Geologic controls on phytoplankton elemental composition.

Planktonic organic matter forms the base of the marine food web, and its nutrient content (C:N:Porg) governs material and energy fluxes in the ocean. Over Earth history, C:N:Porg had a crucial role in marine metazoan evolution and global biogeochemical dynamics, but the geologic history of C:N:Porg is unknown, and it is often regarded constant at the "Redfield" ratio of ∼106:16:1. We calculated C:N:Porg through Phanerozoic time by including nutrient- and temperature-dependent C:N:Porg parameterizations in a model of the long-timescale biogeochemical cycles. We infer a decrease from high Paleozoic C:Porg and N:Porg to present-day ratios, which stems from a decrease in the global average temperature and an increase in seawater phosphate availability. These changes in the phytoplankton's growth environment were driven by various Phanerozoic events: specifically, the middle to late Paleozoic expansion of land plants and the Triassic breakup of the supercontinent Pangaea, which increased continental weatherability and the fluxes of weathering-derived phosphate to the oceans. The resulting increase in the nutrient content of planktonic organic matter likely impacted the evolution of marine fauna and global biogeochemistry.

Trait convergence and niche differentiation of two exotic invasive free-floating plant species in China under shifted water nutrient stoichiometric regimes.

The effects of eutrophication on the growth and phenotypic performance of macrophytes have been widely studied. Experimental evidence suggests that an increase in the water nutrient level would promote the performance of several invasive free-floating macrophytes. However, few studies have focused on how a shift in water nutrient (nitrogen and phosphorus) stoichiometric regimes may influence the performance of invasive free-floating macrophytes. In the present study, two exotic invasive plant species, free-floating Eichhornia crassipes and Pistia stratiotes, were subjected to different water nutrient stoichiometric regimes, and their phenotypic performance was studied. We found that the two species converged in several resource use traits and diverged in lateral root length. This implied that their similarities in fitness-correlated traits and their underwater niche differentiation probably contribute to their stable coexistence in the field. Additionally, the eutrophic conditions in the different N:P regimes scarcely altered the performance of both species compared to their performance in the oligotrophic condition. Based on previous studies, we predicted that moderate eutrophication with slight overloading of nitrogen and phosphorus would not improve the performance of several invasive free-floating plants and thus would scarcely alter the invasive status of these species. However, moderate eutrophication may cause other problems, such as the growth of phytoplankton and algae and increased pollution in the water.

Relationship between plankton-based ß-carotene and biodegradable adaptablity to petroleum-derived hydrocarbon.

Coastal environment are often stress from petroleum-derived hydrocarbon pollution. However, petroleum-derived hydrocarbon is persistent organic pollutants and their biodegradation by phytoplankton is little known. Five species of marine phytoplankton, including Dunaliella salina, Chlorella sp., Conticribra weissflogii, Phaeodactylum tricornutum Bohlin, and Prorocentrum donghaiense, have been used to test their tolerance to petroleum hydrocarbon contamination. D.salina and Chlorella sp can survive in high levels of No. 0 diesel oils water-soluble fractions (WSFs, 5.0 mg L-1), furthermore, petroleum hydrocarbon could be biodegraded effectively by them (Fig. 2). The content of ß-carotene in these two species of phytoplankton has significant correlation with degradation rate of WSFs concentrations (Fig. 4), petroleum hydrocarbons could be biodegraded effectively by algae. Meanwhile, the ·OH in seawater can be removed by ß-carotene effectively so that algal cells could be protected by the ß-carotene for its strong antioxidant capacity. Therefore, ß-carotene as a coin has two sides on the degradation of WSFs. Here we explore the relationship between plankton-based ß-carotene and biodegradable adaptabllity to petroleum-derived hydrocarbon, which offers a green technology for petroleum-derived hydrocarbon treatment.

Copepod nauplii use phosphorus from bacteria, creating a short circuit in the microbial loop.

In subtropical oceans phytoplankton carbon: phosphorus (C : P) ratios are high, and these ratios are predicted to increase further with rising ocean temperatures and stratification. Prey stoichiometry may pose a problem for copepod zooplankton nauplii, which have high phosphorus demands due to rapid growth. We hypothesised that nauplii meet this demand by consuming bacteria. Naupliar bacterial and phytoplankton carbon and phosphorus ingestion, assimilation and incorporation were traced using 33 P and 14 C radioisotopes. Bacterial carbon was incorporated four times less efficiently into biomass than phytoplankton carbon. In contrast, bacterial and phytoplankton phosphorus were incorporated at similar efficiencies, and bacteria could meet a substantial amount of naupliar phosphorus requirements. As parts of the ocean become more oligotrophic, bacteria could help sustain naupliar growth and survival under suboptimal stoichiometric conditions. Thus, nauplii may be a shortcut for phosphorus from the microbial loop to the classical food web.

