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Cyanobacterial blooms have increased in frequency, distribution, and intensity due to climate change and anthropogenic nutrient input. The release of bioactive compounds accumulated in these blooms can affect the health of humans and the environment. The co-occurrence of bioactive metabolites is well-documented in bloom samples from marine and freshwater ecosystems, with fewer reports from unialgal isolates. Cyanobacteria also are important terrestrial ecosystem components, especially in drylands, but reports on bioactive molecules from terrestrial cyanobacteria are sparse. This study determined bioactive metabolite profiles for 71 genera of cyanobacteria from seven orders isolated from freshwater (12 genera), marine (15 genera), and terrestrial (44 genera) habitats originally. Cultures were harvested for bioactive metabolites when entering the late-exponential phase for all 157 strains, and 33 were sampled at both early and late exponential phases. Bioactive metabolites were analyzed using an ultra high performance/pressure liquid chromatography in-line with a time-of-flight mass spectrometer. Overall, 12 bioactive classes of the 28 identified were ubiquitous in all samples. On average, each freshwater genus produced ∼12 bioactive classes, whereas each marine genus contained > 4 bioactive classes, and each terrestrial genus contained ∼6 bioactive classes. While 10 of 12 freshwater genera produced at least 10 bioactive classes, only a single genus each from marine and terrestrial habitats had the same number of bioactive classed accumulated. Aeruginosin was found in 58 of 71 total genera, carmabin in 51 of 71 genera, and anabaenopeptin in 48 of 71 genera. Chemotaxonomic use of these secondary metabolites may help resolve higher-level genetic classification(s). An additional growth curve experiment showed that bioactive metabolites were produced at both early and late exponential growth phases. The bioactive metabolite accumulation pattern between early and late exponential phases differed by bioactive classes, genera, and habitats. This survey of 55 bioactive classes in cyanobacteria isolated from freshwater, marine, and terrestrial habitats (71 genera) provides as one of the first systematic bioactive metabolite profiles for cyanobacteria, which should be useful in environmental and drinking water management. Further, it offers novel insights about the toxin potential of selected terrestrial cyanobacteria., (Copyright © 2021. Published by Elsevier B.V.)

While hypoxia and acidification can be common occurrences in eutrophic coastal zones, the precise, coupled temporal and spatial dynamics of these conditions are poorly described. Here, continuous measurements of water column pH, pCO 2 , carbonate chemistry, and dissolved oxygen (DO) concentrations were made from spring through fall across two, temperate eutrophic estuaries, western Long Island Sound (LIS) and Jamaica Bay, NY, USA. Vertical dynamics were resolved using an underway towing profiler and an automated stationary profiling unit. During the study, high rates of respiration in surface and bottom waters (> -0.2 mg O 2 L -1  h -1 ) yielded strongly negative rates of net ecosystem metabolism during the summer (-4 to -8 g O 2 m -2 d -1 ). Ephemeral surface algal blooms caused brief periods (< one week) of basification and supersaturation of DO that were succeeded by longer periods of acidification and hypoxia. In deeper regions, hypoxia (< 2 mg L -1 DO) and acidic water (pH < 7; total scale; pCO 2 levels >2000 μatm) that persisted continuously for >40 days in both estuaries was often overlain by water with higher DO and pH. Diurnal vertical profiles demonstrated that oxic surface waters saturated with respect to calcium carbonate and DO during the day transitioned to unsaturated and hypoxic at night. Evidence is presented that, beyond respiration, nitrification in surface water promoted by sewage discharge and oxidation processes in sediments also contribute to acidification in these estuaries. Collectively, this study demonstrates the pervasive, persistent, and dynamic nature of hypoxia and acidification in eutrophic estuaries are likely to shape marine food webs., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Harmful algal blooms (HABs) are diverse phenomena involving multiple. species and classes of algae that occupy a broad range of habitats from lakes to oceans and produce a multiplicity of toxins or bioactive compounds that impact many different resources. Here, a review of the status of this complex array of marine HAB problems in the U.S. is presented, providing historical information and trends as well as future perspectives. The study relies on thirty years (1990-2019) of data in HAEDAT - the IOC-ICES-PICES Harmful Algal Event database, but also includes many other reports. At a qualitative level, the U.S. national HAB problem is far more extensive than was the case decades ago, with more toxic species and toxins to monitor, as well as a larger range of impacted resources and areas affected. Quantitatively, no significant trend is seen for paralytic shellfish toxin (PST) events over the study interval, though there is clear evidence of the expansion of the problem into new regions and the emergence of a species that produces PSTs in Florida - Pyrodinium bahamense. Amnesic shellfish toxin (AST) events have significantly increased in the U.S., with an overall pattern of frequent outbreaks on the West Coast, emerging, recurring outbreaks on the East Coast, and sporadic incidents in the Gulf of Mexico. Despite the long historical record of neurotoxic shellfish toxin (NST) events, no significant trend is observed over the past 30 years. The recent emergence of diarrhetic shellfish toxins (DSTs) in the U.S. began along the Gulf Coast in 2008 and expanded to the West and East Coasts, though no significant trend through time is seen since then. Ciguatoxin (CTX) events caused by Gambierdiscus dinoflagellates have long impacted tropical and subtropical locations in the U.S., but due to a lack of monitoring programs as well as under-reporting of illnesses, data on these events are not available for time series analysis. Geographic expansion of Gambierdiscus into temperate and non-endemic areas (e.g., northern Gulf of Mexico) is apparent, and fostered by ocean warming. HAB-related marine wildlife morbidity and mortality events appear to be increasing, with statistically significant increasing trends observed in marine mammal poisonings caused by ASTs along the coast of California and NSTs in Florida. Since their first occurrence in 1985 in New York, brown tides resulting from high-density blooms of Aureococcus have spread south to Delaware, Maryland, and Virginia, while those caused by Aureoumbra have spread from the Gulf Coast to the east coast of Florida. Blooms of Margalefidinium polykrikoides occurred in four locations in the U.S. from 1921-2001 but have appeared in more than 15  U.S. estuaries since then, with ocean warming implicated as a causative factor. Numerous blooms of toxic cyanobacteria have been documented in all 50  U.S. states and the transport of cyanotoxins from freshwater systems into marine coastal waters is a recently identified and potentially significant threat to public and ecosystem health. Taken together, there is a significant increasing trend in all HAB events in HAEDAT over the 30-year study interval. Part of this observed HAB expansion simply reflects a better realization of the true or historic scale of the problem, long obscured by inadequate monitoring. Other contributing factors include the dispersion of species to new areas, the discovery of new HAB poisoning syndromes or impacts, and the stimulatory effects of human activities like nutrient pollution, aquaculture expansion, and ocean warming, among others. One result of this multifaceted expansion is that many regions of the U.S. now face a daunting diversity of species and toxins, representing a significant and growing challenge to resource managers and public health officials in terms of toxins, regions, and time intervals to monitor, and necessitating new approaches to monitoring and management. Mobilization of funding and resources for research, monitoring and management of HABs requires accurate information on the scale and nature of the national problem. HAEDAT and other databases can be of great value in this regard but efforts are needed to expand and sustain the collection of data regionally and nationally., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

