Search Results (82)

Kleptoplastidy is a nutrition mode in which cells of protists and some multicellular organisms acquire, maintain, and exploit chloroplasts of prey algae cells as photosynthesis reactors. It is an important aspect of the mixotrophic feeding strategy, which plays a role in the formation of harmful algae blooms (HABs). We developed a new mathematical model, in which kleptoplastidy is regarded as a mechanism of enhancing mixotrophy of protists. The model is constructed using three thought (theoretical) experiments and the concept of biological time. We propose to measure the contribution of kleptoplastidy to mixotrophy using a new ecological indicator: the kleptoplastidy index. This index is a function of two dimensionless variables, one representing the ratio of photosynthetic production of acquired chloroplasts versus native chloroplasts, and the other representing the balance between autotrophic and heterotrophic feeding modes. The index is tested by data for the globally distributed, bloom-forming potentially toxic mixotrophic dinoflagellates Prorocentrum cordatum. The model supports our hypothesis that kleptoplastidy can increase the division rate of algae significantly (by 40%), thus boosting their population growth and promoting blooms. The proposed model can contribute to advancements in ecological modeling aimed at forecasting and management of HABs that deteriorate marine coastal environments worldwide. Full article

The Arabian Gulf, bordered by major energy-producing nations, harbors diverse microalgal communities with strong potential for the bioremediation of environmental pollutants, particularly petroleum hydrocarbons. This review evaluates two key microalgal groups—micro-green algae and dinoflagellates—highlighting their distinct physiological traits and ecological roles in pollution mitigation. Dinoflagellates, including Prorocentrum and Protoperidinium, have demonstrated hydrocarbon-degrading abilities but are frequently linked to harmful algal blooms (HABs), marine toxins, and bioluminescence, posing ecological and health risks. The toxins produced by these algae can be hemolytic or neurotoxic and include compounds such as azaspiracids, brevetoxins, ciguatoxins, okadaic acid, saxitoxins, and yessotoxins. In contrast, micro-green algae such as Oedogonium and Pandorina are generally non-toxic, seldom associated with HABs, and typically found in clean freshwater and brackish environments. Some species, like Chlorogonium, indicate pollution tolerance, while Dunaliella has shown promise in remediating contaminated seawater. Both groups exhibit unique enzymatic pathways and metabolic mechanisms for degrading hydrocarbons and remediating heavy metals. Due to their respective phycoremediation capacities and environmental adaptability, these algae offer sustainable, nature-based solutions for pollution control in coastal, estuarine, and inland freshwater systems, particularly in mainland Qatar. This review compares their remediation efficacy, ecological impacts, and practical limitations to support the selection of effective algal candidates for eco-friendly strategies targeting petroleum-contaminated marine environments. Full article

Chydorus sphaericus is often a dominant cladoceran zooplankton species in water bodies experiencing harmful cyanobacterial blooms. However, its relationship with toxin-producing algae remains largely unexplored. In this study, the feeding behavior of C. sphaericus on colonial cyanobacteria and potentially toxic Microcystis was investigated in a temperate, shallow, eutrophic lake. Liquid chromatographic analyses of phytoplankton marker pigments in C. sphaericus gut content revealed that pigments characteristic of cyanobacteria (identified a zeaxanthin, echinenone, and canthaxanthin) comprised the majority of its diet. Among them, colonial cyanobacteria (marked by the pigment canthaxanthin) were the highly preferred food source despite their minor contribution to phytoplankton biomass. qPCR targeting Microcystis genus-specific mcyE synthase genes, which are involved in microcystin biosynthesis, indicated that potentially toxic strains of Microcystis were present in C. sphaericus gut content throughout its temporal and spatial presence in the lake. The results suggest that the common small cladoceran in eutrophic waters, C. sphaericus, has a close trophic interaction with colonial cyanobacteria (including Microcystis) and may represent an important vector for transferring toxigenic Microcystis to the food web, even under conditions of low Microcystis biomass in the lake water. Full article