Convergent estimates of marine nitrogen fixation.

Uncertainty in the global patterns of marine nitrogen fixation limits our understanding of the response of the ocean's nitrogen and carbon cycles to environmental change. The geographical distribution of and ecological controls on nitrogen fixation are difficult to constrain with limited in situ measurements. Here we present convergent estimates of nitrogen fixation from an inverse biogeochemical and a prognostic ocean model. Our results demonstrate strong spatial variability in the nitrogen-to-phosphorus ratio of exported organic matter that greatly increases the global nitrogen-fixation rate (because phytoplankton manage with less phosphorus when it is in short supply). We find that the input of newly fixed nitrogen from microbial fixation and external inputs (atmospheric deposition and river fluxes) accounts for up to 50 per cent of carbon export in subtropical gyres. We also find that nitrogen fixation and denitrification are spatially decoupled but that nevertheless nitrogen sources and sinks appear to be balanced over the past few decades. Moreover, we propose a role for top-down zooplankton grazing control in shaping the global patterns of nitrogen fixation. Our findings suggest that biological carbon export in the ocean is higher than expected and that stabilizing nitrogen-cycle feedbacks are weaker than previously thought.

Diagnostic tool to ascertain marine phytoplankton exposure to chemically enhanced water accommodated fraction of oil using Fourier Transform Infrared spectroscopy.

Phytoplankton alter their macromolecule composition in response to changing environmental conditions. Often these changes are consistent and can be used as indicators to predict their exposure to a given condition. FTIR-spectroscopy is a powerful tool that provides rapid snapshot of microbial samples. We used FTIR to develop signature macromolecular composition profiles of three cultures: Skeletonema costatum, Emiliania huxleyi, and Navicula sp., exposed to chemically enhanced water accommodated oil fraction (CEWAF) in artificial seawater and control. Using a multivariate model created with a Partial Least Square Discriminant Analysis of the FTIR-spectra, classification of CEWAF exposed versus control samples was possible. This model was validated using aggregate samples from a mesocosm study. Analysis of spectra and PCA-loadings plot showed changes to carbohydrates and proteins in response to CEWAF. Overall we developed a robust multivariate model that can be used to identify if a phytoplankton sample has been exposed to oil with dispersant.

Simulated bioavailability of phosphorus from aquatic macrophytes and phytoplankton by aqueous suspension and incubation with alkaline phosphatase.

Bioavailability of phosphorus (P) in biomass of aquatic macrophytes and phytoplankton and its possible relationship with eutrophication were explored by evaluation of forms and quantities of P in aqueous extracts of dried macrophytes. Specifically, effects of hydrolysis of organically-bound P by the enzyme alkaline phosphatase were studied by use of solution 31P-nuclear magnetic resonance (NMR) spectroscopy. Laboratory suspensions and incubations with enzymes were used to simulate natural releases of P from plant debris. Three aquatic macrophytes and three phytoplankters were collected from Tai Lake, China, for use in this simulation study. The trend of hydrolysis of organic P (Po) by alkaline phosphatase was similar for aquatic macrophytes and phytoplankton. Most monoester P (15.3% of total dissolved P) and pyrophosphate (1.8%) and polyphosphate (0.4%) and DNA (3.2%) were transformed into orthophosphate (14.3%). The major forms of monoester P were glycerophosphate (8.8%), nucleotide (2.5%), phytate (0.4%) and other monoesters P (3.6%). Proportions of Po including condensed P hydrolyzed in phytoplankton and aquatic macrophytes were different, with the percentage of 22.6% and 6.0%, respectively. Proportion of Po hydrolyzed in debris from phytoplankton was approximately four times greater than that of Po from aquatic macrophytes, and could be approximately twenty-five times greater than that of Po in sediments. Thus, release and hydrolysis of Po, derived from phytoplankton debris would be an important and fast way to provide bioavailable P to support cyanobacterial blooming in eutrophic lakes.

