Growth rate and toxicity ofPrymnesium parvumandPrymnesium patelliferum(haptophyta) in response to changes in salinity, light and temperature

Towards effective management of the marine-origin Prymnesium parvum (Haptophyta): A growing concern in freshwater reservoirs?

Freshwater ecosystems are highly susceptible to harmful algal blooms (HABs), which are often caused by monospecific dense blooms. Effective preventive management strategies are urgently needed to avoid wide-ranging and severe impacts often resulting in costly damage to resources and unsustainable management options. In this study, we utilized SDM techniques focused on Prymnesium parvum, one of the most notorious HABs species worldwide. We first compare the climatic space occupied by P. parvum in North America, Europe and Australia. Additionally, we use MaxEnt algorithm to infer, for the first time, the potentially suitable freshwater environments in the aforementioned ranges. We also discuss the risks of invasion in reservoirs - prone habitats to persistent blooms of pests and invasive phytoplanktonic species. Our results show populations with distinctive niches suggesting ecophysiological tolerances, perhaps reflecting different strains. Our model projections revealed that the potential extent for P. parvum invasions is much broader than its current geographic distribution. The spatial configuration of reservoirs, if not sustaining dense blooms due to non-optimal conditions, favors colonization of multiple basins and ecoregions not yet occupied by P. parvum. Our models can provide valuable insights to decision-makers and monitoring programs while reducing the resources required to control the spread of P. parvum in disturbed habitats. Lastly, as impact magnitude is influenced by toxicity which in turn varies between different strains, we suggest future studies to incorporate intraspecific genetic information and fine-scale environmental variables to estimate potential distribution of P. parvum.

Extreme genome diversity and cryptic speciation in a harmful algal-bloom-forming eukaryote

Harmful algal blooms of the toxic haptophyte Prymnesium parvum are a recurrent problem in many inland and estuarine waters around the world. Strains of P. parvum vary in the toxins they produce and in other physiological traits associated with harmful algal blooms, but the genetic basis for this variation is unknown. To investigate genome diversity in this morphospecies, we generated genome assemblies for 15 phylogenetically and geographically diverse strains of P. parvum, including Hi-C guided, near-chromosome-level assemblies for two strains. Comparative analysis revealed considerable DNA content variation between strains, ranging from 115 to 845 Mbp. Strains included haploids, diploids, and polyploids, but not all differences in DNA content were due to variation in genome copy number. Haploid genome size between strains of different chemotypes differed by as much as 243 Mbp. Syntenic and phylogenetic analyses indicate that UTEX 2797, a common laboratory strain from Texas, is a hybrid that retains two phylogenetically distinct haplotypes. Investigation of gene families variably present across the strains identified several functional categories associated with metabolic and genome size variation in P. parvum, including genes for the biosynthesis of toxic metabolites and proliferation of transposable elements. Together, our results indicate that P. parvum comprises multiple cryptic species. These genomes provide a robust phylogenetic and genomic framework for investigations into the eco-physiological consequences of the intra- and inter-specific genetic variation present in P. parvum and demonstrate the need for similar resources for other harmful algal-bloom-forming morphospecies.

The Effect of pH and Salinity on the Toxicity and Growth of the Golden Alga, Prymnesium parvum

Bioassays using cultures of the toxic haptophyte Prymnesium parvum and the ciliate Cyclidium sp. as prey were conducted to test the effect of pH (range = 6.5 - 8.5), salinity (range = 1.50 - 7.50‰), and a combination of pH and salinity on the toxicity of P. parvum. pH had a significant effect on P. parvum toxicity. Toxicity was rapidly (within 24 hr) induced by increasing pH of the medium, or reduced by lowering pH. Conversely, lowering salinity reduced toxicity, albeit less effectively compared to pH, and P. parvum cells remained toxic at the lowest values tested (1.50‰ at pH 7.5). An additional effect between pH and salinity was also observed: low salinity combined with low pH led to not only decreased toxicity, but also resulted in lower P. parvum growth rates. Such effects of pH and salinity on P. parvum growth and toxicity provide insight into the environmental factors supporting community dominance and toxic blooms of the alga.

