A trait‐based framework for stream algal communities

The use of trait‐based approaches to detect effects of land use and climate change on terrestrial plant and aquatic phytoplankton communities is increasing, but such a framework is still needed for benthic stream algae. Here we present a conceptual framework of morphological, physiological, behavioural and life‐history traits relating to resource acquisition and resistance to disturbance. We tested this approach by assessing the relationships between multiple anthropogenic stressors and algal traits at 43 stream sites. Our “natural experiment” was conducted along gradients of agricultural land‐use intensity (0–95% of the catchment in high‐producing pasture) and hydrological alteration (0–92% streamflow reduction resulting from water abstraction for irrigation) as well as related physicochemical variables (total nitrogen concentration and deposited fine sediment). Strategic choice of study sites meant that agricultural intensity and hydrological alteration were uncorrelated. We studied the relationships of seven traits (with 23 trait categories) to our environmental predictor variables using general linear models and an information‐theoretic model‐selection approach. Life form, nitrogen fixation and spore formation were key traits that showed the strongest relationships with environmental stressors. Overall, FI (farming intensity) exerted stronger effects on algal communities than hydrological alteration. The large‐bodied, non‐attached, filamentous algae that dominated under high farming intensities have limited dispersal abilities but may cope with unfavourable conditions through the formation of spores. Antagonistic interactions between FI and flow reduction were observed for some trait variables, whereas no interactions occurred for nitrogen concentration and fine sediment. Our conceptual framework was well supported by tests of ten specific hypotheses predicting effects of resource supply and disturbance on algal traits. Our study also shows that investigating a fairly comprehensive set of traits can help shed light on the drivers of algal community composition in situations where multiple stressors are operating. Further, to understand non‐linear and non‐additive effects of such drivers, communities need to be studied along multiple gradients of natural variation or anthropogenic stressors.     

Dominance of autochthonous autotrophic carbon in food webs of heterotrophic rivers

This paper addresses the river heterotrophy paradox, “How can animal biomass within riverine food webs be fueled primarily by autochthonous autotrophic production if the ecosystem as a whole is heterotrophic?”. Reviewed, stable isotope data from tropical, temperate, and arctic rivers provide evidence consistent with the revised riverine productivity model (RPM): “The primary, annual energy source supporting overall metazoan production and species diversity in mid‐ to higher‐trophic levels of most rivers (≥4th order) is autochthonous primary production entering food webs via algal‐grazer and decomposer pathways”. The revised RPM does not conflict with the heterotrophy paradox because: (a) the decomposer (microbial loop) food pathway processes most of the transported, allochthonous and autochthonous carbon and, with algal respiration in some cases, is primarily responsible for a river's heterotrophic state (P/R<1); but (b) biomass production of mid‐ to higher‐trophic levels is principally supported by an algal‐grazer (phytoplankton and benthic microalgae) pathway that is only weakly linked to the decomposer pathway. The reason the algal‐grazer pathway supports the majority of metazoan biomass is that allochthonous carbon is mostly recalcitrant, whereas carbon from autochthonous primary production, though much less plentiful, is commonly more labile (easier to assimilate), contains more energy per unit mass, and is typically preferred by metazoa.     

In vitro culture and conservation of microalgae: Applications for aquaculture, biotechnology and environmental research

Summary Microalgae are a highly diverse group of unicellular organisms comprising the eukaryotic protists and the prokaryotic cyanobacteria or blue-green algae. The microalgae have a unique environmental status; being virtually ubiquitous in euphotic aquatic niches, they can occupy extreme habitats ranging from tropical coral reefs to the polar regions, and they contribute to half of the globe’s photosynthetic activity. Furthermore, they form the basis of the food chain for more than 70% of the world’s biomass. Microalgae are a valuable environmental and biotechnological resource, and the aim of this review is to explore the use of in vitro technologies in the conservation and sustainable exploitation of this remarkable group of organisms. The first part of the review evaluates the importance of in vitro methods in the maintenance and conservation of microalgae and describes the central role of culture collections in applied algal research. The second part explores the application of microalgal in vitro technologies, particularly in the context of the aquaculture and biotechnology industries. Emphasis is placed upon the exploitation of economically important algal products including aquaculture feed, biomass production for the health care sector, green fertilizers, pigments, vitamins, antioxidants, and antimicrobial agents. The contribution that microalgae can make to environmental research is also appraised; for example, they have an important role as indicator organisms in environmental impact assessments. Similarly, designated culture collection strains of microalgae are used for ecotoxicity testing. Throughout the review, emphasis is placed on the application of in vitro techniques for the continued advancement of microalgal research. The paper concludes by assessing future perspectives for the novel application of microalgae and their products.     

