Changes of algal biomass as carbon, cell number and volume, in bottles suspended in Lake Constance

Changes of algal biomass, as carbon, cell numbers and volumewere determined for phytoplankton of Lake Constance suspendedin situ in 2 l glass bottles. Phytoplankton placed at the 6%surface penetrating light level (photosynthetically availableradiation) were close to the compensation depth for growth estimatedas total particulate carbon and total cell volumes. Cell countsof individual alga] species however, showed appreciable growthof diatoms offset by the decline of flagellates. Bottles suspendedat two shallower depths in a separate experiment showed somegrowth of all species and indicated a vertical niche separationof growth of Rhodomonas minuta Skuja and R. lens Dascher andRuttner in accordance with their vertical distribution. ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP) First International Workshop heldat the Limnological Institute, University of Konstanz, in April1982.     

Culturing freshwater, planktonic rotifers on Rhodomonas minuta var. nannoplanctica Skuja and Stichococcus bacillaris Nageli

Eleven freshwater, planktonic rotifer species (Brachionus angularis,Brachionus cafyciflorus, Keratella quadrata, Nolholca squamula,Ascomorpha ecattdis, Synchaeta kitina, Synchaela tremula, Potyarthradolichoptera, Polyanhra vulgarii, Pompholyx sulcata, Filiniabrachiata) were cultured successfully on either Rhodomonas minutavar. nannoplanctica Skuja or Stichococcus bacillaris Nägeli,in a totally synthetic medium. Three of these species had notpreviously been kept in laboratory culture. The method is proposedas a simple technique for the routine batch culture of a varietyof planktonic rotifer species. Some important observations onhandling techniques, incubation temperature, culture vesselsand media are discussed.     

Some aspects on the morphology and ecology of Rhodomonas minuta var. nannoplanctica and R. lens (Cryptophyceae) in two Greek lakes

Significant morphological and ecological differences between Rhodomonas minuta var. nannoplanctica and R. lens were observed during the study of phytoplankton in two Greek lakes. The shape and size characteristics support the validity of these species, so the fusion of closely related species of Rhodomonas proposed by Javornicky is not accepted in this study. Apart from the morphological differences between Rhodomonas minuta var. nannoplanctica and R. lens contrasting ecological requirements were noticed. A broader distribution of Rhodomonas minuta var. nannoplanctica in relation to temperature and pH and a preference for lower nutrient concentrations than R. lens were found. The two taxa may coexist by shifting their niches at different times in Lake Volvi and by vertical niche separation in Lake Vegoritis.     

Elemental composition (C:N:P) and growth rates of bacteria and Rhodomonas grazed by Daphnia

The elemental composition and growth rate of Rhodomonas andheterotrophic bacteria were studied in batch cultures in thepresence and absence of Daphnia and at two different levelsof phosphorus limitation. The elemental content of single cellswas measured with X-ray microanalysis. Simultaneously, dilutionexperiments were performed in order to estimate grazing losses,growth rates and dominant nutrient sources for bacteria andRhodomonas. The phosphorus:carbon (P:C) ratios of the bacteriawere generally higher in the experiment with the stronger Plimitation of the system. High P:C ratios were taken as an indicationthat bacteria were carbon limited. The presence of Daphnia resultedin a further increase in bacterial P:C ratios and increasedspecific growth rates. Thus, grazing increased the availabilityboth of inorganic nutrients and organic substrates, stimulatingthe growth of the bacteria. P:C ratios of Rhodomonas decreasedwith increasing P limitation of the system. Only at strong Plimitation did the presence of Daphnia result in increased P:Cratios of Rhodomonas compared with the control without daphnids.This study shows that the elemental content and growth rateof heterotrophic bacteria and Rhodomonas are influenced by grazingand nutrient regeneration by daphnids. The response is dynamicand depends on the level of nutrient limitation of the system. Present address: Department of Microbiology, University of BergenJahnebakken 5, NO-5020 Bergen, Norway     