The coupling between irradiance, growth, photosynthesis and prymnesin cell quota and production in two strains of the bloom-forming haptophyte, Prymnesium parvum

Prymnesium parvum causes harmful algal blooms worldwide that are often associated with massive fish-kills and subsequent economic losses. Most of our knowledge of the toxicity of P. parvum derives from bioassays since methods for the identification and quantification of their toxins have been lacking. Recently, a quantitation method was developed for the causative lytic toxins, the prymnesins. Here, we for the first time present data on the influence of irradiance on cellular content and production of prymnesins under nutrient replete conditions in two P. parvum strains, which both produce B-type prymnesins. Large differences were observed between the two strains with regard to the influence of irradiance on prymnesin cell quota and production rates. At the highest irradiance level (550 µmol photons m-2 s-1), the cellular prymnesin quota was thirty times higher in strain K-0081 strain than in K-0374. The cellular prymnesin quota and production rates were closely linked to rates of growth and photosynthesis in strain K-0081, while this was not the case for K-0374. Yet, growth rate did explain the differences in prymnesin quota in the two strains. Consequently, the maximum prymnesin production rate (414 attomol cell-1 d-1) was only about three times higher in strain K-0081 than in K-0374, and revealed an optimum at the same irradiance of 200 µmol photons m-2 s-1 in both strains. At low irradiance levels, the difference in production rates between both strains became smaller, with 41 and 49 attomol cell-1 d-1 for K-0081 and K-0374, respectively. The carbon content of prymnesins made up for ∼3% and <1% of the total cellular carbon content in strains K-0081 and K-0374, respectively. The fraction of extracellular dissolved prymnesins was measured for strain K-0081, where it accounted for 14-30% of total prymnesin concentration in the cultures, irrespective of irradiance. The concentrations of prymnesins released to the water by the K-0081 strain were not significantly influenced by irradiance. Overall, we observed comparable responses in growth and photosynthesis of both tested strains toward changes in irradiance. However, the effects of irradiance on prymnesin quota and production rates were remarkably different between the two strains.

Assessing the Toxicity and Mitigating the Impact of Harmful Prymnesium Blooms in Eutrophic Waters of the Norfolk Broads

Prymnesium parvum is a toxin-producing microalga, which causes harmful algal blooms globally, frequently leading to massive fish kills that have adverse ecological and economic implications for natural waterways and aquaculture alike. The dramatic effects observed on fish are thought to be due to algal polyether toxins, known as the prymnesins, but their lack of environmental detection has resulted in an uncertainty about the true ichthyotoxic agents. Using qPCR, we found elevated levels of P. parvum and its lytic virus, PpDNAV-BW1, in a fish-killing bloom on the Norfolk Broads, United Kingdom, in March 2015. We also detected, for the first time, the B-type prymnesin toxins in Broads waterway samples and gill tissue isolated from a dead fish taken from the study site. Furthermore, Norfolk Broads P. parvum isolates unambiguously produced B-type toxins in laboratory-grown cultures. A 2 year longitudinal study of the Broads study site showed P. parvum blooms to be correlated with increased temperature and that PpDNAV plays a significant role in P. parvum bloom demise. Finally, we used a field trial to show that treatment with low doses of hydrogen peroxide represents an effective strategy to mitigate blooms of P. parvum in enclosed water bodies.

A Case Study of a Prymnesium parvum Harmful Algae Bloom in the Ohio River Drainage: Impact, Recovery and Potential for Future Invasions/Range Expansion

Inland waters provide valuable ecosystem goods and services and are intrinsically linked to downstream coastal areas. Water quality impairments that lead to harmful algal blooms damage valuable commercial and recreational fishing economies, threaten food security, and damage already declining native species. Prymnesium parvum is a brackish water golden alga that can survive in salinities less than 1 ppm and when it blooms it can create toxins that kill aquatic life. Blooms have been documented globally including 23 U.S. states. We report a case study of an aquatic life kill associated with P. parvum in Dunkard Creek (WV-PA, USA), in the Ohio River Drainage. We document the immediate impact to aquatic life and responses of the aquatic community ten years post-kill. Most fish species returned within a year. Excellent connectivity to unimpacted tributaries and a river downstream likely aided the reestablishment of most species, although some had not reached pre-kill abundances after ten years. Mussel taxa did not recover despite significant efforts to relocate adult mussels and stocking of host fish inoculated with glochidia; probably due to other water quality impairments. Given the potential for lateral transport of P. parvum via industry and natural vectors we conducted an ecological risk assessment mapping the spatial extent of U.S. waters that could be threatened by golden algae colonization and blooms using a national water quality database and a state database. Overall, about 4.5% of lotic systems appeared to have some level of risk of harboring P. parvum, making them at risk for potential golden algae blooms in the face of increasing salinization and eutrophication of freshwaters.

