Chlamydomonas Reinhardii Research Articles

Biodegradation of phenolic compounds from grape pomace of Vitis vinifera Asyrtiko by Chlamydomonas reinhardtii

AbstractBACKGROUNDGrape pomace from Vitis vinifera Asssyrtiko is an important sub‐product of the Greek wine industry. However, its accumulation is a serious problem with a negative environmental impact. Grape pomace is rich in bioactive compounds and its utilization for alternative uses, such as a fertilizer, is an interesting area of research. On the other hand, its high concentration of phenolic compounds inhibits germination processes. Therefore, there is a need to decrease the high phenolic level in grape pomace before it can be used as a fertilizer. The main objective of our study is the fast reduction of polyphenols in grape pomace, and more specifically catechin and epicatechin in Vitis vinifera Assyrtiko. For this purpose, Chlamydomonas reinhardii was used for polyphenol biodegradation in grape pomace extract. It is shown that the bioremediation proceeds very fast, while the final product has a high potential to be used as a soil conditioner.RESULTSThe results of this study identify that after 6 days of cultivation, C. reinhardtii was able to reduce the total polyphenolic amount by 43%, while catechin and epicatechin were decreased by 100%. In addition, it is shown that the final aqueous product is rich in minerals, such as sodium, phosphorus and potassium.CONCLUSIONSThrough this work we were able to develop a method that allows for the efficient decrease of polyphenols in grape pomace. C. reinhardtii biodegrades a sufficient amount of polyphenols in grape pomace with a high rate, while the product obtained 6 days after cultivation contains high concentrations of minerals and low levels of polyphenols. These results suggest that there is a great potential in using the Vitis vinifera Asssyrtiko biodegraded product as a soil conditioner. © 2023 Society of Chemical Industry (SCI).

Differences in heat tolerance within a Daphnia magna population: the significance of body PUFA content

In this study, we use the model organism Daphnia magna to determine variation in heat tolerance within a natural population and relate this to variation in body fatty acid content and composition. As a proxy for heat tolerance we measured time to immobilization (Timm) for 25 clonal lineages isolated from a single lake. The clonal lineages were grown on Chlamydomonas reinhardii at 15°C. Upon deposition of the first clutch, Timm and body fatty acids were determined. We report significant differences of Timm and of the content of PUFAs and of eicosapentaenoic acid (EPA) among the D. magna clonal lineages. Timm was negatively related to total PUFA-content, indicating that increased body PUFA-content may be detrimental for membrane properties at high temperatures. Juvenile somatic growth varied significantly among clonal lineages, and was not related to total body PUFA-content, hence body PUFA-content was no proxy for PUFA-limitation. No correlative evidence for an impact of body EPA-content on Timm or juvenile growth was obtained. We hypothesize that the observed intra-population variability of body PUFA-content might be related to potentially different amplitudes in diel vertical migration in response to fish. These different amplitudes would mean differences in the extent of diurnal temperature fluctuations among the clonal lineages.

Bioaccumulation and subcellular partitioning of Cr(III) and Cr(VI) in the freshwater green alga Chlamydomonas reinhardtii

Chromium occurs in aquatic environments under two main redox forms, namely Cr(III) and Cr(VI), with different geochemical and biochemical properties. Cr(VI) readily crosses biological membranes of living organisms and once inside the cells it undergoes a rapid reduction to Cr(III). The route of entry for the latter form is, however, poorly known. Using the radioactive tracer 51Cr we compared the accumulation (absorption and adsorption) of the two Cr forms by the green unicellular alga Chlamydomonas reinhardii after 1h and 72h of exposure to 100nM of either Cr(III) or Cr(VI) at pH 7. Both Cr forms had similar accumulation, with a major part in the extracellular (adsorbed) fraction after 1h and a major part of total accumulated Cr in the intracellular (absorbed) fraction after 72h. We also investigated the intracellular partitioning of Cr using an operational fractionation scheme and found that both Cr forms had similar distributions among fractions: Cr was mostly associated with organelles (23±12% after 1h and 37±7% after 72h) and cytosolic heat-stable proteins and peptides (39±18% after 1h and 35±3% after 72h) fractions. Further investigations using a metallomic approach (SEC-ICP-MS) were performed with the heat-stable proteins and peptides fraction to compare the distribution of the two Cr forms among various biomolecules of this fraction. One Cr-binding biomolecule (∼28kDa) appeared after 1h of exposure for both Cr species. After 72h another biomolecule of lower molecular weight (∼0.7kDa) was involved in binding Cr and higher signal intensities were observed for Cr(VI) than for Cr(III). We show, for the first time, that both Cr(III) and Cr(VI) have similar fate within algal cells, supporting the tenet that a unique redox form occurs within cells.