Harmful algal blooms can negatively impact freshwater, estuarine, and coastal marine systems globally and pose serious risks to water quality, human and ecosystem health, and food production. Algae can produce toxic compounds, directly interfere with aquaculture species through (e.g.,) the production of foam or mucilage, as well as causing diseases and disorders in fish, and can result in hypoxic conditions when the bloom senesces. Application of US Environmental Protection Agency (USEPA) registered algaecides can be effective, scalable, and inexpensive, but there is growing interest in plant- or bacterial-derived compounds that do not require the use of chemicals such as hydrogen peroxide or copper. The algaecide C7X1 is a plant-based organic algaecide that proves effective against a wide variety of algae, including harmful algal species such as Microcystis, Heterosigma, and Pseudo-nitzschia. Performance is comparable to other USEPA-registered algaecides, with low to moderate extracellular toxin release and a potential lifetime of weeks in treated waters. The mode of action is inhibition of photosynthesis, suggesting that direct off-target impacts on zooplankton and other organisms would be minimal. Full article

Phycosphere niches host rich, unique microbial consortia that harbor complex algae–bacteria interactions with fundamental significance in underpinning most functions of aquatic ecological processes. Therefore, harvesting the uncultured phycobacteria is crucial for understanding the intricate mechanisms governing these dynamic interactions. Here, we characterized and compared microbial community composition of the phycosphere microbiota from six harmful algal bloom-forming marine dinoflagellates, Alexandrium spp., and their bacterial associations. Furthermore, based on a combinational enhanced cultivation strategy (CECS) procedure for the selected isolation for cultivable phycobacteria, a new yellow-pigmented bioactive bacterium designated ABI-6-9 was successfully recovered from cultivable phycobacteria of the highly toxic A. minutum strain amtk4. An additional phylogenomic analysis fully identified this new isolate as a potential novel species of the genus Mameliella within the family Roseobacteraceae. The bioactivity evaluation observed that strain ABI-6-9 can significantly promote the cell growth of its algal host and altered the gonyautoxin accumulation profiles in the co-culture circumstance. Additionally, the bacterial production of active bioflocculanting exopolysaccharides (EPSs) by strain ABI-6-9 was also measured after culture optimization. Thus, these findings revealed the potential environmental and biotechnological implications of this new microalgae growth- promoting phycobacterium. Full article

The region of Eastern Siberia that we have been studying is situated in Yakutia in the permafrost area. We studied five lakes of various geneses, located both in the urbanized territory of Yakutsk city and its suburbs and in natural landscapes at a distance from the impacted area. All lakes were found to have high levels of ammonium nitrogen, total phosphorus and total iron. The lakes’ plankton was found to contain 92 species of algae and cyanobacteria. Cyanobacteria in most lakes accounted for 53 to 98% of the biomass. In one of the natural lakes, 95% of the total biomass was Dinoflagellata. Bioindication, statistics and ecological mapping methods revealed correlations between cyanobacterial production intensity, landscape runoff and lake trophic state. Potentially toxic cyanobacteria containing microcystin and saxitoxin synthesis genes were found in four lakes. Our previous studies established that cyanobacterial harmful algal bloom (CyanoHABs) with microcystin production are characteristic only for lakes in urbanized areas that experience the input of nutrients and organic matter due to anthropogenic runoff. This study indicates that CyanoHABs are possible in lakes in natural areas that are permafrost-dune-type lakes according to their genesis. For the first time in the region, potentially toxic cyanobacteria with saxitoxin synthesis genes have been found. Dune-type lakes do not freeze to the bottom during winter due to taliks underneath them, which provides advantages for cyanobacteria vegetation. Dune-type lakes are very common in the permafrost area, so the extent of CyanoHAB’s distribution in this region may be underestimated. Full article

