Heterosigma akashiwo in Patagonian Fjords: Genetics, Growth, Pigment Signature and Role of PUFA and ROS in Ichthyotoxicity

Salinity as an Abiotic Stressor for Eliciting Bioactive Compounds in Marine Microalgae

This study investigated the impact of culture medium salinity (5-50 PSU) on the growth and maximum photochemical yield of photosystem II (Fv/Fm) and the composition of carotenoids, fatty acids, and bioactive substances in three marine microalgae (Chrysochromulina rotalis, Amphidinium carterae, and Heterosigma akashiwo). The microalgae were photoautotrophically cultured in discontinuous mode in a single stage (S1) and a two-stage culture with salt shock (S2). A growth model was developed to link biomass productivity with salinity for each species. C. rotalis achieved a maximum biomass productivity (Pmax) of 15.85 ± 0.32 mg·L-1·day-1 in S1 and 16.12 ± 0.13 mg·L-1·day-1 in S2. The salt shock in S2 notably enhanced carotenoid production, particularly in C. rotalis and H. akashiwo, where fucoxanthin was the main carotenoid, while peridinin dominated in A. carterae. H. akashiwo also exhibited increased fatty acid productivity in S2. Salinity changes affected the proportions of saturated, monounsaturated, and polyunsaturated fatty acids in all three species. Additionally, hyposaline conditions boosted the production of haemolytic substances in A. carterae and C. rotalis.

Influence of multi-stressor combinations of pCO2, temperature, and salinity on the toxicity of Heterosigma akashiwo (Raphidophyceae), a fish-killing flagellate

Climate change and global warming have led to more frequent harmful algal blooms in the last decade. Among these blooms, Heterosigma akashiwo, a golden-brown phytoflagellate, is one of the 40 species with a high potential to form harmful blooms, leading to significant fish mortality. Climate change leads to rising atmospheric and ocean temperatures. These changes, along with altered rainfall patterns and meltwater input, can cause fluctuations in ocean salinity. Elevated atmospheric carbon dioxide (CO2) levels increase water acidity as oceans absorb CO2. This study investigated the effects of temperature, salinity, and CO2 levels on lipid production, hemolytic activity, and toxicity of H. akashiwo using the design of experiment approach, which can be used to investigate the effect of two or more factors on the same response simultaneously in a precise manner with fewer experiments and materials but in a larger region of the factor space. The lipid content was measured using a high-throughput Nile Red method, and the highest level of lipid content was detected at 25°C, a salinity of 30, and a CO2 concentration of 400 ppm. Hemolytic activity was assessed using rabbit blood erythrocytes in a 96-well plate, and the optimal conditions for achieving the highest hemolytic activity were determined at 15°C, a salinity of 10, and a CO2 concentration of 400 ppm. As the chemical structure of the toxin is not known, we used the toxicity against the cell line RTgill-W1 as the cell toxicity proxy. The maximum toxicity was identified at 15°C, a salinity of 10, and a CO2 level of 700 ppm.

Review of Harmful Algal Blooms (HABs) Causing Marine Fish Kills: Toxicity and Mitigation

Extensive growth of microscopic algae and cyanobacteria results in harmful algal blooms (HABs) in marine, brackish, and freshwater environments. HABs can harm humans and animals through their toxicity or by producing ecological conditions such as oxygen depletion, which can kill fish and other economically or ecologically important organisms. This review summarizes the reports on various HABs that are able to bring about marine fish kills. The predominant HABs, their toxins, and their effects on fishes spread across various parts of the globe are discussed. The mechanism of HAB-driven fish kills is discussed based on the available reports, and existing mitigation methods are presented. Lapses in the large-scale implementation of mitigation methods demonstrated under laboratory conditions are projected. Clay-related technologies and nano-sorption-based nanotechnologies, although proven to make significant contributions, have not been put to use in real-world conditions. The gaps in the technology transfer of the accomplished mitigation prototypes are highlighted. Further uses of remote sensing and machine learning state-of-the-art techniques for the detection and identification of HABs are recommended.

Harmful Algae Impacting Aquatic Organisms: Recent Field and Laboratory Observations

Algal blooms formed by some phytoplankton species can produce toxins or alter environmental conditions that can affect aquatic organisms and water quality, with impacts on the aquaculture and fisheries industries that can pose a risk to public health [...].

Mitigation of Marine Dinoflagellates Using Hydrogen Peroxide (H2O2) Increases Toxicity towards Epithelial Gill Cells

Hydrogen peroxide (H₂O₂) has been shown to efficiently remove toxic microalgae from enclosed ballast waters and brackish lakes. In this study, in vitro experiments were conducted to assess the side effects of mitigating toxic and non-toxic dinoflagellates with H₂O₂. Five H₂O₂ concentrations (50 to 1000 ppm) were used to control the cell abundances of the toxic dinoflagellates Alexandrium catenella and Karenia selliformis and the non-toxic dinoflagellates Lepidodinium chlorophorum and Prorocentrum micans. Photosynthetic efficiency and staining dye measurements showed the high efficiency of H₂O₂ for mitigating all dinoflagellate species at only 50 ppm. In a bioassay carried out to test cytotoxicity using the cell line RTgill-W1, control experiments (only H₂O₂) showed cytotoxicity in a concentration- and time- (0 to 24 h) dependent manner. The toxic dinoflagellates, especially K. selliformis, showed basal cytotoxicity that increased with the application of hydrogen peroxide. Unexpectedly, the application of a low H₂O₂ concentration increased toxicity, even when mitigating non-toxic dinoflagellates. This study suggests that the fatty acid composition of toxic and non-toxic dinoflagellate species can yield toxic aldehyde cocktails after lipoperoxidation with H₂O₂ that can persist in water for days with different half-lives. Further studies are needed to understand the role of lipoperoxidation products as acute mediators of disease and death in aquatic environments.