There is increasing recognition that low dissolved oxygen (DO) and low pH conditions co-occur in many coastal and open ocean environments. Within temperate ecosystems, these conditions not only develop seasonally as temperatures rise and metabolic rates accelerate, but can also display strong diurnal variability, especially in shallow systems where photosynthetic rates ameliorate hypoxia and acidification by day. Despite the widespread, global co-occurrence of low pH and low DO and the likelihood that these conditions may negatively impact marine life, very few studies have actually assessed the extent to which the combination of both stressors elicits additive, synergistic or antagonistic effects in marine organisms. We review the evidence from published factorial experiments that used static and/or fluctuating pH and DO levels to examine different traits (e.g. survival, growth, metabolism), life stages and species across a broad taxonomic spectrum. Additive negative effects of combined low pH and low DO appear to be most common; however, synergistic negative effects have also been observed. Neither the occurrence nor the strength of these synergistic impacts is currently predictable, and therefore, the true threat of concurrent acidification and hypoxia to marine food webs and fisheries is still not fully understood. Addressing this knowledge gap will require an expansion of multi-stressor approaches in experimental and field studies, and the development of a predictive framework. In consideration of marine policy, we note that DO criteria in coastal waters have been developed without consideration of concurrent pH levels. Given the persistence of concurrent low pH-low DO conditions in estuaries and the increased mortality experienced by fish and bivalves under concurrent acidification and hypoxia compared with hypoxia alone, we conclude that such DO criteria may leave coastal fisheries more vulnerable to population reductions than previously anticipated., (© 2016 The Author(s).)

