Filamentous Green Algae Research Articles

Marine macroalgae Chaetomorpha aerea as a dietary supplement: Optimizing immunity and resistance to Edwardsiella tarda in tilapia (Oreochromis mossambicus)

The intensification of aquaculture has led to a rise in fish infections, necessitating the search for alternative antibiotics. In this context, our study investigated the effects of dietary supplementation with Chaetomorpha aerea, a filamentous green algae, on the immune health and resistance to infections in tilapia (Oreochromis mossambicus). Diets containing varying concentrations of C. aerea (0, 1, 2, 5, and 10 g/kg) were prepared and administered to the fish for 30 days, followed by a challenge with Edwardsiella tarda to evaluate survival rates. The results were significant. The diet containing 5 g/kg of C. aerea (group T3) brought about substantial improvements in hematological parameters, including increases in red blood cell count (RBC), hematocrit (Hct), and hemoglobin (Hb). The T3 group exhibited a robust immune response, with higher lysozyme and ceruloplasmin activity in immunological assays. LBP gene expression was significantly elevated in the spleen and thymus of fish in the T3 group, which correlated with higher survival after bacterial challenge compared to the control group. Principal Component Analysis (PCA) and cluster analysis confirmed that the 5 g/kg concentration stood out for maximizing immunological benefits without compromising the overall health of the fish. These findings highlight the robust immune response in the T3 group, a key finding of our study. We conclude that supplementation with C. aerea represents a promising and sustainable alternative in the formulation of diets for tilapia, contributing to improved health and resistance to diseases. Future studies are recommended to explore its application in other species and development stages, in addition to evaluating other health biomarkers.

Regulation of freshwater filamentous green algae (Cladophora) and its impact on malodorous volatile organic sulfur compound (DMS) by biomanipulation

When improving the water quality of natural bodies such as lakes, the explosive growth of filamentous green alga Cladophora can limit the growth of submerged macrophytes and prevent the water from shifting to a clear state. During the decay of Cladophora, it can cause various water quality issues such as reduced dissolved oxygen, increased nutrient levels and water odor. Biomanipulation, involving the introduction of a suitable density of aquatic animals into the water, can reduce the biomass of filamentous algae. We hypothesized that stocking appropriate densities of aquatic animals could reduce filamentous algal biomass and at the same time reduce the concentration of odorants in the water. Our study investigated the impact of stocking swamp shrimp (Macrobrachium nipponense), rosy bitterling (Rhodeus ocellatus), and silver carp (Hypophthalmichthys molitrix) at low (30 g/m3), medium (60 g/m3) and high (120 g/m3) densities on water quality, biomass of primary producers (such as Cladophora, submerged macrophyte and algae) and malodorous volatile organic sulfur compound dimethyl sulfide (DMS) in the water, respectively. It was found that the swamp shrimp treatment groups and the rosy bitterling high-density groups effectively inhibited the growth of filamentous green algae cover, in which the rosy bitterling high-density group reduced the filamentous green algae mat coverage by 29.65 % compared with the control group. Additionally, the high-density swamp shrimp and rosy bitterling groups notably promoted the growth of submerged macrophytes (Vallisneria denseserrulata), and significantly reduced the concentration of the malodorous DMS in the water. Overall, stocking swamp shrimp and rosy bitterling can benefit the restoration of aquatic ecology and the maintenance of clear water. However, it is essential to consider potential changes in water quality resulting from excessive stocking density. Therefore, the appropriate density and proportion of stocking should be determined in conjunction with the specific scale of the aquatic ecological restoration project.

