic matter, is a balanced process that can be regulated by environmental conditions. In field studies during a chrysophyte bloom, phytoflagellate grazing exceeded heterotrophic microflagellate grazing and constituted up to 55% of the bactivory of all microflagellates, ciliates, rotifers, and crustaceans combined. Neither bacterial abundance, light nor temperature were good predicters of grazing rates for the phagotrophic phytoflagellate association as a whole during this unstratified period. Phagotrophs are often most abundant at the metalimnetic plate during stratification.     

Suspended clay reduces Daphnia feeding rate

SUMMARY. 1. Suspended sediments often reduce cladoceran abundance in the field, and reduce the algal feeding rates of cladocerans in the laboratory. This paper explores the behavioural mechanisms by which suspended clay reduces Daphnia feeding rates. Feeding experiments using radiolabelled Cryptomonas cells showed that 50–200 mg 1-^?1 coarse suspended clay (particle size<2 μm) reduced the algal ingestion rate of Daphnia ambigua by 29–87%, but fine suspended clay (<1 μm) had no effect. Suspended clay decreased feeding rate by 60–70% at low algal concentrations (≤5×10³ cells ml^?1), but by only 27% at high algal concentrations (20×10³ cells ml^?1). Thus, the inhibitory effects of suspended clay are greater at low algal concentrations. The sudden addition (or removal) of suspended clay caused immediate reductions (or increases) in algal ingestion rate. 2. Observations of the feeding behaviour of tethered D.pulex showed that the frequency of postabdominal rejections increased greatly in the presence of suspended clay. The rejected boluses contained both algae and clay. Thoracic feeding appendage beat frequency decreased in the presence of suspended clay, decreasing the volume of water searched for food particles. 3. These behavioural responses indicate that clay reduces cladoceran feeding rate by mechanically interfering with both the collection and ingestion of algal cells. Both inhibitory effects are caused because cladocerans collect and ingest suspended clay particles. The behavioural mechanisms by which cladocerans regulate their feeding rate in very high concentrations of algal cells (rejection of excess food and reduction in thoracic limb pumping movements) are the same mechanisms responsible for the inhibition of algal ingestion rate in the presence of high concentrations of suspended clay particles.     

Symbiotic Association Between Symbiodinium and the Gastropod Strombus gigas: Larval Acquisition of Symbionts

The importance of the dinoflagellate Symbiodinium sp. was studied in the early life stages of the gastropod Strombus gigas. This dinoflagellate was not found in the eggs or the gelatinous mass surrounding the eggs of the mollusk; therefore, Symbiodinium is not inherited directly. To determine whether the planktonic veligers can acquire these algae from the environment, they were exposed to freshly isolated Symbiodinium from adult S. gigas (homologous). The optimal stage for Symbiodinium inoculation was found at 48 h post-hatching. Survival and growth rates of veligers and juveniles were higher when inoculated with freshly isolated Symbiodinium in conjunction with daily feeding of Isochrysis spp. Veligers inoculated with Symbiodinium freshly isolated from three host species elicited distinct responses: (1) veligers did not take up Symbiodinium isolated from the hydrozoan Millepora alcicornis suggesting that there is discrimination on contact prior to ingestion, (2) veligers did take up Symbiodinium isolated from the anemone Bartholomea annulata, but the algae did not persist in the host tissue suggesting that selection against this type took place after ingestion or that the algae did not divide in the host, and (3) veligers did take up Symbiodinium isolated from Pterogorgia anceps where it persisted and was associated with metamorphosis of the larvae. In contrast, the Symbiodinium freshly isolated from S. gigas were not associated with metamorphosis and required an inducer such as the red alga Laurencia poitei. These data present a significant advancement for the establishment of a new approach in the aquaculture of this important but declining Caribbean species.     

Evaluation and comparison of four methods of ranking horses based on reactivity

Four methods of ranking horses on reactivity were evaluated and compared: isolation from conspecifics, presentation of a static novel stimulus, traversing a novel stimulus in a runway (isolation, novel stimulus and runway tests, respectively) and assigning subjective emotionality scores. In all tests, horses’ heart rates were recorded and behaviour was videotaped. To be considered a valid test of reactivity, at least one heart rate and one behavioural measurement in the test had to change significantly between treatments (tranquilizer administation versus sham tranquilizer administration), and behavioural measures had to be displayed in at least 75% of the trials. Forty horses performed each of the three tests daily on three different days in a switchback design. Horses were assigned randomly to a daily test sequence, which was maintained throughout the study. In the runway test, no significant difference in heart rate values in tranquilized and non-tranquilized horses was found, and no behavioural attribute was displayed in more than 52% of the trials; therefore it was rejected as a valid test of reactivity. Both isolation and novel stimulus tests produced valid measurements. Mean heart rate was the most precise physiological measure for these tests, and walking and defecation frequency were the most precise behavioural measures for novel stimulus and isolation tests, respectively. Mean heart rates on the novel stimulus and isolation tests were correlated (r_s = 0.79, P < 0.01) indicating that these tests produced similar rankings based on physiological responses. However, behavioural measures ranked horses differently (r_s = 0.27, P < 0.10) on the tests. Rank correlations between mean heart rates and behavioural measures were higher in the novel stimulus (r_s = 0.66, P < 0.01) than the isolation test (r_s = 0.55, P < 0.01), indicating that the novel stimulus test ranked horses based on either physiological or behavioural responses more similarly than did the isolation test. Therefore, the novel stimulus test was considered the more accurate evaluation of reactivity. Subjective emotionality scores were correlated moderately with mean heart rates (r_s > 0.33, P < 0.01) from the novel stimulus and isolation tests and with walking scores (r_s = 0.47, P < 0.01) from the novel stimulus test. Assignment of subjective emotionality scores was not as accurate as the novel stimulus or isolation tests in ranking horses for reactivity. Using physiological data alone, combining physiological and behavioural measurements or using more than one behavioural measurement in reactivity tests may reflect the reactivity of the horse better than a single behavioural measurement.     

