Algal Assay Research Articles

Characterization of the physico-chemical properties of the natural habitat and in vitro culture effects on the biochemistry, proliferation and morphology of Lemna minuta

In this study, the ecological conditions of the natural habitat of Lemna minuta Kunth in Morocco were investigated, and the impact of five synthetic growth media (Murashige-Skoog (MS), Schenk-Hildebrand (SH), Hoagland medium (HM), 10X Algal Assay Procedure (AAP), and Swedish Standard Institute medium (SIS)) on the morphophysiological and biochemical parameters was analysed. The morphophysiological parameters included root length, frond surface area, and fresh weight, while the biochemical parameters included photosynthetic pigments, carbohydrates, and protein content. The study was conducted in vitro in two phases: an uncontrolled aeration system (Phase I) and a controlled aeration system (Phase II).The results showed that the pH, conductivity, salinity, and ammonium levels in the natural habitat were within the optimal range for duckweed growth. The measured orthophosphate concentrations were higher compared to previous observations, while the recorded chemical oxygen demand values were low. The study also revealed a significant effect of the culture medium composition on the morphophysiological and biochemical parameters of the duckweed. The fresh weight biomass, relative growth rate in fronds, relative growth rate in surface area, root length, protein content, carbohydrates, chlorophyll (a), chlorophyll (b), total chlorophyll, carotenoids, and the chlorophyll (a/b) ratio were all affected by the culture medium.The most accurate regression models described the growth index GI(F) based on time and in vitro culture conditions in both phases. In Phase I, the best models for MS, SIS, AAP, and SH media were linear, weighted quadratic, cubic, and weighted cubic, respectively. In Phase II, the best models for all growth media were linear. The time coefficients (in days) for Phase II were 0.321, 0.547, 1.232, 1.470, and 0.306 for AAP, HM, MS, SH, and SIS, respectively.Comparing the morphophysiological and biochemical parameters of fronds from different media and analysing the regression model results showed that the SH and MS media were the best among the tested media for the in vitro culture of L. minuta in controlled aeration conditions. However, further research is needed to develop new synthetic media that best promote the growth and maintenance of this duckweed in long-term culture.

Are natural deep eutectic solvents always a sustainable option? A bioassay-based study

The traditional use of organic solvents in various branches of industry is being rethought as these compounds very often display high volatility, toxicity and lipophilicity (related to the ability to interact with biological membranes). More recently, developments in the field of Green Chemistry are focusing on the design of more sustainable and cost-effective solvent alternatives like Ionic Liquids (ILs), bio-based solvents and natural deep eutectic solvents (NADESs). The present study aimed at performing an ecotoxicological screening of 15 NADESs using an extensive set of marine and freshwater bioassays, based on different endpoints as the following: immobilization of the crustacean Daphnia magna, growth inhibition of Raphidocelis subcapitata and of Phaeodactylum tricornutum, larval development alterations on the serpulid Ficopomatus enigmaticus and bioluminescence inhibition of Aliivibrio fischeri. What emerged was a general absence of toxicity of all samples. However, both algal assays showed a certain degree of biostimulation, up to over 100% growth increase in respect to controls with 8 out of 15 compounds tested with Raphidocelis subcapitata. Despite NADESs-induced negligible toxicity effects to invertebrates, encouraging their labelling as “sustainable” solvents, the liability of their intentional or accidental release into aquatic systems may represent a serious risk in terms of ecosystem functioning impairments.

A simple and rapid algal assay kit to assess toxicity of heavy metal-contaminated water.

