Cyanobacterial Diet Research Articles

Combined effect of freshwater salinization and harmful algae on the benthic invertebrate Chironomus pallidivittatus

Global climate change as well as human activities have been reported to increase the frequency and severity of both salinization and harmful algal blooms (HABs) in many freshwater systems, but their co-effect on benthic invertebrates has rarely been studied. This study simultaneously examined the joint toxicity of salinity and different cyanobacterial diets on the behavior, development, select biomarkers, and partial life cycle of Chironomus pallidivittatus (Diptera). High concentrations of salts (e.g., 1 g/L Ca2+ and Mg2+) and toxic Microcystis had synergistic toxicity, inhibiting development, burrowing ability and causing high mortality of C. pallidivittatus, especially for the Mg2+ treatment, which caused around 90% death. Low Ca2+ concentration (e.g., 0.01 g/L) promoted larval burrowing ability and inhibited toxin accumulation, which increased the tolerance of Chironomus to toxic Microcystis. However, low Mg2+ concentration (e.g., 0.01 g/L) was shown to inhibit the behavior, development and increase algal toxicity to Chironomus. Toxic Microcystis resulted in microcystin (MC) accumulation, inhibited the burrowing ability of larvae, and increased the proportion of male adults (>50%). The combined toxicity level from low to high was verified by the weight of evidence and the grey TOPSIS model, which integrated five lines of evidence to increase the risk assessment accuracy and efficiency. This is the first study that provided insights into ecological risk arising from the joint effect of salinity and harmful algae on benthic organisms. We suggest that freshwater salinization and HABs should be considered together when assessing ecological threats that arise from external stress.

Inhibition of gut digestive proteases by cyanobacterial diets decreases infection in a Daphnia host-parasite system.

Secondary metabolites produced by primary producers have a wide range of functions as well as indirect effects outside the scope of their direct target. Research suggests that protease inhibitors produced by cyanobacteria influence grazing by herbivores and may also protect against parasites of cyanobacteria. In this study, we asked whether those same protease inhibitors produced by cyanobacteria could also influence the interactions of herbivores with their parasites. We used the Daphnia-Metschnikowia zooplankton host-fungal parasite system to address this question because it is well documented that cyanobacteria protease inhibitors suppress trypsin and chymotrypsin in the gut of Daphnia, and because it is known that Metschnikowia infects via the gut. We tested the hypothesis that Daphnia gut proteases are necessary for Metschnikowia spores to be released from their asci. We then also tested whether diets that decrease trypsin and chymotrypsin activity in the guts of Daphnia lead to lower levels of infection. Our results show that chymotrypsin promotes the release of the fungal spores from their asci. Moreover, a diet that strongly inhibited chymotrypsin activity in Daphnia decreased infection levels, particularly in the most susceptible Daphnia clones. Our results support the growing literature that cyanobacterial diets can be beneficial to zooplankton hosts when challenged by parasites and uncover a mechanism that contributes to the protective effect of cyanobacterial diets. Specifically, we demonstrate that host chymotrypsin enzymes promote the dehiscence of Metschnikowia spores; when cyanobacteria inhibit the activity of chymotrypsin in hosts, this most likely traps the spore inside the ascus, preventing the parasite from puncturing the gut and beginning the infection process. This study illustrates how secondary metabolites of phytoplankton can protect herbivores against their own enemies.

Experimental Studies on Zooplankton-Toxic Cyanobacteria Interactions: A Review.

Cyanobacterial blooms have been recognized as a problem in fresh water for about 150 years. Over the past 50 years, experimental studies on the subject have gained importance considering the increasing need to control toxic cyanobacterial blooms. This article presents information on the different lines of research that have been undertaken on zooplankton-cyanobacteria interactions over the past 50 years. These include information on filtering/ingestion rates and phytoplankton preferences of small and large rotifers, cladocerans, and copepods; growth rates of zooplankton on cyanobacterial diets; feeding rates of other freshwater invertebrates on cyanobacteria; role of zooplankton in top-down biomanipulation efforts; effect of cyanotoxins on zooplankton; bioaccumulation of cyanotoxins; and physical and chemical control of cyanobacterial blooms. We also highlight measures that have led to successful lake management and improvement of water quality in selected waterbodies.