Utility of field-based artificial streams for assessing effluent effects on riverine ecosystems

Experimentation using field-based artificial streams provides a promising, complimentary approach to biomonitoring assessments because artificial streams provide control over relevant environmental variables and true replication of treatments. We have used large and small artificial stream systems, based in the field, to examine the effect of treated bleached kraft pulp mill effluent (BKME) on the benthos of three large rivers in western Canada. Under natural regimes of temperature, water chemistry, and insolation, these artificial streams provide current velocities and substrata to food chains or food webs that are representative of those in the study river. With these tools we have shown that BKME stimulated mayfly growth in the Thompson River above that which could be accounted for by fertilization of their algal food supply. In contrast, moulting frequency was inhibited at high BKME concentrations. Results from artificial streams also indicate that increased algal biomass and abundances of benthic communities downstream of BKME outfalls were induced by nutrient enrichment from the effluent. BKME treatments did not change diatom species richness in the Fraser River, or diatom species diversity in either the Athabasca or Fraser Rivers. Artificial streams provide a means of understanding the mechanisms of stressor effects over a continuum ranging from single stressor effects on specific taxa to the effects of multiple stressors on communities and ecosystems. Because riverside deployment provides environmental realism within a replicated experimental design, this approach can (i) address questions that cannot be examined using laboratory tests or field observations, (ii) improve our mechanistic understanding of stressor effects on riverine ecosystems, and (iii) can contribute directly to the development, parameterization, and testing of models for predicting ecosystem-level responses.     

Mechanism and challenges in commercialisation of algal biofuels

Biofuels made from algal biomass are being considered as the most suitable alternative energy in current global and economical scenario. Microalgae are known to produce and accumulate lipids within their cell mass which is similar to those found in many vegetable oils. The efficient lipid producer algae cell mass has been reported to contain more than 30% of their cell weight as lipids. According to US DOE microalgae have the potential to produce 100 times more oil per acre land than any terrestrial plants. This article reviews up to date literature on the composition of algae, mechanism of oil droplets, triacylglycerol (TAG) production in algal biomass, research and development made in the cultivation of algal biomass, harvesting strategies, and recovery of lipids from algal mass. The economical challenges in the production of biofuels from algal biomass have been discussed in view of the future prospects in the commercialisation of algal fuels.     

典型红树林生态系统藻类多样性及其在生态过程中的作用

藻类是红树林生态系统重要的生物类群, 根据生态习性可分为浮游植物、底栖微藻和大型藻类三个生态类群, 它们在红树林生态系统生物多样性、初级生产、元素循环等方面起着重要作用。但在红树林生态系统中, 关注重点多集中在红树植物和动物, 对其中的藻类重视不够, 且多数研究集中在近20年以及亚洲的红树林区。事实上, 红树林生态系统藻类非常丰富, 其多样性研究有助于深入揭示红树林生态系统的结构与功能。本文介绍了红树林生态系统藻类的组成类群及其重要性, 重点对红树林区浮游植物、底栖硅藻和大型海藻的种类组成、地理分布及其与初级生产力、水质污染、元素循环、碳库形成等生态过程中的作用的研究动态和进展等进行了总结。根据已有研究, 红树林区浮游植物和底栖硅藻的种类数一般为几十到上百种, 其中硅藻在种类和数量上都占绝对优势, 它们是重要的初级生产者、饵料生物和水质污染指示生物; 红树林区底栖大型藻类主要由红藻、绿藻、褐藻、蓝藻组成, 绿藻的种类较多, 红藻在数量上占优势; 藻类是红树林湿地碳库的重要贡献者, 在红树林湿地生态系统碳汇和碳循环中起重要作用。红树林生态系统是个高度动态和异质的系统, 今后应加强红树林藻类多样性的长周期、大尺度变化及不同生境藻类的综合研究, 关注大陆径流和潮汐对藻类多样性和蓝碳的影响, 借助沉积物藻类记录, 探明红树林区藻类的长周期变化, 反演气候变化和人类活动对红树林生态系统的影响过程和机制。     