This study presents a novel algal-based toxicity test suitable for simple and rapid assessment of heavy metal (Hg2+, Cr6+, Cd2+, Pb2+, or As3+)-contaminated water. A closed-system kit-type algal assay was developed using Chlorella vulgaris. Toxicity was assessed by oxygen evolution in the gaseous phase of the assay kits, which was measured via a needle-type oxygen sensor. Initial cell density, light intensity, and exposure time that enabled favorable test performance for the algal assay kits were 103cells/mL, 250μmolm-2s-1, and 18h, respectively. Results from the heavy metal toxicity tests demonstrate that Hg2+, Cr6+, Cd2+, and Pb2+ are more toxic in inhibiting algal photosynthetic activity than As3+. The 18h half-maximum effective concentrations (EC50) for Hg2+, Cr6+, Cd2+, Pb2+, and As3+ were determined to be 31.3±0.5, 179.6±7.5, 301.3±6.1, 476.1±10.5, and 2184.1±31.1μg/L, respectively. A strong correlation between oxygen concentrations in the headspace of the assay kits and chlorophyll a production indicates that oxygen evolution in the gaseous phase is able to represent algal photosynthetic activity and serve as the end-point in algal toxicity tests. High test sensitivity and reproducibility as well as an easy test protocol and rapid processing time make the algal assay kit a suitable tool for simple and rapid toxicity testing of heavy metal-contaminated water.

In vitro proliferation of Lebanese Lemna minor and Lemna gibba on different nutrient media

This study aimed to assess the ability of two Lebanese duckweed species, (Lemna minor and L. gibba), to grow under in vitro conditions on three nutritive solutions, Murashige Skoog (MS), Schenk-Hildebrand (SH) and Algal Assay Procedure (AAP). Plant growth of both species, expressed as doubling time, differed significantly (p < .05) between the tested media with best results obtained on SH for L. minor after 7 days of culture and on AAP for L. gibba after 2.7 days for both species. Growth index was significantly higher (P < .05) for L. minor on SH reaching 41.6 after 21 days of culture whereas L. gibba exhibited its highest growth index of 15.51 on AAP. These results indicate the efficiency of SH and AAP media in promoting the vegetative proliferation of L. minor and L. gibba to further provide a good source of duckweed material for phytoremediation applications.

Phosphorus bioavailability in rivers flowing through contrasting land uses

Bioavailable phosphorus (BAP) is a fraction of total phosphorus (TP) that accelerates algae growth in aquatic ecosystems. BAP is comprised of dissolved phosphorus (DP) and a portion of particulate phosphorus (PP). Algal assays and chemical extractions can be applied to determine BAP. However, several constraints such as long extraction time and high costs, hinder their use. We used a new rapid procedure which involves ultrasonic treatment to extract BAP from suspended sediment (SS) samples. This study aimed to assess particulate bioavailable phosphorus (PBAP) and BAP in runoff from rivers flowing through different land uses, and the relationship with SS and TP respectively. PP was the dominant fraction of TP at high flow and between 5 to 54% of PP was estimated to be bioavailable. A strong statistical relationship was observed between PBAP and SS in the river classed as agricultural (r2 = 0.79), in contrast to the urban one where no correlation was observed, implying that the particle size and composition of SS in both rivers was markedly different. A strong correlation was observed between BAP and TP in the urban river (r2 = 0.78), indicating that merely using TP as a substitute for BAP is questionable as this would overestimate the eutrophication potential of some phosphorus sources. The BAP and TP relationship in the agricultural river revealed that elevated PP concentration at high flow may not translate into higher BAP in runoff, implying that quantification of BAP in SS is critical for the effective implementation of watershed management programs.

Aquatic Ecosystem Impacts of Land Sharing Versus Sparing: Nutrient Loading to Southeast Asian Rivers