Microalgae of OBIO-AKPOR Community in Southern Nigeria as Potential Source for Biodiesel Production

The highlighting of the immense potentials of indigenous microalgae as a sustainable and advantageous source of biofuel and a more efficient utiliser of carbon dioxide is the thrust of this study. Soil and water samples were collected within Obio–Akpor community in Rivers State, Nigeria and taken to the Plant Science and Biotechnology Laboratory in University of Port Harcourt for identification. Prominent microalgae found were characterised and studied for their ability to accumulate lipids for biofuel production. Microalgae isolated include Chlamydomonas reinhardii, Scenedesmus obliquus, Chlorella vulgaris, Euglena gracilis and Prymnesium parvum. The results showed that biomass as dry matter and lipid content were 2.9, 3.32, 3.2, 1.81, 1.71 mg ml−1 and 8.53, 17.35, 12.39, 4.51, 5.92% w/w for Chlamydomonas reinhardii, Scenedesmus obliquus, Chlorella vulgaris, Euglena gracilis and Prymnesium parvum respectively. Among all, Chlorella vulgaris seems to be the best candidate for high lipid productivity (2.8 mg ml−1). The study revealed that Chlamydomonas reinhardii and Scenedesmus obliquus also have high lipid productivity levels of 2.64 and 2.74 mg ml−1, respectively. Based on their high lipid contents, Chlorella vulgaris, Chlamydomonas reinhardii and Scenedesmus obliquus are considered suitable for use in biodiesel production.

Identification of a soybean chloroplast DNA replication origin-binding protein

Replication of chloroplast DNA (ctDNA) in several plants and in Chlamydomonas reinhardii has been shown to occur by a double displacement loop (D-loop) mechanism and potentially also by a rolling circle mechanism. D-loop replication origins have been mapped in several species. Minimal replication origin sequences used as probes identified two potential binding proteins by southwestern blot analysis. A 28 kDa (apparent molecular weight by SDS-PAGE analysis) soybean protein has been isolated by origin sequence-specific DNA affinity chromatography from total chloroplast proteins. Mass spectrometry analysis identified this protein as the product of the soybean C6SY33 gene (accession number ACU14156), which is annotated as encoding a putative uncharacterized protein with a molecular weight of 25,897 Da, very near the observed molecular weight of the purified protein based on gel electrophoresis. Western blot analysis using an antibody against a homologous Arabidopsis protein indicates that this soybean protein is localized specifically in chloroplasts. The soybean protein shares some homology within a single-stranded DNA binding (SSB) domain of E. coli SSB and an Arabidopsis thaliana mitochondrial-localized SSB of about 21 kDa (mtSSB). However, the soybean protein induces a specific electrophoretic mobility shift only when incubated with a double-stranded fragment containing the previously mapped ctDNA replication oriA region. This protein has no electrophoretic mobility shift activity when incubated with single-stranded DNA. In contrast, the Arabidopsis mtSSB causes a mobility shift only with single-stranded DNA but not with the oriA fragment or with control dsDNA of unrelated sequence. These results suggest that the 26 kDa soybean protein is a specific origin binding protein that may be involved in initiation of ctDNA replication.

