The longer Oscillatoria filaments are more likely to clump and, therefore, are more liable to be rejected by Daphnia during the food collection and ingestion processes. The shorter filaments, in comparison, are apparently less prone to clumping and, therefore, are cleared by the daphnids at higher rates than the longer filaments. Daphnia 0. This preference for detritus over live Oscillatoria, as indicated by Chesson's selectivity coefficient a, was apparently a passive process, rather than a case of active food selection.
At very high food concentrations 15—25 mg C l —1 , with the share of the live Oscillatoria filaments 2 to 2. This implies that the larger animals had greater interfering effects of the Oscillatoria filaments on the food collection and ingestion processes.
The eutrophication-related increases of filamentous cyanobacteria blue-green algae and detritus in lakes are now well known. However, the edibility of cyanobacteria for filter-feeding zooplankton, especially Daphnia spp. Coexistence of some larger-bodied Daphnia spp. That the cyanobacterial filaments may be important for Daphnia as a source of nutrition positive , but may interfere with the process of food collection, related to the filament concentration and length negative , has been analysed thoroughly by Gliwicz Gliwicz, a , b ; Gliwicz and Lampert, The nutritive value of detritus compared with that of the live algae often appears tobe low Starkweather and Bogdan, Despite the dominance of detritus in some lakes, its share in the nutrition of daphnids may be negligible Ojala et al.
However, daphnids appear to be indifferent to detritus and algae Bosselmann and Riemann, , primarily because they are non-selective in their feeding behaviour. When good-quality food is scarce there may be a weaker selection for the low-quality food, e. This latter has been shown for copepods using dual labelling with live and dead algae DeMott, Thus, detritus may, in such cases, contribute a substantial proportion to the energy requirements of grazing zooplankton and form an important food source for cladocerans Toth et al.
In smaller-bodied cladocerans Chydorus sphaericus , cyanobacterial detritus, added to laboratory cultures of green algae, has been reported to even increase the fitness of these animals Vijverberg and Boersma, It was also reported that the juveniles of 11 clones of Daphnia cucullata from Dutch lakes of varying trophy grew and reproduced in the laboratory on a sole diet of Oscillatoria limnetica Repka, However, it was observed that this cyanobacterium was a poor food compared with Scenedesmus.
Some cyanobacteria are known to possess morphological defences size or chemical defences toxins against herbivory by zooplankton Kirk and Gilbert, The relative edibilities of the cyanobacteria for the taxa of filter-feeding zooplankton of different sizes, and the effect of variance in the assimilation efficiency of different algae on the growth and reproduction of the filter-feeding zooplankton are important.
Mechanical aspects of food particle interception, collection and channelling to the food groove Porter and McDonough, ; Hartmann and Kunkel, show increased handling time of filaments, as well as their entanglement with the feeding limbs of Daphnia. Daphnia galeata erroneously cited as D.
Nevertheless, it is virtually absent in certain highly eutrophic water bodies, e. Loosdrecht lakes Gulati, ; Lammens et al. These lakes are dominated by cyanobacteria spp. Dawidowicz fed Daphnia magna in a flow-through system containing the Lake Loosdrecht water, very rich in Oscillatoria limnetica filaments Dawidowicz, He not only observed a significant decrease in these filaments but also a significant reduction in the filament length, caused by the Daphnia feeding activity.
Nevertheless, the existing circumstantial evidence shows that the quality of sestonic food, dominated by these filamentous cyanobacteria, for Daphnia spp. Also, size selective predation on zooplankton by planktivorous fish, particularly by the bream which are abundant in these lakes, could contribute importantly to the scarcity of daphnids in these lakes [see papers in Van Liere and Gulati, ].
What we do not know, however, is how, when and to what extent the two factors, edibility and quality of food and predation, are important for Daphnia spp.