As world food demand continues to increase, two broad strategies for agricultural production have been widely discussed: land sparing and land sharing. Reflecting tradeoffs between the extent and intensity of agricultural use, land sparing maximizes the ratio of conserved to agricultural land, whereas land sharing allows more extensive, nature-friendly transformation of the agroecological matrix. Freshwater ecosystems are rarely considered in weighing these strategies, despite being strongly affected by land-use change. Here we analyze how shifting from extensive to intensive agricultural practices is altering dry season riverine nutrient availability and algal growth in upland Southeast Asia, which is experiencing rapid conversion from swidden—or shifting—cultivation to fertilized row crops. In situ algal growth assays and nutrient concentration data from eleven catchments representing a spectrum of land use and population densities show that intensive agriculture is associated with significantly elevated nitrate concentrations but no shift in phosphorus. As a result, nitrogen to phosphorus ratios increases dramatically, shifting algal growth toward colimitation by nitrogen and phosphorus. Geochemical analysis of suspended solids suggested comparable geological inputs across basins, but dissolved rare earth elements reveal that inorganic fertilizers are changing water chemistry in parallel with land use. Taken together, our analyses suggest that the transition from low-input land-sharing management (swidden) to high-input land-sparing practices (intensive row-crop agriculture) underway in Southeast Asia has profound consequences for river ecosystems. Such nutrient loading can affect river productivity and food webs, suggesting that land-use conservation strategies for Southeast Asia need to account for impacts on freshwater ecosystems.

Role of initial cell density of algal bioassay of toxic chemicals.

A variety of toxicants such as, metal ions, pesticides, dyes, etc. are continuously being introduced anthropogenically in the environment and adversely affect to the biotic component of the ecosystem. Therefore, the assessment of negative effects of these toxicants is required. However, toxicity assessment anticipated by chemical analysis are extremely poor, therefore the application of the living systems for the same is an excellent approach. Concentration of toxicant as well as cell density both influenced the result of the algal toxicity assay. Here, Scenedesmus sp, a very fast growing green microalgae was selected for study the effects of initial cell densities on the toxicity of Cu(II), Cd(II), Zn(II), paraquat and 2,4-D. Results demonstrated concentration dependent decrease in biomass and specific growth rate of Scenedesmus sp. on exposure of abovesaid toxicants. Paraquat and 2,4-D emerged as extremely toxic to the test alga which reflected from the lowest EC value and very steep decline in biomass was evident with increasing concentration of paraquat and 2,4-D in the medium. Result also demonstrated that initial cell density is a very important parameter than specific growth rate for algal bioassay of various toxicants. Present study clearly illustrated that the use of smaller cell density is always recommended for assaying toxicity of chemicals in algal assays.

Sorption of silver nanoparticles to laboratory plastic during (eco)toxicological testing

Here, we evaluate the extent of sorption of silver nanoparticles (AgNPs) with different primary sizes (30 and 70 nm) and surface properties (branched polyethylene imine, “bPEI” and citrate coating) to laboratory plastic during (eco)toxicological testing. Under conditions of algal growth inhibition assay, up to 97% of the added AgNPs were sorbed onto the test vessels whereas under conditions of in vitro toxicological assay with mammalian cells, the maximum loss of AgNPs was 15%. We propose that the high concentration of proteins and biomolecules in the in vitro toxicological assay originating from serum-containing cell culture medium prevented NP sorption due to steric stabilisation. The sorption of AgNPs to test vessels was clearly concentration dependent. In the conditions of algal growth inhibition assay at 10 ng AgNPs/mL, up to 97% of AgNPs were lost from the test while at higher concentrations (1000 ng AgNPs/mL), the loss of AgNPs was remarkably smaller, up to 64%. Sorption of positively charged bPEI-coated AgNPs was more extensive than the sorption of negatively charged citrate-coated AgNPs and, when calculated on a mass basis, more 70 nm-sized Ag than 30 nm Ag sorbed to plastic surfaces. In summary, this study demonstrates that the loss of AgNPs during (eco)toxicological tests due to sorption on test vessel surfaces is significant, especially in diluted media (e.g. in algal growth medium) and at low NP concentrations. Thus, to ensure the accurate interpretation of (eco)toxicological results, the loss of AgNPs due to adsorption to test vessels should not be overlooked and considered for each specific case.