Role of acetate and light attenuation in hydrogen production by chlamydomonas reinhardii

Role of acetate and light attenuation in hydrogen production by chlamydomonas reinhardii

Tocopherol quinone content of green algae and higher plants revised by a new high-sensitive fluorescence detection method using HPLC – Effects of high light stress and senescence

A rapid, sensitive fluorescence method was applied here for detection of oxidized tocopherol quinones in total plant tissue extracts using HPLC, employing a post-column reduction of these compounds by a Zn column. Using this method, we were able to detect both alpha- and gamma-tocopherol quinones in Chlamydomonas reinhardii with a very high degree of sensitivity. The levels of both compounds increased under high light stress in the presence of pyrazolate in parallel to a decrease in the content of the corresponding tocopherols. The formation of tocopherol quinones from tocopherols was apparently due to their oxidation by singlet oxygen, which is formed in photosystem II under high light stress. alpha-Tocopherol quinone was also detected in a variety of higher plants of different age, and its level was found to increase during senescence in leaves grown under natural conditions. In contrast to alpha-tocopherol quinone, gamma-tocopherol quinone was not found in the higher plant species investigated with the exception of young runner bean leaves, where the levels of both compounds increased dramatically during cold and light stress. Taking advantage of native fluorescence of the reduced alpha-tocopherol quinone (alpha-tocopherol quinol), it can be detected in plant tissue extracts with a high sensitivity. In young runner bean leaves, alpha-tocopherol quinol was found at a level similar to alpha-tocopherol.

Performance Evaluation of a Waste Stabilization Pond in a Rural Area in Egypt

The performance evaluation of the waste stabilization pond (WSP) as a model of domestic wastewater treatment unit in rural area was carried out. The unit comprised of anaerobic, facultative and maturation ponds in two series. The effluents of WSP which are discharged in the drain had the BOD reduced to 109-245 mg L -1 (Mean = 145.3 mg L -1 , 50.65% removal), while the COD was reduced to 221-400 mg L -1 (Mean = 289 mg L -1 , 48.95% removal) and the total suspended solids (TSS) were reduced to 118-190 mg L -1 (Mean = 157.8 mg L -1 , 44.3% removal). The reduction percentages of total coliform (TC), faecal coliform (FC), E.coli, faecal streptococci (FS), salmonellae and Listeria were 98.8, 95.6, 79.4, 96.8, 97.9 and 89.5% respectively. Also, the removal percentages of coliphage and infectious rotaviruses were 49.03 and 99.66% respectively. Identical sequences of rotaviruses VP-6 detected in the final effluent of the pond and the drain were observed. Euglena variables and Chlamydomonas reinhardii were predominant in anaerobic, facultative and maturation effluents. It has been noticed that pollution affected species diversity of zooplankton; the number of species in facultative pond was 8 species because of high pollution level, whereas in maturation pond increased to 21 species. Also, pollution in anaerobic pond increased density of ciliates (Protozoa) which are known to be bio-indicators of organic pollution. The percent removal of ciliates in the maturation pond was 70%. It is recommended to make some modifications in the design to increase the efficiency of WSP.

ProMEX: a mass spectral reference database for proteins and protein phosphorylation sites.