Effects of Harmful Blooms of Large-Sized and Colonial Cyanobacteria on Aquatic Food Webs

Cyanobacterial blooms are the most important and best studied type of harmful algal blooms in fresh waters and brackish coastal seas. We here review how and to which extent they resist grazing by zooplankton, how zooplankton responds to cyanobacterial blooms and how these effects are further transmitted to fish. Size, toxicity and poor nutritional value are widespread mechanisms of grazing defense by cyanobacteria. In some cases, defenses are inducible, in some they are obligate. However, to some extent zooplankton overcome grazing resistance, partly after evolutionary adaptation. Cyanotoxins are also harmful to fish and may cause fish kills. However, some fish species feed on Cyanobacteria, are able to reduce their abundance, and grow on a cyanobacterial diet. While reduced edibility for crustacean zooplankton tends to elongate the food chain from primary producers to fish, direct feeding by fish tends to shorten it. The few available comparative studies relating fish yield to nutrients or phytoplankton provide no indication that cyanobacteria should reduce the ratio fish production: primary production.

Life-history responses of Daphnia sinensis simultaneously exposed to Microcystis aeruginosa and Cylindrospermopsis raciborskii.

Many cyanobacterial species co-occur commonly in a freshwater ecosystem and can be consumed simultaneously by zooplankton. Both Microcystis aeruginosa and Cylindrospermopsis raciborskii are the dominant species and coexist in eutrophic tropical waters, and they together are assumed to have exert a stronger effect on the life history traits of cladocerans than a single cyanobacterial species. In the present study, we tested the hypothesis with life-history experiments of Daphnia sienesis, a large cladoceran species in tropics. In the experiments, M. aeruginosa and C. raciborskii were used as a mixture of food with Chlorella pyrenoidosa for the experimental animals. D. sienesis showed excellent growth and survival on sole diets of C. pyrenoidosa (CP). By contrast, Daphnia's growth decreased significantly and reproduction was completely inhibited when cyanobacteria comprised 100% of the food offered. The supplementation of C. pyrenoidosa into cyanobacterial diets significantly decreased their harmful effects on Daphnia, who improved the life history traits with the reduction of cyanobacterial percentage in mixed foods, irrespective of cyanobacterial species. Compared with the cultures of D. sienesis fed with a single cyanobacteria species, the animals in the treatments fed both M.aeruginosa-FACHB469 (F469) and C. raciborskii N8 (N8) had a lower growth rate in all the proportion of C. pyrenoidosa (25% CP, 50% CP or 75% CP). The strongest synergistic inhibition by the two cyanobacterial strains was found in the treatments with the 25% CP (i.e., 25% CP + 37.5% F469 + 37.5% N8), and no animal survived to maturity and reproduced. Thus, the simultaneous exposure to the two cyanobacterial species should be taken into account in assessing the ecological risks of cyanobacterial blooms, since multiple cyanobacterial coexistence can result in strong synergistic inhibition on growth and reproduction of zooplankton.

Temperature and host diet jointly influence the outcome of infection in a Daphnia‐fungal parasite system