The timing of activity in motor neurons that produce radula movements distinguishes ingestion from rejection in Aplysia

1. We have studied the neural circuitry mediating ingestion and rejection in Aplysia using a reduced preparation that produces ingestion-like and rejection-like motor patterns in response to physiological stimuli.
2. We have characterized 3 buccal ganglion motor neurons that produce specific movements of the radula and buccal mass. B8a and B8b act to close the radula. B10 acts to close the jaws and retract the radula.
3. The patterns of activity in these neurons can be used to distinguish the ingestion-like and rejection-like motor patterns. B8a, B8b and B10 are active together during the ingestion-like pattern. Activity in B8a and B8b ends prior to the onset of activity in B10 during the rejection-like pattern.
4. Our data suggest that these neurons undergo similar patterns of activity in vivo. During both feeding-like patterns, the activity and peripheral actions of B8a, B8b, and B10 are consistent with radula movements observed during ingestion and rejection. In addition, the extracellular activity produced by these neurons is consistent with neural activity observed in vivo during ingestion and rejection.
5. Our data suggest that the different activity patterns observed in these motor neurons contribute to the different radula movements that distinguish ingestion from rejection.

     

Mixotrophy in the sand-dwelling dinoflagellate Thecadinium kofoidii

Thecadinium kofoidii is a marine sand-dwelling dinoflagellate that sometimes forms dense blooms. This species was previously thought to be an exclusively autotrophic dinoflagellate, and its mixotrophic ability has not been explored yet. By investigating its ecophysiology, its trophic mode should be revealed. We explored the mixotrophic ability of T. kofoidii by examining its protoplasm under light and transmission electron microscopes with diverse algal prey species. Furthermore, the feeding mechanism of T. kofoidii and prey species on which it feeds were investigated. In addition, the growth and ingestion rates of T. kofoidii as a function of prey concentration were determined when feeding on the benthic cryptophyte Rhodomonas salina. Thecadinium kofoidii was able to feed on R. salina and the dinoflagellate Symbiodinium voratum, which had equivalent spherical diameters (ESDs) ≤ 10.1?µm, while it did not feed on the benthic dinoflagellates Levanderina fissa, Prorocentrum concavum or Ostreopsis cf. ovata, which had ESDs ≥ 15?µm. Thecadinium kofoidii fed on the edible prey cells using the peduncle. The maximum ingestion rate of T. kofoidii on R. salina was 1.3 cells predator^?1 d^?1. However, feeding on R. salina did not significantly increase the growth rate of T. kofoidii. The low ingestion rate of T. kofoidii on R. salina may have partially resulted in the lack of significant increase in its growth rate due to mixotrophy. The present study discovered predator–prey relationships between T. kofoidii and R. salina and S. voratum, which may change our view of the energy flow and carbon cycling in marine benthic food webs.     

Feeding efficiency of a marine copepod Acartia erythraea on eight different algal diets

Acartia erythraea is a dominant zooplankton copepod in the South China coastal waters during summer. This paper examined its feeding behavior (food gut passage, clearance rate and ingestion rate) on eight phytoplankton diets. The food gut passage time and ingestion rate were negatively related to the size and concentration of food supply, whereas the clearance rate was positively related to the food concentration. The ingestion rate decreased with the food concentration when it reached a threshold level. Generally, the clearance rate of copepods decreased with increasing cell density, but was very low at both low and high algal densities when the food were small in sizes. The optimum food size was about 10 μm for the copepods, and the dinoflagellate, Prorocentrum minimum, was considered as a good food choice for A. erythraea.     

Tracking losses of brevetoxins on exposure to phytoplankton competitors: Ecological impacts

The frequent occurrence of devastating blooms of the harmful dinoflagellate Karenia brevis in the Gulf of Mexico has motivated research into bloom dynamics and potential mitigation strategies. The use of competing phytoplankton to lower waterborne concentrations of the most abundant and toxic brevetoxins produced during these blooms has been proposed. However the ecological impacts of using such biocontrol agents have not been addressed. This study investigated the impact on marine invertebrates of lowered brevetoxin concentrations due to the presence of competing phytoplankton. Even at low brevetoxin concentrations, the presence of the common diatom Skeletonema grethae ameliorated harmful toxic effects of brevetoxins upon the brine shrimp, Artemia salina, and reduced the incidence of negative physiological and morphological responses of the sea anemone Aiptasia pallida. In addition, brevetoxin biotransformation products formed by competing phytoplankton appear to be non-toxic or do not trigger the same physiological responses as brevetoxins in the model organisms used. These findings may impact the interpretation of ecotoxicological data gathered during bloom events, since the presence of phytoplankton competitors in Karenia blooms is likely to reduce the harmful effects seen on many marine invertebrates.     

