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Abstract Sea ice algal communities are generally dominated by pennate diatoms, which commonly occur at the ice-water interface and in brine channels. They also make a significant contribution to higher trophic levels associated with sea ice habitats. Here, the photosynthetic responses of two sea ice diatom species, Navicula directa and Navicula glaciei, to changes in pCO2 under controlled laboratory conditions were compared. pCO2 (390 ppm and 750 ppm) was manipulated to simulate a shift from present levels (1990) to predicted “IPCC year 2100 worst-case scenario” levels. To investigate these effects, a pulse-amplitude modulation (PAM) fluorometer was used to measure the photosynthetic performance. The ability of the sea ice algae to grow and photosynthesize within physio-chemical gradients in the sea ice suggests that both sea ice species are likely to be well adapted to cope with changes in pCO2 concentrations. Lower pH and higher pCO2 for 7 days resulted in increased biomass, especially for N. directa. However, a decline in photosynthetic capacity (rETRmax) was observed for both species (highest value 11.375 ± 0.163, control; and 8.322 ± 1.282, treatment). Navicula glaciei showed significant effects of elevated pCO2 (p < 0.05) on its photosynthetic response, while N. directa did not. Future changes in CO2 and pH may thus not significantly affect all diatoms but may lead to changes in the photosynthetic activities in some species.

The global temperature increase has significant implications on the survival of microalgae which form the basis of all aquatic food webs. The aim of this study was to compare the response of similar taxa of microalgae from the Antarctic (Chlamydomonas UMACC 229, Chlorella UMACC 237, and Navicula glaciei UMACC 231), temperate (Chlamydomonas augustae UMACC 247, Chlorella vulgaris UMACC 248, and Navicula incerta UMACC 249), and tropical (C. augustae UMACC 246, C. vulgaris UMACC 001, and Amphiprora UMACC 239) regions to changing temperature. The Antarctic, temperate, and tropical strains were grown over specific temperature ranges of 4 °C to 30 °C, 4 °C to 32 °C, and 13 °C to 38 °C, respectively. The three Antarctic strains survived at temperatures much higher than their ambient regime. In comparison, the tropical strains are already growing at their upper temperature limits. The three Chlorella strains from different regions are eurythermal, with a large overlap on tolerance ranging from 4 °C to 38 °C. The specific growth rate (μ) of the Antarctic Navicula decreased (<0.34 day⁻¹) at temperatures above 4 °C, showing it to be sensitive to temperature increase. If further warming of Earth occurs, N. glaciei UMACC 231 is likely to have the most deleterious consequences than the other two Antarctic microalgae studied. The percentage of polyunsaturated fatty acids (PUFA) decreased with increasing temperature in the Antarctic Navicula. As temperature increases, the growth and nutritional value of this commonly occurring diatom in the Antarctic may decrease, with consequences for the aquatic food web. Of the three Chlamydomonas strains, only the Antarctic strain produced predominantly PUFA, especially 16:3 (48.4–57.2 % total fatty acids).

Influence of temperature and pCO sub(2), reflecting the future climatic scenario, on the marine periphytic diatom (Navicula distans) and its associated organisms was evaluated. Navicula distans along with its associated picoperiphyte and heterotrophic bacteria were exposed to two temperatures (30 degree C-present day, and 34 degree C-projected for year 2100) and pCO sub(2) levels (~500 mu atm-present day, and ~1500 mu atm-projected for year 2100) in a 2 2 factorial design. It was observed that rising temperature reduced the abundance of N. distans and picoperiphyte, but increased that of heterotrophic bacteria. On the other hand, rising pCO sub(2) favoured the growth of N. distans and picoperiphyte and had no significant effect on the bacterial growth. Synergistically, rising temperature and pCO sub(2) had a negative effect on N. distans, and a positive effect on picoperiphyte and heterotrophic bacteria. Additionally, this also resulted in the reduction of diatom cell size. This study suggests that in the future climatic scenario, increased abundance of picoperiphyte and heterotrophic bacteria along with smaller N. distans cells might influence the carbon budget and may have a cascading effect on higher trophic levels.

Cell adhesion is always the first step in biofilm development. With the emergence of attached cultivation systems, this study aims to promote a cost-effective approach for sustainable cultivation of microalgae, Navicula incerta , by pre-coating the main substrates, commercial polyvinylidene fluoride (PVDF) membranes with its own washed algal cells and self-produced soluble extracellular polymeric substances (EPS) for strengthened biofilm development. The effects of pH value (6 to 9), cell suspension volume (10 to 30 mL), and EPS volume (10 to 50 mL) were statistically optimized by means of response surface methodology toolkit. Model outputs revealed good agreement with cell adhesion data variation less than 1% at optimized pre-coating conditions (7.20 pH, 30 mL cell suspension volume, and 50 mL EPS volume). Throughout long-term biofilm cultivation, results demonstrated that EPS pre-coating substantially improved the attached microalgae density by as high as 271% than pristine PVDF due to rougher surface and the presence of sticky exopolymer particles. Nutrients absorbed via the available EPS coating from the bulk medium made the immobilized cells to release less polysaccharides on an average of 30% less than uncoated PVDF. This work suggests that adhesive polymer binders derived from organic sources can be effectively integrated into the development of high-performance novel materials as biocoating for immobilized microalgae cultivation.