Abstract Climate change has the potential to shape the future of infectious diseases, both directly and indirectly. In aquatic systems, for example, elevated temperatures can modulate the infectivity of waterborne parasites and affect the immune response of zooplanktonic hosts. Moreover, lake warming causes shifts in the communities of primary producers towards cyanobacterial dominance, thus lowering the quality of zooplankton diet. This may further affect host fitness, resulting in suboptimal resources available for parasite growth. Previous experimental studies have demonstrated the respective effects of temperature and host diet on infection outcomes, using the zooplankter Daphnia and its microparasites as model systems. Although cyanobacteria blooms and heat waves are concurrent events in nature, few attempts have been made to combine both stressors in experimental settings. Here, we raised the zooplankter Daphnia (two genotypes) under a full factorial design with varying levels of temperature (the standard 19°C and elevated 23°C), food quality (Scenedesmus obliquus as high‐quality green algae, Microcystis aeruginosa and Planktothrix agardhii as low‐quality cyanobacteria) and exposed them to the parasitic yeast Metschnikowia bicuspidata. We recorded life history parameters of the host as well as parasite traits related to transmission. The combination of low‐quality cyanobacterial diets and elevated temperature resulted in additive detrimental effects on host fecundity. Low‐quality diets reduced parasite output, while temperature effects were context dependent. Overall, we argue that the combined effects of elevated water temperature and poor‐quality diets may decrease epidemics of a common fungal parasite under a climate change scenario.

Transcriptome sequencing of a keystone aquatic herbivore yields insights on the temperature-dependent metabolism of essential lipids

BackgroundNutritional quality of phytoplankton is a major determinant of the trophic transfer efficiency at the plant-herbivore interface in freshwater food webs. In particular, the phytoplankton’s content of the essential polyunsaturated omega-3 fatty acid eicosapentaenoic acid (EPA) has been repeatedly shown to limit secondary production in the major zooplankton herbivore genus Daphnia. Despite extensive research efforts on the biological model organism Daphnia, and the availability of several Daphnia genomes, little is known regarding the molecular mechanisms underlying the limitations in Daphnia related to dietary EPA availability.ResultsWe used RNA-seq to analyse the transcriptomic response of Daphnia magna which were fed with two different diets — each with or without supplementation of EPA — at two different temperature levels (15 and 20 °C). The transcripts were mapped to the D. magna genome assembly version 2.4, containing 26,646 translations. When D. magna fed on green alga, changing the temperature provoked a differential expression of 2001 transcripts, and in cyanobacteria-fed daphnia, 3385 transcripts were affected. The supplementation of EPA affected 1635 (on the green algal diet), or 175 transcripts (on the cyanobacterial diet), respectively. Combined effects for diet and temperature were also observed (669 for the green algal and 128 transcripts for the cyanobacterial diet). Searching for orthologous genes (COG-analysis) yielded a functional overview of the altered transcriptomes. Cross-matched transcript sets from both feed types were compiled to illuminate core responses to the factors temperature and EPA-supplementation.ConclusionsOur highly controlled eco-physiological experiments revealed an orchestrated response of genes involved in the transformation and signalling of essential fatty acids, including eicosanoid-signalling pathways with potential immune functions. We provide an overview of downstream-regulated genes, which contribute to enhance growth and reproductive output. We also identified numerous EPA-responsive candidate genes of yet unknown function, which constitute new targets for future studies on the molecular basis of EPA-dependent effects at the freshwater plant-herbivore interface.

Effect of a cyanobacterial diet on the competition between rotifers: a case study in Lake Albufera of Valencia, Spain