Alexandrium pacificum, a dinoflagellate known for causing harmful algal blooms (HABs), has garnered significant attention due to its potential toxicity to marine ecosystems, fisheries, and human health. However, the effects of this toxin-producing alga on shrimp are not yet comprehensively understood. This study aimed to assess the hepatopancreas damage induced by A. pacificum in the economically important shrimp species E. carinicauda and to elucidate the underlying molecular mechanisms through histology, antioxidant enzyme activity, and transcriptome analysis. The shrimp were assigned to either a control group or an exposed group, with the latter involving exposure to A. pacificum at a concentration of 1.0 × 10⁴ cells/mL for 7 days. A histological analysis subsequently revealed pathological changes in the hepatopancreas tissue of the exposed group, including lumen expansion and the separation of the basement membrane from epithelial cells, while antioxidant enzyme activity assays demonstrated that exposure to A. pacificum weakened the antioxidant defense system, as evidenced by the reduced activities of catalase, superoxide dismutase, and glutathione, along with increased malondialdehyde levels. Transcriptome analysis further identified 663 significantly upregulated genes and 1735 significantly downregulated ones in the exposed group, with these differentially expressed genes being primarily associated with pathways such as protein processing in the endoplasmic reticulum, mitophagy, glycolysis/gluconeogenesis, sphingolipid metabolism, and glycerophospholipid metabolism. This study provides novel insights into the toxicological effects of A. pacificum on aquatic organisms and enhances the current understanding of the ecotoxicological risks posed by HABs. Full article

Algal blooms caused by Microcystis aeruginosa are a common occurrence and pose significant threats to freshwater ecosystems. This study investigates the antialgal effects and underlying mechanisms of two plant-derived fatty acids, nonanoic acid and palmitic acid, on Microcystis aeruginosa. The results show that the inhibitory effects of both fatty acids on M. aeruginosa increase with higher concentrations. Algal recovery occurs when nonanoic acid concentrations are below 0.5 mg/L and palmitic acid concentrations are below 50 mg/L. Acute toxicity tests indicate that the safe concentrations of nonanoic acid and palmitic acid are below 1.87 mg/L and 263.3 mg/L, respectively. The inhibitory effect of nonanoic acid is more pronounced under conditions of pH 5.5, 15 °C temperature, 0.75 mg/L nitrogen, and 2 mg/L phosphorus, with inhibition efficiency remaining unaffected by increased light intensity. Both fatty acids exert their strongest inhibitory effects in the early stages of addition (0–8 days), causing cell death and the release of extracellular organic matter primarily consisting of aromatic compounds and proteins. Oxidative stress analysis reveals that high concentrations of fatty acids can cause irreversible damage to the algae’s antioxidant defense system. These findings provide valuable insights for the prevention and control of cyanobacterial blooms, which can help promote the sustainable development of freshwater ecosystems. Full article

The effects of toxic and non-toxic Microcystis aeruginosa on the Ceratophyllum demersum–Scenedesmus obliquus system were simulated in the laboratory, and some parameters in relation to these organisms were measured. In this experiment, C. demersum increased the biomass of S. obliquus, and both toxic and non-toxic M. aeruginosa significantly inhibited the colony formation of S. obliquus and inhibited the promotion of S. obliquus biomass. On the 14th day, the soluble polysaccharide content of C. demersum decreased when it was coexisted with S. obliquus, but it rose again because of M. aeruginosa, which significantly increased the protein content of C. demersum. The species composition and diversity of epiphytic microorganisms also vary with different treatments. Proteobacteria is dominant in all the groups, especially in the Toxic_SMC group. In addition, bacteria that can degrade organic pollutants are more abundant in Toxic_SMC group. This study focuses on the defense response of S. obliquus induced by C. demersum under the pressure of toxic or non-toxic M. aeruginosa and evaluates the changes to C. demersum and its epiphytic microorganisms, which provides insights for the study of aquatic plant–algae integrated action systems in eutrophic or cyanobacterial blooms. Full article