Plankton biodiversity and species co-occurrence based on environmental DNA – a multiple marker study

Metabarcoding in combination with high-throughput sequencing (HTS) allows simultaneous detection of multiple taxa by targeting single or several taxonomically informative gene regions from environmental DNA samples. In this study, a multiple-marker HTS approach was applied to investigate the plankton diversity and seasonal succession in the Baltic Sea from winter to autumn. Four different markers targeting the 16S, 18S, and 28S ribosomal RNA genes were employed, including a marker for more efficient dinoflagellate detection. Typical seasonal changes were observed in phyto- and bacterioplankton communities. In phytoplankton, the appearance patterns of selected common, dominant, or harmful species followed the patterns also confirmed based on 20 years of phytoplankton monitoring data. In the case of zooplankton, both macro- and microzooplankton species were detected. However, no seasonal patterns were detected in their appearance. In total, 15 and 2 new zoo- and phytoplankton species were detected from the Baltic Sea. HTS approach was especially useful for detecting microzooplankton species as well as for investigating the co-occurrence and potential interactions of different taxa. The results of this study further exemplify the efficiency of metabarcoding for biodiversity monitoring and the advantage of employing multiple markers through the detection of species not identifiable based on a single marker survey and/or by traditional morphology-based methods.

Growth of the harmful alga, Prymnesium parvum (Prymnesiophyceae), after gradual and abrupt increases in salinity

Prymnesium parvum is a euryhaline, toxin-producing microalga. Although its abundance in inland waters and growth potential in the laboratory is reduced at high salinity (>20), the ability of inland strains to adjust their growth after long-term residence in high salinity is uncertain. An inland strain of P. parvum maintained at salinity of 5 in modified artificial seawater medium (ASM-5) was subjected to the following treatments over five sequential batch culture rounds: ASM-5 (control); modified ASM at salinity of 30, raised with NaCl; modified ASM at salinity incrementally increased to 30 with NaCl; and Instant Ocean^® at salinity of 30 (IO-30). Exponential growth rate (r) was reduced when salinity was increased from 5 to 30 in ASM but returned to control values during the second round. When salinity was incrementally increased, a reduction in r still occurred when salinity reached 25-30. Maximum density was reduced at salinity of 30 in ASM upon abrupt transfer or incremental increase, and compensation did not occur. Growth performance in IO-30 was comparable to control values. In conclusion, (i) long-term compensation for acute inhibitory effects of high salinity occurred for r but not maximum density, (ii) incremental increases in salinity did not prevent growth inhibition, suggesting the existence of a salinity threshold of 25-30 for onset of salinity stress, and (iii) the presence of a seawater-like salt mixture prevented growth inhibition by high salinity. These findings provide new insights on P. parvum's long-term ability to adjust its growth in environments of different salinity and ionic composition.

The current state of knowledge on taxonomy, modulating factors, ecological roles, and mode of action of phytoplankton allelochemicals

Allelopathy is widespread in marine, brackish, and freshwater habitats. Literature data indicate that allelopathy could offer a competitive advantage for some phytoplankton species by reducing the growth of competitors. It is also believed that allelopathy may affect species succession. Thus, allelopathy may play a role in the development of blooms. Over the past few decades, the world's coastal waters have experienced increases in the numbers of cyanobacterial and microalgal blooming events. Understanding how allelopathy is implicated with other biological and environmental factors as a bloom-development mechanism is an important topic for future research. This review focuses on a taxonomic overview of allelopathic cyanobacteria and microalgae, the biological and environmental factors that affect allelochemical production, their role in ecological dynamics, and their physiological modes of action, as well as potential industrial applications of allelopathic compounds.

