Natural Algal Communities Research Articles

Comparison of single strain, natural algal communities and a native algal bloom: Application for wastewater treatment and biomass generation in cassava biogas effluent

AbstractPhycoremediation of Chlorella sorokiniana P21 as indigenous strain (P21), four algal communities from different wastewater treatment ponds (P1, P2, P3 and P4) and a native algal bloom (CTRL) were examined to treat cassava biogas effluent wastewater (CBEW) and generate algal biomass. All cultures showed higher biomass production in unsterilized CBEW than in the sterilized CBEW, whereas nutrient removal efficiency was not significantly different in both conditions for all cultures. Verhulst kinetics models showed P21 culture has the highest maximum biomass (1440.94 mg L−1), whereas P3 showed the highest growth rate (0.68 day−1). The removal efficiencies of these cultures for nitrate, phosphate and chemical oxygen demand were above 75%. Iron coagulants attained the removal to be more than 90% only in P21 culture. Indigenous and algal community cultures had similar potencies to treat wastewater, and thus, this result showed vast potency of phycoremediation using various inoculum sources.

Single-cell RNA sequencing of batch Chlamydomonas cultures reveals heterogeneity in their diurnal cycle phase.

The photosynthetic unicellular alga Chlamydomonas (Chlamydomonas reinhardtii) is a versatile reference for algal biology because of its ease of culture in the laboratory. Genomic and systems biology approaches have previously described transcriptome responses to environmental changes using bulk data, thus representing the average behavior from pools of cells. Here, we apply single-cell RNA sequencing (scRNA-seq) to probe the heterogeneity of Chlamydomonas cell populations under three environments and in two genotypes differing by the presence of a cell wall. First, we determined that RNA can be extracted from single algal cells with or without a cell wall, offering the possibility to sample natural algal communities. Second, scRNA-seq successfully separated single cells into nonoverlapping cell clusters according to their growth conditions. Cells exposed to iron or nitrogen deficiency were easily distinguished despite a shared tendency to arrest photosynthesis and cell division to economize resources. Notably, these groups of cells not only recapitulated known patterns observed with bulk RNA-seq but also revealed their inherent heterogeneity. A substantial source of variation between cells originated from their endogenous diurnal phase, although cultures were grown in constant light. We exploited this result to show that circadian iron responses may be conserved from algae to land plants. We document experimentally that bulk RNA-seq data represent an average of typically hidden heterogeneity in the population.

Luxury phosphorus uptake in microalgae

Phosphorus (P) is central to storing and exchange of energy and information in cells including those of microalgae. The overwhelming majority of microalgae are naturally acclimated to low-P environments; hence, they are capable of taking up and storing P in large amounts whenever it becomes available. The ability to take up more P than necessary for immediate growth is termed “luxury uptake.” Understanding this phenomenon constitutes a crucial insight into nutrient-driven processes in natural algal communities such as harmful algal blooms, as well as into the operation of algae-based technologies for sustainable usage of P such as recycling of the nutrient from wastewater to biofertilizers. The bulk of P acquired during luxury uptake is stored in the form of inorganic polyphosphate, the compound with nearly ubiquitous presence and multifaceted function in the cell. Although seminal works on luxury P uptake and polyphosphate metabolism were carried out fifty years ago, application of modern “omics” approaches and advanced imaging microscopy techniques enabled obtaining a deeper mechanistic insight into these processes. Nevertheless, our knowledge about luxury P uptake remains much more limited in comparison with that about P shortage and mechanism tolerance to this stress in microalgae. In this review the knowledge of luxury P uptake originating from classical phycological and biochemical methods is confronted with the recently obtained understanding of molecular mechanisms of P transport to the cell, polyphosphate biosynthesis, regulation, and genetic control of these processes. Biotechnological implications of the knowledge about luxury P uptake accumulated to date are discussed in the context of algae-based approaches to sustained usage of nutrients and industrial cultivation of microalgae.