Determinants of environmental changes in human-modified ecosystems: Effects of plastics on moisture gradients, nutrients, and clay properties

Plastic pollution poses a significant threat to ecosystem health worldwide. This study examines the determinants of environmental changes in human-modified ecosystems through a quantitative-qualitative system dynamics modeling approach: field experiments conducted on a 310 m2 unsaturated clay-rich bed and a 2.5 m2 clay-rich shore of a plastic-impacted pond in Shenzhen, China, and a 1.17 ha plastic-impacted clay pit in Musanze, Rwanda; laboratory experiments involving Modified Proctor (MP) and California Bearing Ratio (CBR) tests on natural clay reinforced with polyethylene terephthalate (PET) microplastics, with diameters ranging from 0.25 to 5 mm and at concentrations of 1.25 %, 2.5 %, 3.75 %, 5 %, and 10 % by weight of clay; and plastic dynamic flows analyzed by modeling the life cycle of PET. Field experiments showed that mulch type and thickness were critical factors influencing crack distribution in a plastic-impacted pond bed. Specifically, cracks were dominant in areas with pronounced desiccation and lacking filamentous green algae and PET-dominated plastic waste. Along the 2.5 m moisture gradient in a plastic-impacted pond bed, temperature and moisture significantly influenced nutrients, particularly in pronounced desiccation zones. Laboratory experiments showed that microplastics altered the structural properties of natural clay, decreasing moisture content while increasing dry density and load-bearing capacity. The plastic life cycle underscored the roles of industrial and consumer practices, environmental conditions, and waste management and recycling inefficiencies in driving environmental changes in human-modified ecosystems. The findings underscore the need for effective plastic waste management and recycling to mitigate the ecological impacts of plastic pollution in ecosystems.

Daily and other short-term changes in the ecosystem components of the world's largest hypersaline lagoon Bay Sivash (Crimea)

The interrelationship between various processes and components in the daily cycle of water bodies has been little studied, especially in hypersaline water bodies. A three-day study was conducted in the world's largest hypersaline lagoon Bay Sivash (the Sea of Azov). 16 biotic and abiotic parameters were measured 21–80 times in the studied site (wind direction and speed, photosynthetically active radiation (PAR), temperature, oxygen content, pH, Eh, turbidity, chlorophyll a fluorescence, zooplankton abundance, and others). There was a clear daily rhythm of PAR in the surface layer of the water, however, the stochastic weather factor (cloudiness, wind speed and direction) influenced the quantitative expression of it. The proportion of PAR entering deeper layers as shown, depends on the height of the Sun, as well as intra-ecosystem factors, for example turbidity and the development of mats of filamentous algae. Fluctuating from 1.69 to 98.03 NTU, turbidity depended on the speed and direction of the wind with windward winds leading to the resuspension of bottom sediments to a greater extent than leeward ones. Wind speed and direction also significantly influenced the distribution of biotic components such as the filamentous green alga Cladophora and zooplankton. Oxygen content fluctuated from between 1.8 and 16.58 mg L−1. An increase in oxygen concentration was observed only at PAR above approximately 500–1000 μE m−2;s−1. The increase in temperature and the virtual absence of wind, which was observed on 05/28/2022 and 05/29/2022, contributed to an increase in the oxygen concentration in the water on these days and the formation of hyperoxic conditions in this hypersaline lagoon.

Enhancing wastewater treatment with a novel separated algae membrane oxygenated activated sludge reactor

In this investigation, a separated algae membrane oxygenated activated sludge wastewater treatment reactor was developed. During the phase of aeration pump absence, the system, featuring a separated algae biofilm oxygenation activated sludge mechanism with an internal reflux ratio of 5 and a C/N ratio of 10, demonstrated remarkable efficiency in pollutant removal. Specifically, it achieved COD, TN, NH4+-N, and TP removal rates of 96.6 %, 81.9 %, 98.6 %, and 95.5 %, respectively. Despite a decline in dissolved oxygen (DO) during the transition of wastewater from the algae membrane reactor to the aerobic tank, the internal circulation reflux ratio of 5 ensured that the oxygen-enriched effluent from the algae membrane photoreactor maintained a stable DO level in the aerobic tank, ranging from 1.5 to 2.0 mg/L, thus meeting the oxygen demand of the activated sludge. Alterations in the aeration method had a notable impact on the diversity of the microbial community. Notably, the community shifted from bacteria adapted to intermittent aeration to those acclimated to internal recirculation for oxygen supply. The dominant microbial position was reinforced, with the Patescibacteria phylum and the norank_f__norank_o __ Saccharimonadales genus emerging as the dominant entities within the community. Under internal circulation reflux aeration, filamentous green algae persisted, resulting in a significant increase in biomass and chlorophyll content by 3.07 and 2.93 times, respectively. Furthermore, microalgae exhibited elevated protein and polysaccharide content, which increased by 3.14 and 3.16 times, respectively, due to the influence of the internal circulation reflux process, promoting the maturation of the algae membrane.