Live prey used by the aquaculture industry are usually poor in some essential nutrients including long chain polyunsaturated fatty acids (LC-PUFA) and must be enriched to improve their nutritional value prior to larval feeding. Standard enrichment protocols are commonly based on lipid emulsions, being associated to a high oxidative stress condition. The combination of microalgae and lipid emulsion can palliate this situation, where the oxidative stress can be partially compensated by the antioxidant compounds present in microalgae. The maintenance of living microalgae in culture facilities is laborious, and the produced biomass may present fluctuating properties, leading to a serious bottleneck in the cultivation of live prey. Hence, substitutes for live microalgae including pastes or dried formats are receiving increasing research attention due to its nutritional stability, longer shelf-life and easy handling. In this study four different microalgae formats combined with a lipid emulsion are tested as enrichment products for Brachionus plicatilis and Artemia . Thus, fresh, frozen and spray-dried Navicula salinicola (NFRE, NFRO and NSD, respectively), and spray-dried Isochrysis galbana (ISD) were mixed with a commercial oil concentrate (Incromega TM ) or a marine lecithin (LC 60®), and added for 5 h to the rotifer or Artemia culture media. The antioxidant capacity of the microalgae extracts and the live prey activity of antioxidant enzymes, peroxides index (PxI) and thiobarbituric acid reactive substances (TBARS) were evaluated. The lipid profile of microalgae formats and enriched live preys was also determined. Ethyl acetate extract was the most antioxidant active extract of all microalgae formats. In addition, overall, I. galbana seems to be better than any N. salinicola format for a more effective protection against oxidative stress and for live prey lipid enrichment. Both rotifer and Artemia cultured with the mixture of I. galbana and the lipid emulsion generally showed higher DHA/EPA and EPA/ARA ratios. Moreover, the combination of the microalgae with LC 60® lipid emulsion highly favored Artemia ´s polar lipid and DHA incorporation. Among microalgae products, both spray-dried formats better enhanced live prey n-3 LC-PUFA content. Our results highlight the great potential of new microalgae-derived products to improve effectiveness of current live prey lipid enrichment protocols used in aquaculture.

This study investigated the effects of herbicide exposure on Navicula sp. (MASCC-0035) algae, focusing on growth density, chlorophyll content, antioxidant system, and lipid metabolism. Navicula cultures were exposed to different concentrations of atrazine (ATZ), glyphosate (Gly), and acetochlor (ACT) for 96 h. Results showed a significant decrease in cell numbers, with higher herbicide concentrations having the most noticeable impacts. For instance, Gly-G2 had reduced cell populations by 21.00% at 96 h. Chlorophyll content varied, with Gly having a greater impact on chlorophyll a compared to ATZ and ACT. Herbicide exposure also affected the antioxidant system, altering levels of soluble sugar, soluble protein, and reactive oxygen species (ROS). Higher herbicide rates increased soluble sugar content (e.g., ATZ, Gly, and ACT-G2 had increased by 14.03%, 19.88%, and 19.83%, respectively, at 72 h) but decreased soluble protein content, notably in Gly-G2 by 11.40%, indicating cellular stress. Lipid metabolism analysis revealed complex responses, with changes in free proline, fatty acids, and lipase content, each herbicide exerting distinct effects. These findings highlight the multifaceted impacts of herbicide exposure on Navicula algae, emphasizing the need for further research to understand ecological implications and develop mitigation strategies for aquatic ecosystems.

The occurrence of antibiotics in surface waters has been reported worldwide with concentrations ranging from ng L −1 to low µg L −1 levels. During environmental risk assessments, effects of antibiotics on algal species are assessed using standard test protocols (e.g., the OECD 201 guideline), where the cell number endpoint is used as a surrogate for growth. However, the use of photosynthetic related endpoints, such as oxygen evolution rate, and the assessment of effects on algal pigments could help to inform our understanding of the impacts of antibiotics on algal species. This study explored the effects of three major usage antibiotics (tylosin, lincomycin, and trimethoprim) on the growth and physiology of two chlorophytes ( Desmodesmus subspicatus and Pseudokirchneriella subcapitata ), a cyanobacteria ( Anabaena flos-aquae ), and a diatom ( Navicula pelliculosa ) using a battery of parameters, including cell density, oxygen evolution rate, total chlorophyll content, carotenoids, and the irradiance–photosynthesis relationship. The results indicated that photosynthesis of chlorophytes was a more sensitive endpoint than growth (i.e., EC 50 derived based on the effects of tylosin on the growth of D. subspicatus was 38.27 µmol L −1 compared with an EC 50 of 17.6 µmol L −1 based on photosynthetic rate), but the situation was reversed when testing cyanobacteria and the diatom (i.e., EC 50 derived based on the effects of tylosin on the growth of A. flos-aquae was 0.06 µmol L −1 ; EC 50 0.33 µmol L −1 based on photosynthetic rate). The pigment contents of algal cells were affected by the three antibiotics for D. subspicatus . However, in some cases, pigment content was stimulated for P. subcapitata , N. pelliculosa , and A. flos-aquae . The light utilization efficiency of chlorophytes and diatom was decreased markedly in the presence of antibiotics. The results demonstrated that the integration of these additional endpoints into existing standardised protocols could provide useful insights into the impacts of antibiotics on algal species.