Cell size and the blockage of electron transfer in photosynthesis: Proposed endpoints for algal assays and its application to soil alga Chlorococcum infusionum

This study evaluated multiple endpoints of algal assays to identify sensitive and easy to use endpoints that could be applied to evaluate algal toxicity in metal-polluted soil extracts. Soil algae play an important role in trophic levels; thus, Chlorococcum infusionum was selected as the test species. Soil extracts were used because they might help identify potential soil retention and ecological hazards caused by pollutants that are present in the soil aqueous phase. The multi-endpoints measured were growth yield, photosynthetic activities, and cell viabilities. Nine parameters were measured to evaluate photosynthetic activity; namely, specific energy fluxes per quinone A-reducing photosystem II reaction center (absorption flux, trapped energy flux, electron transport flux, and dissipated energy flux per reaction center), quantum yields (maximum quantum yield of primary photochemistry, quantum yield of electron transport, quantum yield of energy dissipation, and average quantum yield of primary photochemistry), and the blockage of electron transfer from the reaction center to the quinone pool. Cell viability was evaluated by measuring cell size, cell granularity, and the autofluorescence of chlorophyll using flow cytometry. The results showed that heavy metals reduced growth yield, cell viability, and the photosynthetic activity of C. infusionum in soil extracts. Out of the 13 tested endpoints, the blockage of electron transfer from the reaction center to the quinone pool and cell size represented the most sensitive endpoints. We propose that both endpoints should be measured, along with conventional growth yield, to determine the effect of soil pollutants and to lower pollutant concentrations in soils.

Uptake by Algae of Dissolved Organic Nitrogen from BNR Treatment Plant Effluents

The importance of dissolved organic nitrogen (DON) in wastewater treatment effluent has dramatically increased as permitted effluent total nitrogen (TN) concentrations have been decreased to very low levels in response to problems with impaired surface water quality from eutrophication. For conventional secondary treatment, DON typically accounts for less than 10% of the effluent TN, but it is a major component (>50%) in effluents from advanced biological nutrient removal (BNR) treatment plants, for which most of the inorganic nitrogen species and effluent suspended solids are removed. DON persists in effluents from BNR systems and little is known about the potential impact of the effluent DON from these facilities on surface water quality. Of particular interest is what portion of DON is readily available for algae consumption or can be converted to forms to support algal growth, and what type of substances compose DON. To develop a better understanding of the occurrence and bioavailability of DON in effluents from advanced BNR systems, a new protocol was developed for measuring the readily bioavailable DON and forms of DON that are not readily taken up by algae (recalcitrant DON). An anion exchange resin was used to remove nitrate while an XAD-8 resin was used to remove hydrophobic forms of DON. To assess the bioavailability of wastewater-derived DON, algal growth assays were performed in the presence of bacteria in effluents from ten municipal BNR wastewater treatment plants. The results showed only minor difference in the algal growth and DON consumption between the untreated and XAD-8 treated samples. Growth of algae and DON consumption were not observed in the eluent from XAD-8 resins, despite the fact that this fraction contained up to approximately 30% of the DON. These findings indicate that the hydrophobic DON retained on the XAD-8 resin is not bioavailable to algae over periods of several weeks and that the XAD-8 treatment combined with an anion exchange resin can be used to quantify and separate this recalcitrant form of DON from bioavailable DON and nitrate. This title belongs to WERF Research Report Series . ISBN: 9781780401386 (eBook)

An integrated microfluidic device in marine microalgae culture for toxicity screening application

Algal assay using marine microalgae has emerged as an important method to evaluate the toxicity of chemicals, which is currently undertaken using conventional culture and additional detection of physiological cellular endpoints. While effective, this approach can be labor-intensive and thus could benefit from a more streamlined, integrated approach. Microfluidics offers a way to accomplish this goal. Here, we demonstrate a microfluidic device which consists of a concentration gradient generator (CGG), diffusible culturing module and power-free valve system. It allows the processes of chemical liquid dilution and diffusion, micro-scale microalgal culture (in batch or chemostatic conditions), cell stimulation and on-lined screening to be integrated into a single device. Using the device, marine microalgae were successfully cultured and stressed on-chip. The simple assay provides multi-biological response measurements of cell division rate, autofluorescence and esterase activity. This work showed promising in developing a microfluidic platform for toxicity screening based on marine microalgal culture.