Fitness consequences for copepods feeding on a red tide dinoflagellate: deciphering the effects of nutritional value, toxicity, and feeding behavior

Phytoplankton exhibit a diversity of morphologies, nutritional values, and potential chemical defenses that could affect the feeding and fitness of zooplankton consumers. However, how phytoplankton traits shape plant–herbivore interactions in the marine plankton is not as well understood as for terrestrial or marine macrophytes and their grazers. The occurrence of blooms of marine dinoflagellates such as Karenia brevis suggests that, for uncertain reasons, grazers are unable to capitalize on, or control, this phytoplankton growth—making these systems appealing for testing mechanisms of grazing deterrence. Using the sympatric copepod Acartia tonsa, we conducted a mixed diet feeding experiment to test whether K. brevis is beneficial, toxic, nutritionally inadequate, or behaviorally rejected as food relative to the palatable and nutritionally adequate phytoplankter Rhodomonas lens. On diets rich in K. brevis, copepods experienced decreased survivorship and decreased egg production per female, but the percentage of eggs that hatched was unaffected. Although copepods showed a 6–17% preference for R. lens over K. brevis on some mixed diets, overall high ingestion rates eliminated the possibility that reduced copepod fitness was caused by copepods avoiding K. brevis, leaving nutritional inadequacy and toxicity as remaining hypotheses. Because egg production was dependent on the amount of R. lens consumed regardless of the amount of K. brevis eaten, there was no evidence that fitness costs were caused by K. brevis toxicity. Copepods limited to K. brevis ate 480% as much as those fed only R. lens, suggesting that copepods attempted to compensate for low food quality with increased quantity ingested. Our results indicate that K. brevis is a poor food for A. tonsa, probably due to nutritional inadequacy rather than toxicity, which could affect bloom dynamics in the Gulf of Mexico where these species co-occur.     

Isolation and characterization of CAC antenna proteins and photosystem I supercomplex from the cryptophytic alga Rhodomonas salina

In the present paper, we report an improved method combining sucrose density gradient with ion‐exchange chromatography for the isolation of pure chlorophyll a/c antenna proteins from the model cryptophytic alga Rhodomonas salina. Antennas were used for in vitro quenching experiments in the absence of xanthophylls, showing that protein aggregation is a plausible mechanism behind non‐photochemical quenching in R. salina. From sucrose gradient, it was also possible to purify a functional photosystem I supercomplex, which was in turn characterized by steady‐state and time‐resolved fluorescence spectroscopy. R. salina photosystem I showed a remarkably fast photochemical trapping rate, similar to what recently reported for other red clade algae such as Chromera velia and Phaeodactylum tricornutum. The method reported therefore may also be suitable for other still partially unexplored algae, such as cryptophytes.     

Characterization of cryptomonad phycoerythrin and phycocyanin

Phycoerythrin, a chromoprotein, from the cryptomonad alga Rhodomonas lens is composed of two pairs of nonidentical polypeptides (α₂β₂). This structure is indicated by a molecular weight of 54,300, calculated from osmotic pressure measurements and by sodium dodecyl sulfate (SDS) gel electrophoresis, which showed bands with molecular weights of 9800 and 17,700 in a 1:1 molar ratio. The s_20,w⁰ of 4.3S is consistent with a protein of this molecular weight. Similar results were obtained with another cryptomonad phycoerythrin and a cryptomonad phycocyanin. Electrophoresis after partial cross-linking by dimethyl suberimidate revealed seven bands for the cryptomonad phycocyanin and six bands for cryptomonad phycoerythrin and confirmed the proposed structure. Spectroscopic studies on α and β subunits of cryptomonad phycocyanin and phycoerythrin were carried out on the separated bands in SDS gels. The individual polypeptides possessed a single absorption band with the following maxima: phycoerythrin (R. lens), α at 565 nm, β at 531 nm; phycocyanin (Chroomonas sp.), α at 644 nm, β at 566 nm. Fluorescence polarization was not constant across the visible absorption band regions of phycoerythrin (R. lens and C. ovata) with higher polarizations located at higher wavelengths, as had also been previously shown for cryptomonad phycocyanin (Chroomonas sp.). Combining the absorption spectra and the polarization results indicates that in each case the β subunit contains sensitizing chromophores and the α subunit fluorescing chromophores. The CD spectra of cryptomonad phycocyanin and both phycoerythrins were similar and were related to the spectra of the individual subunits. In Ouchterlony double-diffusion experiments the cryptomonad phycoerythrins and phycocyanins cross-reacted, with spurring, with phycoerythrin isolated from a red alga. The cryptomonad phycoerythrins were immunochemically very similar to each other and to cryptomonad phycocyanin, with little spurring detected.     

