Sten-Åke Wängberg

Species-dependent variation in algal sensitivity to chemical compounds.

Nineteen miscellaneous chemical compounds were tested on thirteen freshwater algal species grown in 250-microliter liquid cultures on plastic microtitration plates. It was demonstrated that the species-dependent variation in algal sensitivity (EC100) may reach over three orders of magnitude, the degree of variation depending on the chemical tested. No generally sensitive or generally insensitive species could be identified. An effort was made to quantify the predictive value of algal test batteries, at a given confidence level with respect to chemicals. The predictive value of small test batteries was low. Although it did increase with size it took the presence of more than nine members in the test batteries to improve the value to 0.1. This means that a nine-membered test battery might underestimate the sensitivity of the most susceptible algae by a factor of 0.1. A predictive value of 0.01 requires a three-membered test battery when accounting for 95% of the chemicals and a five-membered battery at the 99% confidence level. Implications for toxicity test strategies are discussed and it is suggested that algal test batteries, using simple test techniques, replace single unialgal cultures in routine work.

Tolerance induction and succession in microalgae communities exposed to copper and atrazine

Abstract A major need in ecotoxicology is the development of sensitive and robust ecotoxicological methods to detect the effects of toxic substances in complex aquatic ecosystems. In this study, we investigated how copper and atrazine affect the tolerance of microalgal communities and the succession of species. The effects of atrazine and copper on microalgal communities in large freshwater enclosures were investigated for a 20-day period. The communitys tolerance of copper and atrazine was determined by short-term photosynthesis tests. Species composition was evaluated using a similarity index and multivariant analysis. In enclosures exposed to copper, tolerance gradually increased during the experiment. In the enclosures exposed to the highest copper concentration (0.24 μM), an increased tolerance of copper was found in phytoplankton communities even after 2 days, and in the enclosure exposed to the lowest copper concentration (0.016 μM), increased tolerance was found after 12 days. In accordance with the PICT (pollution-induced community tolerance) concept, the added copper was sufficient to affect the phytoplankton community, as was confirmed by changes in species composition. Communities exposed to increased copper concentrations also showed increased tolerance for zinc, indicating common tolerance mechanisms for copper and zinc. The effects of atrazine in the enclosures were small and did not induce changes in community tolerance for atrazine or diuron, although the same concentration was high enough to reduce photosynthesis activity by 20% in the short-term test and cause minor changes in species composition. Tolerance levels in phytoplankton and periphyton communities were compared. Neither copper nor atrazine induced changes in the tolerance of the periphyton communities. The short-term EC50 values for atrazine were very similar in periphyton and phytoplankton communities, but for copper, EC50 values for periphyton were about ten times higher than for phytoplankton.

Effects of broodstock diets on fatty acid composition, survival and growth rates in larvae of the European flat oyster, Ostrea edulis

Abstract Thirteen broods of Ostrea edulis larvae from four specific broodstock treatments were analysed for growth, mortality and fatty acid composition. Larvae from different broodstock treatments, reared under the same standard hatchery conditions with identical diets for 12 days, showed different growth rates but mortality was similar. Growth rates ranged from 1.4 to 5.9 μm per day. Growth rate was significantly related to the content of total polyunsaturated fatty acids (PUFAs) and 22:6 n − 3 fatty acids in newly released larvae. The content of 22:6 n − 3 from different broodstocks explained 50% of the variation in growth rate among broods. However the content of PUFA and the 22:6 n − 3 fatty acid did not differ among broodstock treatments. It is suggested that a fast assay for essential PUFA like 22:6 n − 3 may significantly improve management of commercial bivalve hatcheries.