BackgroundIn the last decade, techniques were established for the large scale genome-wide analysis of proteins, RNA, and metabolites, and database solutions have been developed to manage the generated data sets. The Golm Metabolome Database for metabolite data (GMD) represents one such effort to make these data broadly available and to interconnect the different molecular levels of a biological system [1]. As data interpretation in the light of already existing data becomes increasingly important, these initiatives are an essential part of current and future systems biology.ResultsA mass spectral library consisting of experimentally derived tryptic peptide product ion spectra was generated based on liquid chromatography coupled to ion trap mass spectrometry (LC-IT-MS). Protein samples derived from Arabidopsis thaliana, Chlamydomonas reinhardii, Medicago truncatula, and Sinorhizobium meliloti were analysed. With currently 4,557 manually validated spectra associated with 4,226 unique peptides from 1,367 proteins, the database serves as a continuously growing reference data set and can be used for protein identification and quantification in uncharacterized biological samples. For peptide identification, several algorithms were implemented based on a recently published study for peptide mass fingerprinting [2] and tested for false positive and negative rates. An algorithm which considers intensity distribution for match correlation scores was found to yield best results. For proof of concept, an LC-IT-MS analysis of a tryptic leaf protein digest was converted to mzData format and searched against the mass spectral library. The utility of the mass spectral library was also tested for the identification of phosphorylated tryptic peptides. We included in vivo phosphorylation sites of Arabidopsis thaliana proteins and the identification performance was found to be improved compared to genome-based search algorithms. Protein identification by ProMEX is linked to other levels of biological organization such as metabolite, pathway, and transcript data. The database is further connected to annotation and classification services via BioMoby.ConclusionThe ProMEX protein/peptide database represents a mass spectral reference library with the capability of matching unknown samples for protein identification. The database allows text searches based on metadata such as experimental information of the samples, mass spectrometric instrument parameters or unique protein identifier like AGI codes. ProMEX integrates proteomics data with other levels of molecular organization including metabolite, pathway, and transcript information and may thus become a useful resource for plant systems biology studies. The ProMEX mass spectral library is available at .

Effects of free amino acids on the photosynthetic carbon metabolism of symbiotic dinoflagellates

Synthetic host factor (SHF) was used in parallel with crude cnidarian’s host factor (CHF) to investigate their effects on both photosynthetic carbon metabolism and the first step of lipid synthesis in the symbiotic dinoflagellates Symbiodium purchrorum of the sea anemone Aiptasia pulchella. Several species have been studied, namely, sea anemone A. pulchella, reef coral Pocillopora damicornis, and green alga Chlamydomonas reinhardii. Both short-term and long-term experiments with radioactive carbon have shown a higher rate of the alga 14C photoaccumulation with host factor(s) than of dinoflagellates located in artificial sea water (ASW) alone. In dinoflagellates incubated with both ASW and CHF, 14C-labeled glycerol was detectable after 15 s of alga illumination. In dinoflagellates isolated from P. damicornis and incubated in CHF and SHF and in dinoflagellates isolated from A. pulchella and incubated in CHF, a higher percentage of 14C was found in the glycerol as compared to the ASW trial. At the same time, in ASW trial the radioactive label was primarily located in ethanol-soluble lipid fraction. Similar results were observed when dinoflagellates isolated from P. damicornis were incubated with aspartate or glutamate. But there was no effect with taurine, serine, valine, glycine, or lysine. C. reinhardii, incubated in salt-free CHF, partitioned a greater percent of 14C into the glycerol and less into the ethanol-soluble lipids as compared to the corresponding control incubations. The amount of 14C in neutral and polar lipids was identical in that in A. pulchella dinoflagellates incubated in ASW or CHF. The arrays of neutral 14C-lipids produced under both ASW alone and ASW with CHF conditions, and over time were not significantly distinguishable. Host factors appeared to provide an optimum environment to sustain maximum metabolic efficiency. A biochemical model, based on the quantitative and qualitative assessment of carbon pathways in dinoflagellates incubated both in host factor and sea water alone, is presented.

Mycosporines from freshwater yeasts: a trophic cul-de-sac?