espanolBrachionus havanaensis se distribuye predominantemente en las regiones Neartica y Neotropical. Ahora se encuentra incluso en las regiones Paleartica y Oriental. Durante el verano de 2015, encontramos altas densidades (> 500 ind./l) de esta especie y bajas abundancias de Brachionus angularis en la laguna de la Albufera, donde la cianobacteria (Microcystis aeruginosa) fue dominante en la comunidad de fitoplancton. Nuestra hipotesis fue que la cianobacteria era toxica para B. angularis pero no para B. havanaensis, por lo que este ultimo superaria al primero en presencia de dicha cianobacteria. Para probar la hipotesis, realizamos experimentos de competencia entre estas dos especies de rotiferos (B. angularis y B. havanaensis) que coexisten en la laguna de la Albufera de Valencia utilizando como alimento el alga verde (Nannochloropsis oculata) y colonias sonicadas de M. aeruginosa (celulas individuales) por separado y juntas (en relacion 1:1 basada en biomasa). Los experimentos de competencia basados en el seguimiento del crecimiento poblacional mostraron que en los controles B. havanaensis conseguia un mayor crecimiento poblacional que B. angularis cuando lo hacian separadamente. Sin embargo, cultivandolos ambos juntos, B. havanaensis tuvo una reduccion del crecimiento poblacional (casi 50 %), con respecto a B. angularis, en ausencia de Microcystis en la dieta. Esta reduccion del crecimiento fue mayor que en el tratamiento de B. havanaensis individualmente, cuando se cultivo con una dieta mixta de Microcystis y Nannochloropsis oculata. Brachionus havanaensis en todos los tratamientos (solos o en presencia de B. angularis) murio completamente cuando se cultivo en 100 % de M. aeruginosa. Las tasas de crecimiento poblacional de B. angularis, solos o en competencia con B. havanaensis, fueron similares cuando se excluyo a Microcystis de la dieta. Sin embargo, el cultivo solo con Microcystis o junto con Nannochloropsis fue altamente perjudicial para el crecimiento poblacional de B. angularis. Nuestros resultados mostraron el diferente resultado de los experimentos de competencia entre estos dos rotiferos en funcion de la presencia o ausencia de cianobacterias toxicas en la dieta. Nuestro estudio tambien mostro que una dieta exclusiva de esta cianobacteria era toxica para ambas especies de rotiferos EnglishBrachionus havanaensis is predominantly distributed in the Nearctic and Neotropical regions. It is now found even in the Palearctic and Oriental regions. During the summer of 2015 we found high densities (> 500 ind./l) of this species and low numbers of Brachionus angularis in Lake Albufera where the cyanobacterium (Microcystis aeruginosa) was dominant in the phytoplankton community. We hypothesized that the cyanobacterium was toxic to B. angularis but not to B. havanaensis hence the latter would outcompete the former in the presence of this cyanobacterium. To test the hypothesis, we conducted competition experiments between two coexisting rotifer species (B. angularis and B. havanaensis) from the Lake Albufera of Valencia using as food the green alga (Nannochloropsis oculata) and sonicated colonies of M. aeruginosa (single cells), separately and together (1:1 ratio based on biomass). The competition experiments using the population growth approach showed that B. havanaensis in controls had higher population abundances than B. angularis. However, when grown both together, B. havanaensis had a reduced population growth (nearly 50 %) in relation to B. angularis, in the absence of Microcystis in the diet. This reduced growth was more than that in the treatment of B. havanaensis alone when grown on a mixed diet of Microcystis and Nannochloropsis oculata. Brachionus havanaensis in all treatments (alone or in the presence of B. angularis) died completely when cultured on 100 % M. aeruginosa. The population growth rates of B. angularis, alone or in competition with B. havanaensis, were similar when Microcystis was excluded from the diet. However, Microcystis alone or together with Nannochloropsis was highly detrimental for the population growth of B. angularis. Our results showed the differences in the competitive outcome between the rotifers depending on the presence or absence of toxic cyanobacteria in the diet. Our study also showed that an exclusive diet of this cyanobacterium was toxic to both rotifers.

The molecular basis of essential fatty acid limitation in Daphnia magna: A transcriptomic approach.