Multivariate patterns of algal sensitivity to chemicals in relation to phylogeny

Species-dependent variations in algal sensitivity make predictions from conventional algal growth tests uncertain. The use of test batteries comprising several unialgal tests improves the predictive value drastically. To select the members for an optimal test battery is a multivariate problem. To be an efficient member of the battery a species should have a sensitivity pattern that is complementary to the other members. Sensitivity patterns were analyzed with a principal component method (SIMCA). Toxicity data for 19 chemical compounds and 16 microalgal strains were used as input in the analysis. Two separate groups with significantly different sensitivity patterns were recognized, belonging to Chlorococcales and Cyanophyta, respectively. No algal species, belonging to other taxa of Chlorophyta or to Xanthophyta, had sensitivity patterns that fitted into any of the two groups. It is concluded that the phylogeny of the algae is toxicologically relevant and as a tentative strategy for test battery design we suggest that a taxonomically wide range of algal species should be used.

Pattern of cotolerance in marine periphyton communities established under arsenate stress

Abstract Arsenate-tolerant marine periphyton communities established under arsenate stress in a flow-through aquarium system, were investigated for cotolerance to various inhibitors of photosynthesis. A short-term test system for inhibition of periphyton photosynthesis was used to quantify the community tolerance levels. Preexposure to arsenate at 10 μM increased arsenate tolerance > 16,000-fold compared to control communities established at background levels of arsenate. A substantial cotolerance was observed only for thiophosphate which is a phosphate analog uncoupler of photophosphorylation with a mode of action similar to that of arsenate. For the uncouplers CCCP (carbonyl cyanide m -chloro-phenylhydrazone) and Primene JMT (a primary amine with a branched C 18 –C 22 aliphatic chain), the inhibitor of photosynthetic electron transport DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and arsenite, there was a general tendency for a small cotolerance, although for Primene JMT and DCMU an increased sensitivity was some-times observed. The general increase in tolerance was however quantitatively insignificant compared to the specific cotolerance observed for thiophosphate, suggesting that the mode of action and tolerance mechanisms are similar for arsenate and thiophosphate, and most likely related to their phosphate analogy. We suggest that significant cotolerance is not ubiquitous nor common in periphyton, and that the emerging cotolerance pattern may be indicative of the toxicity and tolerance mechanisms.

SEASONAL VARIABILITY IN POLYUNSATURATED ALDEHYDE PRODUCTION POTENTIAL AMONG STRAINS OF SKELETONEMA MARINOI (BACILLARIOPHYCEAE)1

The cosmopolitan bloom‐forming diatom Skeletonema marinoi Sarno et Zingone is known to produce toxic polyunsaturated aldehydes (PUAs) in response to cell damage that can affect a diverse suite of organisms, including grazing species and competitor plankton species. The production of PUAs in nine different S. marinoi strains isolated at three different times of the year (spring, summer, and autumn) was assessed in relation to the predominant conditions at the time of isolation from Gullmar Fjord, Skagerrak. During the initial stages of growth, PUA production potential of S. marinoi was generally the highest in summer strains, although there was a substantial variation among strains isolated at the same time. Spring strains, however, showed a strong capacity for increased PUA production potential in later stage cultures with diminishing nutrient levels, reaching amounts similar to those observed in summer strains. In contrast, PUA production potentials of summer and autumn strains did not change significantly from the original values. There is negligible grazing pressure during the spring bloom in Gullmar Fjord, but a potential for high competition for resources, such as nutrients, toward the later stages of the bloom. In contrast, grazing pressure is much greater during summer and autumn, and there may also be nutrient limitation at this time. The PUA production potentials of S. marinoi appear to reflect the ecological conditions at the time of isolation with higher production potentials in strains isolated when conditions were likely to be less beneficial for survival.

Effects of UV-B radiation on synthesis of mycosporine-like amino acid and growth in Heterocapsa triquetra (Dinophyceae)

Abstract Unialgal cultures of the dinoflagellate Heterocapsa triquetra (Ehrenberg) Stein were exposed to artificial UV-B radiation and the growth and synthesis of mycosporine-like amino acids (MAAs) were compared with cultures shielded from UV-B radiation by sharp cut-off films. The UV-B radiation did not affect the growth (the increase in total cell volume of the culture) but resulted in an increase in the size of the individual cells and synthesis of MAAs. The synthesis of MAAs during UV-B radiation was synchronised with the cell cycle, being maximal during periods of increases in cell size without division. The absorbance spectra of the MAAs during UV-B radiation changed, showing higher absorption in the UV-B range as compared to the controls.