Mycosporine-like amino-acids (MAAs) are found in aquatic bacteria, algae, and animals. A related compound, the mycosporine-glutaminol-glucoside (myc-glu-glu), has recently been reported in freshwater yeasts. Although animals depend on other organisms as their source of MAAs, they can efficiently accumulate them in their tissues. In this work we assessed the potential transfer of the yeast mycosporine myc-glu-glu from the diet into the copepod Boeckella antiqua and the ciliate Paramecium bursaria. For this purpose, we performed experiments to study the feeding of B. antiqua and P. bursaria on the yeast Rhodotorula minuta and their ability to bioaccumulate myc-glu-glu. Bioaccumulation of myc-glu-glu in B. antiqua was assessed through long-term factorial experiments manipulating the diet (Chlamydomonas reinhardii and C. reinhardii + yeasts) and radiation exposure (PAR and PAR + UVR). Shorter term experiments were designed in the case of P. bursaria. The composition and concentration of MAAs in the diet and in the consumers were determined by HPLC analyses. Our results showed that even though both consumers ingested yeast cells, they were unable to accumulate myc-glu-glu. Moreover, when exposed to conditions that stimulated the accumulation of photoprotective compounds (i.e. UVR exposure), an increase in MAAs concentration occurred in copepods fed C. reinhardii plus yeasts as well as in those fed only C. reinhardii. This suggests that the copepods were able to modify their tissue concentrations of MAAs in response to environmental clues but also that the contribution of yeast mycosporines to total MAAs concentration was negligible.

Is non photochemical quenching protective

Plants exposed to high photon fluence are susceptible to photooxidative damage (photoinhibition). As photoinhibition is linear with the number of absorbed photons (reciprocity rule) it is generally thought that the antenna-based, non-photochemical quenching (qNP) represents an important protective strategy by lowering the excited singlet state levels in PSII antenna. We have investigated the relation between the lowering of the singlet excited state levels (quenching) and photoinhibition in thylakoids isolated from a variety of species (spinach, barley, Arabidopsis) and intact cells of the unicellular alga Chlamydomonas reinhardii. The results show that antenna quenching affords only a minimal protection against photoinhibition which is, at the most no more than 35% of that expected based on the reciprocity rule. Moreover the light-induced degradation of the reaction centre protein D1, generally considered to constitute an initial phase of the photoinhibition repair mechanism, is demonstrated to be insensitive to the excited state level in PSII antenna. The low level of protection afforded by antenna quenching is probably due to both photoinhibition and D1 degradation being caused by uncoupled or weakly coupled chlorophylls, an interpretation supported by the action spectra.

Energy Supply for ATP-Synthase Deficient Chloroplasts of Chlamydomonas reinhardii

The mutant F54 of the unicellular green alga Chlamydomonas reinhardii is not able to perform photophosphorylation. Nevertheless, it grows on acetate and the chloroplasts accomplish most of their energy-requiring synthetic processes. However, no light-dependent chloroplast protein synthesis could be detected in intact F54 chloroplasts isolated from a cell wall-deficient double mutant F54-cw-15. Exogenous ATP was not able to induce this in organello protein synthesis to an appreciable degree. In contrast, the strictly ATP-dependent protein synthesis was stimulated very efficiently by glyceraldehyde-3-phosphate, dihydroxyacetone phosphate and glycerol-3-phosphate, but strongly inhibited by 3-phosphoglycerate. These compounds can be transported across the envelope membrane by the triose phosphate translocator. Pyridoxal phosphate, a specific inhibitor of the translocator, abolished the stimulation by triose phosphates. Spermidine, which activates initiation of translation in chloroplasts, enhanced triose phosphate-stimulated protein synthesis even further. In the dark, no stimulation was observed, indicating that a light-dependent reaction was also involved in this kind of ATP production in chloroplasts. The results suggest that chloroplasts defective in photophosphorylation recruit their energy via an ATP shuttle which was shown in this study to import rather than export ATP across the chloroplast envelope.

Coprophagy: a supplementary food source for two freshwater gastropods?