Chemical composition and biomass of Coscinodiscus asteromphalus in Jiaozhou Bay, China.

The large diatom Coscinodiscus asteromphalus was separated from seawater in Jiaozhou Bay using a repeated precipitation method and then its chemical compositions of carbon (C), nitrogen (N), phosphorus (P), and silicon (Si) combined with chlorophyll a (Chl a) were examined for the first time for a natural population in this study. Results show that the contents of carbon, nitrogen, phosphorus, silicon, and Chl a in C. asteromphalus cells were 35,610.5, 9374.2, 352.4, 1105.5, and 1767.0 pg/cell, respectively, and the corresponding molar ratios of C/N, N/P, Si/P, and Si/N in C. asteromphalus cells were 4.5, 66.0, 2.7, and 0.07, respectively, which are different from the Redfield ratio. Additionally, their C/Chl a mass ratio was 23.2. High N/P ratio and low Si/P and Si/N ratios in C. asteromphalus cells were consistent with those in particulates of any size and seawater in the bay, reflecting an ecological response of phytoplankton to the nutrient structure of seawater, suggesting Si limitation to phytoplankton growth. The fact that C. asteromphalus spread all over the bay mainly in summer and autumn and the fact that Chl a content in C. asteromphalus cells could account for a maximum percentage of 78% of those in the water column suggest that the contribution of C. asteromphalus to phytoplankton biomass was significant in Jiaozhou Bay.

Effects of portable solar water quality control machines on aquaculture ponds.

The effects of a portable solar water quality control machine (PSWM) on water quality and sediment of aquaculture ponds were studied in bream aquaculture ponds in Shanghai, China. PSWM operation reduced the temperature and dissolved oxygen (DO) differences between upper and lower water levels. Concentrations of NH4+-N, NO2--N, TN, TP, COD and TSS increased rapidly and reached maximums at 12 h. The density and biomass of phytoplankton and levels of chlorophyll a reached maximums after 40 h of PSWM operation. In a 165-day study, the mean concentrations of NH4+-N, NO2--N and the available phosphorous (AP) in the PSWM ponds were significantly lower than in the control ponds, but the TP was significantly greater than the control ponds. Compared with the test began, the thickness of the sediment in PSWM ponds declined by 12.4 ± 4.3 cm, the control ponds increased by 5.0 ± 2.3 cm and the TN and AP levels in sediment significantly declined. PSWM treatment increased the production of bream and silver carp by 30 and 25%, respectively, and the feed coefficient was reduced by 24.2%. Use of PSWM in bream aquaculture ponds improved water quality, reduced sediment, reduced aquaculture pollution emissions and increased production.

Polar Lipids Analysis of Cultured Phytoplankton Reveals Significant Inter-taxa Changes, Low Influence of Growth Stage, and Usefulness in Chemotaxonomy.

The high lipid diversity of microalgae has been used to taxonomically differentiate phytoplankton taxa at the class level. However, important lipids such as phospholipids (PL) and betaine lipids (BL) with potential chemotaxonomy application in phytoplankton ecology have been scarcely studied. The chemotaxonomy value of PL and BL depends on their intraspecific extent of variation as microalgae respond to external changing factors. To determine such effects, lipid class changes occurring at different growth stages in 15 microalgae from ten different classes were analyzed. BL occurred in 14 species and were the less affected lipids by growth stage with diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-b-alanine (DGTA) showing the highest stability. PL were more influenced by growth stage with phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidyletanolamine (PE) declining towards older culture stages in some species. Glycolipids were the more common lipids, and no evident age-related variability pattern could be associated to taxonomic diversity. Selecting BL and PL as descriptor variables optimally distinguished microalgae taxonomic variability at all growth stages. Principal coordinate analysis arranged species through a main tendency from diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-b-alanine (DGCC) containing species (mainly dinoflagellates and haptophytes) to DGTA or PC containing species (mainly cryptophytes). Two diatom classes with similar fatty acid profiles could be distinguished from their respective content in DGTA (Bacillariophyceae) or DGCC (Mediophyceae). In green lineage classes (Trebouxiophyceae, Porphyridophyceae, and Chlorodendrophyceae), PC was a better descriptor than BL. BL and PL explained a higher proportion of microalgae taxonomic variation than did fatty acids and played a complementary role as lipid markers.

Accumulation of petroleum hydrocarbons in intracellular lipid bodies of the freshwater diatom Synedra acus subsp. radians.