Sunlight concurrently reduces Prymnesium parvum elicited acute toxicity to fish and prymnesins

Prymnesium parvum continues to spread globally, producing harmful algal blooms that release toxins known to cause fish kills. While previous work has identified possible P. parvum toxin(s) (e.g., prymnesins, fatty acids, fatty acid amides) and investigated treatment strategies targeted at minimizing cell abundance, studies examining efficacy of treatment approaches to remove toxins are lacking. To understand influences of sunlight on toxins stability and toxicity to fish, acutely toxic P. parvum cultures were exposed to three light scenarios (lab dark control, field dark, and field light) and then evaluated for acute toxicity to fish and prymnesins abundance. Previous work showed acute toxicity to fathead minnow larvae was ameliorated after 2 h of sunlight exposure, and results observed herein found an identical trend. Acute toxicity disappeared in light exposed filtrate, but filtrate exposed to 35 ^°C without sunlight remained acutely toxic to fish. Additionally, six prymnesins were identified through high-resolution mass spectrometry and abundance corresponded to acute toxicity levels. Prymnesins were present at the highest level in filtrate that was acutely toxic but diminished in filtrate that was exposed to light and correspondingly ameliorated acute toxicity to fish. These findings suggest prymnesins are responsible for measured acute toxicity and are photo-labile, which represents an important implication for treatment strategies.

Toxic effects and mechanisms of Prymnesium parvum (Haptophyta) isolated from the Pearl River Estuary, China

Prymnesium (Haptophyta) species form toxic blooms throughout the world resulting in large fish-kills and economic losses. A culture of Prymnesium parvum JX12 was isolated and established from the Pearl River Estuary of China. The toxic characteristics of JX12 to aquatic animals were investigated, considering the effects of temperature, salinity, and nutrients. Cultures of JX12 exhibited significant lethal toxicity to the fish, Mugil sp., M. soiuy, M. cephalus, Ctenogobius sp. and Chrysiptera parasema, and the brine shrimp, Artemia salina, but no significant effects on the shellfish Ruditapes variegatus and the shrimp Penacus orientalis. The toxicity of JX12 to A. salina increased with growth of the culture. The decline phase displayed the strongest potency, followed by the stationary phase, exponential phase and lag phase. Also, there was a significant difference in toxicity among culture fractions of JX12 compared to whole-cell culture. For example, the toxicity of a cell-free culture filtrate on brine shrimp was reduced by 50% by the end of the experiment, while the sonicated and re-suspended cultures caused near 100% mortality. The toxicity of JX12 was also regulated by environmental factors such as temperature, salinity and nutrients. The strongest toxicities were at moderate water temperature (20-25 °C) and salinity (35 psu). The toxicity was reduced significantly at higher or lower temperatures and salinities. Furthermore, the toxicity of JX12 was greatly enhanced when ambient nutrients were deficient. Due to the potent toxicity of JX12 to multiple aquatic animals, especially fish and zooplankton, this species threatens the food web and trophic dynamics of coastal ecosystems. This study suggested that the ability to produce and release toxin(s) is an effective competition strategy for P. parvum to suppress predators and sympatric competitors and thus form blooms.

Progress and promise of omics for predicting the impacts of climate change on harmful algal blooms

Climate change is predicted to increase the severity and prevalence of harmful algal blooms (HABs). In the past twenty years, omics techniques such as genomics, transcriptomics, proteomics and metabolomics have transformed that data landscape of many fields including the study of HABs. Advances in technology have facilitated the creation of many publicly available omics datasets that are complementary and shed new light on the mechanisms of HAB formation and toxin production. Genomics have been used to reveal differences in toxicity and nutritional requirements, while transcriptomics and proteomics have been used to explore HAB species responses to environmental stressors, and metabolomics can reveal mechanisms of allelopathy and toxicity. In this review, we explore how omics data may be leveraged to improve predictions of how climate change will impact HAB dynamics. We also highlight important gaps in our knowledge of HAB prediction, which include swimming behaviors, microbial interactions and evolution that can be addressed by future studies with omics tools. Lastly, we discuss approaches to incorporate current omics datasets into predictive numerical models that may enhance HAB prediction in a changing world. With the ever-increasing omics databases, leveraging these data for understanding climate-driven HAB dynamics will be increasingly powerful.