1. The freshwater pulmonate snail Radix peregra voluntarily and regularly fed on its faeces, whereas Bithynia tentaculata (Prosobranchia) did not.2. With high‐quality faeces as food (faeces with C : N‐values below ten) Radix could grow and survived for 11 weeks. Growth was 24–30% of that achieved with control food (lettuce, Chlamydomonas and Tetramin), and body mass was close to the expected value.3. As with real food, the percentage organic content of faeces was reduced during gut passage, with the exception of very low‐quality faeces.4. Faeces contained living cells of green algae (Chlamydomonas reinhardii) and diatoms (Achnanthes lanceolata, Eunotia pectinalis), which survived the gut passage of R. peregra and B. tentaculata. Faecal material was also rich in bacteria, with up to 150 × 106 cells mg–1 dry mass. Bacteria increased in abundance in faeces which had been evacuated for 7 days or more.5. A further degradation of partly digested food in the faeces was indicated by the activity of the extracellular digestive enzymes cellobiase and chitobiase. These enzymes hydrolysed material with an activity of 0.2–14.5 pkat mg–1 faecal dry mass in 1–12‐day‐old faeces. In faeces of Bithynia fed control food or incubated sycamore leaves, chitobiase activity was correlated with bacterial abundance.6. Coprophagy is considered to be a suitable strategy for further degradation and utilization of refractory material for which one gut passage is too short and/or too inefficient.

The impact of Chironomus plumosus larvae on organic matter decay and nutrient (N, P) exchange in a shallow eutrophic lake sediment following a phytoplankton sedimentation

The importance of Chironomus plumosuslarvae on benthic metabolism and nutrient exchange across the sediment‐ water interface was evaluated in a shallow eutrophic lake (Lake Arreskov, Denmark) following a phytoplankton sedimentation. Chironomus plumosuslarvae were added to laboratory sediment microcosms, corresponding to a density of 2825 larvae m 2 . Non-inhabited microcosms served as controls. A sedimentation pulse of organic matter was simulated by adding fresh algal material (Chlamydomonas reinhardii ) to sediment cores (36 g dry weight m 2 ). The mineralization was followed by measuring fluxes of O 2 ,C O 2, dissolved inorganic nitrogen and phosphate. A rapid clearance of algae from the water column in faunated microcosms suggested that chironomids may be of major importance in controlling phytoplankton concentrations in shallow eutrophic lakes. Chironomids increased the sediment O2 uptake 3 times more than what would be expected from their own respiration, indicating a stimulation of microbial activity and decomposition of organic matter in the sediment. Addition of algae enhanced the release of CO2 ,N H 4 and o-P. The excess inorganic C, N and P released in amended non-inhabited sediment after 36 days corresponded to 65, 31 and 58% of the C, N and P in the added algae. In sediment inhabited by Chironomus plumosusthe corresponding numbers were 147, 45 and 73%, indicating that mineralization of organic matter also from the indigenous sediment pool was stimulated by chironomids.

Laser speckle spectroscopy—a new method for using small swimming organisms as biomonitors

A novel method has been devised for the study of swimming organisms by using speckle patterns produced by their scattering of coherent laser light. The speckle patterns show fluctuations in space and time which may be correlated with the activity of the organisms. The fluctuations give an immediate indication of mobility and a more detailed analysis of the frequency spectrum of the speckle fluctuations shows characteristic resonance-like features which are specific to the organism. The speckle patterns produced by several protozoans, including Paramecium bursaria, Entosiphon sulcatum, and by the alga Chlamydomonas reinhardii and the rotifer Brachionus calyciflorus have been studied. Laser speckle spectroscopy (LSS) allows a rapid non-invasive monitoring of the activity of the organisms and could find application in ecotoxicity studies and environmental biomonitoring. The results presented here are the first reports of LSS and its use in this way and demonstrate its viability and potential for further development.

Involvement of NAD(P)+-glutamate dehydrogenase isoenzymes in carbon and nitrogen metabolism in Chlamydomonas reinhardii

Involvement of NAD(P)+-glutamate dehydrogenase isoenzymes in carbon and nitrogen metabolism in Chlamydomonas reinhardii

Food selection by calanoid copepods in response to between‐lake variation in food abundance