Assessing hydrothermal liquefaction for the production of bio-oil and enhanced metal recovery from microalgae cultivated on acid mine drainage

The hydrothermal liquefaction (HTL) of algal biomass is a promising route to viable second generation biofuels. In this investigation HTL was assessed for the valorisation of algae used in the remediation of acid mine drainage (AMD). Initially the HTL process was evaluated using Arthrospira platensis (Spirulina) with additional metal sulphates to simulate metal remediation. Optimised conditions were then used to process a natural algal community (predominantly Chlamydomonas sp.) cultivated under two scenarios: high uptake and low uptake of metals from AMD. High metal concentrations appear to catalyse the conversion to bio-oil, and do not significantly affect the heteroatom content or higher heating value of the bio-oil produced. The associated metals were found to partition almost exclusively into the solid residue, favourable for potential metal recovery. High metal loadings also caused partitioning of phosphates from the aqueous phase to the solid phase, potentially compromising attempts to recycle process water as a growth supplement. HTL was therefore found to be a suitable method of processing algae used in AMD remediation, producing a crude oil suitable for upgrading into hydrocarbon fuels, an aqueous and gas stream suitable for supplementing the algal growth and the partitioning of most contaminant metals to the solid residue where they would be readily amenable for recovery and/or disposal.

Lipid markers of diet history and their retention during experimental starvation in the Bering Sea euphausiid Thysanoessa raschii

Two extended pulsed feeding experiments, following the spring bloom period, investigated lipid retention in the prominent Bering Sea euphausiid (krill) Thysanoessa raschii. These experiments occurred during late spring and early summer of 2010. Concurrent taxonomic analysis of the natural algal community allowed prey type to be linked to lipid composition of the natural communities. In late spring, experimental periods of feeding followed by starvation showed an overall decrease in total lipid for T. raschii. In early summer, no consistent trend was observed for total lipid with the visible presence of storage lipid in some animals. Polar lipids, as phospholipids, were the dominant krill lipid class in both experiments constituting ≥88% of total lipid, and triacylglycerols reached a maximum of 5% of total lipid. The sterols cholesterol and brassicasterol+desmosterol comprised 98–99% of total sterol abundances in T. raschii throughout both experiments, even after feeding periods when alternative sterols (i.e. the algal sterol 24-methylenecholesterol) accounted for up to 39% of sterols in potential food particles. Cholesterol abundance and concentration increased during both incubations, likely due to the metabolism of dietary sterols. Major fatty acids observed in krill included C14:0n, C16:0n, C16:1(n-7), C18:1(n-7), C18:1(n-9), C20:5(n-3), and C22:6(n-3) with the diatom-attributed C16:1(n-7) decreasing in abundance and concentration during starvation. Low concentrations of the dinoflagellate-derived sterol and a novel C28:8 PUFA, typically found in dinoflagellates and prymnesiophytes, indicated predation on protozooplankton in early summer when diatom abundances were low. The stability of lipid distributions over periods of starvation and intermittent feeding suggest that fatty acid and sterol biomarkers present in this polar euphausiid principally reflect long-term diet history rather than short-term feeding episodes.

Contrasting responses of phytoplankton and benthic algae to recent nutrient enrichment in Arctic tundra ponds

Summary Tundra ponds are a dominant feature on the Arctic Coastal Plain, but their response to warming, especially in the long‐term, is largely unknown. Our study assessed changes in algal nutrient limitation over a 40‐year period in historically studied ponds that may have been affected by either human development in the region or increased temperatures leading to permafrost thaw and nutrient release. We also compared nutrient limitation of algae in the pelagic and benthic zones at a landscape level. Nutrient diffusing substrata (NDS) and bottled nutrient incubations, which expose natural algal communities to known quantities of nitrogen (N) and phosphorus (P), were utilised to determine benthic and phytoplankton algal nutrient limitation, respectively, in a series of ponds on the north slope of Alaska, USA. This included ponds where phytoplankton nutrient limitation was examined in 1971–1973 as part of the International Biological Program (IBP), as well as ponds in a remote protected area and others near the village of Barrow. Nutrient limitation status of phytoplankton has changed since the original IBP study 40 years ago from P limitation to NP co‐limitation. One‐third of regional phytoplankton enrichment experiments indicated no nutrient limitation of algal growth, and none exhibited single‐nutrient P limitation. This shift in nutrient limitation was coincident with increased water column nutrients due to degrading permafrost, and to the expansion into the ponds of macrophytes, which may compete with algae for available nitrogen. A comparison of pelagic and benthic experiments across the landscape revealed differences among these zones with a predominance of NP limitation of phytoplankton and absence of nutrient limitation in the benthic zone, reflecting contrasting nutrient limitation status within the same ponds. Permafrost thaw is probably reintroducing previously frozen stores of P or N to the sediment surface, which are quickly taken up by periphyton but become limited in the water column. Grazing by invertebrates, which were not excluded from the benthic assays, may also have influenced the results. While ponds within the village of Barrow had higher nutrient and algae levels, there was no obvious effect of urban development on nutrient limitation status, nor did development appear to have influenced the historic IBP pond sites.