Growth response of the ichthyotoxic haptophyte, Prymnesium parvum Carter, to changes in sulfate and fluoride concentrations

Golden alga Prymnesium parvum Carter is a euryhaline, ichthyotoxic haptophyte (Chromista). Because of its presumed coastal/marine origin where SO₄^2- levels are high, the relatively high SO₄^2- concentration of its brackish inland habitats, and the sensitivity of marine chromists to sulfur deficiency, this study examined whether golden alga growth is sensitive to SO₄^2- concentration. Fluoride is a ubiquitous ion that has been reported at higher levels in golden alga habitat; thus, the influence of F^- on growth also was examined. In low-salinity (5 psu) artificial seawater medium, overall growth was SO₄^2—dependent up to 1000 mg l^-1 using MgSO₄ or Na₂SO₄ as source; the influence on growth rate, however, was more evident with MgSO₄. Transfer from 5 to 30 psu inhibited growth when salinity was raised with NaCl but in the presence of seawater levels of SO₄^2-, these effects were fully reversed with MgSO₄ as source and only partially reversed with Na₂SO₄. Growth inhibition was not observed after acute transfer to 30 psu in a commercial sea salt mixture. In 5-psu medium, F^- inhibited growth at all concentrations tested. These observations support the hypothesis that spatial differences in SO₄^2- –but not F^-–concentration help drive the inland distribution and growth of golden alga and also provide physiological relevance to reports of relatively high Mg²⁺ concentrations in golden alga habitat. At high salinity, however, the ability of sulfate to maintain growth under osmotic stress was weak and overshadowed by the importance of Mg²⁺. A mechanistic understanding of growth responses of golden alga to SO₄^2-, Mg²⁺ and other ions at environmentally relevant levels and under different salinity scenarios will be necessary to clarify their ecophysiological and evolutionary relevance.

The effect of pH on the acute toxicity of phenanthrene in a marine microalgae Chlorella salina

Phenanthrene is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) found in continental shelf environment of China and is on the EPA’s Priority Pollutant list. In this study, the effects of phenanthrene on marine algal growth rate were determined after 96-h exposure at pH 6.0, 7.0, 8.0, 9.0, and 10.0 in seawater of salinity 35. Two measuring techniques to assess growth inhibition were also compared using prompt fluorescence and microscopic cell count. The results showed that the toxicity of phenanthrene increased significantly (p < 0.05) with decreasing pH, with the nominal concentration required to inhibit growth rate by 50%, EC₅₀, decreasing from 1.893 to 0.237 mg L⁻¹ as pH decreased from 9.0 to 6.0, with a decrease higher than 55% from 10.0 to 9.0. In addition, the nominal EC₅₀ values calculated in this study were at the same range of some environmental concentrations of phenanthrene close to areas of crude oil exploration. Based on the two measuring techniques, the results showed that cell count and fluorescence measurement were significantly different (p < 0.05), and the nominal EC₅₀ values calculated with cell count measurement were significantly higher than fluorescence measurement at pH 8.0, 9.0 and 10.0. In conclusion, the present studies confirmed that acidification of seawater could affect the toxicity of phenanthrene to this species of microalgae, and which encouraged further studies involving responses of marine organisms to ocean acidification.

Insights into toxic Prymnesium parvum blooms: the role of sugars and algal viruses

Prymnesium parvum is a toxin-producing microalga that causes harmful algal blooms globally, which often result in large-scale fish kills that have severe ecological and economic implications. Although many toxins have previously been isolated from P. parvum, ambiguity still surrounds the responsible ichthyotoxins in P. parvum blooms and the biotic and abiotic factors that promote bloom toxicity. A major fish kill attributed to P. parvum occurred in Spring 2015 on the Norfolk Broads, a low-lying set of channels and lakes (Broads) found on the East of England. Here, we discuss how water samples taken during this bloom have led to diverse scientific advances ranging from toxin analysis to discovery of a new lytic virus of P. parvum, P. parvum DNA virus (PpDNAV-BW1). Taking recent literature into account, we propose key roles for sialic acids in this type of viral infection. Finally, we discuss recent practical detection and management strategies for controlling these devastating blooms.