As a part of the food-chain research we examined the effects of food quality on growth and reproduction rates of Daphnia species, and edibility and assimilation rates of Daphnia spp. In the present study, we determined the grazing and assimilation rates and assimilation efficiencies of a D. The animals, including those in the length range 0. Notably, in the Loosdrecht Lakes, the abundance of cyanobacteria and of the smaller-bodied cladocerans, D. We, therefore, expect that the present study, comparing the food-size-related edibility for the daphnids of these filaments, could provide a clue to the disadvantage the larger animals might have in such lakes.
In the feeding experiments, a strain of Oscillatoria limnetica was used that was originally isolated from Lake Loosdrecht and is now maintained in cultures in laboratory-scale enclosures LSE , which are designed to simulate the growth conditions for this cyanobacterium in the lake Gons et al. The length frequency distribution of about live Oscillatoria filaments was measured at random under a microscope, using a digitizing tablet Hoogveld and Moed, Roughly comparable length classes of the live filaments and detritus see below were obtained by sonifying both food types for 50 s at a sonifier intensity of 3 Sonifier B, Branson Sonic Company, CT, USA.
Nonsonified and sonified Oscillatoria filaments are hereafter distinguished as long filaments and short filaments, respectively. Live, long filaments were longer than the detrital filaments, with a greater tendency to aggregate. We know that when growth is prevented, the cyanobac-teria decompose rather rapidly Fallon and Brock, , and that the detritus thus formed can be an important food source for cladocerans in lakes Toth et al.
After incubating the filaments for between 3 and 6 days, usually 4 days, the detritus was ready. This was indicated by the colour of the suspensions, which turned from blue-green to yellow to yellowish-brown during the incubation.
Microscopic examination confirmed that the filamentous material in suspension did not have any viable filaments. The detritus was centrifuged twice for 10 min at r. Clumps, if any, were broken up by sonification as for the live filaments, using intensities of between 3 and 7 for 5—60 s, with a stepwise increase of 5 s. An intensity of 3 for 50 s was usually found to be adequate to break up any left-over clumps, without causing notable damage to the filament morphology or leaching loss of the cell contents.
The filtrate with detritus was stored in a refrigerator. The sonifying and filtration procedures prevented the detritus in suspension from sedimenting. Some contamination with ciliates of both the live filaments and the detritus was observed but was unavoidable.
The Daphnia galeata used in the experiments belonged to a clone derived from a single female. The carbon concentrations of Oscillatoria and of detritus were derived from separate calibration curves between spectrophotometric extinction nm values and the corresponding carbon contents of Oscillatoria and detritus in the suspensions.
The carbon content was computed from the measurements of Chemical Oxygen Demand using a modified method Gulati et al. The uptake and assimilation rates of detritus and livefilaments by daphnids were compared using both 14 C-labelled detritus and 32 P-labelled live algae in mixture or 32 P-labelled detritus and 14 C-labelled live algae. This enabled us to measure possible discrepancies due to differential leakage losses of C and P during the handling and collection of the filaments by the daphnids.
It also allowed comparison of the assimilation rates of C and P by the daphnids, because it is known that P is better assimilated than C by D. In addition, we concurrently measured in an experiment the assimilation efficiencies of C and P in the dual-labelled detrital food, by simultaneously incubating the live Oscillatoria filaments with both 14 C and 32 P. The detritus was thereafter prepared from these filaments in the same way as explained in the section above. A ml suspension of Oscillatoria obtained from the LSE was mixed with ml fresh culture medium Rijkeboer et al.
The suspension was split into two equal parts: to one part 3. For measuring assimilation efficiencies of C and P, the detritus filaments in suspension were dual-labelled.
A 14 : 10 h light : dark cycle was used for the incubation, which lasted 4 days. We assumed that this 4 day labelling period was long enough to ensure uniform distribution of the label over the different cell parts. Thereafter, the algae in both beakers were filtered and centrifuged, as mentioned under the procedure for preparing the detritus. The procedures for measuring clearance and assimilation rates are essentially the same as those used previously Gulati et al.