It is widely accepted that in many food webs, the trophic transfer efficiency among primary producers and herbivores is determined by the nutritional value of primary producers. In pelagic freshwater and marine ecosystems, secondary production by herbivorous crustacean zooplankton is often limited by the seston's content of essential ω3 polyunsaturated fatty acids (ω3 PUFAs). However, little is known about the genetic network behind the positive relationship between phytoplankton ω3 PUFA content and zooplankton growth and reproduction. In our experimental study, we analysed gene expression changes of the freshwater cladoceran Daphnia magna under different food regimes differing in their ω3 PUFA composition. To disentangle ω3 PUFA effects from other factors, we fed D.magna with different pure phytoplankton cultures (i.e., algal and cyanobacterial diets) with or without supplementing the essential ω3 PUFA eicosapentaenoic acid (EPA). As hypothesized, we observed enhanced growth on diets supplemented with EPA. We applied an Illumina RNA-seq approach to D.magna from different diet treatments to find and monitor genes that are regulated dependent on EPA availability. Of 26,646 potential protein products (mapped to the D.magna genome), we identified transcriptomic signatures driven by the different food sources. Further analyses revealed specific candidate genes involved in EPA metabolism, irrespective of the basal food source. This allows a first functional annotation of previously uncharacterized genes involved in the EPA-specific response of D.magna and may finally provide a link to molecular processes connected to ω3 PUFA metabolism and conversion and thus trophic transfer efficiency in pelagic food webs.

High dietary quality of non-toxic cyanobacteria for a benthic grazer and its implications for the control of cyanobacterial biofilms

BackgroundMass occurrences of cyanobacteria frequently cause detrimental effects to the functioning of aquatic ecosystems. Consequently, attempts haven been made to control cyanobacterial blooms through naturally co-occurring herbivores. Control of cyanobacteria through herbivores often appears to be constrained by their low dietary quality, rather than by the possession of toxins, as also non-toxic cyanobacteria are hardly consumed by many herbivores. It was thus hypothesized that the consumption of non-toxic cyanobacteria may be improved when complemented with other high quality prey. We conducted a laboratory experiment in which we fed the herbivorous freshwater gastropod Lymnaea stagnalis single non-toxic cyanobacterial and unialgal diets or a mixed diet to test if diet-mixing may enable these herbivores to control non-toxic cyanobacterial mass abundances.ResultsThe treatments where L. stagnalis were fed non-toxic cyanobacteria and a mixed diet provided a significantly higher shell and soft-body growth rate than the average of all single algal, but not the non-toxic cyanobacterial diets. However, the increase in growth provided by the non-toxic cyanobacteria diets could not be related to typical determinants of dietary quality such as toxicity, nutrient stoichiometry or essential fatty acid content.ConclusionsThese results strongly contradict previous research which describes non-toxic cyanobacteria as a low quality food resource for freshwater herbivores in general. Our findings thus have strong implications to gastropod-cyanobacteria relationships and suggest that freshwater gastropods may be able to control mass occurrences of benthic non-toxic cyanobacteria, frequently observed in eutrophied water bodies worldwide.

Demographic responses of Heterocypris incongruens (Ostracoda) related to stress factors of competition, predation and food

<em>Heterocypris incongruens</em> is a widely distributed ostracod which can maintain its populations under stressful conditions such as those in temporary ponds and under low-quality diets, for example, detritus. It often co-occurs with cladocerans and fish living in shallow water bodies. Nevertheless, little is known about its response to the presence of predators, its consumption capacity of cyanobacteria typically present in eutrophic systems, and its interaction with other species in similar habits. We studied here the demographic responses of <em>H. incongruens</em> fed the green alga <em>Scenedesmus</em> <em>acutus</em>, two strains of <em>Microcystis </em>cf. <em>aeruginosa</em> and <em>Limnothrix</em> sp. Experiments were conducted separately and together in the presence of the cladoceran <em>Simocephalus vetulus </em>and the cichlid fish, <em>Oreochromis</em> kairomones. The ostracod maintained growth in all treatments, the reproductive output decreased on dietary <em>Limnothrix </em>sp., and its life expectancy was significantly lower with the toxic strain of <em>Microcystis</em>. The coexistence of both crustacean species increased the rate of population growth (~ 0.33 day<sup>-1</sup>) of <em>S. vetulus</em> and life expectancy (36-44 days) of <em>H. incongruens</em> on the test diets compared with controls (23-33 days). Our study suggests facilitation affects the interaction between the two microcrustaceans, especially on poor quality cyanobacterial diets.