Nutritional value of the cryptophyte Rhodomonas lens for Artemia sp.

Juvenile or adult Artemia sp. are often used as live prey for the rearing of early life stages of some crustacean, fish and cephalopod species. The improvements of both Artemia growth and its biochemical composition are key issues for the suitable use of Artemia biomass in these rearing processes. In this study we evaluated the growth and survival rates of Artemia fed with the cryptophyte Rhodomonas lens in comparison with different microalgal species commonly used in aquaculture: the prasinophyte Tetraselmis suecica, the prymnesiophyte Isochrysis galbana Parke, and the eustigmatophyte Nannochloropsis gaditana. Microalgae were cultured semi-continuously in nutrient saturated conditions and with a daily renewal rate of 30% of the volume of cultures, to obtain biomass of controlled and optimized composition. Considerable differences in Artemia growth were observed, as well as in the survival rate. At day 8 of rearing, Artemia fed R. lens had the highest length (4.9 ±0.6 mm, P < 0.001), followed by individuals fed T. suecica (4.2 ± 0.7 mm), I. galbana (3.6 ± 0.7 mm) and finally those fed N. gaditana (1.5 ± 0.2 mm). The survival rate of Artemia fed N. gaditana (18 ± 3%) was much lower (P < 0.001) than values found for the remaining groups (69 to 88%). The growth rate of Artemia obtained with R. lens was in general much higher than with other microalgal diets previously reported in the literature. The higher protein content of R. lens could explain the higher growth obtained with this species, but differences of Artemia growth with the different diets could not be explained solely on the basis of the gross composition of microalgae. Factors such as cell size and digestibility all seem to contribute to the results observed. Another trial was carried out to investigate differences in Artemia growth and on its biochemical composition when fed the best two diets: R. lens or T. suecica. The fatty acid (FA) and total amino acid (AA) composition of both microalgal species and the composition of Artemia were assessed as well. As found in the first experiment individuals fed R. lens (group ARHO) grew faster than those fed T. suecica (group ATET), attaining 3.6 ± 0.3 mm and 3.2 ± 0.4 mm (P < 0.001), respectively, after 5 days of rearing. The much higher AA content obtained in R. lens may be on the basis of the higher growth obtained with this species. Protein and carbohydrate levels in Artemia juveniles were very similar in both groups (64-68% of dry weight, and 8-10%, respectively). Lipid was slightly lower in ARHO (12%) than in ATET (15%, P < 0.01). Regarding the FA composition, juveniles from group ARHO contained higher levels of eicosapentaenoic acid (EPA, 6.2%) than juveniles from ATET (4.1%, P < 0.01), whereas docosahexaenoic acid (DHA) was only found in juveniles from ARHO (1.1%). Taking into account that the daily productivity of R. lens culture was higher than, or at least equal, the remaining microalgal species this cryptophyte is confirmed as an excellent diet to optimize the growth of Artemia, as well as to improve its biochemical composition.     