Insight into the studies of the practical use of microalgae in the former Soviet Union

Microalgae have been intensively cultivated and used in the national economy of the Soviet Union in Russia (Moscow, Leningrad, Pushcino, Krasnoyarsk, Irkutsk), the Ukraine, Byelorussia (Minsk), Azerbaijan (Baku), Uzbekistan (Tashkent), Latvia (Riga) and other former Soviet republics. The first studies on the practical use of microalgae started already at the beginning of last century and were connected with treatment of waste water in biological ponds. Ecophysiological studies of marine plankton algae in mono- and mixed cultures as well as in experimental systems with zooplankton organisms started at the end of the 1950s. In the 1960s, started to apply different equipments for cultivation of microalgae in open water basins and closed ecological systems. Research innovations were introduced in agriculture. The productivity of aquatic ecosystems and the distribution of energy within food chains were studied. Intensive research on microalgae continued, paying attention to the chemical composition, physiological and biochemical features. Nutrient supply appeared as one of the main problem for productivity of algal cultures, along with the procession, biochemistry of nutrients and nutrition value of organic matter produced by algae. The most attention was paid to the Chroococcales proteins and possibilities for their use in man-made closed ecological systems. The potential use of microalgae for regeneration of the atmosphere and purification of water in spacecrafts was studied. During the 1970s attention was paid to the role of algae in self-purification processes and biodegradation of surface-active substances in water bodies. Research in microalgae as bioindicators for the assessment of environment quality of aquatic ecosystems and as test objects for biotesting of natural and waste waters was conducted from the 1970s to 1980s.     

Biotechnological potential of immobilized algae for wastewater N, P and metal removal: A review

This presentation comprises a review on the use of immobilized algae for wastewater nitrogen, phosphorus and metal removal purposes. Details of the use of immobilized algae, the techniques of immobilization and the effects of immobilization on cell function are included. Particularly relevant in their use for heavy metal removal from wastewaters; upon enriching the biomass in metal, can be recoverd, thereby providing economic advantages. The use of immobilized microalgae in these processes is very adequate and offers significant advantages in bioreactors. The future of this area of algal cell biotechnology is considered.     

Roles of benthic algae in the structure,function, and assessment of stream ecosystems affected by acid mine drainage

Tens of thousands of stream kilometers worldwide are degraded by a legacy of acid loads, high metal concentrations, and altered habitat caused by acid mine drainage (AMD) from abandoned underground and surface mines. As the primary production base in streams, the condition of algal‐dominated periphyton communities is particularly important to nutrient cycling, energy flow, and higher trophic levels. Here, we synthesize current knowledge regarding how AMD‐associated stressors affect (i) algal communities and their use as ecological indicators, (ii) their functional roles in stream ecosystems, and (iii) how these findings inform management decisions and evaluation of restoration effectiveness. A growing body of research has found ecosystem simplification caused by AMD stressors. Species diversity declines, productivity decreases, and less efficient nutrient uptake and retention occur as AMD severity increases. New monitoring approaches, indices of biological condition, and attributes of algal community structure and function effectively assess AMD severity and effectiveness of management practices. Measures of ecosystem processes, such as nutrient uptake rates, extracellular enzyme activities, and metabolism, are increasingly being used as assessment tools, but remain in their infancy relative to traditional community structure‐based approaches. The continued development, testing, and implementation of functional measures and their use alongside community structure metrics will further advance assessments, inform management decisions, and foster progress toward restoration goals. Algal assessments will have important roles in making progress toward improving and sustaining the water quality, ecological condition, and ecosystem services of streams in regions affected by the legacy of unregulated coal mining.     

