Evaluation of short-term copper toxicity in a co-culture of Synechococcus sp., Chaetoceros gracilis and Pleurochrisys cf. roscoffensis exposed to changes in temperature and salinity levels.

Metals such as copper (Cu) enter marine environments from natural and anthropogenic sources, causing changes in the biodiversity of marine microalgae and cyanobacteria. Cu plays a dual role as either a micronutrient or toxicant depending on the environmental concentration. Many studies have summarized the potential of Cu to become more toxic to microalgae under environmental stress (for instance climate change). Most of the data available on Cu toxicity concerning microalgae and cyanobacteria have been produced using single-species laboratory tests, and there is still a significant gap in the information concerning the behavior of a group of algae exposed to environmental stressors. Thus, the objective of this study was to evaluate the toxicity of Cu at two concentrations (C1 = 2 µg L-1 and C2 = 5 µg L-1) in multispecies bioassays using three phytoplankton species (one cyanobacteria, Synechococcus sp., and two microalgae, Chaetoceros gracilis and Pleurochrisys cf. roscoffensis). Combinations of two temperatures (20 and 23 °C) and two salinities (33 and 36 PSU), were applied in a 96 h study using flow cytometry analysis (FCM). Algal growth and reactive oxygen species (ROS) production by 2'7'-dichlorofluorescein (DCFH) were monitored by FCM. The results indicated that Synechococcus sp. was more sensitive than C. gracilis and P. roscoffensis to Cu stress at a temperature 23 °C and salinity of 36 PSU under both concentrations of Cu. Chlorophyll a fluorescence showed a significant decrease (p < 0.05) in Synechococcus sp. under 5 µg L-1 of Cu in the combined treatment of 20 °C and 33 PSU; however, there was a significant increase in P. roscoffensis in all combinations at C2 = 5 µg L-1 compared to the control with no Cu, indicating a potential hormetic response to Cu for P. roscoffensis. ROS levels were triggered in a combination of 23 °C and 33 PSU and 5 µg L-1 of Cu, which was higher than all the other combinations studied. Our study resulted in data concerning the potential impacts caused by possible future climate change scenarios in aquatic habitats chronically exposed to metals.

Microalgae biomass as a conditioner and regulator of soil quality and fertility.

Characteristics of an acid soil cultivated with Urochloa brizantha cv. Marandu were evaluated in relation to two types of fertilization: a conventional one, chemical based on nitrogen and potassium, and a biofertilizer, based on microalgae biomass. The results were compared among three treatments, control, conventional, and biological fertilization, with seven replications each. The study evaluated microalgae community, total carbon and nitrogen contents, mineral nitrogen, and enzymatic activity. Chlorella vulgaris showed the highest organism density, which can be explained by its rapid growth and high resistance. The highest species diversity was detected in the control 1,380,938 org cm-3 and biological 1,841,250 org cm-3 treatments, with the latter showing a higher density of cyanobacteria, especially Pseudanabaena limnetica with 394,554 org cm-3. The soil treated with chemical fertilization showed higher nitrate (9.14 mg NKg-1 NO3--N) and potassium (52.32 mg dm-3) contents. The highest levels of sulfur (21.73 mg dm-3) and iron (96.46 mgdm-3) were detected in the biological treatment. The chemical treatment showed higher activity of the enzymes acid phosphatase, acetylglucosaminidase, and sulfatase, while α-glucosidase and leucine aminopeptidase stood out in the biological treatment. Soil properties were not significantly affected by the treatments. The use of microalgae biomass derived from wastewater treatment from milking parlors was evaluated and presented as a promising biofertilizer for agriculture, following the line of recovering nutrient-rich wastes. In this sense, although many challenges need to be overcome, the results suggest that microalgal-based fertilizers could lead to low-impact agriculture.

Population and functional changes in a multispecies co-culture of marine microalgae and cyanobacteria under a combination of different salinity and temperature levels.