Mechanical and anatomical adaptations in terrestrial and aquatic buttercups to their respective environments

The mechanical adaptations of the stems of four species of Ranunculusto their respective environments were studied by combining tensile,bending and flow-tunnel tests, with anatomical observation. Stems of the two terrestrial species, R. acris and R. repens,had high values for rigidity, EI, because they were stiffenedby large quantities of peripherally placed lignified material.This trend is less evident in R. repens, which had a lower rigidity,though it with stood a higher breaking strain than R. acris.This may adapt R. repens to its creeping habit and help it withstandtrampling. The aquatic R. peltatus and R. fluitans, which live in stilland fast-flowing water, respectively, are both more flexibleand have higher breaking strains, of 0.1–0.15, than terrestrialplants, which may allow them to withstand sudden tugs due toflow. R. peltatus maintains the central lumen, places structuralelements away from the centre, and has a higher rigidity thanR. fluitans, which may allow it to avoid self-shading, and supportitself when the water level falls. The stem of R. fluitans shows adaptations for withstanding dragfrom fast-flowing water. The stem has a low rigidity which allowsit to minimize inertial drag forces by aligning itself parallelto the direction of the local flow. However, the rigidity (andthe second moment of area, I) does not appear to be minimized.This may allow the plant to avoid drag due to flag-like fluttering.A weak region of the stem near the base may act as a ‘mechanicalfuse’ which protects the root system by allowing seasonalgrowth to be lost. Key words: Ranunculus, mechanics, flow, anatomy     

Effect of pH on Rhodomonas salina growth,biochemical composition,and taste,produced in semi-large scale under sunlight conditions

Journal of Applied Phycology - Rhodomonas salina is a microalgal species, belonging to the cryptophytes, and is widely used as aquaculture feed because of its high nutritional profile and...     

Dissolved organic carbon released by zooplankton grazing activity-a high-quality substrate pool for bacteria

Experiments were designed to investigate whether processes relatedto zooplankton feeding have a positive effect on bacterial growth.Bacterial abundance and [³H]thymidine incorporation rates werefollowed in grazer-free batch cultures originally containingeither Scenedesmus quadricauda or Rhodomonas lacustris as foodsources, and Daphnia cucullata or Eudiaptomus graciloides asgrazers. Compared with controls lacking either animals or algae,a significantly higher bacterial abundance and productivityoccurred in cultures which contained both phyto- and zoo-plankton.The same experimental methodology was tested during the declineof a diatom spring bloom in a eutrophic, temperate lake. A significantincrease in bacterial biomass was observed due to the grazingactivity of in situ mesozooplankters during the clear-waterphase. Our results demonstrated that the dissolved carbon pathwayfrom mesozooplankton to bacteria averaged 57% (26–78%)of the algal carbon filtered from suspension.     

Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.     

Vertical distributions, diel and ontogenetic vertical migrations and net avoidance of leptocephali of Anguilla and other common species in the Sargasso Sea

Day- and night-time vertical distributions and their ontogeneticchanges in Anguilla leptocephali and other common species ofleptocephali were determined and compared during five cruisesin the Sargasso Sea using an opening - closing 2-m ring netto sample discrete depth strata between 0 m and 350 m deep.No difference in vertical distribution was ever found betweenAnguilla rostrata (American eel) and A. anguilla (European eel).Anguilla leptocephali <5 mm long did not exhibit a diel verticalmigration, as they were distributed between 50 m and 300 m bothby day and by night. The vertical distribution of these smalllepto-cephali is probably roughly representative of the depthdistribution of adult spawning. Anguilla     

Non-photochemical quenching in cryptophyte alga Rhodomonas salina is located in chlorophyll a/c antennae