The accumulation of hydrophobic compounds by phytoplankton plays a crucial role in the biogeochemical cycle of persistent organic pollutants (POPs) in aquatic environments. We studied the accumulation of polycyclic aromatic hydrocarbons (PAHs) in the freshwater diatom Synedra acus subsp. radians during its cultivation with crude oil hydrocarbons, using epifluorescent and laser confocal microscopy as well as gas chromatography-mass spectrometry (GC/MS) analysis. Our results revealed that in the presence of crude oil or an extract of a crude oil/n-hexane solution (light oil), S. acus subsp. radians accumulated PAHs in its lipid bodies. During cultivation in the presence of a crude oil/n-hexane solution, the cells selectively accumulated C12-C18 alkanes, with a preference for C15 and C16 homologues. The length of n-alkane hydrocarbon chains accumulated in cells was similar to the acyl chains of fatty acids of the diatom. We therefore suggest that the insertion of n-alkanes into the membrane lipid bilayer promotes the transmembrane transport of PAH in diatoms. Our results confirm the hypothesis that diatoms play a role in the elimination of hydrophobic hydrocarbons from aquatic systems.

9-cis ß-Carotene Increased Cholesterol Efflux to HDL in Macrophages.

Cholesterol efflux from macrophages is a key process in reverse cholesterol transport and, therefore, might inhibit atherogenesis. 9-cis-ß-carotene (9-cis-ßc) is a precursor for 9-cis-retinoic-acid (9-cis-RA), which regulates macrophage cholesterol efflux. Our objective was to assess whether 9-cis-ßc increases macrophage cholesterol efflux and induces the expression of cholesterol transporters. Enrichment of a mouse diet with ßc from the alga Dunaliella led to ßc accumulation in peritoneal macrophages. 9-cis-ßc increased the mRNA levels of CYP26B1, an enzyme that regulates RA cellular levels, indicating the formation of RA from ßc in RAW264.7 macrophages. Furthermore, 9-cis-ßc, as well as all-trans-ßc, significantly increased cholesterol efflux to high-density lipoprotein (HDL) by 50% in RAW264.7 macrophages. Likewise, food fortification with 9-cis-ßc augmented cholesterol efflux from macrophages ex vivo. 9-cis-ßc increased both the mRNA and protein levels of ABCA1 and apolipoprotein E (APOE) and the mRNA level of ABCG1. Our study shows, for the first time, that 9-cis-ßc from the diet accumulates in peritoneal macrophages and increases cholesterol efflux to HDL. These effects might be ascribed to transcriptional induction of ABCA1, ABCG1, and APOE. These results highlight the beneficial effect of ßc in inhibition of atherosclerosis by improving cholesterol efflux from macrophages.

Characterization of total retinoid-like activity of compounds produced by three common phytoplankton species.

Phytoplankton can produce various bioactive metabolites, which may affect other organisms in the aquatic environment. This study provides the first information on the total retinoid-like activity associated with both intracellular and extracellular metabolites produced by selected phytoplankton species that could play a role in teratogenic effects and developmental disruption in exposed organisms. The studied species included a coccoid cyanobacteria (Microcystis aeruginosa), a filamentous cyanobacteria (Aphanizomenon gracile) and a green alga (Desmodesmus quadricauda), all of which commonly occur in freshwater bodies in Europe. Methanolic extracts from cellular material and extracellular exudates were prepared from cultures cultivated in two light-intensity variants with five replicates for each species. The retinoid-like activity was evaluated by in vitro assays along with chemical analyses of two potent retinoic acids (all-trans retinoic acid (ATRA) and 9cis-RA). The mean total retinoid-like activity of metabolites produced by the three studied species representing different phytoplankton taxonomic groups ranged from 705 to 5572ng ATRA equivalent/g dry matter corresponding to 0.064-0.234ng ATRA/106 cells. Retinoid-like activity was found in the cellular extracts of all species, while only the extracellular exudates of cyanobacteria exhibited detectable activity (41-1081ng ATRA/L). The greatest extracellular as well as total (extra- and intra- cellular together) retinoid-like activity was detected for Microcystis aeruginosa. The two potent retinoic acids studied were more frequently detected in cellular extracts than in extracellular exudates of all species. Their contribution to observed in vitro effects was relatively low for all tested samples (<10%), indicating a substantial contribution of other retinoid-like compounds to the overall activity. The results indicate possible influence of light intensity and cell density on the production of metabolites with retinoid-like activity and the cyanotoxin microcystin by the studied species. The recalculation of the results per dry weight, water volume, per 106 cells and biovolume enables a direct comparison of the retinoid-like activity distribution between extracts and exudates and the use of the data for risk assessment in water bodies.