Ecological assessments with algae: a review and synthesis

Algae have been used for a century in environmental assessments of water bodies and are now used in countries around the world. This review synthesizes recent advances in the field around a framework for environmental assessment and management that can guide design of assessments, applications of phycology in assessments, and refinements of those applications to better support management decisions. Algae are critical parts of aquatic ecosystems that power food webs and biogeochemical cycling. Algae are also major sources of problems that threaten many ecosystems goods and services when abundances of nuisance and toxic taxa are high. Thus, algae can be used to indicate ecosystem goods and services, which complements how algal indicators are also used to assess levels of contaminants and habitat alterations (stressors). Understanding environmental managers' use of algal ecology, taxonomy, and physiology can guide our research and improve its application. Environmental assessments involve characterizing ecological condition and diagnosing causes and threats to ecosystems goods and services. Recent advances in characterizing condition include site‐specific models that account for natural variability among habitats to better estimate effects of humans. Relationships between algal assemblages and stressors caused by humans help diagnose stressors and establish targets for protection and restoration. Many algal responses to stressors have thresholds that are particularly important for developing stakeholder consensus for stressor management targets. Future research on the regional‐scale resilience of algal assemblages, the ecosystem goods and services they provide, and methods for monitoring and forecasting change will improve water resource management.     

The contribution of riffles and riverine wetlands to benthic macroinvertebrate biodiversity

Benthic macroinvertebrates collected in biomonitoring programs are a potentially valuable source of biodiversity information for conservation planning in river ecosystems. Biomonitoring samples often focus on riffles; however, we have only partially assessed the extent to which riffle biodiversity patterns reflect those of other river habitats, particularly riverine wetlands. Using a standard biomonitoring protocol, we assessed the richness, composition and magnitude of variation of macroinvertebrate assemblages in riffles across 18 sites in the Nashwaak river catchment, and compared these to samples from adjacent riverine wetlands. Despite containing on average fewer taxa per site than riffles, riverine wetlands demonstrated similar levels of taxon richness at the catchment scale. There was strong assemblage separation between habitat types, and riverine wetlands displayed significantly greater assemblage variation than riffles. Riffles and riverine wetlands did not demonstrate significant correlations in terms of taxon richness or assemblage variation, though this may be partially due to the scale at which we collected observations. Principal component analysis with vector fitting suggested that (log) sub-catchment area was an important factor structuring riffle assemblages, while depth was potentially important for riverine wetland assemblages. We discuss the implications of these results for the use of biomonitoring data in systematic conservation planning, and identify future research that will improve our understanding of the role riverine wetlands play in maintaining catchment biodiversity and ecosystem processes.     

Life-cycle assessment of microalgae culture coupled to biogas production

Due to resource depletion and climate change, lipid-based algal biofuel has been pointed out as an interesting alternative because of the high productivity of algae per hectare and per year and its ability to recycle CO₂ from flue gas. Another option for taking advantage of the energy content of the microalgae is to directly carry out anaerobic digestion of raw algae in order to produce methane and recycle nutrients (N, P and K). In this study, a life-cycle assessment (LCA) of biogas production from the microalgae Chlorella vulgaris is performed and the results are compared to algal biodiesel and to first generation biodiesels. These results suggest that the impacts generated by the production of methane from microalgae are strongly correlated with the electric consumption. Progresses can be achieved by decreasing the mixing costs and circulation between different production steps, or by improving the efficiency of the anaerobic process under controlled conditions. This new bioenergy generating process strongly competes with others biofuel productions.     

Micro and macroalgal biomass: A renewable source for bioethanol

Population outburst together with increased motorization has led to an overwhelming increase in the demand for fuel. In the milieu of economical and environmental concern, algae capable of accumulating high starch/cellulose can serve as an excellent alternative to food crops for bioethanol production, a green fuel for sustainable future. Certain species of algae can produce ethanol during dark-anaerobic fermentation and thus serve as a direct source for ethanol production. Of late, oleaginous microalgae generate high starch/cellulose biomass waste after oil extraction, which can be hydrolyzed to generate sugary syrup to be used as substrate for ethanol production. Macroalgae are also harnessed as renewable source of biomass intended for ethanol production. Currently there are very few studies on this issue, and intense research is required in future in this area for efficient utilization of algal biomass and their industrial wastes to produce environmentally friendly fuel bioethanol.     