Food web structures of irrigated rice fields estimated from carbon and nitrogen stable isotopes: Special reference to the role of filamentous green algae as a food resource of aquatic consumers

AbstractRice fields are characterized by high algal production and dense mats of filamentous green algae, and they function as habitats for various aquatic organisms. However, how algal production supports the secondary production of aquatic consumers in rice fields has not been assessed. Herein, aquatic food web structures in two adjacent rice fields in northeastern Japan were examined using carbon and nitrogen stable isotope analyses. Filamentous algae often showed higher δ13C values (mean, −23.1‰ to −21.4‰) than other organic matter sources, including particulate organic matter, benthic microalgae, and soil organic matter (−30.1‰ to −25.4‰). A δ13C‐based isotopic mixing model estimated that among 19 taxa of herbivores and omnivores, most taxa depended on filamentous algae‐derived carbon (ca. >30%). Particularly, Peltodytes intermedius larvae, a specialist feeder for filamentous algae, showed the highest reliance (mean, 66.7%–80.0%). The microcrustacean, Ostracoda sp. also utilized a diet consisting of a substantial proportion of filamentous algae‐derived carbon (57.6%). Seven out of 10 carnivorous taxa showed reliance on filamentous algae‐derived carbon by >30%. Particularly, larvae of beetles (Berosus sp., Enochrus sp., and Hydrochara affinis) showed the highest reliance (40.2%–44.3%). They could assimilate filamentous algae‐based carbon by consuming herbivores, such as P. intermedius. Because fresh filamentous green algae were eaten less by aquatic consumers, the herbivores could consume decomposed filamentous algae rather than fresh ones. Our results suggest that filamentous algae are one of the major organic matter sources supporting secondary production in rice field food webs.

Inhibitory effect and mechanism of algicidal bacteria on Chaetomorpha valida

Chaetomorpha valida, filamentous green tide algae, poses a significant threat to both aquatic ecosystems and aquaculture. Vibrio alginolyticus Y20 is a new algicidal bacterium with an algicidal effect on C. valida. This study aimed to investigate the physiological and molecular responses of C. valida to exposure to V. alginolyticus Y20. The inhibitory effect of V. alginolyticus Y20 on C. valida was content dependent, with the lowest inhibitory content being 3 × 105 CFU mL−1. The microscopic results revealed that C. valida experienced severe morphological damage under the influence of V. alginolyticus Y20, with a dispersion of intracellular pigments. V. alginolyticus Y20 caused the decrease in chlorophyll-a content and Fv/Fm in C. valida. At the molecular level, V. alginolyticus Y20 downregulated the expression of genes related to photosynthetic pigment synthesis, light capture, and electron transport. Furthermore, V. alginolyticus Y20 induced oxidative damage to algal cells. The production of reactive oxygen species significantly increased after 11 days of exposure. Malondialdehyde content significantly increased, and the cell membranes were severely damaged by lipid peroxidation. The content of superoxide dismutase and peroxidase also markedly increased, whereas catalase content decreased significantly. Additionally, peroxisomes were inhibited due to the downregulation of PEX expression, leading to irreversible oxidative damage to algal cells. Our findings provided a new theoretical basis for exploring the interaction between algicidal bacteria and green tide algae at the molecular level.

Performance and mechanism of U(vi) removal from solution by humic acid-coated Fe3O4 nanoparticle-modified biochar from filamentous green algae.