Dewatering as a non-toxic control of nuisance midge larvae in algal wastewater treatment floways.

Attached-algae floways have tremendous potential for use in wastewater treatment because natural algal communities show high nutrient removal efficiencies, have low operating costs, and are easy to maintain. Algal wastewater floways may also serve as a sustainable option for producing renewable energy because algae grow rapidly, are easily harvested, and can serve as a source of biomass for biofuel. However, pests such as chironomids (Diptera) colonize open channel periphyton floways and their larvae damage the biofilms. While pesticides can control midge larvae, little information is known about alternative, non-toxic controls. This study examined the effectiveness of periodic, short-term dewatering (4 hours every 9 days) on midge abundance and periphyton growth in 16 recirculating, outdoor floways (3 m long, 0.1 m wide). We compared midge abundance and algal accumulation (chlorophyll a, b, c, and pheophytin) among control (n=8) and dewatered (n=8) floways filled with secondarily treated wastewater (27 days, 10 hours of daylight). Dewatered flumes had 42% fewer midges and 28-49% lower algal productivity (as measured by chlorophyll a, b, c, and pheophytin pigments). Chlorophyll a production rates averaged (±1 SD) 0.5±0.2 μg/cm2/day in control floways compared to 0.3±0.1 μg/cm2/day dewatered floways. Short-term dewatering effectively reduced midges but also damaged periphyton. To maximize the recovery of periphyton biomass, operators should harvest periphyton from floways during dewatering events before periphyton is damaged by desiccation or direct exposure to sunlight.

An Engineered Community Approach for Industrial Cultivation of Microalgae.

Although no species lives in isolation in nature, efforts to grow organisms for use in biotechnology have generally focused on a single-species approach, particularly where a product is required at high purity. In such scenarios, preventing the establishment of contaminants requires considerable effort that is economically justified. However, for some applications in biotechnology where the focus is on lower-margin biofuel production, axenic culture is not necessary, provided yields of the desired strain are unaffected by contaminants. In this article, we review what is known about interspecific interactions of natural algal communities, the dynamics of which are likely to parallel contamination in industrial systems. Furthermore, we discuss the opportunities to improve both yields and the stability of cultures by growing algae in multi-species consortia.

Use of live, fluorescently-labeled algae for measuring microzooplankton grazing in natural communities

Here, our goal was to develop a technique for staining live algae with vital fluorochromes and to further test whether this method may serve as a tool for examining the trophic roles and functional diversity of microzooplankton. We tested 4 fluorochromes on a total of 10 phytoplankton species, out of which only 3 proved effective, and only on some of the species tested. The fluorochrome Vybrant did not dye any algal species, CellTracker Blue successfully dyed 2 nanoflagellate species (Isochrysis galbana and Tetraselmis sp.) and one dinoflagellate (Heterocapsa sp.), and LysoSensor and LysoTracker each dyed 2 diatom species (Thalassiosira weissflogii and Skeletonema costatum). Further experiments with the 2 most successful fluorochromes (CellTracker and LysoSensor) indicated that optimum incubation times ranged from 4 to 8h and that the percentage of stained cells was not improved at concentrations higher than 10μM and 2μM for CellTracker and LysoSensor, respectively. The residence times of the fluorochromes under natural light conditions were greater than 24h (60–80% of stained algae). Labeling algae with CellTracker had no significant effect on their growth rate or C:N molar ratio. LysoSensor, however, had minor (although significant) effects on the growth rates of stained vs. unstained algae. Bottle grazing experiments showed that Oxyrrhis marina grazed on unstained nanoflagellate species at equal rates to those stained with CellTracker; however, a positive discrimination for stained cells was detected when Gyrodinium dominans was used as the grazer. We also measured microzooplankton ingestion rates in natural algal communities by combining the dilution method with the addition of live algae into a natural plankton suspension. The addition of stained algae did not significantly affect phytoplankton growth or mortality rates due to microzooplankton grazing. The low toxicity of fluorochromes and the easy visualization of labeled algae inside predators make this method a useful tool for estimating grazing rates of microzooplankton and for the quantification of different trophic interactions among protists in the microbial food web. However, given the limited number of algae species successfully stained further research is needed to obtain more universal dyes.

