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Journal ArticleDOI

Digestion of diatoms by planktonic copepods and doliolids

01 Aug 2005-Marine Ecology Progress Series (Inter-Research)-Vol. 297, pp 303-310
TL;DR: The results imply that doliolids are not able to utilize diatoms as efficiently as calanoid copepod, and will most likely rely more on soft- walled food particles such as flagellates, which could become available to the benthic communities of continental shelves since the dolioletta gegenbauri pellets sink quite rapidly.
Abstract: The goal of our studies was to quantify the digestive performance of a calanoid copepod in comparison to a commonly occurring pelagic tunicate. A comparison of the carbon and nitrogen content of quantitatively recovered fecal pellets with ingested amounts revealed that the large calanoid Eucalanus hyalinus digested the diatoms Thalassiosira weissflogii and Rhizosolenia alata significantly better than the doliolid Dolioletta gegenbauri did. This was attributed to the copepods' ability to crush the diatom cells after ingestion, while the doliolids caused minimal physical damage to the diatom cells. As for D. gegenbauri, it digested the large diatom R. alata far better than the small diatom T. weissflogii. The pellets from the latter contained nearly 50% of the ingested carbon and nitrogen. These findings are supported by visual observations. The results imply that doliolids are not able to utilize diatoms as efficiently as calanoid copepods, and will most likely rely more on soft- walled food particles such as flagellates. These findings also imply that a considerable percentage of particulate organic matter ingested by doliolids, in water masses dominated by diatoms, could become available to the benthic communities of continental shelves since the doliolid pellets sink quite rapidly.

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Citations
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Journal ArticleDOI
TL;DR: Large planktonic microphages are focused on as a model of selective mucus feeding because of their important roles in the ocean food web: as bacterivores, prey for higher trophic levels, and exporters of carbon via mucous aggregates, faecal pellets and jelly-falls.
Abstract: Mucous-mesh grazers (pelagic tunicates and thecosome pteropods) are common in oceanic waters and efficiently capture, consume and repackage particles many orders of magnitude smaller than themselves. They feed using an adhesive mucous mesh to capture prey particles from ambient seawater. Historically, their grazing process has been characterized as non-selective, depending only on the size of the prey particle and the pore dimensions of the mesh. The purpose of this review is to reverse this assumption by reviewing recent evidence that shows mucous-mesh feeding can be selective. We focus on large planktonic microphages as a model of selective mucus feeding because of their important roles in the ocean food web: as bacterivores, prey for higher trophic levels, and exporters of carbon via mucous aggregates, faecal pellets and jelly-falls. We identify important functional variations in the filter mechanics and hydrodynamics of different taxa. We review evidence that shows this feeding strategy depends not only on the particle size and dimensions of the mesh pores, but also on particle shape and surface properties, filter mechanics, hydrodynamics and grazer behaviour. As many of these organisms remain critically understudied, we conclude by suggesting priorities for future research.

68 citations

Journal ArticleDOI
TL;DR: The acidic and suboxic–anoxic environments of the copepod gut may support iron dissolution and anaerobic microbial activities that otherwise are not favored in the well-buffered and oxygenated ambient ocean.
Abstract: The environmental conditions inside the gut of Calanus hyperboreus and C. glacialis were measured with microelectrodes. An acidic potential hydrogen (pH) gradient was present in the gut of C. hyperboreus, and the lowest pH recorded was 5.40. The gut pH of a starved copepod decreased by 0.53 after the copepod resumed feeding for a few hours, indicating the secretion of acidic digestive fluid. A copepod feeding on Thalassiosira weissflogii (diatom) had slightly lower pH than that feeding on Rhodomonas salina (cryptophyte). Oxygen was undersaturated in the gut of both C. hyperboreus and C. glacialis, with a steep gradient from the anal opening to the metasome region. The central metasome region was completely anoxic. Food remains in the gut led to a lower oxygen level, and a diatom diet induced a stronger oxygen gradient than a cryptophyte diet. The acidic and suboxic–anoxic environments of the copepod gut may support iron dissolution and anaerobic microbial activities that otherwise are not favored in the well-buffered and oxygenated ambient ocean.