This review summarizes the present state of knowledge regarding the toxic, bloom-forming cyanobacterium, Microcystis, with a specific focus on its geographic distribution, toxins, genomics, phylogeny, and ecology. A global analysis found documentation suggesting geographic expansion of Microcystis, with recorded blooms in at least 108 countries, 79 of which have also reported the hepatatoxin microcystin. The production of microcystins (originally "Fast-Death Factor") by Microcystis and factors that control synthesis of this toxin are reviewed, as well as the putative ecophysiological roles of this metabolite. Molecular biological analyses have provided significant insight into the ecology and physiology of Microcystis, as well as revealed the highly dynamic, and potentially unstable, nature of its genome. A genetic sequence analysis of 27 Microcystis species, including 15 complete/draft genomes are presented. Using the strictest biological definition of what constitutes a bacterial species, these analyses indicate that all Microcystis species warrant placement into the same species complex since the average nucleotide identity values were above 95%, 16S rRNA nucleotide identity scores exceeded 99%, and DNA-DNA hybridization was consistently greater than 70%. The review further provides evidence from around the globe for the key role that both nitrogen and phosphorus play in controlling Microcystis bloom dynamics, and the effect of elevated temperature on bloom intensification. Finally, highlighted is the ability of Microcystis assemblages to minimize their mortality losses by resisting grazing by zooplankton and bivalves, as well as viral lysis, and discuss factors facilitating assemblage resilience., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Although toxic cyanobacterial blooms in western Lake Erie threaten drinking water supplies and are promoted by nutrient loading, the precise nutrient regime that selects specific cyanobacteria populations is poorly understood. Here, we assess shifts in cyanobacterial abundances and global gene-expression patterns in response to natural and manipulated gradients in nitrogen and phosphorus to identify gene pathways that facilitate dominance by different cyanobacteria. Gradients in soluble reactive phosphorus shaped cyanobacterial communities and elicited the largest transcriptomic responses. Under high-P conditions (closest to the mouth of the Maumee River), Anabaena and Planktothrix were the dominant cyanobacterial populations, and experimental P and ammonium enrichment promoted nitrogen fixation gene (nifH) expression in Anabaena. For Microcystis, experimental additions of P up-regulated genes involved in phage defense, genomic rearrangement, and nitrogen acquisition but led to lower abundances. Within offshore, low-P regions of the western basin of Lake Erie, Microcystis up-regulated genes associated with P scavenging (pstSCAB, phoX) and dominated cyanobacterial communities. Experimental additions of ammonium and urea did not alter Microcystis abundances but did up-regulate protease inhibitors (aer and mcn gene sets) and microcystin synthetase genes (mcy), with urea enrichment yielding significant increases in microcystin concentrations. Our findings suggest that management plans that reduce P loads alone may not significantly reduce the risk of cyanobacterial blooms in western Lake Erie but rather may promote a shift among cyanobacterial populations (Microcystis, Anabaena, and Planktothrix) toward a greater dominance by toxic strains of Microcystis.

Diarrhetic Shellfish Poisoning (DSP) is a globally significant human health syndrome most commonly caused by dinoflagellates within the genus Dinophysis. While blooms of harmful algae have frequently been linked to excessive nutrient loading, Dinophysis is a mixotrophic alga whose growth is typically associated with prey availability. Consequently, field studies of Dinophysis and nutrients have been rare. Here, the temporal dynamics of Dinophysis acuminata blooms, DSP toxins, and nutrients (nitrate, ammonium, phosphate, silicate, organic compounds) were examined over four years within two New York estuaries (Meetinghouse Creek and Northport Bay). Further, changes in the abundance and toxicity of D. acuminata were assessed during a series of nutrient amendment experiments performed over a three year period. During the study, Dinophysis acuminata blooms exceeding one million cells L-1 were observed in both estuaries. Highly significant (p<0.001) forward stepwise multivariate regression models of ecosystem observations demonstrated that D. acuminata abundances were positively dependent on multiple environmental parameters including ammonium (p = 0.007) while cellular toxin content was positively dependent on ammonium (p = 0.002) but negatively dependent on nitrate (p<0.001). Nitrogen- (N) and phosphorus- (P) containing inorganic and organic nutrients significantly enhanced D. acuminata densities in nearly all (13 of 14) experiments performed. Ammonium significantly increased cell densities in 10 of 11 experiments, while glutamine significantly enhanced cellular DSP content in 4 of 5 experiments examining this compound. Nutrients may have directly or indirectly enhanced D. acuminata abundances as densities of this mixotroph during experiments were significantly correlated with multiple members of the planktonic community (phytoflagellates and Mesodinium). Collectively, this study demonstrates that nutrient loading and more specifically N-loading promotes the growth and toxicity of D. acuminata populations in coastal zones.

Harmful algal blooms (HABs) cause significant economic and ecological damage worldwide. Despite considerable efforts, a comprehensive understanding of the factors that promote these blooms has been lacking, because the biochemical pathways that facilitate their dominance relative to other phytoplankton within specific environments have not been identified. Here, biogeochemical measurements showed that the harmful alga Aureococcus anophagefferens outcompeted co-occurring phytoplankton in estuaries with elevated levels of dissolved organic matter and turbidity and low levels of dissolved inorganic nitrogen. We subsequently sequenced the genome of A. anophagefferens and compared its gene complement with those of six competing phytoplankton species identified through metaproteomics. Using an ecogenomic approach, we specifically focused on gene sets that may facilitate dominance within the environmental conditions present during blooms. A. anophagefferens possesses a larger genome (56 Mbp) and has more genes involved in light harvesting, organic carbon and nitrogen use, and encoding selenium- and metal-requiring enzymes than competing phytoplankton. Genes for the synthesis of microbial deterrents likely permit the proliferation of this species, with reduced mortality losses during blooms. Collectively, these findings suggest that anthropogenic activities resulting in elevated levels of turbidity, organic matter, and metals have opened a niche within coastal ecosystems that ideally suits the unique genetic capacity of A. anophagefferens and thus, has facilitated the proliferation of this and potentially other HABs.