Changes in Diatom Biodiversity in Lake Sinclair, Baldwin County, Georgia, USA

The effects of increased water temperature on algal community composition were investigated in Lake Sinclair, Baldwin County, Georgia, USA. The lake received waste cooling water from a coal burning power plant. Discharges of recycled lake water were, on average, 15°C ± 1.5°C (and up to 23°C) warmer than typical ambient temperatures. Seasonal changes in algal composition were observed, and the warmer sample site had a greater diversity of diatom species year round independent of changes in temperature. Thermal pollution created a high percent dissimilarity between diatoms at the warmer site and the remainder of the lake. Species turnover observed in natural samples was not detected for the warmer site. Anthropogenic thermal pollution was implicated as the factor inducing changes in the natural algal community composition, which may impact other trophic levels and ultimately the overall ecology of Lake Sinclair.

Inorganic carbon acquisition in algal communities: are the laboratory data relevant to the natural ecosystems?

Most of the experimental work on the effects of ocean acidification on the photosynthesis of algae has been performed in the laboratory using monospecific cultures. It is frequently assumed that the information obtained from these cultures can be used to predict the acclimation response in the natural environment. CO(2) concentration is known to regulate the expression and functioning of the CCMs in the natural communities; however, ambient CO(2) can become quite variable in the marine ecosystems even in the short- to mid-term. We propose that the degree of saturation of the photosynthesis for a given algal community should be defined in relation to the particular characteristics of its habitat, and not only in relation to its taxonomic composition. The convenience of high CO(2) experiments to infer the degree of photosynthesis saturation by CO(2) in the natural algal communities under the present ocean conditions, as well as its trend in a coming future is discussed taking into account other factors such as the availability of light and nutrients, and seasonality.

Substratum as a driver of variation in periphyton chlorophyll and productivity in lakes

Quantifying periphyton (attached algal) contributions to autotrophic production in lakes is confounded by properties of substratum that affect community biomass (as chlorophyll content) and productivity. We compared chlorophyll content and productivity of natural algal communities (phytoplankton, epipelon, epilithon, epixylon, and epiphyton) experiencing high (.10%) incident radiation in lakes in the US, Greenland, and Quebec, Canada. Chlorophyll content and productivity differed significantly among regions, but they also differed consistently among communities independent of region. Chlorophyll content of periphyton on hard substrata (rocks and wood) was positively related to water- column total P (TP), whereas chlorophyll content of algae on sediment (epipelon) and TP were not significantly related. Chlorophyll content was up to 1003 higher on sediments than on hard substrata. Within regions, chlorophyll-specific primary productivity was highest for phytoplankton and lowest for epipelon. Periphyton on hard substrata and on macrophytes (epiphyton) had similar rates of chlorophyll- specific productivity that were intermediate to those of epipelon and phytoplankton. Area-specific productivity of epipelon was 5 to 103 higher than area-specific productivity of periphyton on hard substrata. This broad geographic comparison indicates that, in low to moderately productive lakes under high-light conditions, algal communities have predictable differences in area-specific and chlorophyll- specific productivity based on substratum. As such, chlorophyll alone is an inadequate predictor of the relative contributions of different algal communities to total primary production. Our results highlight the importance of the relative abundance and spatial distributions of substrata in determining the role of the littoral zones in nutrient and energy cycles in lakes.

Selective feeding of littoral harpacticoids on diatom algae: hungry gourmands?

We studied benthic harpacticoid grazing on diatom algae from two sites on the White Sea intertidal sandflat. Diatoms from sediments and from harpacticoid gut contents were sampled in situ, identified and counted, and grazing rates were calculated by two ways: (1) using potential daily ration estimations and (2) from the gut content and gut-residence time data. Paraleptastacus kliei did not contain any diatoms in the guts and presumably fed on other objects (bacteria or flagellates). Two other dominating species studied, Heterolaophonte minuta and Huntemannia jadensis, contained an average of 604 and 222 diatom cells per specimen. Diet composition differed significantly from the natural algal community. Two diatoms of intermediate cell size (Nitzschia palea var. debilis and Navicula sp.) contributed 92–97% of gut content for H. minuta and 58–81% for Hn. jadensis, whereas these diatoms amounted to only about 10% of biomass in native community. Mean consumption rates were estimated as 50–200 μg of wet biomass/day/cm2, so the harpacticoids grazed only between 3 and 11% of the total microalgae biomass per day. The grazing impact on the two preferred diatom populations, however, was much more intensive, 10–30% per day for Navicula sp. and 55–228% for N. palea. Therefore, native harpacticoid populations demonstrate highly selective feeding and could be strongly limited by their food in spite of seemingly plentiful total abundance of microphytobenthos. This disproportionally high grazing pressure upon some species apparently could affect the structure of microalgae communities resulting in low relative abundance of mid-sized forms. We hypothesize that a very dynamic spatio-temporal distribution of epibenthic harpacticoids (short-living micropatches) may be the possible adaptation to such local food limitation.