Algal biofilms on tree bark to monitor airborne pollutants

Algae are used in biomonitoring systems to detect water or soil pollution. So it is conceivable to establish a biomonitoring system for the detection of airborne pollutants (ozone and particulate matter (PM-10)) in urban habitats by algae. Autotrophic biofilms are widely present, cover nearly every exposed surface, especially tree bark and consist of a large variety of species of algae, cyanobacteria and fungi. To explore the diversity of green algae at different air pollution monitoring sites we choose trees with different structures of bark at three locations in and near Leipzig. We compared the measured levels of air pollution with the algal species and communities present. The sites differed in the quality and amount of airborne pollutants, among which we concentrated on ozone and particulate matter (PM-10). The collection sites were Leipzig-Centre, Leipzig-West and a forest area east of Leipzig (Collmberg). Autotrophic biofilms were collected, algae cultures established and taxonomic and morphological studies were carried out with light microscopy. Green algae were present on tree bark at all sites and forty-eight different algal species and cyanobacteria were isolated. Preliminary results suggested a correlation between pollutants and occurrence of some specific algal species and the specific algal assemblages at a given site. It is concluded that this could provide the basis for a biomonitoring system involving aero-terrestrial algae for the detection of airborne pollutants. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

Axenic cultures for microalgal biotechnology: Establishment,assessment, maintenance,and applications

The impact of microalgae (including blue-green algae or cyanobacteria) on human life can be both beneficiary and deleterious. While microalgae can be cultivated and used as feedstocks for the production of bioenergy and high value-added products in nutraceuticals, pharmaceuticals, and aquaculture feeds, some microalgae cause harmful algal blooms (HABs) that cause large-scale mortality in aquatic environments around the world. Thus, with the development of microalgal biotechnology and increasing concern about HABs, research on microscopic algae has increased significantly. However, this growth of academic research and application fields has been hindered by difficulties in obtaining axenic cultures. Therefore, this review provides a brief explanation of diverse establishment techniques, along with their strengths and weaknesses, with the hope of facilitating successful axenic cultures. A compilation of research fields and relevant important findings is also presented to clarify the importance of pure algal cultures. Finally, several controversial and sometimes overlooked issues related to the establishment, maintenance, and utilization of axenic cultures are discussed.     

Effects of grazer immigration and nutrient enrichment on an open algae-grazer system

After disturbance, recovery dynamics of local populations depend on arrival rates of immigrants and local growth conditions. We studied the effects of herbivore immigration rates and nutrient enrichment on the dynamics of grazing insect larvae, benthic microalgae, and filamentous macroalgae recovering from low local densities in an open stream system. The two types of algae approximate a trade‐off between capabilities for growing at low resource levels and resisting herbivory. Many microalgae achieve relatively high growth rates at low nutrient levels but are vulnerable to grazers, whereas many macroalgae require high nutrient levels for growth but become increasingly defended with filament growth. We hypothesized that macroalgae should benefit more strongly than microalgae from increasing nutrient levels and decreasing grazer immigration rates, because both conditions increase macroalgal chances to grow into a size refuge from herbivory. We created a gradient of nutrient concentrations and manipulated drift immigration rates of macroinvertebrates. Macro‐ and microalgal biomass and the relative contribution of macroalgae to total algal biomass increased with increasing nutrient enrichment and decreased with increasing grazer immigration. Grazer densities responded positively to nutrient enrichment. The densities of large baetids responded positively to higher immigration rates of large baetids, whereas small baetids and chironomid larvae showed the opposite response. Per capita emigration of small baetids decreased with increasing algal biomass. The data suggest that large baetids negatively affected algal biomass and that small baetid and chironomid densities tracked resource levels set by nutrient enrichment and large baetids. Our experiments highlight the prospects of integrating disturbance with nutrient supply, immigration rates and local trophic interactions (determining recovery trajectories) into conceptual models of open system dynamics. We suggest that recovery trajectories towards micro‐ or macroalgal dominated states may depend on the spatial scale of disturbance relative to the movement ranges of migrating grazers and to nutrient supply.     

Temperature indirectly affects benthic microalgal diversity by altering effects of top–down but not bottom–up control

Understanding the ecological mechanisms that underlie species diversity decline in response to environmental change has become an urgent objective in current ecological research. Not only direct (lethal) effects on single species but also indirect effects altering biotic interactions between species within and across trophic levels comprise the driving force of ecosystem change. In an experimental marine benthic microalgae–grazer system we tested for indirect effects of moderate temperature change on algal diversity by manipulation of temperature, nutrient supply and grazer density. In our model system warming did not exert indirect effects on microalgal diversity via effects on resource competition. However, moderate warming strengthened consumer control and thereby indirectly affected algal community structure which ultimately resulted in decreased diversity. Only in low temperature and low nutrient regimes did the antagonizing mechanisms of bottom–up and top–down regulation establish a balancing effect on algal diversity within 29 days (corresponding to 15–29 algae generations). Effects of thermal habitat change did not appear before 9–18 algae generations, which points to the relevance of longer‐term experiments and ecological monitoring in order to separate transient biotic responses and subtle changes of community dynamics in consequence to global change.     