Influence of genetic background, salinity, and inoculum size on growth of the ichthyotoxic golden alga (Prymnesium parvum)

Salinity (5-30) effects on golden alga growth were determined at a standard laboratory temperature (22°C) and one associated with natural blooms (13°C). Inoculum-size effects were determined over a wide size range (100-100,000cellsml^-1). A strain widely distributed in the USA, UTEX-2797 was the primary study subject but another of limited distribution, UTEX-995 was used to evaluate growth responses in relation to genetic background. Variables examined were exponential growth rate (r), maximum cell density (max-D) and, when inoculum size was held constant (100cellsml^-1), density at onset of exponential growth (early-D). In UTEX-2797, max-D increased as salinity increased from 5 to ∼10-15 and declined thereafter regardless of temperature but r remained generally stable and only declined at salinity of 25-30. In addition, max-D correlated positively with r and early-D, the latter also being numerically highest at salinity of 15. In UTEX-995, max-D and r responded similarly to changes in salinity - they remained stable at salinity of 5-10 and 5-15, respectively, and declined at higher salinity. Also, max-D correlated with r but not early-D. Inoculum size positively and negatively influenced max-D and r, respectively, in both strains and these effects were significant even when the absolute size difference was small (100 versus 1000 cells ml^-1). When cultured under similar conditions, UTEX-2797 grew faster and to much higher density than UTEX-995. In conclusion, (1) UTEX-2797's superior growth performance may explain its relatively wide distribution in the USA, (2) the biphasic growth response of UTEX-2797 to salinity variation, with peak abundance at salinity of 10-15, generally mirrors golden alga abundance-salinity associations in US inland waters, and (3) early cell density - whether artificially manipulated or naturally attained - can influence UTEX-2797 bloom potential.

Discovery of Bioactive Metabolites in Biofuel Microalgae That Offer Protection against Predatory Bacteria

Microalgae could become an important resource for addressing increasing global demand for food, energy, and commodities while helping to reduce atmospheric greenhouse gasses. Even though Chlorophytes are generally regarded safe for human consumption, there is still much we do not understand about the metabolic and biochemical potential of microscopic algae. The aim of this study was to evaluate biofuel candidate strains of Chlorella and Scenedesmus for the potential to produce bioactive metabolites when grown under nutrient depletion regimes intended to stimulate production of triacylglycerides. Strain specific combinations of macro- and micro-nutrient restricted growth media did stimulate neutral lipid accumulation by microalgal cultures. However, cultures that were restricted for iron consistently and reliably tested positive for cytotoxicity by in vivo bioassays. The addition of iron back to these cultures resulted in the disappearance of the bioactive components by LC/MS fingerprinting and loss of cytotoxicity by in vivo bioassay. Incomplete NMR characterization of the most abundant cytotoxic fractions suggested that small molecular weight peptides and glycosides could be responsible for Chlorella cytotoxicity. Experiments were conducted to determine if the bioactive metabolites induced by Fe-limitation in Chlorella sp. cultures would elicit protection against Vampirovibrio chlorellavorus, an obligate predator of Chlorella. Introduction of V. chlorellavorus resulted in a 72% decrease in algal biomass in the experimental controls after 7 days. Conversely, only slight losses of algal biomass were measured for the iron limited Chlorella cultures (0–9%). This study demonstrates a causal linkage between iron bioavailability and bioactive metabolite production in strains of Chlorella and Scenedesmus. Further study of this phenomenon could contribute to the development of new strategies to extend algal production cycles in open, outdoor systems while ensuring the protection of biomass from predatory losses.

The niche of an invasive marine microbe in a subtropical freshwater impoundment

Growing attention in aquatic ecology is focusing on biogeographic patterns in microorganisms and whether these potential patterns can be explained within the framework of general ecology. The long-standing microbiologist's credo 'Everything is everywhere, but, the environment selects' suggests that dispersal is not limiting for microbes, but that the environment is the primary determining factor in microbial community composition. Advances in molecular techniques have provided new evidence that biogeographic patterns exist in microbes and that dispersal limitation may actually have an important role, yet more recent study using extremely deep sequencing predicts that indeed everything is everywhere. Using a long-term field study of the 'invasive' marine haptophyte Prymnesium parvum, we characterize the environmental niche of P. parvum in a subtropical impoundment in the southern United States. Our analysis contributes to a growing body of evidence that indicates a primary role for environmental conditions, but not dispersal, in the lake-wide abundances and seasonal bloom patterns in this globally important microbe.