Toxicity of a Mixture of Dissimilarly Acting Substances to Natural Algal Communities: Predictive Power and Limitations of Independent Action and Concentration Addition

Predictive studies of chemical mixtures are typically based on experiments with single species. To study the applicability of the concepts of independent action (IA) and concentration addition (CA) on a multispecies level, the carbon fixation of natural algal communities under toxicant exposure was studied. The presented study focused on a mixture of six dissimilarly acting substances. Conceptual reasoning as well as empirical evidence from single-species tests suggest that IA is more appropriate for this type of mixture. Nonetheless, the potential of CA was also investigated, to assess whether this concept may be applicable as a reasonable worst case prediction of mixture toxicities also on a community level. IA predicted the experimental EC50 precisely. CA underestimated the EC50 by a factor of only 1.4, although the shape of the predicted concentration-response curve was clearly different from experimental data. Hence, it can be concluded that the applicability of the concepts is not restricted to the level of single species. However, some limitations of both concepts became apparent, when stimulating (hormesis-like) effects were observed fo rtwo of the mixture components. These effects were also seen in the experimental mixture toxicity data but cannot be adequately modeled by either concept.

Comparison of the ecotoxicological impact of the triazines Irgarol 1051 and atrazine on microalgal cultures and natural microalgal communities in Lake Geneva

The antifouling herbicide Irgarol 1051 has been detected in recent years in numerous estuaries, marinas, harbors and coastal areas, and in some harbors on Lake Geneva, but so far only a few studies have investigated the ecotoxicological effects of this compound on microalgae. The purpose of this study was to assess the ecotoxicological impact of Irgarol 1051 on the algal communities of Lake Geneva, and to compare its phytotoxicity to that of the common triazine herbicide, atrazine. We investigated the response of phytoplanktonic and periphytonic algal communities and single-species isolates collected from the lake, to the PS II inhibitor Irgarol 1051 (growth, proxy of photosynthetic activity and community structure). A short-term bioassay was developed based on in vivo fluorescence, together with nanocosm experiments with natural algal communities, and single-species tests on algal strains isolated from the lake. The toxicity of Irgarol 1051 towards periphyton and phytoplankton was shown to be higher than that of atrazine. Indications of the tolerance induced by this triazine in the algal communities of Lake Geneva, suggests that even at the levels of contamination reported in some parts of the lake, Irgarol 1051 is already exerting selection pressure. Information about sensitivities, selection and tolerance from laboratory experiments are used to explain the observations in natural microalgal communities from the lake.

Effects of three pharmaceutical and personal care products on natural freshwater algal assemblages.

Treated wastewaters in the United States contain detectable quantities of surfactants, antibiotics, and other types of antimicrobial chemicals contained in pharmaceutical and personal-care products (PPCPs) that are released into stream ecosystems. The degradation characteristics of many of these chemicals are not yet known, nor are the chemical properties of their byproducts. They also are not currently mandated for removal under the U.S. Clean Water Act. Three representative PPCPs were individually tested in this study using a series of laboratory dilution bioassays: Ciprofloxacin (an antibiotic), Triclosan (an antimicrobial agent), and Tergitol NP 10 (a surfactant), to determine their effects on natural algal communities sampled both upstream and downstream of the Olathe, KS wastewater treatment plant (WWTP). There were no significant treatment effects on algal community growth rates during the exponential phase of growth, but significant differences were observed in the final biomass yields (p < 0.001). All three compounds caused marked shifts in the community structure of suspended and attached algae at both the upstream and downstream sites (p < 0.05). Increasing the concentrations of all three compounds over a 3 orders of magnitude range also caused a consistent decline in final algal genus richness in the bioassays. Our results suggest that these three PPCPs may potentially influence both the structure and the function of algal communities in stream ecosystems receiving WWTP effluents. These changes could result in shifts in both the nutrient processing capacity and the natural food web structure of these streams.

Sequence analysis of marine virus communities reveals that groups of related algal viruses are widely distributed in nature.