Macronutrient processing by temperate lakes: A dynamic model for long-term, large-scale application.

We developed a model of the biogeochemical and sedimentation behaviour of carbon (C), nitrogen (N) and phosphorus (P) in lakes, designed to be used in long-term (decades to centuries) and large-scale (104-105km2) macronutrient modelling, with a focus on human-induced changes. The model represents settling of inflow suspended particulate matter, production and settling of phytoplankton, decomposition of organic matter in surface sediment, denitrification, and DOM flocculation and decomposition. The model uses 19 parameters, 13 of which are fixed a priori. The remaining 6 were obtained by fitting data from 109 temperate lakes, together with other information from the literature, which between them characterised the stoichiometric incorporation of N and P into phytoplankton via photosynthesis, whole-lake retention of N and P, N removal by denitrification, and the sediment burial of C, N and P. To run the model over the long periods of time necessary to simulate sediment accumulation and properties, simple assumptions were made about increases in inflow concentrations and loads of dissolved N and P and of catchment-derived particulate matter (CPM) during the 20th century. Agreement between observations and calculations is only approximate, but the model is able to capture wide trends in the lakewater and sediment variables, while also making reasonable predictions of net primary production. Modelled results suggest that allochthonous sources of carbon (CPM and dissolved organic matter) contribute more to sediment carbon than the production and settling of algal biomass, but the relative contribution due to algal biomass has increased over time. Simulations for 8 UK lakes with sediment records suggest that during the 20th century average carbon fixation increased 6-fold and carbon burial in sediments by 70%, while the delivery of suspended sediment from the catchments increased by 40% and sediment burial rates of N and P by 131% and 185% respectively.

Changes in nutrients ratio along the central Bay of Bengal coast and its influence on chlorophyll distribution.

Elemental ratio of nutrients and its influence on chlorophyll a distribution was studied along the central coast of Bay of Bengal using multivariate statistical methods. High chlorophyll concentration was observed during summer (1.81 µg l⁻¹) and premonsoon (1.95 µgl⁻¹), however, it was high in top 20 m during premonsoon season in tandem with high nitrate (N) and silicate (Si) concentration. N:P (phosphate) ratio was less than Redfield ratio (16:1) during all seasons, indicating the Bay of Bengal as nitrate limited and confirmed the results of Principal ComponentAnalysis (PCA) with positive loading and multiple regression analysis showing negative correlation between this ratio and chlorophyll concentration during all seasons. Whereas, N:Si ratio was < 1 and Si:P ratio > 7 in top 20 m during all seasons explained the deficiency of phosphorus and enrichment of silicate in the central Bay of Bengal. Regression analysis between Si:P and N:Si ratios with chlorophyll showed negative correlation during premonsoon and summer respectively. Thus, the present results confirmed that nutrient molar ratios such as N:P<16; Si:P>7 and N:Si<1 was indicative of a potential N and Si limitation and are the primary limiting nutrients in the central Bay of Bengal in determining chlorophyll concentration.

Stoichiometric regulation of phytoplankton toxins.

Ecological Stoichiometry theory predicts that the production, elemental structure and cellular content of biomolecules should depend on the relative availability of resources and the elemental composition of their producer organism. We review the extent to which carbon- and nitrogen-rich phytoplankton toxins are regulated by nutrient limitation and cellular stoichiometry. Consistent with theory, we show that nitrogen limitation causes a reduction in the cellular quota of nitrogen-rich toxins, while phosphorus limitation causes an increase in the most nitrogen-rich paralytic shellfish poisoning toxin. In addition, we show that the cellular content of nitrogen-rich toxins increases with increasing cellular N : P ratios. Also consistent with theory, limitation by either nitrogen or phosphorus promotes the C-rich toxin cell quota or toxicity of phytoplankton cells. These observed relationships may assist in predicting and managing toxin-producing phytoplankton blooms. Such a stoichiometric regulation of toxins is likely not restricted to phytoplankton, and may well apply to carbon- and nitrogen-rich secondary metabolites produced by bacteria, fungi and plants.