Photosynthesis uses light as a source of energy but its excess can result in production of harmful oxygen radicals. To avoid any resulting damage, phototrophic organisms can employ a process known as non-photochemical quenching (NPQ), where excess light energy is safely dissipated as heat. The mechanism(s) of NPQ vary among different phototrophs. Here, we describe a new type of NPQ in the organism Rhodomonas salina, an alga belonging to the cryptophytes, part of the chromalveolate supergroup. Cryptophytes are exceptional among photosynthetic chromalveolates as they use both chlorophyll a/c proteins and phycobiliproteins for light harvesting. All our data demonstrates that NPQ in cryptophytes differs significantly from other chromalveolates - e.g. diatoms and it is also unique in comparison to NPQ in green algae and in higher plants: (1) there is no light induced xanthophyll cycle; (2) NPQ resembles the fast and flexible energetic quenching (qE) of higher plants, including its fast recovery; (3) a direct antennae protonation is involved in NPQ, similar to that found in higher plants. Further, fluorescence spectroscopy and biochemical characterization of isolated photosynthetic complexes suggest that NPQ in R. salina occurs in the chlorophyll a/c antennae but not in phycobiliproteins. All these results demonstrate that NPQ in cryptophytes represents a novel class of effective and flexible non-photochemical quenching.     

Rhodomonas lacustris (Pascher & Ruttner) Javornicky (Cryptomonadida): Ultrastructure of the Vegetative Cell

The ultrastructure of Rhodomonas lacustris was examined using scanning and transmission electron microscopy, and the pigments were scanned in vivo by the opal plate technique. The periplast is composed of hexagonal plates, with trichocysts at the corners. This cryptomonad lacks a gullet but has a deep ventral furrow, in which more than 20 large ejectosomes are located. The chloroplast has mainly three thylakoids per lamella, and it is structurally reminiscent of that of certain haptophycean flagellates. The pigments appear to be as usual within the photosynthetic cryptomonads, with phycoerythrin type PE I (phycocyanin was not detected). Other cellular inclusions (e.g., lysosome-like vesicles and the contractile vacuolar complex) are also discussed.     

Aspects of the Comparative Physiology of Ranunculus bulbosus L. and Ranunculus repens L.: I. Response to Nitrogen

Ranunculus bulbosus and R. repens are closely related taxonomicallyand coexist in the same general habitat but differ in that R.bulbosus only exceptionally shows vegetative multiplicationcontrasting with R. repens which reproduces extensively by meansof long branched stolons which root and form new daughter plantsat the nodes. The response of these two species to nitrogen was similar inthat an increase from 10 to 50 ppm nitrogen gave rise to greatlyincreased total dry weight and higher shoot to root ratios,whereas further nitrogen increase from 50 to 200 ppm had littleeffect. However, they differed in that at low nitrogen levelsthe perennating organ (corm) took priority in R. bulbosus withsexual reproduction assuming greater importance at the highernitrogen levels, whereas in R. repens the main storage organ(the stock) was not especially favoured at low nitrogen levelsreflecting perhaps the differences between this structure andthe corm in R. bulbosus. In R. repens the greatest responseto nitrogen was shown by the stolons although this was due toincreased branching and a higher dry weight per unit lengthat the higher levels of nitrogen (50 and 200 ppm). Primary stolonlength was not greatly affected by nitrogen level. Dry weightsof flowers and fruits in R. repens were very much lower thanin R. bulbosus. It is suggested that in R. bulbosus the emphasis lies firstin replacement of the parent at approximately the same siteby a daughter from the new corm and secondly in sexual reproductivespread. In R. repens lateral spread by vegetative propagationtakes precedence over all else and under low nitrogen conditionsbranching is sacrificed and energy is diverted to maintaininglong primary stolons. These, in turn, have the potential forproducing daughter plants at some distance from the parent andthis may be of considerable importance in field situations sincethe daughter may come to occupy more favourable sites than theparent.     

