A major reduction in hydropeaking from Glen Canyon Dam into the Colorado River (Arizona, USA) was initiated in the 1990s to protect downstream riverine habitats. As a result, diel discharge varied significantly less in 2020 than in prior years in the Colorado River tailwaters, a section in which a diverse macrophyte assemblage recently developed. We conducted a year-long study in 2020 to characterize the recent epiphytic diatom assemblage by assessing present-day species richness, taxonomic composition, ecological guilds, and spatial patterns under the current flow regime. We also examined the 2020 assemblage in one section of the river previously studied in the 1980s and 1990s when Cladophora glomerata served as the dominant macrophyte host. We sampled epiphytes from all major macrophytes at 2–5 km intervals over four seasonal periods, identifying 218 diatom species, more than doubling the previously documented species richness. Fifty taxa comprised 99% of valves in the assemblage, with a majority (54%) of high-profile forms, along with 24% low-profile, 14% motile, and 8% planktonic guilds. Hierarchical clustering revealed that diatom species composition and ecological guilds along the 25 km reach varied according to differences in river depth and macrophyte host and varied less with distance from the dam.
Growing pressure to make aquaculture more sustainable has renewed attention on bioactive feed ingredients obtained from natural sources. In the present work, juvenile FFRC-strain common carp (Cyprinus carpio L.) were used to examine how graded dietary inclusion of Euglena gracilis powder (EP) influences growth, redox status, immune responsiveness and the underlying molecular regulation. Four hundred and fifty fish (2.23 ± 0.01 g) were distributed at random among five isonitrogenous and isolipidic diets supplying 0 (control), 0.25, 0.5, 1 or 2% EP, and were reared for eight weeks. Survival, growth and feed use were all improved by EP, most evidently at 0.25% and 0.5%. Within this window, both antioxidant capacity and the activity of nonspecific immune enzymes increased, and hepatic transcription of genes governing antioxidant defence and cytokine signalling was correspondingly altered, notably through genes linked to the Nrf2/Keap1 axis. Inclusion at 2%, by contrast, conferred no further advantage and was accompanied by poorer feed conversion, so that the overall response was clearly dose-dependent and non-linear. Taken together, EP acts in a biphasic manner in common carp: 0.25–0.5% improves growth and physiological regulation, whereas higher levels are counterproductive. The results underline the promise of Euglena biomass as a renewable, algae-derived functional ingredient for aquafeed formulation. Future work should validate their effects in larger-scale and longer-term feeding trials, assess the consistency of raw material quality and feed processing, and evaluate production costs and economic returns to determine their feasibility for commercial application.
The cyanobacteria Synechococcus spp. are key contributors to marine primary productivity. They are found from equatorial to polar waters where these organisms are exposed to changed levels of pCO2 and solar ultraviolet radiation (UVR, 280–400 nm). To investigate how elevated pCO2 modulates the physiological responses of a coastal pico-cyanobacterium to UVR, Synechococcus XM24 was used and acclimated to periodic (90 min per day) near-surface UVR exposure under ambient (418 µatm) and elevated (1000 µatm) pCO2 conditions for 17 days. Our results indicate that elevated pCO2 markedly enhanced its specific growth, cellular pigment accumulation (chlorophyll a, carotenoids), and particulate organic carbon/nitrogen (POC/PON) quotas in the cells grown under light (without exposure to UVR). However, such stimulatory effects were substantially abolished in UVR-exposed cells. UVR significantly inhibited the effective photochemical quantum yield of photosystem II (PSII) and accelerated PSII damage without a compensatory increase in repair, thereby reducing the repair/damage ratio (r/k) by up to 4-fold. The cells acclimated to the UVR exposures reduced their carbon fixation rate by 56–60% regardless of the pCO2 levels. In addition, UVR exposure led to drastic reductions in cellular POC and PON content, reflecting a potential energy shift from biomass production towards cellular maintenance. Reduced contents of Chl a and carotenoids under the combination of UVR and elevated pCO2 should be responsible for the reductions in photosynthetic carbon fixation and POC/PON contents. Our results imply that while progressive ocean acidification with increasing pCO2 can stimulate growth of the coastal Synechococcus XM24 under PAR-alone conditions, exposures to UV radiation can diminish such enhancement.
Commercial seaweed farming in India began in 1984 and expanded after experimental trials in the late 1990s, with Kappaphycus alvarezii cultivation emerging in 2001. Production peaked in 2013 but subsequently declined because of challenges including mass mortality, with current dry production estimated at 200–300 t annually. To revive the sector, Pradhan Mantri Matsya Sampada Yojana (PMMSY) proposed an investment of USD 76.8 million to achieve 1.12 Mt fresh biomass by 2025. However, expansion is constrained by inadequate availability of quality planting material (QPM), highlighting the need for dedicated seaweed nurseries. To meet 60% of the PMMSY target, approximately 66 nurseries, each producing 102 tons of fresh biomass annually, would be required (model-based projections from laboratory data, not yet validated at commercial scale in India). This would require an estimated 13,254 trained laboratory workers and 13,539 field workers, potentially generating employment equivalent to 0.27% of India’s marine fishers. Successful implementation will require coordinated support from government agencies, research institutions, private enterprises, and NGOs, along with subsidies and incentives for entrepreneurs. Establishing seaweed nurseries can ensure reliable QPM, strengthen raw material supply, create employment, and support India’s seaweed industry toward achieving PMMSY targets and long-term sustainability through resource-efficient nursery infrastructure and training.
This study analyzes the diversity of thin filamentous cyanobacteria from the volcanic Lake Terkhiin-Tsagaan, Mongolia. We isolated and characterized two strains from benthic samples collected from the lake. Using light microscopy, phylogenetic analysis of 16S rRNA gene sequences, and examination of the secondary structures of the 16S–23S ITS helices, we describe a new genus, Dgebuadzia, and a new species, Dgebuadzia mongoliensis. The 16S rRNA gene similarity to Phormidesmis was below the genus-level threshold (89.5% to P. mollis NIES-2126; minimum 94.19% to non-mollis Phormidesmis species), and the strains formed a well-supported monophyletic clade (BI/ML = 1/100) that is distinct from all other Leptolyngbyaceae included in the analysis. The strains also differed from Phormidesmis in the secondary structure of the Box-B and V3 helix. The new genus is closely related to P. arctica, a taxon whose original description is nomenclaturally invalid and which therefore cannot be formally transferred, although its phylogenetic position places it within the Dgebuadzia lineage. The data presented here contribute to our understanding of the diversity of thin filamentous cyanobacteria and expand current knowledge of the algal flora of Mongolian volcanic lakes.