Changes in the temperature or salinity of ocean waters can affect marine organisms at multiple trophic levels. Both environmental variables could have an impact on marine microalgae populations. Therefore, the effect of the combination of three levels of temperature (20, 24 and 28 °C), and three levels of salinity (33, 36, and 39 PSU) were evaluated on the growth of a multispecies community of five common species of phytoplankton: (one cyanobacteria, Synechococcus sp., and four microalgae, Chaetoceros gracilis, Amphidinium carterae, Pleurochrysis roscoffensis and Rhodomonas baltica). The co-culture was monitored by flow cytometry under controlled conditions in a 96 h study. The effect of both variables on dissolved oxygen concentrations was measured using the SDR SensorDish Reader system. The results demonstrated that Synechococcus sp., C. gracilis, and A. carterae displayed a high growth at the temperature of 28 °C combined with the lowest salinity assayed. However, salinity increases negatively affected the growth of P. roscoffensis and R. baltica. Decreased salinity combined with decreased temperature exhibited a higher net O2 production. The interaction of two environmental factors related to global change such as temperature and salinity can cause structural (community growth) and functional (net oxygen production) changes in a phytoplanktonic community.

Multi-level biological responses of Daphnia magna exposed to settleable atmospheric particulate matter from metallurgical industries.

Metallurgical industries are a continuous source of air pollution due to the amount of settleable particulate matter (SePM) they release. This SePM is a complex mixture formed by metallic nanoparticles and metals, which reach terrestrial and aquatic ecosystems and can be a significant source of contamination. The aim of this study was to evaluate the adverse effects of SePM at different levels of biological organization in order to estimate its ecological impacts on aquatic ecosystems. For this purpose, the crustacean Daphnia magna was exposed to different concentrations of SePM (0.01, 0.1, 1, 5, 10 g/L) using a multi-level response approach. The endpoints studied were: avoidance throughout 24 h in a non-forced exposure system, reproduction (total number of neonates per female after 21 days of exposure), acetylcholinesterase activity (AChE) after 48 h, and finally, the feeding rates during a short-term exposure (48 h) and a long-term exposure (21 day + 48 h). There was a negative effect of SePM on all responses measured at high concentrations. The avoidance was concentration-dependent and represented 88 % and 100 % at the two highest concentrations. The AChE activity was significantly inhibited at 5 and 10 g/L. The total number of neonates increased from 1 g/L of SePM and the first brood occurred earlier as of 5 g/L compared to control. The post-exposure feeding rates were lower during long-term exposure at the highest concentration. Chemical analyses were performed to characterize the metals present in this SePM, but this study did not report any direct relationship with toxicity, due to the chemical heterogeneity of the particles. The emission of compounds caused by anthropogenic activity may have significant ecological consequences, so it is important to consider these possible effects on aquatic biota generated by the mixture of metals present in SePM originated from metallurgical activities. Environmental and sectorial regulations are needed to prevent contamination and ecological disturbances.

Influence of salinity and temperature on the growth, productivity, photosynthetic activity and intracellular ROS of two marine microalgae and cyanobacteria [Mar. Environ. Res. 2023 Apr; 186:105932. Epub 2023 Feb 24].

Global Climate Change could change physical parameters in oceans, such as salinity and temperature. The impact of such changes in phytoplankton has not been well stated yet. In this study the effect of combination of three levels of temperature (20, 23, and 26 °C), and three levels of salinity (33, 36, and 39) on growth of a mixture co-cultivation of three common species from phytoplankton (one cyanobacteria, Synechococcus sp., and two microalgae, Chaetoceros gracilis, and Rhodomonas baltica), is monitored by flow cytometry under controlled cultivation conditions in a 96 h study. Chlorophyll content, enzymes activities and oxidative stress were also measured. Results demonstrate that cultures of Synechococcus sp. Exhibited a high growth at the highest temperature chosen in this study (26 °C) combined with the three selected salinity levels 33, 36, and 39. Nevertheless, Chaetoceros gracilis grew very slowly with the combination of high temperature (39 °C) and all salinities, while Rhodomonas baltica did not grow at temperatures higher than 23 °C. Maximum dry biomass and ash-free dry weight for the microalgal mixture were reached at salinity of 39 and temperature of 20 °C, the but highest chlorophyll fluorescence values were found at 30 salinity and 20 °C, decreasing as salinity and temperature increased.

Corrigendum to "Influence of salinity and temperature on the growth, productivity, photosynthetic activity and intracellular ROS of two marine microalgae and cyanobacteria" [Mar. Environ. Res. 186 (2023) 105932].