Cholesterol Degradation Effect Analyzed using Marine Cyanobacterial Species Spirulina subsalsa

In this study was designed to understand the mechanisms of cholesterol degradation by cyanobacterial species Spirulina subsalsa. We analyzed the degradation of cholesterol in albino mice using basal feed diet (control) and different concentration (1%, 2% and 4%) of cyanobacterial diet. Cholesterol was estimated from the control and cyanobacterial fed to the albino mice. Blood cholesterol level reduced 8.1, 24.3, 30.6 % in 1, 2 and 4% cyanobacterial diet respectively. Phycobiliproteins are the most abundant soluble protein complexes in cyanobacteria and phycocyanin have 75% in phycobiliprotein. We concluded, phycocyanin was major role for cholesterol degradation in albino mice.

Effects of cyanobacteria, fish kairomones, and the presence of ostracods on the demography of Simocephalus vetulus (Cladocera)

AbstractSimocephalus vetulus is a large (2.0–4.0 mm at maturity) cladoceran often found in the littoral region of lakes and ponds, and capable of moderate growth rates even on poor‐quality cyanobacterial diets. It frequently co‐occurs with fishes and similar sized ostracods such as Heterocypris incongruens, but little is known of its response to fish kairomones or its interactions with potential competitors. We studied the demographic responses of S. vetulus fed the green alga Scenedesmus acutus, Microcystis cf. aeruginosa strain A, Microcystis cf. aeruginosa strain B, or Limnothrix sp. Experiments were conducted separately and together in the presence of Heterocypris incongruens and cichlid fish (Oreochromis) kairomones. A diet of Limnothrix sp. resulted in the lowest population growth rate (0.21±0.023 d−1), while on diets of S. acutus or Microcystis, population growth was higher (0.30±0.009 d−1). The presence of ostracods resulted in significantly higher growth rates of S. vetulus fed Limnothrix (0.33±0.01 d−1), but not Microcystis or S. acutus. Regardless of the diet, the presence of fish kairomones resulted in significantly higher growth rates as compared with controls, particularly when ostracods were also present. Coexistence with ostracods may be beneficial to S. vetulus, particularly when food quality is poor.

Dietary supply with essential lipids affects growth and survival of the amphipod Gammarus roeselii

Growth and survival of benthic macroinvertebrates depend on the availability and the quality of potential food sources. The significance of essential biochemical nutrients, such as sterols and polyunsaturated fatty acids (PUFAs), for benthic invertebrates has been insufficiently studied. We investigated the effects of these essential lipids on growth and survival of the benthic gammarid Gammarus roeselii , a widespread species in streams, rivers and lentic waters of Central Europe, in standardized feeding experiments. Juvenile gammarids were fed a mixture of three cyanobacteria with no evidence of toxin production, either unsupplemented or supplemented with cholesterol or the long-chain PUFA docosahexaenoic acid (DHA) using bovine serum albumin (BSA) to load algal or cyanobacterial cells with single lipid, and a mixture of three eukaryotic algae containing various sterols and long-chain PUFAs. Our results revealed that growth and especially survival of gammarids on the cyanobacterial diet significantly increased upon supplementation with cholesterol and DHA, indicating that the nutritional inadequacy of cyanobacteria for gammarids and potentially other benthic invertebrates is at least partially due to a deficiency in these essential lipids. We propose that the expected increase in the frequency of pelagic cyanobacterial mass developments as a consequence of global warming will also affect benthic food web processes to an as-yet-unknown magnitude.