The pursuit of highly effective, low-toxicity, and eco-friendly algicides for controlling and eradicating harmful algal blooms (HABs) is of paramount importance. The natural allelochemical bacillamide A has displayed impressive algicidal activity against harmful algae with favorable safety profiles. However, the poor synthetic efficiency and large dose requirements of bacillamide A limit its further application. In this paper, 17 thiazole-containing bacillamide derivatives (BDs) were designed and synthesized in three linear steps as potential algicides. Eight compounds (6a, 6c, 6j, 7b, 7c, 7d, 7e, and 7g) displayed potent inhibitory effects against Prorocentrum minimum, Skeletonema costatum, and Alexandrium pacificum, and they had similar or better activity than the positive control (CuSO₄) and bacillamide A. Compound 6a exhibited the most potent algicidal activity against S. costatum (half-maximal effective concentration [EC₅₀] = 0.11 μg/mL), being 23-fold more potent than bacillamide A, 28-fold more potent than CuSO₄, and 39-fold more potent than Diuron. Compound 6j exhibited significant algicidal activity against the toxic dinoflagellates P. minimum (EC₅₀ = 1.0 μg/mL) and A. pacificum (EC₅₀ = 0.47 μg/mL), being 3–5-fold more potent than natural bacillamide A, Diuron, and CuSO₄. Micrographs and SEM images revealed that 6j induced cell wall rupture and cellular content leakage. Biochemical and physiological studies indicated that 6j might partially disrupt the antioxidant and photosynthetic systems in algal cells, resulting in morphological changes, cell wall rupture, and inclusion leakage. Our work suggests that 6j has a distinct mode of action from CuSO₄ and provides a promising candidate for the development of new algicides, worthy of further investigation. Full article

Over the recent decades, an apparent worldwide rise in Harmful Algae Blooms (HABs) has been observed due to the growing exploitation of the coastal environment, the exponential growth of monitoring programs, and growing global maritime transport. HAB species like Alexandrium catenella—responsible for paralytic shellfish poisoning (PSP)—Protoceratium reticulatum, and Lingulaulax polyedra (yessotoxin producers) are a major public concern due to their negative socioeconomic impacts. The significant northward geographical expansion of A. catenella into more oceanic-influenced waters from the fjords where it is usually observed needs to be studied. Currently, their northern boundary reaches the 36°S in the Biobio region where sparse vegetative cells were recently observed in the water column. Here, we describe the environment of the Biobio submarine canyon using sediment and water column variables and propose how toxic resting cyst abundance and excystment are coupled with deep-water turbulence (10⁻⁷ Watt/kg) and intense diapycnal eddy diffusivity (10⁻⁴ m² s⁻¹) processes, which could trigger a mono or multi-specific harmful event. The presence of resting cysts may not constitute an imminent risk, with these resting cysts being subject to resuspension processes, but may represent a potent indicator of the adaptation of HAB species to new environments like the anoxic Biobio canyon. Full article

Protoceratium reticulatum, a dinoflagellate species known for producing yessotoxins (YTX), can form harmful algal blooms (HABs) impacting marine life. This study examined how P. reticulatum influenced the physiological rates and affected the tissue health of juvenile scallops, Argopecten purpuratus. The scallops were exposed to non-toxic algae Isochrysis galbana (diet A) and mixtures where 30 and 70% of the non-toxic algae were replaced by the toxic algae P. reticulatum (diet B and C, respectively) for 15 days, followed by a 15-day recovery period (I. galbana). Results showed that the clearance rate (CR), inorganic ingestion rate (IIR), organic ingestion rate (OIR), and absorption rate (AR) were significantly reduced within the first seven days of exposure to toxic diets, with reductions of approximately 25% and 50% in diets B and C, respectively, compared to the non-toxic diet, and an increase in these parameters during the recovery stage. Histological observations revealed greater tissue damage in the digestive gland than in the gills, with a higher frequency of scallops with severe damage correlating with higher toxic diet content. Despite no direct impact on survival, the compromised physiological health of A. purpuratus juveniles suggests increased vulnerability to other stressors. These findings provide new insights into the filter-feeding behavior and selective filtration capabilities of scallops in the presence of toxic dinoflagellates and how scallops health can be compromised, contributing to the understanding of how HABs and associated toxins affect A. purpuratus. Full article