Global Climate Change (GCC) could change physical parameters in oceans, such as salinity and temperature. The impact of such changes in phytoplankton has not been well stated yet. In this study, the effect of combination of three levels of temperature (20, 23, and 26 °C) and three levels of salinity (33, 36, and 39) on growth of a mixture co-cultivation of three common species from phytoplankton (one cyanobacteria, Synechococcus sp., and two microalgae, Chaetoceros gracilis, and Rhodomonas baltica), is monitored by flow cytometry under controlled cultivation conditions in a 96 h study. Chlorophyll content, enzymes activities and oxidative stress were also measured. Results demonstrate that cultures of Synechococcus sp. Exhibited a high growth at the highest temperature chosen in this study (26 °C) combined with the three selected salinity levels 33, 36, and 39. Nevertheless, Chaetoceros gracilis grew very slowly with the combination of high temperature (26 °C) and all salinities, while Rhodomonas baltica did not grow at temperatures higher than 23 °C. Maximum dry biomass and ash-free dry weight for the microalgal mixture were reached at salinity of 39 and temperature of 20 °C, and the highest chlorophyll fluorescence values were found at 30 salinity and 20 °C, decreasing as salinity and temperature increased.

Influence of salinity and temperature on the growth, productivity, photosynthetic activity and intracellular ROS of two marine microalgae and cyanobacteria.

Global Climate Change could change physical parameters in oceans, such as salinity and temperature. The impact of such changes in phytoplankton has not been well stated yet. In this study the effect of combination of three levels of temperature (20, 23, and 26 °C), and three levels of salinity (33, 36, and 39) on growth of a mixture co-cultivation of three common species from phytoplankton (one cyanobacteria, Synechococcus sp., and two microalgae, Chaetoceros gracilis, and Rhodomonas baltica), is monitored by flow cytometry under controlled cultivation conditions in a 96 h study. Chlorophyll content, enzymes activities and oxidative stress were also measured. Results demonstrate that cultures of Synechococcus sp. Exhibited a high growth at the highest temperature chosen in this study (26 °C) combined with the three selected salinity levels 33, 36, and 39. Nevertheless, Chaetoceros gracilis grew very slowly with the combination of high temperature (39 °C) and all salinities, while Rhodomonas baltica did not grow at temperatures higher than 23 °C. Maximum dry biomass and ash-free dry weight for the microalgal mixture were reached at salinity of 39 and temperature of 20 °C, the but highest chlorophyll fluorescence values were found at 30 salinity and 20 °C, decreasing as salinity and temperature increased.

Effects of global environmental change on microalgal photosynthesis, growth and their distribution.

Global climate change (GCC) constitutes a complex challenge posing a serious threat to biodiversity and ecosystems in the next decades. There are several recent studies dealing with the potential effect of increased temperature, decrease of pH or shifts in salinity, as well as cascading events of GCC and their impact on human-environment systems. Microalgae as primary producers are a sensitive compartment of the marine ecosystems to all those changes. However, the potential consequences of these changes for marine microalgae have received relatively little attention and they are still not well understood. Thus, there is an urgent need to explore and understand the effects generated by multiple climatic changes on marine microalgae growth and biodiversity. Therefore, this review aimed to compare and contrast mechanisms that marine microalgae exhibit to directly respond to harsh conditions associated with GCC and the potential consequences of those changes in marine microalgal populations. Literature shows that microalgae responses to environmental stressors such as temperature were affected differently. A stress caused by salinity might slow down cell division, reduces size, ceases motility, and triggers palmelloid formation in microalgae community, but some of these changes are strongly species-specific. UV irradiance can potentially lead to an oxidative stress in microalgae, promoting the production of reactive oxygen species (ROS) or induce direct physical damage on microalgae, then inhibiting the growth of microalgae. Moreover, pH could impact many groups of microalgae being more tolerant of certain pH shifts, while others were sensitive to changes of just small units (such as coccolithophorids) and subsequently affect the species at a higher trophic level, but also total vertical carbon transport in oceans. Overall, this review highlights the importance of examining effects of multiple stressors, considering multiple responses to understand the complexity behind stressor interactions.