Arsenate sensitivity in marine periphyton communities established under various nutrient regimes

Abstract Arsenate sensitivity to carbon dioxide fixation was measured in marine periphyton communities established under different nutrient regimes in flow-through aquaria. An increase of the phosphate concentration in the incubation media from 0.1 to 0.8 μM did not cause any immediate changes in sensitivity to arsenate. However, after 72 h of phosphate enrichment, sensitivity to arsenate had decreased > 3000-fold (EC 20 values increased from 0.3 μM to > 1 mM). Decreases in sensitivity to arsenate were also seen during natural and simulated upwelling episodes when both the phosphate and nitrate concentrations increased. The sensitivity to arsenate correlated with the phosphorus status of the communities, measured either as total phosphorus or surplus phosphorus, but not with their nitrogen or chlorophyll contents. The role of internal or external competition between arsenate and phosphate is discussed in relation to possible mechanisms for the phosphate-dependent tolerance. The key role of nutrient prehistory in modifying periphyton sensitivity to arsenate is stressed. The time of the year and current nutrient situation will affect the phosphorus status of the algae, and should therefore be considered, both when performing toxicity tests and when making hazard assessments for arsenate.

Pollution-Induced Community Tolerance (PICT) in coastal phytoplankton communities exposure to copper

The toxic effect of copper to coastal phytoplankton communities was studied in 6 m3 enclosures during 15 days using the PICT (Pollution-Induced Community Tolerance) methodology. PICT, primary production, algal biomass, species composition and diversity in phytoplankton communities were measured in control enclosures and enclosures with 1, 3, 6 and 15 μg Cu l-1 added. Increased copper tolerances were induced in the enclosures with added copper and, related to the pooled mean value of the controls, the mean values for copper tolerance were significantly higher in enclosures with 1, 6 and 15 μg Cu l-1. In enclosures with 6 and 15 μg Cu l-1, photosynthetic activity was significantly depressed. Fundamental changes in taxonomic diversity and species composition occurred in enclosures with 15 μg Cu l-1. Algal biomass was not affected by the addition of copper. The distribution and concentration of copper in the enclosures showed that copper exposure was almost constant over time in the enclosures and was proportional to the amount of copper added to them. Our studies indicate that the PICT methodology is sensitive enough to detect even minor effects of copper on phytoplankton communities. The PICT measurements indicate effects from concentrations as low as 1 μg Cu l-1 in highly eutrophic coastal areas, where the bioavailability of copper is assumed to be low. Copper concentration in the fjord and control enclosures was high, about 0.5 μg Cu l-1, only a factor two below the effect concentration measured by PICT. These results are significant in view of the increased release of copper to the coastal marine environment as results of the substitution of copper-based ship paints for tri-n-butyltin (TBT) antifouling paints.

Effects of arsenate and copper on the algal communities in polluted lakes in the northern parts of Sweden assayed by PICT (Pollution-Induced Community Tolerance)

The tolerance for arsenate and copper in the carbon dioxide fixation activity of phytoplankton communities coming from lakes around the smelter at Rönnskär at the Swedish east-coast were measured during three years (1989–1991). The smelter have for several decades discharged arsenic and heavy metals into the air, and their concentrations in the lakes were clearly correlated with the distance from the smelter. The tolerance of communities from the three most polluted lakes were higher than communities from reference lakes with background concentrations of arsenic and copper. In accordance with the PICT concept it is indicated that those communities have been affected by these substances. These communities also had lower diversity than the others, but no clear correlation could be done with phytoplankton species number, or between phytoplankton biomass and pollution levels.