Effects of zinc oxide and titanium dioxide nanoparticles on green algae under visible, UVA, and UVB irradiations: No evidence of enhanced algal toxicity under UV pre-irradiation

Some metal oxide nanoparticles are photoreactive, thus raising concerns regarding phototoxicity. This study evaluated ecotoxic effects of zinc oxide nanoparticles and titanium dioxide nanoparticles to the green algae Pseudokirchneriella subcapitata under visible, UVA, and UVB irradiation conditions. The nanoparticles were prepared in algal test medium, and the test units were pre-irradiated by UV light in a photoreactor. Algal assays were also conducted with visible, UVA or UVB lights only without nanoparticles. Algal growth was found to be inhibited as the nanoparticle concentration increased, and ZnO NPs caused destabilization of the cell membranes. We also noted that the inhibitory effects on the growth of algae were not enhanced under UV pre-irradiation conditions. This phenomenon was attributed to the photocatalytic activities of ZnO NPs and TiO2 NPs in both the visible and UV regions. The toxicity of ZnO NPs was almost entirely the consequence of the dissolved free zinc ions. This study provides us with an improved understanding of toxicity of photoreactive nanoparticles as related to the effects of visible and UV lights.

A resin-buffered nutrient solution for controlling metal speciation in the algal bottle assay

Metal speciation in solution is uncontrolled during algal growth in the traditional algal bottle assay. A resin-buffered nutrient solution was developed to overcome this problem and this was applied to test the effect of chloride (Cl−) on cadmium (Cd) uptake. Standard nutrient solution was enriched with 40mM of either NaNO3 or NaCl, and was prepared to contain equal Cd2+ but varying dissolved Cd due to the presence of CdCln2−n complexes. Both solutions were subsequently used in an algal assay in 100mL beakers that contained only the solution (designated “−R”) or contained the solution together with a cation exchange sulfonate resin (2gL−1, designated “+R”) as a deposit on the bottom of the beaker. Pseudokirchneriella subcapitata was grown for 72h (1.4×105–1.4×106cellsmL−1) in stagnant solution and shaken three times a day. Growth was unaffected by the presence of the resin (p>0.05). The Cd concentrations in solution of the −R devices decreased with 50–58% of initial values due to Cd uptake. No such changes were found in the +R devices or in abiotic controls. Cd uptake was unaffected by either NaNO3 or NaCl treatment in the +R device, confirming that Cd2+ is the preferred Cd species in line with the general concept of metal bioavailability. In contrast, Cd uptake in the −R devices was two-fold larger in the NaCl treatment than in the NaNO3 treatment (p<0.001), suggesting that CdCln2−n complexes are bioavailable in this traditional set-up. However this bioavailability is partially, but not completely, an apparent one, because of the considerable depletion of solution 109Cd in this set-up. Resin-buffered solutions are advocated in the algal bottle assay to control trace metal supply and to better identify the role of metal complexes on bioavailability.

Rapid algal toxicity assay using variable chlorophyll fluorescence for Chlorella kessleri (chlorophyta)

Three methods of algal assays--the standard assay, microassay, and the proposed fluorescence assay--are compared from the point of view of reliability of EC50 detection, the minimum required time for the detection, sensitivity of individual measurement, i.e. at which cell density the particular assay can be used for EC50 estimation, and the time stability of the EC50 values. The assays were performed with green alga Chlorella kessleri strain LARG/1 growing in potassium dichromate solution in Z-medium ranging from 0.01 to 100 mg Cr L⁻¹. The inoculation cell density was set according to the standards to 10⁴ cells mL⁻¹ and according to spectrophotometer/plate reader detection limit. The average EC50 ranged from 0.096 to 0.649 mg Cr L⁻¹ and there were no significant differences in EC50 between the assay type and the inoculation methods with the exception of the significant difference between EC(c)50₇₂ (EC50 established from biomass measured as chlorophyll a concentration after 72 h of cultivation) in the standard assay and EC(r)50 (EC50 derived from growth rate) in the microassay in the standard inoculation experiment due to low variability of their values. The EC(f)50 (EC50 derived from variable fluorescence measurement) values correspond to EC50 values derived from the growth rates. Fluorescence measurement revealed the toxic effect of the chromium after 24 h of exposure at cell density of 5 x 10⁴ cells mL⁻¹, less by half than other used assay methods. The positive correlation of EC(f)50 and time was found in the standard inoculation experiment but opposite effect was observed at the spectrophotometric one.