Development and comparison of stream indices of biotic integrity using diatoms vs. non-diatom algae vs. a combination

Stream algal indices of biotic integrity (IBIs) are generally based entirely or largely on diatoms, because non-diatom (“soft”) algae can be difficult to quantify and taxonomically challenging, thus calling into question their practicality and cost-effectiveness for use as bioindicators. Little has been published rigorously evaluating the strengths of diatom vs. soft algae-based indices, or how they compare to indices combining these assemblages. Using a set of ranked evaluation criteria, we compare indices of biotic integrity (IBIs) (developed for southern California streams) that incorporate different combinations of algal assemblages. We split a large dataset into independent “calibration” and “validation” subsets, then used the calibration subset to screen candidate metrics with respect to degree of responsiveness to anthropogenic stress, metric score distributions, and signal-to-noise ratio. The highest-performing metrics were combined into a total of 25 IBIs comprising either single-assemblage metrics (based on either diatoms or soft algae, including cyanobacteria) or combinations of metrics representing the two assemblages (for “hybrid IBIs”). Performance of all IBIs was assessed based on: responsiveness to anthropogenic stress (in terms of surrounding land uses and a composite water-chemistry gradient) using the validation data, and evaluated based on signal-to-noise ratio, metric redundancy, and degree of indifference to natural gradients. Hybrid IBIs performed best overall based on our evaluation. Single-assemblage IBIs ranked lower than hybrids vis-à-vis the abovementioned performance attributes, but may be considered appropriate for routine monitoring applications. Trade-offs inherent in the use of the different algal assemblages, and types of IBI, should be taken into consideration when designing an algae-based stream bioassessment program.     

An analytical perspective on detection,screening, and confirmation in phycology,with particular reference to toxins and toxin‐producing species

Knowledge concerning the ability of microalgae to produce metabolites of interest such as toxins or high‐value secondary metabolites requires exhaustive details to be supplied on how the research was conducted. These should include the microalgal species and strain characterization, the culture conditions, the cell density, and physiological state at the time of harvesting, the harvesting method, the sample pre‐treatment protocol, and the subsequent instrumental analytical separation/detection system. In this comment, we discuss issues that affect algal research from an analytical chemistry perspective, particularly (i) the need to specify detection capabilities of the entire method (i.e., limits of detection or threshold detection levels), which we illustrate in relation to classification of a species or strain as being “toxin producing” or “non‐toxin producing”; and (ii) the requirements that have to be satisfied to confirm a microalgal species (new or not) as a producer of a particular chemical of interest for phycologists, which again we illustrate in relation to toxins. A successful collaboration among phycologists and analytical chemists will only be achieved as a result of a synergistic collaboration between the two disciplines, with a reciprocal understanding at least at a background level.     

Progress on lipid extraction from wet algal biomass for biodiesel production

Lipid recovery and purification from microalgal cells continues to be a significant bottleneck in biodiesel production due to high costs involved and a high energy demand. Therefore, there is a considerable necessity to develop an extraction method which meets the essential requirements of being safe, cost‐effective, robust, efficient, selective, environmentally friendly, feasible for large‐scale production and free of product contamination. The use of wet concentrated algal biomass as a feedstock for oil extraction is especially desirable as it would avoid the requirement for further concentration and/or drying. This would save considerable costs and circumvent at least two lengthy processes during algae‐based oil production. This article provides an overview on recent progress that has been made on the extraction of lipids from wet algal biomass. The biggest contributing factors appear to be the composition of algal cell walls, pre‐treatments of biomass and the use of solvents (e.g. a solvent mixture or solvent‐free lipid extraction). We compare recently developed wet extraction processes for oleaginous microalgae and make recommendations towards future research to improve lipid extraction from wet algal biomass.