On the day of the experiment, 10 daphnids were transferred to ml fresh food suspension 4 mg C l —1 in a beaker, and placed in a culture cabinet at the same temperature and light settings as for culturing and acclimatization of the animals.
About 2—3 ml each of the two tracers, 14 C-labelled detritus and 32 P-labelled O. This caused only a negligible increase in the food concentration for the animals Gulati et al.
A feeding period of between 10 and 13 min was used to measure the clearance rates CR. This time is shorter than the gut passage time Gulati et al. The assimilation rates of Daphnia were determined the same way as the CR, except that the daphnids were fed for 30 min instead of 10—13 min, and were subsequently fed for 45 min on unlabelled food to clear their guts, appendages and carapace of labelled food, before transferring the animals to the vials and adding ethanol.
The radioactivities of animals in the vials and the tracer food were measured using a Packard Liquid Scintillator Counter Model and a standard procedure for counting the two tracers simultaneously, and for deriving the respective radioactivities DPM of these tracers.
The calculation procedures are summarized below [for details see Gulati et al. Net clearance rate NCR , or assimilation, is measured in ml daphnid —1 day —1 , i. It is calculated like CR, but replacing t with the corresponding feeding period value i. In addition, the differences in grazing rates and assimilation rates were tested statistically two sample analysis of variance, t -test of the differences between two means using the computer program css Statsoft, A total of 10 experiments was carried out.
The variation between the SCR replicates of longer filaments was high for both the tracer foods. The assimilation efficiencies on shorter filaments were higher than on longer filaments for both tracer foods 32 P: shorter filaments, This experiment was carried out using non-labelled Oscillatoria and detritus in the ratio of about total food, 4. The CR for Oscillatoria based on the 14 C tracer 4.
In this experiment, double-labelled and sonified detritus was fed to six size weight classes of daphnids Figure 3b to examine the specific ingestion rates SIR of detritus in the presence of Oscillatoria in the food mixture. Such low daily rations areapparently due to very high rejection rates of the food comprising mixed live and dead filaments of Oscillatoria , especially by the larger animals.
The protocol of the seven grazing experiments carried out using mixed food comprising detritus and Oscillatoria is summarized in Table 1.
The purpose of these experiments was to examine the following: firstly, whether the differences in filament size of mixed detritus and live Oscillatoria affect their relative uptake rates by the daphnids; secondly, if the relative or absolute concentrations of detritus and Oscillatoria in the mixture influence selection between detritus and Oscillatoria in daphnids; and thirdly, if switching the labels affects the CR and NCR of the daphnids differently, and thus also the assimilationefficiency.
The data enabled us to calculate selectivity coefficients for detritus and Oscillatoria for the daphnids of different sizes. In experiments 1—5, the ingestion rates IR of the daphnids were measured using mixtures of detritus and long Oscillatoria filaments see Table 1. Whereas in experiments 1, 2 and 3 the animal size was kept constant, in experiments 4 and 5, different size classes of daphnids were used.
In experiments 6 and 7, the shorter Oscillatoria filaments and detritus filaments were used in equal biomass proportions. The labelled detritus and long Oscillatoria filaments were offered together to the animals. In the first two experiments, food concentrations, 6. The main difference between these two experiments was the switching of the labels between the detritus and Oscilla-toria. In both experiments, the daphnids ingested the detritus at significantly higher rates, irrespective of the tracer.
In the third experiment, total food level was raised about 2. This enabled us to examine if a much higher proportion of Oscillatoria in the food mixture than in the preceding two experiments would interfere with the ingestion of detritus.
The CR i. Also, the IR for detritus was between 1. We compared the IR of different size classes of the daphnids on a mixture of live and dead filaments. The concentration of long Oscillatoria filaments was kept between 1. The total food concentrations used were much higher than those generally prevailing in Lake Loosdrecht at the time of Oscillatoria blooms. The intercepts of the regressions indicate that even the 1 mm length animals ingested about four times more detritus than live Oscillatoria filaments.