In vivo buccal nerve activity that distinguishes ingestion from rejection can be used to predict behavioral transitions in Aplysia

1. We are studying the neural basis of consummatory feeding behavior in Aplysia using intact, freely moving animals.
2. Video records show that the timing of radula closure during the radula protraction-retraction cycle constitutes a major difference between ingestion (biting or swallowing) and rejection. During ingestion, the radula is closed as it retracts. During rejection, the radula is closed as it protracts.
3. We observed two patterns of activity in nerves which are likely to mediate these radula movements. Patterns I and II are associated with ingestion and rejection, respectively, and are distinguished by the timing of radula nerve activity with respect to the onset of buccal nerve 2 activity.
4. The association of ingestion with pattern I is maintained when the animal feeds on a polyethylene tube, the same food substrate used to elicit rejection responses. Under these conditions, pattern I is associated with either swallowing or no net tube movement.
5. Most transitions from swallowing to rejection were preceded by one or more occurrences of pattern I in which there was no net tube movement, suggesting that these transitions can be predicted.
6. Our data suggest that these two patterns can be used to distinguish ingestion from rejection.

     

Photoadaptation Alters the Ingestion Rate of Paramecium bursaria, a Mixotrophic Ciliate

Bacteriovorous protozoa harboring symbiotic algae are abundant in aquatic ecosystems, yet despite a recent interest in protozoan bacterivory, the influence of light on their ingestion rates has not been investigated. In this study, Paramecium bursaria containing endosymbiotic Chlorella was tested for the effect of light on its ingestion rate. P. bursaria was grown for 4 to 6 days under five different light fluxes ranging from 1 to 90 microeinsteins s^-1 m^-2. Ingestion rates were determined by using 0.77-μm-diameter fluorescent microspheres. 4′,6-Diamidino-2-phenylindole dihydrochloride-labeled Enterobacter cloacae was used in one experiment to confirm differences in uptake rates of bacteria by P. bursaria. Unlike phagotrophic phytoflagellates, the ciliates demonstrated different ingestion rates in response to different light intensities. Although symbionts contribute carbon to their host via photosynthesis, the paramecia of the present study fed faster after exposure to higher light intensities, whereas their aposymbiotic counterparts (lacking endosymbionts) were unaffected. Light-induced changes in ingestion rates were not immediate, but corresponded to the period of time required for endosymbiont populations to change significantly. This strongly suggests that the symbionts, stimulated by higher light levels, may dictate the feeding rates of their hosts. Thus, light, apart from temperature, may influence the impact of certain protists on natural bacteria and may affect laboratory-based determinations of protistan feeding rates.     

North Atlantic right whales,Eubalaena glacialis,exposed to paralytic shellfish poisoning (PSP) toxins via a zooplankton vector,Calanus finmarchicus

The seriously endangered north Atlantic right whale (Eubalaena glacialis) is regularly exposed to the neurotoxins responsible for paralytic shellfish poisoning (PSP) through feeding on contaminated zooplankton acting as a vector of these dinoflagellate toxins. This chronic exposure occurs during several months each summer while the whales are present on their late summer feeding ground in Grand Manan Basin in the lower Bay of Fundy. Based on estimated ingestion rates, we suggest that these toxins could affect respiratory capabilities, feeding behavior, and ultimately the reproductive condition of the whale population.     

Inducible Mixotrophy in the Dinoflagellate Prorocentrum minimum

Prorocentrum minimum is a neritic dinoflagellate that forms seasonal blooms and red tides in estuarine ecosystems. While known to be mixotrophic, previous attempts to document feeding on algal prey have yielded low grazing rates. In this study, growth and ingestion rates of P. minimum were measured as a function of nitrogen (‐N) and phosphorous (‐P) starvation. A P. minimum isolate from Chesapeake Bay was found to ingest cryptophyte prey when in stationary phase and when starved of N or P. Prorocentrum minimum ingested two strains of Teleaulax amphioxeia at higher rates than six other cryptophyte species. In all cases ‐P treatments resulted in the highest grazing. Ingestion rates of ‐P cells on T. amphioxeia saturated at ~5 prey per predator per day, while ingestion by ‐N cells saturated at 1 prey per predator per day. In the presence of prey, ‐P treated cells reached a maximum mixotrophic growth rate (μ_max) of 0.5 d^?1, while ‐N cells had a μ_max of 0.18 d^?1. Calculations of ingested C, N, and P due to feeding on T. amphioxeia revealed that phagotrophy can be an important source of all three elements. While P. minimum is a proficient phototroph, inducible phagotrophy is an important nutritional source for this dinoflagellate.     

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.