Nitrogen deposition and warming - effects on phytoplankton nutrient limitation in subarctic lakes.

The aim of this study was to predict the combined effects of enhanced nitrogen (N) deposition and warming on phytoplankton development in high latitude and mountain lakes. Consequently, we assessed, in a series of enclosure experiments, how lake water nutrient stoichiometry and phytoplankton nutrient limitation varied over the growing season in 11 lakes situated along an altitudinal/climate gradient with low N-deposition (<1 kg N ha(-1)  yr(-1) ) in northern subarctic Sweden. Short-term bioassay experiments with N- and P-additions revealed that phytoplankton in high-alpine lakes were more prone to P-limitation, and with decreasing altitude became increasingly N- and NP-colimited. Nutrient limitation was additionally most obvious in midsummer. There was also a strong positive correlation between phytoplankton growth and water temperature in the bioassays. Although excess nutrients were available in spring and autumn, on these occasions growth was likely constrained by low water temperatures. These results imply that enhanced N-deposition over the Swedish mountain areas will, with the exception of high-alpine lakes, enhance biomass and drive phytoplankton from N- to P-limitation. However, if not accompanied by warming, N-input from deposition will stimulate limited phytoplankton growth due to low water temperatures during large parts of the growing season. Direct effects of warming, allowing increased metabolic rates and an extension of the growing season, seem equally crucial to synergistically enhance phytoplankton development in these lakes.

Interactive effects of phosphorus and copper on Hyalella azteca via periphyton in aquatic ecosystems.

This research examined the interaction between dissolved copper and phosphorus, with respect to their effects on the freshwater amphipod Hyalella azteca feeding on periphyton. Field-collected periphyton communities were exposed to different nutrient and metal conditions in indoor recirculating streams. H. azteca were then exposed to water and periphyton from these streams. There was rapid Cu accumulation by periphyton but the total Cu concentration of periphyton was not directly related to dissolved P. In terms of H. azteca growth, an interactive effect was found between Cu and P as growth was reduced more than expected in the low Cu-high P treatment. Our data suggest that eutrophic conditions result in greater Cu toxicity to benthic macroinvertebrates at lower metal concentrations, likely due to higher assimilation efficiency of dietary Cu from periphyton incubated under eutrophic conditions. These results imply that non-additive interactions between multiple stressors may cause ecosystem effects as detected in standard laboratory bioassays conducted under controlled conditions.

Phytobenthos and phytoplankton community changes upon exposure to a sunflower oil spill in a South African protected freshwater wetland.

The occurrence of a sunflower oil spill in 2007 in the Con Joubert Bird Sanctuary freshwater wetland, South Africa, inhibited the growth of sensitive phytoplankton species and promoted that of tolerant species. The algal divisions Chlorophyta and Euglenophyta were well represented in the sunflower oil contaminated water, especially the species Euglena sociabilis, Phacus pleuronectes and Chlamydomonas africana. Young and mature resting zygotes of Chlamydomonas africana were recorded in high abundance at all the sunflower oil contaminated sampling sites. The phytobenthos diversity and abundance were significantly suppressed and negatively associated with low Dissolved Oxygen concentrations and the negative redox potential of the bottom sediment. At the intracellular level, phytoplankton chlorophyll a and b concentrations as physiological variables were more sensitive indicators of the adverse effects of sunflower oil than the 72 h Selenastrum capricornutum algal bioassay conducted.

Distribution and abundance of MAAs in 33 species of microalgae across 13 classes.

We provide a direct comparison of the distribution and abundance of mycosporine-like amino acids (MAAs) in a diverse range of microalgal cultures (33 species across 13 classes) grown without supplementary ultraviolet radiation (UV). We compare the MAAs in cultures with those present in characterised natural phytoplankton populations from the English Channel. We detected 25 UV absorbing compounds including at least two with multiple absorption maxima. We used LC-MS to provide chemical characterisation of the six most commonly occurring MAAs, namely, palythene, palythine, mycosporine-glycine, palythenic acid, porphyra-334 and shinorine. MAAs were abundant (up to 7 pg MAA cell(-1)) in 10 species, with more minor and often unknown MAAs in a further 11 cultures. Shinorine was the most frequently occurring and abundant MAA (up to 6.5 pg cell(-1)) and was present in all but two of the MAA-containing species. The study provides further insight into the diversity and abundance of MAAs important from an ecological perspective and as potential source of natural alternatives to synthetic sunscreens.