The adsorbent material humic acid-coated Fe3O4 nanoparticle-modified biochar from filamentous green algae was fabricated by introducing the composites of humic acid-coated Fe3O4 nanoparticles onto biochar from filamentous green algae using the co-precipitation method. Then, the removal of U(vi) from solution by humic acid-Fe3O4/BC was carried out through batch experiments. The results of the characterization showed that the reaction conditions had an important influence on U(vi) removal by humic acid-Fe3O4/BC. The pseudo-second-order kinetic model and Langmuir model better illustrate the adsorption process of U(vi) on the surface of humic acid-Fe3O4/BC. The adsorption processes were dominated by chemisorption and monolayer adsorption. The maximum adsorption capacity of U(vi) by humic acid-Fe3O4/BC could be calculated, and it could reach 555.56 mg g-1. The probable mechanisms of U(vi) removal by humic acid-Fe3O4/BC were reduction reaction, inner-sphere surface complexation and electrostatic adsorption. The high stability and reusability of humic acid-Fe3O4/BC made it more promising in U(vi) removal applications.

Maternal diet influences fecundity in a freshwater turtle undergoing population decline.

Food availability determines the amount of energy animals can acquire and allocate to reproduction and other necessary functions. Female animals that are food limited thus experience reduced energy available for reproduction. When this occurs, females may reduce frequency of reproductive events or the number or size of offspring per reproductive bout. We assessed how maternal diet affects reproductive output in adult female Murray River short-necked turtles, Emydura macquarii, from four wetlands in Victoria. We previously found that turtle diets differ in the composition of plants and animals between our study wetlands. In this study, we tested whether differences in turtle diet composition (i.e. plants and animals) at these wetlands were associated with differences in clutch mass, individual egg mass, bulk egg composition and hatching success. We found total clutch mass increased with maternal body size at each site. At sites where filamentous green algae were scarce and E. macquarii were carnivorous, females produced smaller clutches relative to body size compared to females from sites where algae were abundant, and turtles were more herbivorous. Individual egg mass, bulk egg composition and hatching success did not differ across wetlands. Isotopic analysis revealed significant positive relationships between the carbon and nitrogen isotopes (δ13C, δ15N) of the eggs and those of the mothers, indicating that mothers allocated ratios of carbon and nitrogen isotopes to their eggs similar to those present in their tissues. Our study suggests that at sites where females are more carnivorous due to a relative absence of algae, females produce smaller clutches, but other aspects of their reproduction are not significantly impacted. The reduction in clutch size associated with differences in the availability of dietary plants and animals may have long-term consequences for E. macquarii and other freshwater turtle species that are experiencing population declines.

Comparative disease incidence and prevalence in green and brown varieties of Kappaphycus alvarezii cultivated in Pelakak Village, Lingga District

This study was aimed to analyze the disease incidence and prevalence development of Kappaphycus alvarezii from green and brown varieties. This study used a completely randomized design experimental method with two treatments and four replications. Seaweeds were reared with a longline culture method. The initial weight of seaweeds from each replication unit was 2.70 kg. Incidence and prevalence were observed every day until the 42-th day of culture period. All data obtained were analyzed with an independent t-test. The results showed that there were six incidents of pests and disease attack/infection on two seaweed varieties, namely: (1) Rabbitfish Siganus sp., (2) Epiphytic Filamentous Algae (EFA), (3) Green filamentous algae (Chaetomorpha sp.), (4) Brown seaweeds Sargassum sp., (5) Ice-ice disease, and (6) Fusarium sp. mold. Each attack/infection from six pests and disease was insignificantly different (p>0.05) on both seaweed varieties during observation. The weight gain of green variety slightly increased at 0.15±1.48kg, but the value was lower than brown variety at 0.73±0.39 kg. Therefore, both varieties of K. Alvarezii can be cultured at the same planting period. Pest and disease attacks can be reduced by moving the seaweed to other safer locations.