The regression slopes of less than 2, for both detritus and Oscillatoria , imply that IR increased proportionately less with size than expected on the basis of the length-related increase of the daphnid weights. This was especially true in Exp. In these experiments detritus 14 C-labelled and Oscilla-toria 32 P-labelled of similar filament length were offered at a ratio of 1 : 1 to the daphnids and their CR and NCR measured.
It is found growing on moist rocks, submerged stones, and damp soils close to the riverside. Other typical habitats include rivers, streams and lakes. It is usually found in colonies that are densely united. It possesses heteropolar cyanobacterial filaments which have heterocytes at their bases. Akinetes are absent in Rivularia.
False branching is lacking as well. There are no organelles present in the cells of Rivularia. Filaments disintegrate by developing an intercalary heterocyte which separates form the parent filament and develops parallel to it within that colony. Trichomes show radial arrangement within a colony and each trichome is partially or wholly enveloped by a gelatinous sheet.
Reproduction in Rivularia takes place by the formation of hormogones. Colonies is Rivularia are hemispherical in shape and the filaments are parallelly arranged forming irregular, flat or hemispherical layers. The colonies are lime encrusted or gelatinous, either few millimetres thick or can be seen through microscope, clinging at the base to substrata.
Cells are cylindrical or barrel shaped and without aerotopes. Filaments show pseudo branching, are heteropolar, widening at the base with heterocysts, and narrowing hair like narrowing towards the ends. Oscillatoria is a genus of filamentous blue-green algae occurring singly or in tangled mats in freshwater environments that includes hot springs as well.
This filamentous cyanobacterium is unbranched and named after its oscillatory movements. The blue green algae have derived its name from its very slow and rhythmic oscillatory motions which is caused by the secretion of mucilage which forces the filament away from the course of excretion. Reproduction in Oscillatoria happens by fragmentation in which dead separation disks concave cells disintegrate sections of the filaments process called as hormogonia.
Every single filament of Oscillatoria consists of a trichome which comprises of a row of cells. The tip of the trichome is able to oscillate like a pendulum. The hormogonia is able to grow into a new, longer filament.
Disintegration of filaments occurs where the dead cells called necridia are found. Filaments occurring in colonies slide back and forth again one another till the time the entire mass is reoriented to the light source. Rivularia is a genus of blue-green algae belonging to the family Rivulariaceae. The filaments are arranged radially and the branching is false. Filaments are heteropolar, differentiated into apical and basal parts, and joined parallelly into firm.
The trichomes possess a basal heterocyst. Oscillatoria is a genus of filamentous blue-green algae with long un-branching filamentous morphology. It is an important blue-green alga as it plays an important role in photosynthetic activities. At low pH levels, and in the absence of light, anatoxins may persist in the aquatic environment for a few weeks.
There is some evidence that anatoxins can be degraded by specialized bacteria, similar to Microcystis , but this process is not well documented. BMAA can bioaccumulate in zooplankton and fish, so this nerve toxin can contribute to health risks long after the toxic bloom has died back. Algae, cyanobacteria blooms, and climate change. Climate Institute Report, April Berg, M and M.
Factors affecting the growth of cyanobacteria with special emphasis on the Sacramento-Jan Joaquin Delta. Caldwell Eldridge, S. Wood, and K.
Spatial and temporal dynamics of cyanotoxins and their relation to other water quality variables in Upper Klamath Lake, Oregon, Chorus, I. Bartram Eds. Toxic cyanobacteria in water: a guide to their public health consequences, monitoring and management. D'Anglada, L. Donohue, J. Strong, and B. Health effects support document for the cyanobacterial toxin anatoxin-A. Graham, L. Wilcox, and M. Algae, Third Ed. LJLM Press, ww. Turner Eds. Ecology of Harmful Algae. Ecological Studies, Vol.
Gury, M. Lage, S. Annadotter, U. Rasmussen, and S. Marine Drugs Matthews, Robin A. Meriluoto, J. Spoof, and G.
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