A global pattern of thermal adaptation in marine phytoplankton

Rising ocean temperatures will alter the productivity and composition of marine phytoplankton communities, thereby affecting global biogeochemical cycles. Predicting the effects of future ocean warming on biogeochemical cycles depends critically on understanding how existing global temperature variation affects phytoplankton. Here we show that variation in phytoplankton temperature optima over 150 degrees of latitude is well explained by a gradient in mean ocean temperature. An eco-evolutionary model predicts a similar relationship, suggesting that this pattern is the result of evolutionary adaptation. Using mechanistic species distribution models, we find that rising temperatures this century will cause poleward shifts in species' thermal niches and a sharp decline in tropical phytoplankton diversity in the absence of an evolutionary response.

Toxin-assisted micropredation: experimental evidence shows that contact micropredation rather than exotoxicity is the role of Prymnesium toxins

Blooms of Prymnesium parvum can severely harm fish and zooplankton, presumably through the release of allelopathic exotoxins that offer advantages for Prymnesium in its interactions with competitors and prey. We show that Prymnesium attaches to zooplankton and fish, causing mortality, whereas exposure of these organisms to Prymnesium across a permeable membrane does not cause mortality. We also show that Prymnesium exotoxins are released independently of contact toxicity only in response to experimental procedures or natural causes of stress. Our results are consistent with the idea that toxins have evolved for release during cell-to-cell contact in support of heterotrophy. The evolution of toxin-assisted micropredation would be consistent with mechanisms of natural selection favouring individual fitness as opposed to broadcast allelopathy from which the benefits are more dispersed. Research into the toxicity of Prymnesium and other harmful algal species may profit from focus on processes following physical contact with potential prey.

Prymnesins: toxic metabolites of the golden alga, Prymnesium parvum Carter (Haptophyta)

Increasingly over the past century, seasonal fish kills associated with toxic blooms of Prymnesium parvum have devastated aquaculture and native fish, shellfish, and mollusk populations worldwide. Protracted blooms of P. parvum can result in major disturbances to the local ecology and extensive monetary losses. Toxicity of this alga is attributed to a collection of compounds known as prymnesins, which exhibit potent cytotoxic, hemolytic, neurotoxic and ichthyotoxic effects. These secondary metabolites are especially damaging to gill-breathing organisms and they are believed to interact directly with plasma membranes, compromising integrity by permitting ion leakage. Several factors appear to function in the activation and potency of prymnesins including salinity, pH, ion availability, and growth phase. Prymnesins may function as defense compounds to prevent herbivory and some investigations suggest that they have allelopathic roles. Since the last extensive review was published, two prymnesins have been chemically characterized and ongoing investigations are aimed at the purification and analysis of numerous other toxic metabolites from this alga. More information is needed to unravel the mechanisms of prymnesin synthesis and the significance of these metabolites. Such work should greatly improve our limited understanding of the physiology and biochemistry of P. parvum and how to mitigate its blooms.

Metal complexes and free radical toxins produced by Pfiesteria piscicida

Metal-containing organic toxins produced by Pfiesteria piscicida were characterized, for the first time, by corroborating data obtained from five distinct instrumental methods: nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma mass spectrometry (ICP-MS), liquid chromatography particle beam glow discharge mass spectrometry (LC/PB-G DMS), electron paramagnetic resonance spectroscopy (EPR), and X-ray absorption spectroscopy (XAS). The high toxicity of the metal-containing toxins is due to metal-mediated free radical production. This mode of activity explains the toxicity of Pfiesteria, as well as previously reported difficulty in observing the molecular target, due to the ephemeral nature of radical species. The toxins are highly labile in purified form, maintaining activity for only 2-5 days before all activity is lost. The multiple toxin congeners in active extracts are also susceptible to decomposition in the presence of white light, pH variations, and prolonged heat. These findings represent the first formal isolation and characterization of a radical forming toxic organic-ligated metal complex isolated from estuarine/marine dinoflagellates. These findings add to an increased understanding regarding the active role of metals interacting with biological systems in the estuarine environment, as well as their links and implications to human health.