Small-scale habitat selection by larvae of a reef-building coral

When animals select habitats, they integrate positive and negative cues in the environment that shape their choices about where to live. We conducted a settlement experiment with the larvae of Orbicella faveolata, a reef-building scleractinian coral on Caribbean reefs. We investigated the settlement decisions of O. faveolata larvae in relation to communities of benthic spaceholders and explicitly investigated how benthic communities influence how larvae may make settlement decisions at small spatial scales. Settlement tiles that attracted at least one O. faveolata settler had a significantly different community composition than tiles with no settlers. Red filamentous algae and crustose coralline algae were abundant on tiles with no settlers, while bare substrate was abundant on tiles with settlers. When we analyzed the spatial patterns of coral settlement within tiles, coral settlers avoided areas with sediment, sponges, and red filamentous algae and preferred areas with green filamentous algae. Selection among individual taxa was dominated by selecting against rather than for taxa. Our results show that coral larvae make complex decisions about where to settle even down to the millimeter scale. Importantly, these coral larvae select their habitat by balancing contrasting forces to avoid risks.

Experimental riparian forest gaps and increased sediment loads modify stream metabolic patterns and biofilm composition

AbstractForest management operations greatly influence stream habitats. Canopy clearing and subsequent canopy development during succession, site preparation, and ditching alter the light environment, and increase sediment inputs and nutrient exports from upland and riparian soils to streams. These physicochemical changes affect aquatic biofilms and metabolic rates, and in this study, we tested their individual and combined effects. We used 12 artificial streamside channels, together with a field survey of nine streams in and around clear‐cuts, to assess the effects of shading, substrate composition, and nutrient addition on biofilm biomass and composition, as well as metabolic rates. We found that biofilm biomass and gross primary production (GPP) were light limited in channels under 70% canopy shading. Nitrate additions at this shading level only marginally increased autotrophic biomass, while the rates of respiration increased 10‐fold when carbon was added. Open (unshaded) channels had three times higher rates of GPP compared with channels with 70% shading, and autotrophic biomass was twice as high, largely caused by the colonization of filamentous green algae. These changes to biofilm biomass, composition, and GPP were caused by differences in light alone, as temperature was not affected by the shading treatment. Notably, higher rates of GPP led to no positive effect on net ecosystem production. Further, fine‐grained substrates negatively affected GPP as compared with stone substrates in the experimental channels. In the surveyed streams, the negative effects of fine‐grained substrates exceeded the positive influence of light on biofilm biomass. Altogether, our results highlight the need for riparian management that protects headwaters from unwanted stressors by focusing on preventing sediment erosion and carbon transport in clear‐cuts, while providing variable shade conditions in second‐growth forests.

Impact of mixed microalgal and bacterial species on organic micropollutants removal in photobioreactors under natural light

Single microalgae species are effective at the removal of various organic micropollutants (OMPs), however increased species diversity might enhance this removal. Sixteen OMPs were added to 2 continuous photobioreactors, one inoculated with Chlorella sorokiniana and the other with a microalgal-bacterial community, for 112 d under natural light. Three media were sequentially used in 3 Periods: I) synthetic sewage (d 0–28), II) 10x diluted anaerobically digested black water (AnBW) (d 28–94) and III) 5x diluted AnBW (d 94–112). Twelve OMPs were removed > 30 %, while 4 were < 10 % removed. Removal efficiencies were similar for 9 OMPs, yet the mixed community showed a 2–3 times higher removal capacity (µg OMP/g dry weight) than C. sorokiniana during Period II pseudo steady state. The removal decreased drastically in Period III due to overgrowth of filamentous green algae. This study shows for the first time how microbial community composition and abundance are key for OMPs removal.

Hidden diversity in high-latitude Southern Hemisphere environments: Reinstatement of the genus Rama and description of Vandenhoekia gen. nov. (Cladophoraceae, Ulvophyceae, Chlorophyta), two highly variable genera.