A comparative study on the ability of tropical micro-crustaceans to feed and grow on cyanobacterial diets

Controlling noxious phytoplankton blooms by biomanipulation largely depends on the presence of large-sized (.3000 mm) generalist grazers, not common in the tropics. Therefore, we compared the ability of small ( 2000 mm) microcrustaceans Ceriodaphnia dubia, Moina macrocopa, Daphnia pulex, Simocephalus vetulus and Heterocypris incongruens to feed and grow on cyanobacterial diets. We studied their feeding preferences on phytoplankton from natural lake water with a dominance of Microcystis sp., Fragilaria sp. or Planktothrix sp. to which we added Scenedesmus acutus. Also tested were the ability of D. pulex, S. vetulus and H. incongruens to reduce cyanobacterial densities by grazing, and the rate of grazing and demographic responses of S. vetulus and H. incongruens on diets of S. acutus, Microcystis sp. and Planktothrix sp. All species fed on small colonies of Microcystis sp., but not on filamentous Planktothrix sp. or colonial Fragilaria sp. Simocephalus vetulus and H. incongruens were generalists and most capable of reducing cyanobacterial densities. Demographic variables of S. vetulus, but not H. incongruens, were significantly lower on the cyanobacterial diet; for instance, the population growth rates were between 0.07– 0.2 day on cyanobacterial diets, but 0.31 on S. acutus while for H. incongruens they ranged between 0.07 and 0.08 day, regardless of whether the diet was a cyanobacteria or S. acutus. Our study warrants further tests on the ostracod H. incongruens in order to test its efficacy in reducing cyanobacterial densities in shallow tropical ponds.

Absence of sterols constrains food quality of cyanobacteria for an invasive freshwater bivalve

The accumulation of cyanobacterial biomass may severely affect the performance of aquatic consumers. Here, we investigated the role of sterols in determining the food quality of cyanobacteria for the invasive clam Corbicula fluminea, which has become a common benthic invertebrate in many freshwater ecosystems throughout the world. In standardized growth experiments, juvenile clams were fed mixtures of different cyanobacteria (Anabaena variabilis, Aphanothece clathrata, Synechococcus elongatus) or sterol-containing eukaryotic algae (Cryptomonas sp., Nannochloropsis limnetica, Scenedesmus obliquus). In addition, the cyanobacterial food was supplemented with different sterols. We provide evidence that somatic growth of C. fluminea on cyanobacterial diets is constrained by the absence of sterols, as indicated by a growth-enhancing effect of sterol supplementation. Thus, our findings contribute to our understanding of the consequences of cyanobacterial mass developments for benthic consumers and highlight the importance of considering sterols as potentially limiting nutrients in aquatic food webs.

Efficacy of micro algae and cyanobacteria as a live feed for juveniles of shrimp Penaeus monodon

Growth performance and survival of giant tiger shrimp Penaeus monodon fed with five different micro algal diets as a live feed, was evaluated under laboratory condition. The experimental design consisted of feeding the juvenile with micro algal diets and cyanobacterial diets at the same concentrations. Fresh biomass of Chlorella sp., Tetraselmis sp., Isochrysis sp., Synechococcus sp. and Phormidium sp. were used as feed for shrimp P. monodon . Mean total length of shrimp was higher when fed with Chlorella sp. (4.8 cm) followed by Phormidium sp. (4.4 cm) and mean total weight was also higher in shrimp fed with Chlorella sp. (0.59 g) followed by Phormidium sp. (0.569 g). The survival rate of the shrimp was improved in shrimp fed Phormidium sp. (83.33%) and it was decreased in shrimp fed with Isochrysis sp. (36.67%). The shrimp that performed best had significantly more edible flesh (59.35%) (with Chlorella sp.) protein and lipid content (with Phormidium sp.) carbohydrate (with Tetraselmis sp.) Further more, water quality of the tank was better in shrimp fed with Chlorella sp. In general, the research of this study revealed that Chlorella sp. and Phormidium sp. could be used as a live feed for better growth of P. monodon . Key words: Penaeus monodon, micro algae, Synechococcus, Phormidium, Shrimp growth, Chlorella.