67 citations

Journal ArticleDOI
TL;DR: Reciration rates, ammonium and phosphate excretion rates, and the net growth efficiencies of early developmental stages of Oithona davisae as related to stage, body weight, temperature, and food availability were determined, indicating lipid-oriented metabolism.
Abstract: The genus Oithona has been considered the most abundant and ubiquitous copepod in the world's oceans. However, despite its importance, the metabolism of its developmental stages (nauplii and copepodites), crucial to explain their evolutionary success, is almost unknown. We determined respiration rates, ammonium and phosphate excretion rates, and the net growth efficiencies of early developmental stages of Oithona davisae as related to stage, body weight, temperature, and food availability. Respiration and excretion rates increased with increasing body weight and were positively related to temperature and food. Specific respiration rates of nauplii and copepodites varied from 0.11 to 0.55 d -1 depending on stage, body weight, temperature, and food availability. Metabolic C: N ratios were higher than 14, indicating lipid-oriented metabolism. Assimilation efficiencies and net growth efficiencies ranged from 65% to 86% and from 23% to 32%, respectively, depending on body weight, stage, and temperature. Assimilation efficiencies and net growth efficiencies estimated using the respiration rates of nauplii with food were 1.7 times higher and 0.6 times lower, respectively, than those calculated using respiration rates of nauplii without food. Therefore, the use of respiration rates measured in filtered seawater led to substantial bias on the estimations of zooplankton carbon budget. O. davisae developmental stages exhibited similar assimilation and growth efficiencies but lower carbon-specific respiratory losses than calanoid copepods. Hence, the low metabolic costs of Oithona compared with calanoids may be one reason for their success in marine ecosystems.

59 citations


Cites background from "Digestion of diatoms by planktonic ..."

  • ...The AE and NGEs of zooplankton vary depending on food concentration and food quality (Paffenhöfer and Köster 2005)....

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Journal ArticleDOI
TL;DR: The results demonstrate that thickening of silica walls is an effective defence strategy against copepods, and suggests that the plasticity of silicification in diatoms may have evolved as a response to copepod grazing pressure, whose specialized tools to break silicified walls have coevolved with diatom species.
Abstract: Diatoms contribute nearly half of the marine primary production. These microalgae differ from other phytoplankton groups in having a silicified cell wall, which is the strongest known biological material relative to its density. While it has been suggested that a siliceous wall may have evolved as a mechanical protection against grazing, empirical evidence of its defensive role is limited. Here, we experimentally demonstrate that grazing by adult copepods and nauplii on diatoms is approximately inversely proportional to their silica content, both within and among diatom species. While a sixfold increase in silica content leads to a fourfold decrease in copepod grazing, silicification provides no protection against protozoan grazers that directly engulf their prey. We also found that the wall provides limited protection to cells ingested by copepods, since less than 1% of consumed cells were alive in the faecal pellets. Moreover, silica deposition in diatoms decreases with increasing growth rates, suggesting a possible cost of defence. Overall, our results demonstrate that thickening of silica walls is an effective defence strategy against copepods. This suggests that the plasticity of silicification in diatoms may have evolved as a response to copepod grazing pressure, whose specialized tools to break silicified walls have coevolved with diatoms.