The continental coasts and remote islands in the high-latitude Southern Hemisphere, including the subantarctic region, are characterized by many endemic species, high abundance of taxa, and intermediate levels of biodiversity. The macroalgal flora of these locations has received relatively little attention. Filamentous green algae are prolific in the intertidal of southern islands, but the taxonomy, distribution, and evolutionary history of these taxa are yet to be fully explored, mostly due to the difficulty of access to some of these locations. In this study, we examined specimens of the order Cladophorales from various locations in the high-latitude Southern Hemisphere including the subantarctic (the Auckland Islands, Bounty Islands, Campbell Island, Macquarie Island, and Kerguelen Islands), as well as mainland New Zealand, the Chatham Islands, Chile, and Tasmania. The analyses of the rDNA sequences of the samples revealed the existence of two new clades in a phylogeny of the Cladophoraceae. One of these clades is described as the novel genus Vandenhoekia gen. nov., which contains three species that are branched or unbranched. The amended genus Rama is reinstated to accommodate the other clade, and contains four species, including the Northern Hemisphere "Cladophora rupestris." In Rama both branched and unbranched morphologies are found. It is remarkable that gross morphology is not a predictor for generic affiliations in these algae. This study illustrates that much can still be learned about diversity in the Cladophorales and highlights the importance of new collections, especially in novel locations.

Dynamics of dissolved organic phosphorus in the nearshore of eastern Lake Erie

Abstract The east basin of Lake Erie continues to suffer from blooms of filamentous green algae (primarily Cladophora). Potential management action through reduced phosphorus loadings have and continue to focus on the dissolved inorganic phosphorus pool but other potentially bioavailable phosphorus pools are not always considered. In this study, we describe the dissolved organic phosphorus pool in eastern Lake Erie, with an extensive sampling of four transects along the north shore of the eastern basin from May to September 2019. The dissolved organic phosphorus pool was characterized and quantified using sequential enzymatic hydrolysis to provide information on the enzymatically hydrolysable phosphorus fraction and component monoester P, diester P and a phytase hydrolysable component. These dissolved organic phosphorus fractions were compared to the soluble reactive phosphorus and total dissolved phosphorus pools. Results from this study revealed that a significant fraction (up to 63%) of the dissolved organic phosphorus pool is potentially bioavailable via enzymatic hydrolysis. Vertical differences in soluble reactive phosphorus, total dissolved phosphorus, and phosphate diester pools were also observed when comparing water column with near lake-bed samples, suggesting that the new benthic ecosystem since dreissenid colonization may be a greater source of dissolved inorganic phosphorus to the east basin than prior to colonization.

Fertilizer-induced manganese oxide formation enhances cadmium removal by paddy crusts from irrigation water

Fertilization is a crucial agrological measure for agricultural production that can significantly impact the removal of Cd from irrigation water by paddy crusts (PC). In this study, laboratory and field experiments were conducted to investigate the impact of fertilization at low, medium, and high concentrations on the accumulation of Cadmium (Cd) in PC and the underlying mechanisms involved. The results showed that only low fertilizer concentration could promote the removal of Cd by PC, which reduced the Cd concentration in irrigation water from 19.52 μg/L to 5.35 μg/L. Conversely, medium and high fertilizer concentrations reduced the accumulation of Cd by PC. After fertilizer addition, the proportion of Fe-Mn oxidizable-Cd in PC reached 55 % (with low concentration of fertilizer treatment). The application of low concentration of fertilizer was found to stimulate the growth of filamentous green algae, leading to a significant increase in the relative abundance of sphingomonadaceae (by 1.39 %) and comamonadaceae (by 1.29 %). The XRD, SEM and correlation analysis show that a large amount of manganese oxide is formed on the surface of PC, which increases the fixation of Cd. These findings provide a new perspective for the remediation of heavy metal contamination in paddy fields.

Role of the Lethabo Weir in altering the phytoplankton community structure of the Vaal River, South Africa

During 2012, aerial photographs of the Vaal River, South Africa, showed differences in water colour on either side of the Lethabo Weir. Water upstream of the weir was muddy brown, while water downstream was olive-green. Physical and chemical analyses indicated water quality differences upstream and downstream from the weir; furthermore, microscopic examination of water samples revealed that the colour difference were the result of different types of phytoplankton blooms. The upstream section was dominated by cryptophytes and green algae, while the downstream section experienced a cyanobacterial bloom dominated by Microcystis aeruginosa. The same phenomenon was again observed regularly between 2012 and 2022, and routine monitoring of the phytoplankton assemblage likewise indicated differences in the phytoplankton community composition upstream and downstream of the weir. The upstream section was characterised by various eukaryotic algae; in contrast, frequent and intensive cyanobacteria blooms occurred in the downstream section. Multivariate analyses showed a correlation between the different phytoplankton assemblages and physico-chemical properties of the river water. Many freshwater cyanobacteria and algae taxa are problematic: Microcystis and Dolichospermum produce potent cyanotoxins; flagellated green algae, cryptomonads and dinoflagellates produce substances that cause bad tastes and odours, plus the cells can cause floc disruption during drinking water treatment processes; and certain filamentous green algae and diatoms are known for clogging filters.