Arctic ocean environments are receiving increasing attention, due to the rapid thinning and recession of marine sea ice caused by climate change. The present study characterizes the structure and chlorophyll a (Chl a) of summer microphytoplankton communities in western Arctic Ocean surface layers, in terms of species composition, periodical succession, geographic distribution, community types, abundance, and Chl a variation during the Fourth Chinese National Arctic Research Expedition (CHINARE, July–September, 2010). Possible effects of environmental forces on microphytoplankton communities were analyzed, and associations with water masses and sea-ice retreat were assessed. Results show high species diversity in surface microphytoplankton communities, with significant geographic and temporal zonation relative to taxonomic composition, species abundance, and Chl a. A total of 153 taxa were identified, distributed among 68 genera of 9 phyla, and cluster analysis and multi-dimensional scaling showed a continual distribution of a distinct shelf assemblage and deep basin assemblage. Average abundance (892.7 × 102 cells/l), Chl a (1.63 mg/m3), species diversity (2.54), and species richness (19) were established for the shelf assemblage, with dominant species ranked as Navicula pelagica Cleve, Thalassiosira nordenskiöeldii Cleve, Chaetoceros diadema (Ehrenberg) Gran, Leptocylindrus danicus Cleve, Pseudo-nitzschia seriata (Cleve) H. Peragallo, Cylindrotheca closterium (Ehrenberg) Reimann & Lewin, Nitzschia longissima (Brébisson) Ralfs, and Navicula vanhoeffenii Gran. It is of note that a succession from pennate to centric diatom was accompanied by a significantly decreased amplitude of abundance and Chl a, between the inbound and the return voyage across the Chukchi shelf. Comparatively, deep basin assemblage displayed lower values of abundance (27.7 × 102 cells/l), Chl a (0.12 mg/m3), species diversity (2.49), and species richness (11), and the community was dominated by Thalassionema nitzschioides Grunow and Navicula pelagica Cleve. Silicate and nitrate concentrations were major factors that affected abundance and Chl a variability in both Pearson correlation analysis and canonical correspondence analysis, while the dynamics of oceanic circulation and sea-ice retreat affected summer microphytoplankton community assembly and fluctuations in the surface layer of the western Arctic Ocean.

Bisphenol S (BPS), one of the most widely used bisphenol A substitutes, has recently received more attention because of its high detection in water and potential toxicity. In the present study, the toxicity and removal of BPS in typical freshwater algae Navicula sp. were investigated under laboratory conditions and the comparative study with Chlorella vulgaris was also explored. BPS was more toxic to Navicula sp. than C. vulgaris with their 120-h EC 50 values of 3.89 and 25.19 mg/L, respectively. It may be mainly ascribed to the high tolerance of C. vulgaris to BPS. For instance, the superoxide dismutase (SOD) and catalase (CAT) activities of C. vulgaris were increased under the exposure of 20 mg BPS/L, whereas they were increased in Navicula sp. at 1 mg BPS/L. It is implied that the detoxification mechanism of C. vulgaris was activated until BPS concentration reach to 20 mg L −1 . Moreover, the results had demonstrated that both algae had promoted the removal of BPS at 0.5 mg/L, but the removal could be inhibited as BPS concentration increased. Navicula sp. presented a better removal of BPS because of their higher accumulation, implying that they may be good materials for the removal of BPS. In addition, the sharp increase of BCF value at 72 h in Navicula sp. under the exposure of environmental-related BPS concentration (0.5 mg/L) may indicate a high risk of BPS to aquatic ecosystem. These findings will provide a reference for the risk assessment of BPS in natural waters.

Microalgal biodiesel has attracted much attention because of its potential to replace fossil fuels and reduce carbon dioxide (CO2) emissions. In this work, six species of microalgae were isolated from the Three Gorges Reservoir for the first time. The abilities of fixing CO2 and producing lipid of these species, along with four supplemental species, were measured. The lipid contents of Navicula minima and Actinastrum hantzschii were (28.0±2.8)% and (30.8±1.2)%, respectively, close to the highest value reported before. Navicula minima was found to have the highest lipid productivity, 2.9 mg/L/d, and a high CO2-fixing efficiency of 17.2 mg/L/d. The quality of biodiesel derived from the lipids of Navicula minima was closest to international standards, supporting the promising potential of microalgal biodiesel production. These findings provide an important reference for the industrial cultivation of microalgae in the Three Gorges Reservoir for biodiesel production and CO2 fixation.