Barley (Hordeum vulgare)-induced growth inhibition of algae: a review

Many field and laboratory studies have attempted to explain the inhibitory effect of rotting barley on algae. Early field studies lacked controls and replication and results depended on visual observations. Such studies offer information on barley bale field construction and application rates. In the laboratory, discrepancies in the barley variety used, algal species tested, barley liquor preparation and phenol extraction methodologies existed. Inconsistencies have led to different growth responses for the same species of algae tested, i.e. with some studies finding an inhibitory response and other studies reporting an accelerated growth response of algae. Two successful forms of investigation have been identified: (a) using commercially available compounds, i.e. with known shikimate-pathway-producing phenols and acids, which can then be combined with algal assays of different algal species and (b) using commercially available algal species from which batch cultures are grown, which are then added to barley liquor of different ages. Algal growth may then be investigated using in vivo fluorescence and the filtrate can be analysed via HPLC/MS. The identification of allelochemicals, which range from phenolics to quinones within the Poaceae family of which barley is a member, has received a lot of attention in recent years.

Algal‐available Phosphorus Entering the Gulf of Finland as Estimated by Algal Assays and Chemical Analyses

Algal-available phosphorus (Paa) in river water and wastewater entering the Gulf of Finland (a Baltic Sea sub-basin) was estimated by a fresh-water and a brackish-water modification of the dual-culture algal assay. The assay results were further related to those obtained by routine chemical analyses. According to the brackish-water assay, an average of 44% (range, 9-88%) of total phosphorus (TP) in water samples from the Neva, Kymijoki, and Narva rivers consisted of Paa, whereas the mean value given by the fresh-water assay was 22% (range, 0-48%). Phaeodactylum tricornutum Bohlin, which was used as the test alga in the brackish-water assay, had higher phosphoesterase activity and P affinity than did Pseudokirchneriella subcapitata Korschikov, which was used in the fresh-water assay. This difference may explain the higher values of Paa shown by the brackish-water assay. Of the analytical P forms, total dissolved P best approximated, yet underestimated, the Paa in river water samples. As for the biologically purified wastewaters of the city of St. Petersburg, both assays suggested that about 80% of TP (range, 59-103%) was available. That the assays gave similar results was probably due to the fact that most of the P in the wastewater samples was in the form of readily available dissolved reactive P. In untreated urban wastewaters, the mean proportion of Paa in TP was 46% (range, 19-76%). Although the true Paa may not be obtained by any assay, our findings corroborate the view that severe underestimation may occur if the test conditions are suboptimal for the release and uptake of P.

Dose–response regressions for algal growth and similar continuous endpoints: Calculation of effective concentrations

We derive equations for the effective concentration giving 10% inhibition (EC10) with 95% confidence limits for probit (log-normal), Weibull, and logistic dose-response models on the basis of experimentally derived median effective concentrations (EC50s) and the curve slope at the central point (50% inhibition). For illustration, data from closed, freshwater algal assays are analyzed using the green alga Pseudokirchneriella subcapitata with growth rate as the response parameter. Dose-response regressions for four test chemicals (tetraethylammonium bromide, musculamine, benzonitrile, and 4-4-(trifluoromethyl)phenoxy-phenol) with ranges of representative slopes at 50% response (0.54-2.62) and EC50s (2.20-357 mg/L) were selected. Reference EC50s and EC10s with 95% confidence limits using probit or Weibull models are calculated by nonlinear regression on the whole dataset using a dose-response regression program with variance weighting and proper inverse estimation. The Weibull model provides the best fit to the data for all four chemicals. Predicted EC10s (95% confidence limits) from our derived equations are quite accurate; for example, with 4-4-(trifluoromethyl)phenoxy-phenol and the probit model, we obtain 1.40 (1.22-1.61) mg/L versus 1.40 (1.20- 1.64) mg/L obtained from the nonlinear regression program. The main advantage of the approach is that EC10 or ECx (where x = 1-99) can be predicted from well-determined responses around EC20 to EC80 without experimental data in the low- or high-response range. Problems with the estimation of confidence interval for EClow,x (concentration predicted to cause x% inhibition) from algal growth inhibition also are addressed. Large confidence intervals may be the result of experimental error and lack of a well-defined reference response value.