SUMMARY1. Food selection experiments were conducted by acclimating calanoid copepods (Eudiaptomus spp.) in suspensions of natural seston and then adding pairs of dual‐labelled (14C/32P) algae. Each feeding trial measured selectivity between a small, high‐quality reference alga, Chlamydomonas reinhardii, and a test alga that differed in size and/or food quality. The influence of food concentration on food selection was tested by using seston from two lakes with contrasting food abundance and by including treatments with filtered lake water ('starved’) and seston diluted with filtered water or enriched with cultured algae.2. Copepods that had been starved or acclimated to natural seston with low food abundance preferred the larger of two labelled algae, regardless of the nutritional quality of the algae. In agreement with the predictions of an optimal diet model, however, copepods that were acclimated to high food conditions discriminated against low‐quality foods, including digestion‐resistant algae and dead algae.3. Selectivity coefficients showed excellent agreement with a previous study involving the same taxa of copepods and labelled algae but in which the copepods had been acclimated to pairs of cultured algae rather than natural seston. Thus, these comparisons emphasize the importance of food availability in modulating copepod selectivity for foods that differ in nutritional quality and suggest that such behaviour occurs in nature.

Optimal foraging by a suspension-feeding copepod: responses to short-term and seasonal variation in food resources

Laboratory radioisotope experiments were used to investigate the effects of phytoplankton seasonal succession on the selectivity and clearance rates of a suspension-feeding copepod in two Indiana lakes. Responses to particle size and quality were tested by allowing adult female Diaptomus birgei feeding in natural seston to select between a small (6×7 μm) flagellate (Chlamydomonas reinhardii) and a large, poor quality food (heat-killed Carteria olivieri, 22×25 μm). Short-term responses were tested in one lake by additional treatments in which copepods were acclimated for 5-6 h in filtered lake water ("starved") or natural seston with added Chlamydomonas ("enriched"). Copepods from both lakes fed selectively on the small live flagellate during the spring bloom of edible phytoplankton but fed selectively on the larger, poor quality particle during the "clear water phase" when food was scarce. These results are interpreted as an interaction between the concentration-dependent selectivity for high quality foods predicted by optimal diet theory and a perceptual bias for large-sized particles. Selectivity for high-quality food was intermediate and clearance rates were depressed when total phytoplankton abundance was high but dominated by filamentous cyanobacteria. In each experiment copepods also responded to the short-term manipulations by exhibiting weaker discrimination against the poor quality particle in the starvation treatment and stronger discrimination in the enriched treatment. A two-way mixed model ANOVA revealed substantial short term (37%) and seasonal (53%) components to the total variance in selectivity. Clearance rates were also influenced by both phytoplankton succession and the short-term resource manipulations. As expected, clearance rates on the poor quality food were more sensitive to the abundance of alternative foods. These results show how the feeding behavior of a freshwater copepod is modulated by both seasonal and short-term variation in natural food.

Nutritional suitability of some uni‐algal diets for freshwater calanoids: unexpected inadequacies of commonly used edible greens and others

SUMMARY Naupliar and copepodid development times (Dn and Dc, respectively) of two African freshwater calanoids (Metadiaptomus meridianus and Tropodiaptomus spectabilis) were measured on mono‐specific diets of comparably sized Chlamydomonas reinhardii, Scenedesmus acutus, Cryptomonas sp., Rhodomonas minuta, Cyclotella meneghiniana, and Selenastrum capricornutum, to test the nutritional adequacy of these algae. Comparisons were made at a standard temperature (17°C) and food supply level (1 mgCl−1). All diets other than Scenedesmus and Selenastrum supported complete naupliar development at broadly comparable times within and between calanoids, apart from greatly protracted Dn values for M. meridianus on Cyclotella. Dc durations were more variable between diet types, and both Chlamydomonas and Cyclotella were inferior or inadequate for copepodid development. Both naupliar and copepodid stages ingested radiolabelled Scenedesmus and Selenastrum readily. Comparative incorporation rate measures of Selenastrum and Cryptomonas respectively exceeded estimated metabolic maintenance needs of stage 3/4 nauplii of T. spectabilis by some 56% and 790%. Scope for growth (‘surplus’ energy) was accordingly fourteen‐fold greater on Cryptomonas than on Selenastrum /Scenedesmus. The dietary inadequacy of these two green algae is thus attributed largely to low digestibility, and perhaps some biochemical deficiency.