Useful Carriers for Cyanobacteria: Their Response to Cyanobacterial Growth, Acetylene-Reductase Activity, Cyanobacterial Grazers and Paddy Yield in Calcareous Soil

Snails and nematodes, the potential cyanobacterial grazers, differ in their choice for cyanobacterial diet. Snails prefer non-mucilaginous forms while nematodes prefer mucilaginous forms. Such differences in feeding choice between the cyanobacteria suggests that it may not be possible to select strains of diazotrophic cyanobacteria that are resistant to all grazers. The potential consumption of cyanobacteria at an average field density of 20,000 snails ha−1 was estimated to be about 50 kg (fresh weight) ha−1 day−1. Dorylamus sp. was most dominant nematode associated with cyanobacterial consumption. Phytoextracts of neem (Azadirachta indica), bel (Aegle marmelos) and tobacco (Nicotiana tabacum) were effective in controlling these cyanobacterial grazers. The minimum concentration of neem, bel and tobacco phytoextract in water for 100 % mortality of snails were 0.1, 2.0 and 0.05%, respectively. However, trepellent level was only 0.01% for neem and tobacco phytoextract. Complete mortality of nematode (Dorylamus spp.) required a higher concentration level (2%) even in the most effective tobacco phytoextract. Lower levels of phytoextract (0.1%) were found to stimulate growth and nitrogen fixation of cyanobacteria. Application of these plant biomasses resulted in significant increase in cyanobacterial acetylene-reducing activity (ARA) and rice yield and a significant decrease in snail and nematode population. Augmentation of cyanobacterial acetylene-reducing activity was two to three times higher in comparison to the control in both the years of experimentation. Rice yield also increased between 3.8 and 58.5% over the control, depending on the quantity and nature of plant biomass. Tobacco waste was significantly superior in comparison to neem and bel biomass as carrier of cyanobacterial culture.

Local adaptation of Daphnia pulicaria to toxic cyanobacteria

We quantified within-species variation in the tolerance of the large, lake-dwelling daphnid, Daphnia pulicaria, to toxic cyanobacteria in the diet. Juvenile growth rates on diets consisting of 100% Ankistrodesmus falcatus (a nutritious green alga) or 100% Microcystis aeruginosa(toxic) were compared for D. pulicaria clones isolated from lakes expected to have low and high levels of bloom-forming cyanobacteria during summer. Growth rates of clones isolated from high-nutrient lakes (range of total phosphorus, 31‐235 m gL 21 ) were higher, and showed less relative inhibition, on the cyanobacterial diet compared to clones isolated from low-nutrient lakes (range of total phosphorus, 9‐13 m gL 21 ). Our results suggest that D. pulicaria populations exposed to high cyanobacterial levels over long periods of time can adapt to being more tolerant of toxic cyanobacteria in the diet.

Strong influences of larval diet history on subsequent post-settlement growth in the freshwater mollusc Dreissena polymorpha.

A significant seasonal variation in size at settlement has been observed in newly settled larvae of Dreissena polymorpha in Lake Constance. Diet quality, which varies temporally and spatially in freshwater habitats, has been suggested as a significant factor influencing the life history and development of freshwater invertebrates. Accordingly, experiments were conducted with field-collected larvae to test the proposal that diet quality can determine planktonic larval growth rates, size at settlement and subsequent post-metamorphic growth rates. Larvae were fed one of two diets or starved. One diet was composed of cyanobacterial cells, which are deficient in polyunsaturated fatty acids (PUFAs) and the other was a mixed diet rich in PUFAs. Freshly metamorphosed animals from the starvation treatment had a carbon content per individual 70% lower than that of larvae fed the mixed diet. This apparent exhaustion of larval internal reserves resulted in a 50% reduction of the post-metamorphic growth rates. Growth was also reduced in animals previously fed the cyanobacterial diet. Hence, low food quantity or low food quality during the larval stage of D. polymorpha, lead to irreversible effects for post-metamorphic animals and are related to inferior competitive abilities.