Subtle differences in growth rate drive contrasting responses of ephemeral primary producers to recurrent disturbances

AbstractAlthough the importance of time after disturbance is well established in the ecological literature, studies examining how differences in growth rate affect species recovery and persistence in relation to the interval between recurrent perturbations are rare. We examined the response of two ephemeral primary producers inhabiting high‐shore rock pools, epilithic microphytobenthos (EMPB), and green filamentous algae, to disturbance regimes varying for the time interval between consecutive events. Informed from an empirically parametrized growth model's outcomes, we tested the hypothesis that EMPB would be able to recover from more frequent disturbance compared with filamentous algae in a field experiment involving three physical disturbance patterns differing for the clustering degree: high, moderate, and low (20, 40, and 80 days between disturbances). We predicted that: high clustering would prevent the recovery of both taxa; moderate clustering would prevent the recovery of the slower growing taxon only (filamentous algae); both taxa would recover under low clustering. Results showed that EMPB persisted independently of the clustering degree, whereas filamentous algae did not withstand any disturbance regime. Dramatically different effects of disturbance on organisms with subtle differences in their growth rate indicate that even stronger responses may be expected from taxa with more markedly contrasting life histories.

Barranca variabilis sp. nov.—A New Terrestrial Alga of the Genus Barranca (Chaetophorales, Chlorophyta) from the Baikal Region (Russia)

Filamentous green chaetophoralean algae are distributed mainly in aquatic ecosystems, less known from terrestrial habitats. Many of them have a complicated thalli and complex life cycles that make it difficult to determine these organisms by morphology. Description of new representatives of the Chaetophorales continues. In this study, we have explored the filamentous green alga IRK–A 341 from soil of the Baikal Region by light and electron microscopy along with molecular phylogeny. Based on the results of morphological, ecological, and molecular phylogenetic analyses (18S–28S rDNA, tufA), we described the studied alga as the new species, Barranca variabilis sp. nov. The study complements the data on the diversity of soils green filamentous algae, and their biogeography. For the first time, the data on the structure of the cell walls and the cell ultrastructure of Barranca were established. The information on the morphology of the reproductive and resting cells is updated.

Top-down and bottom-up control of phytoplankton communities by zebra mussels Dreissena polymorpha (Pallas, 1771)

Zebra mussels (ZM), Dreissena polymorpha (Pallas, 1771), are one of the most aggressive invasive species. ZM have a strong bidirectional impact on phytoplankton because of their high nutrient excretion rates and high grazing pressure. Furthermore, the interactions between excretion and selective grazing are related to the trophic status of a waterbody and could cause unpredictable changes in phytoplankton. We performed three types of experiments: (i) bottom-up where we measured ZM excretion rates; (ii) top-down where we analyzed the effects of ZM on phytoplankton taxonomic structure via grazing in different trophic conditions; (iii) mesocosm experiment where we estimated the combined top-down and bottom-up effects of ZM on phytoplankton assemblages under different trophic conditions. Our first experiment confirmed high excretion rates of dissolved nutrients (PO43− and NH4+) and dissolved organic carbon (DOC) by ZM. The other experiments revealed selective grazing by ZM, where diatoms were mostly selectively rejected, while green algae were preferred. In the top-down experiment, ZM decreased the total biomass of phytoplankton, while in mesocosm experiments where top-down and bottom-up controls acted simultaneously, we observed increased phytoplankton biomass mainly through increases in filamentous green algae. Our experiments show that ZM can influence phytoplankton through a combination of bottom-up and top-down effects that vary with trophic state.