52 citations

Journal ArticleDOI
TL;DR: The main finding of this study is that the metabolic activity of minute metazooplankton organisms, while they are feeding, can now be determined with good precision over a period of hours without any invasion of the experimental vessels.
Abstract: The goal of this study was to determine over time with high temporal resolution the oxy- gen consumption rates of nauplii of marine planktonic copepods while feeding on phytoplankton at environmental concentrations. The determination of the nauplii's oxygen consumption was achieved by applying a fluorescence-based non-invasive technology. The hourly oxygen consumption at 21°C ranged from near 18 nl O2 Nauplius IV -1 to about 33 nl O2 Nauplius VI -1 of the calanoid Eucalanus pileatus. The nauplii's feeding activity was reflected by an average reduction of food concentration of about 50% of the initial abundance and a production of 2.2 pellets nauplius -1 h -1 . The nauplii's aver- age food consumption, at a rate equal to 17.7% of body weight d -1 , did not cover their metabolic expenses of 29.7% of body weight d -1 . Their feeding performance could have been to some extent limited by the size of the experimental vessels. Microscopic observations showed that the motion of late nauplii of E. pileatus was continuous (i.e. as previously observed) in vessels of 250 ml and larger. The main finding of this study is that the metabolic activity of minute metazooplankton organisms, while they are feeding, can now be determined with good precision over a period of hours without any invasion of the experimental vessels.

42 citations

References
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Book
01 Jan 1971
TL;DR: Probability Theory. Statistical Inference. Contingency Tables. Appendix Tables. Answers to Odd-Numbered Exercises and Answers to Answers to Answer Questions as discussed by the authors.
Abstract: Probability Theory. Statistical Inference. Some Tests Based on the Binomial Distribution. Contingency Tables. Some Methods Based on Ranks. Statistics of the Kolmogorov-Smirnov Type. References. Appendix Tables. Answers to Odd-Numbered Exercises. Index.

10,382 citations

Journal ArticleDOI
TL;DR: In this article, a method for direct measurement of percentage of assimilation of organic matter by zooplankton that does not require the quantitative recovery of feces and can be adapted for use in the field as well as in laboratory investigations is described.
Abstract: A method for direct measurement of percentage of assimilation of organic matter by zooplankton that does not require the quantitative recovery of feces and can be adapted for use in the field as well as in laboratory investigations is described. If it is assumed that only the organic fraction of the food ingested by a zooplankton animal is affected by the digestive process, it can be shown that percentage of utilization is defined as where F′ is the ash-free dry weight: dry weight ratio (fraction of organic matter) in the ingested food, and E’ is the same ratio in a representative sample of feces. The method compares favorably, as a measure of assimilation, with direct measurement of the quantity of organic matter lost from food during passage through the digestive tract.

828 citations


"Digestion of diatoms by planktonic ..." refers result in this paper

  • ...…efficiencies of E. hyalinus were unusually high when compared to earlier observations on the assimilation efficiency of planktonic copepods (Table 2); however, they were near the upper end of the ranges of the studies cited on Calanus hyperboreus (Conover 1966) and C. helgolandicus (Corner 1961)....

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Journal ArticleDOI
01 Apr 1988
TL;DR: The model indicates that generalist grazers, zooplankton that consume a broad size spectrum of prey (including pico-and nanoplankton), play a critical role in exporting particles, which could control the average, long-term exports from surface oceanic communities.
Abstract: The size distribution of pelagic producers and the size and trophic position of consumers determine the composition and magnitude of sinking fluxes from the surface communities in a simple model of oceanic food webs. Picoplankton, the dominant producers in the model, contribute little to the sinking material, due primarily to the large number of trophic steps between picoplankton and the consumers that produce the sinking particles. Net phytoplankton are important contributors to the sinking materials, despite accounting for a small fraction of the total primary production. These net phytoplankton, especially those capable of nitrogen fixation, also dominate the fraction of the new production that is exported on its first pass through the food chain. The sinking flux is strongly determined by the community structure of the consumers and varies by an order of magnitude for different food webs. The model indicates that generalist grazers, zooplankton that consume a broad size spectrum of prey (including pico-and nanoplankton), play a critical role in exporting particles. The role of generalists that occasionally form swarms, such as thaliaceans (salps and doliolids), can be particularly difficult to assess. Short-term studies probably miss the relatively infrequent population blooms of these grazers, events that could control the average, long-term exports from surface oceanic communities.