In Europe, climate change will increase hydrologic extremes, resulting in shorter flood peaks and longer droughts. Extended low flows will significantly alter physico-chemical water quality, paving the way for compound, novel impacts. We analyze the Oder River catastrophe of August 2022, where the complex interplay of increased salinity, temperature, low flows, reduced water volumes and sunlight enabled Prymnesium parvum blooming. This brackish water alga grew to 100 million cells per liter and killed about 1000 tons of fish. We assess the impact on and the recovery potential of the fish population to guide both preventing future catastrophes and enhancing river resilience. Stock decline rates were assessed while accounting for natural population fluctuations. Significant relative declines in both fish and biomass density reached up to 76% and 62%, respectively. The mid-channel was more severely affected than littoral areas. Littoral shelter, depth variability, and especially lateral and longitudinal connectivity appeared essential for fish survival and recovery. The compound nature of this catastrophic event highlights the urgent need to rethink the present mismanagement of rivers. Resilient rivers are the backbone of climate change-resilient landscapes. Therefore, we argue for holistic approaches to water resource management, aiming to increase the resilience of aquatic ecosystems. Full article

Prymnesium parvum is a harmful alga found in brackish waters worldwide whose toxins can be lethal to aquatic organisms. Established field methods to control blooms of this species, however, are unavailable. Earlier studies showed that various extracts of giant reed (Arundo donax) can suppress P. parvum growth and that ellipticine, an allelochemical present in giant reed, is a potent algicide against this species. The unintended effects of giant reed products on nontarget organisms, however, are not fully understood. This study determined the effects of giant reed leachate (aqueous extract of dried chips) and ellipticine on growth of P. parvum and the green microalga Chlorella sorokiniana; survival and reproduction of the planktonic crustacean Daphnia pulex; and hatching success, larval survival, and larval swimming behavior of the teleost fish Danio rerio. Leachate made with 3 g chips L⁻¹ was lethally toxic to P. parvum and D. pulex, stimulated C. sorokiniana growth, and impaired D. rerio behavior. Leachate at 1 g L⁻¹ fully suppressed P. parvum growth, had moderate effects on D. pulex reproductive output, and had no effects on D. rerio. Ellipticine at 0.01 mg L⁻¹ irreversibly inhibited P. parvum growth, acutely but reversibly inhibited C. sorokiniana growth, slightly delayed D. pulex reproduction, and had no effects on D. rerio. These observations suggest that when applied at appropriate concentrations, natural products derived from giant reed can be used as tools to specifically control P. parvum growth with minimal effects on nontarget species. Full article

Shellfish aquaculture farms, due to their coastal position, face the threat of exposure to harmful algal blooms. Such blooms can release, among others, paralytic shellfish toxins (PST) produced by the dinoflagellate Alexandrium catenella and are known to cause the restriction of bivalve harvesting sites. Shellfish can accumulate PSTs in levels that are poisonous for humans, therefore making them unfit for consumption. Thus, the ability to detect PSTs before they reach the critical threshold is crucial for minimizing losses in the industry. Previous studies have demonstrated that toxic algae detection is possible with the use of an early warning system based on the valve-gaping behaviour of blue mussel Mytilus edulis. However, some studies observed the presence of toxin resistance in other species of bivalves when they are regularly exposed to PSTs. If no resistance is observed whatever the past history of the populations would be with regard to PST exposure, this species could be appropriate as a sentinel candidate. In this study, we compare the valve-gaping behaviour of two blue mussel populations with contrasting long-term histories of PSTs events (i.e., regularly vs. not previously exposed to the PSTs producer) were compared using experimental exposure of A. catenella to M. edulis. It was found that mussels from both populations exhibited similar gaping behaviour patterns when exposed to A. catenella. For both populations, the number of valve closures and closure duration tended to increase in the presence of A. catenella, which suggested an avoidance response to the toxic dinoflagellate. In conclusion, our results support the use of M. edulis without origin discrimination Full article