Algal-virus-specific PCR primers were used to amplify DNA polymerase (pol) gene fragments from geographically isolated natural virus communities. Natural algal virus communities were obtained from coastal sites in the Pacific Ocean in British Columbia, Canada, and the Southern Ocean near the Antarctic peninsula. Genetic fingerprints of algal virus communities were generated using denaturing gradient gel electrophoresis (DGGE). Sequencing efforts recovered 33 sequences from the gradient gel. Of the 33 sequences examined, 25 encoded a conserved amino acid motif indicating that the sequences were pol gene fragments. Furthermore, the 25 pol sequences were related to pol gene fragments from known algal viruses. In addition, similar virus sequences (>98% sequence identity) were recovered from British Columbia and Antarctica. Results from this study demonstrate that DGGE with degenerate primers can be used to qualitatively fingerprint and assess genetic diversity in specific subsets of natural virus communities and that closely related viruses occur in distant geographic locations. DGGE is a powerful tool for genetically fingerprinting natural virus communities and may be used to examine how specific components of virus communities respond to experimental manipulations.

Metal and phytochelatin content in phytoplankton from freshwater lakes with different metal concentrations

AbstractThe tace metal (Cu, Zn, Cd, Mn) and phytochelatin(an intracellular chelator for metal ions) cellular content were determined in phytoplankton samples originating from four lakes (Greifen, Sempach, Lucerne, and Orta). The lakes differ in their metal concentrations and in other conditions (pH, trophic state, organic matter). Total and intracellular contents of Cu and Cd were related to the experimentally determined free metal ion concentration and the total and intracellular content of Mn to the dissolved Mn. The intracellular Zn content was tightly regulated over a broad range of [Zn2+]. Phytochelatin concentrations were measurable in phytoplankton communities from three of the lakes, in spite of low levels of free Cu, Zn, and Cd ion concentrations. Culture experiments showed that the concentration of intracellular phytochelatin in Scenedesmus subspicatus and in a natural algal community increased upon addition of copper in a similar concentration range as in the lakes. Phytochelatin concentrations were below detection in the phytoplankton collected from the highly contaminated Lake Orta, perhaps suggesting that this algal community has adapted in some other way to high metal concentrations. Although we only sampled a few lakes, the lack of any clear relationship between phytochelatin and metal concentrations calls into question the feasibility of using phytochelatins as a bioindicator of metal exposure in lakes.

Phytoplankton community growth in enrichment bioassays: Possible role of the nutrient intracellular pools

Examination of published experimental data showed that nutrient addition can sometimes inhibit growth rate of natural algal communities. Such reductions in algal growth might be due to toxic effects of some enrichments. This hypothesis could not however explain inhibitions following moderate additions of nitrate and phosphate. A new hypothesis is proposed to account for such “unexplained” results. It considers a limitation of algal community growth by several different resources. Experimental observations are consistent with resource competition determining the coexistence of several species competing for the same resources. Intracellular nutrient storage may reduce bioavailability of many resources involved in algal growth limitation. A simplified mathematical approach, derived from the Droop growth model (1973) , was developed to describe possible relationships between species diversity and algal community growth. Coexistence of several species competing for different resources might provide a partial buffer against large variations in algal community growth following nutrient enrichments.

Photo-induced toxicity of anthracene to the green alga, Selenastrum capricornutum

The photo-induced toxicity of the polycyclic aromatic hydrocarbon (PAH), anthracene, to the green alga, Selenastrum capricornutum, was characterized. The dose-response relationships among anthracene concentration, ultraviolet (UV) radiation intensity, and algal growth rate and 14C-bicarbonate incorporation were determined. The 22 h EC50 for specific growth rate was inversely related to UV-A radiation intensity and ranged from 37.4 to 3.9 μg/L anthracene. For 14C-bicarbonate incorporation on a volume basis (primary production), the 24 h EC50 ranged from 24.0 to 3.3 μg/L anthracene depending on the UV-A intensity. The incorporation of 14C-bicarbonate on a per cell basis (cellular photosynthesis) was more resistant than cell growth or primary production. The threshold for photo-induced toxicity of anthracene was 1.5–3 μg/L anthracene, however, no UV-A radiation threshold was evident for many of the measurements of toxicity studied. Algae appeared to be slightly more resistant to photo-induced toxicity of anthracene than fishes and invertebrates. An environmental hazard assessment suggests that some aquatic systems are sufficiently contaminated by PAH that a hazard to natural algal communities due to photo-induced toxicity of PAH may be present.