Evaluation of nitrogen fixation in the diatom genus Rhizosolenia Ehr. in the absence of its cyanobacterial symbiont Richelia intracellularis Schmidt

Aggregates of two species of Rhizosolenia (R. castracanei andR. imbricata var. shrubsolei) have been reported to containendosymbiotic bacteria and to fix nitrogen. The general importanceof this process to the genus is not known, although of greatpotential significance. Clonal cultures of five species of Rhizosolenia(R. alata, R. bergonii, R. calcar-avis, R. imbricata var. shrubsoleiand R. setigera) were examined for nitrogen fixation using acetylenereduction and compared to cyanobacterial controls. Mecososmaggregates of R. imbricata var. shrubsolei were tested, as wellas chains of R. debyana hand-collected using SCUBA. The Rhizosoleniaspecies did not contain the endosymbiotic cyanobacterium Richeliaintracellularis and were not examined for the presence of endosymbioticbacteria. Nitrogen fixation was not found in the Rhizosoleniaspp.; in contrast, the diazotrophic cyanobacterial controlsOscillatoria erythraea and Anabaena sp. reduced acetylene atsignificant rates. The absence of nitrogen fixation in the Rhizosoleniaspp. suggests diazotrophy by endosymbiotic bacteria is not widespreadin the genus Rhizosolenia, nor is it necessary for survivalof these large diatom cells in nutrient-poor, near-shore waters.     

Differential effects of changes in spectral irradiance on photoacclimation,primary productivity and growth in Rhodomonas salina (Cryptophyceae) and Skeletonema costatum (Bacillariophyceae) in simulated blackwater environments

The underwater light field in blackwater environments is strongly skewed toward the red end of the electromagnetic spectrum due to blue light absorption by colored dissolved organic matter (CDOM). Exposure of phytoplankton to full spectrum irradiance occurs only when cells are mixed up to the surface. We studied the potential effects of mixing‐induced changes in spectral irradiance on photoacclimation, primary productivity and growth in cultures of the cryptophyte Rhodomonas salina and the diatom Skeletonema costatum. We found that these taxa have very different photoacclimation strategies. While S. costatum showed classical complementary chromatic adaption, R. salina showed inverse chromatic adaptation, a strategy previously unknown in the cryptophytes. Transfer of R. salina to periodic full spectrum light (PFSL) significantly enhanced growth rate (μ) by 1.8 times and primary productivity from 0.88 to 1.35 mg C · (mg Chl^?1) · h^?1. Overall, R. salina was less dependent on PFSL than was S. costatum, showing higher μ and net primary productivity rates. In the high‐CDOM simulation, carbon metabolism of the diatom was impaired, leading to suppression of growth rate, short‐term ¹⁴C uptake and net primary production. Upon transfer to PFSL, μ of the diatom increased by up to 3‐fold and carbon fixation from 2.4 to 6.0 mg C · (mg Chl^?1) · h^?1. Thus, a lack of PFSL differentially impairs primarily CO₂‐fixation and/or carbon metabolism, which, in turn, may determine which phytoplankton dominate the community in blackwater habitats and may therefore influence the structure and function of these ecosystems.     

OBSERVATIONS ON THE SWIMMING AND BUOYANCY OF SOME THECOSOMATOUS PTEROPOD GASTROPODS

Cymbulia peroni produces forward propulsion only on the upstrokeof its ‘wingbeat’ the downstroke opposing slightnegative buoyancy. The species' torpedo-shaped pseudoconchaprovides stability as well as buoyancy. Corolla ovata producespropulsive power on the downstroke of its ’wings‘and shows periods of active upward swimming alternating withpassive downward gliding/parachuting. Both cymbuliid speciesare gelatinous slow movers, close to neutral buoyancy, and areincapable of effective diurnal vertical migration. Two cavoliniidspecies were also studied; Cilo pyramida and Cuvierina columnella.Both were dense and sank quickly if they ceased active swimming.Both had postural responses to slow sinking, but vigorous activitywas required to hover in the water column. Clio could not climbrapidly enough to carry out effective diurnal vertical migration,but was capable of fast horizontal swimming during which thetriangular shell appeared to act as a hydrofoil. The smallerCuvierina could not swim quickly in a horizontal direction,but was capable of swimming vertically at rates sufficient tomaintain station with moving isolumes and may therefore carryout significant diurnal vertical migrations. (Received 28 September 1989; accepted 12 December 1989)