The effect of some herbicides on duckweed and freshwater planktonic algae and their biodegradability

The objective of this study was to evaluate and compare the sensitivity of the freshwater green algae Pseudokirchneriella subcapitata, Desmodesmus subspicatus and Chlorella kessleri as well as duckweed Lemna minor to herbicides alachlor and metribuzin using conventional Erlenmeyer flask and miniaturized microplate algal growth inhibition assays. The results showed that alachlor was very toxic for alga Desmodesmus subspicatus, and extremely toxic for other investigated species, while metribuzin was extremely toxic for all test organisms. The ultrastructural changes observed by transmition electron microscopy confirmed the obtained toxicity results. Biodegradability test showed that these herbicides were not biodegradable – the rate of biodegradability was 43.3% for alachlor and 34.4% for metribuzin. The results indicate that battery test could be very useful in biomonitoring of area contaminated with these herbicides as well as for getting better insights in their toxicity, influence on environment and thereby in production of good quality food.

Microalgal photosynthetic activity measurement system for rapid toxicity assessment

A systematic biosensor is constructed for the estimation of toxic compounds based on photosynthetic activity measurement in Selenastrum capricornutum cells. The photosynthetic response was evaluated as a function of light intensity, cell concentration and initial dissolved oxygen. The inhibitory effect of some toxicants (1-butyl-3-methylimidazolium tetrafluoroborate, methanol) on dissolved oxygen production was also determined. In all cases, a toxic response was detected (i.e. a dose-related inhibition of photosynthetic activity was observed). For the present system, a time of only 2 h was needed to predict EC50 values as compared to 96 h for a conventional algal assay based on algal growth rate. Thus, the developed biosensor was proved to be useful as a rapid and simple test method in environmental toxicity assessment.

Macroalgal grazing selectivity among herbivorous coral reef fishes

Despite growing interest in examining functional groups among coral reef species, few studies have examined the relative functional impacts of individual herbivorous fish species in coral reef ecosystem processes. We investigated potential functional roles within an herbivorous reef fish assemblage by assessing the feeding selectivity of fishes on macroalgae. Transplanted multiple-choice algal assays and remote stationary underwater digital video cameras were used to quantify the feeding selectivity of 6 herbivorous reef fish species: Siganus doliatus and S. canaliculatus (Siganidae); Chlorurus microrhinos, Hipposcarus longiceps, and Scarus rivulatus (Labridae); and Pomacanthus sexstriatus (Pomacanthidae). The siganids strongly selected Sargassum sp. (Phaeophyta) and, to a lesser extent, Hypnea sp. (Rhodophyta), but strongly avoided calcified macroalgae. However, S. doliatus displayed strong selection for Hypnea sp., whereas S. canaliculatus exhibited stronger selection for Sargassum sp. In contrast, the parrotfishes exhibited similar selectivities, with all 3 species selecting heavily calcified Halimeda spp. (Chlorophyta), but strongly avoiding Galaxaura sp. (Rhodophyta) and other red and brown macroalgal species. The pomacanthid was the least selective of the 6 fish species, exhibiting no clear selection or avoidance. These results emphasize the potential variation among species within presumed functional groups, and the need for care when defining functional groups at the family or the genus level. The extent of specialization, with strong selection and avoidance, suggests that functional redundancy among herbivores may be less than previously assumed.