573 citations

Journal ArticleDOI
TL;DR: The results suggest that Daphnia was limited by the 20:5ω3 concentration during most of the summer, and the modest suitability of carbon and nitrogen as food parameters seems to be due to co-occurrence with 20: 5ω3.
Abstract: This study relates measured sestonic food parameters to growth rates of Daphnia galeata. Daphnia growth rates were obtained from standardized laboratory experiments feeding the animals natural lake seston. The experimental period spanned one season. Elemental (carbon, nitrogen, phosphate) and biochemical (fatty acids) food parameters of this natural food source were compared. The correlation between growth rates and sestonic phosphorus was very weak (r 2 = 0.08). The regressions with the nitrogen (r 2 = 0.42) and carbon (r 2 = 0.62) content were significantly better but still exhibited the usual considerable scatter around the regression line. In contrast, a very tight correlation (r 2 = 0,93) was found between Daphnia growth rates and the sestonic content of eicosapentaenoic acid (20:5ω3), an essential, highly unsaturated fatty acid. This relationship exhibited a normal asymptotic curve with a distinct plateau above concentrations of 0.8 μg 20:5ω3/L. In contrast, a plateau was not observed for particulate organic carbon, nitrogen or phosphate. Carbon, nitrogen and other essential fatty acids were not only moderatly correlated to Daphnia's growth rates but also to 20:5ω3. Thus, the modest suitability of carbon and nitrogen as food parameters seems to be due to co-occurrence with 20:5ω3. This shows, that the sestonic 20:5ω3 content is a parameter for natural food quantity including its food quality. High 20:5ω3 concentrations within the plateau region occurred mostly during spring. These results suggest that Daphnia was limited by the 20:5ω3 concentration during most of the summer

300 citations

Journal ArticleDOI
01 Jun 1995
TL;DR: The results temper recent assertions concerning the overwhelming importance of bacterial biomass in the oligotrophic Sargasso Sea but still support a major role for these microorganisms in the open ocean as repositories for carbon and nutrients.
Abstract: Seawater samples were collected from the euphotic zone of the Sargasso Sea near Bermuda in August of 1989 and March–April of 1990. Microbial population abundances, chlorophyll concentration, particulate carbon and particulate nitrogen were measured. Calculations were performed to establish the relative and absolute importance of the various microbial assemblages. The choice of conversion factors (g C and N cell −1 , or g C and N μm −3 ) for the microbial populations dramatically affected the estimation of “living” and “detrital” particulate material in the samples, and the relative importance of the various microbial groups. Averaged over all samples on either of the two cruises, microbial biomass constituted a greater proportion of the total particulate carbon and nitrogen during March–April (55% and 63%, respectively), than during August (≈24% and 30%, respectively) using “constrained” conversion factors that were derived. Accordingly, detrital material constituted the bulk of the particulate material during August, but was similar to the amount of microbial biomass during March–April. The bacterial assemblage constituted the largest single pool of microbial carbon (35%) and nitrogen (45%) in the water, and a significant fraction of the total particulate carbon (≈10–20%) and nitrogen (≈15–30%). Phototrophic nanoplankton (microalgae 2–20 μm in size) were second in overall biomass, and often dominated the microbial biomass in the deep chlorophyll maxima that were present during both cruises. The results temper recent assertions concerning the overwhelming importance of bacterial biomass in the oligotrophic Sargasso Sea but still support a major role for these microorganisms in the open ocean as repositories for carbon and nutrients.

262 citations


"Digestion of diatoms by planktonic ..." refers background in this paper

  • ...…in the nanoplankton range from the warm open ocean are mostly soft-walled with concentrations usually much lower than in neritic waters (e.g. Caron et al.1995), their digestion should be rather effective, resulting in the removal of most nitrogenous contents from food particles and high C:N…...

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