Effects of iron stress on chromatic adaptation by natural phytoplankton communities in the Southern Ocean

Effects of iron stress on chromatic adaptation were studied in natural phytoplankton communities collected in the Pacific region of the Southern Ocean. Iron enrichment experiments (48 to 72 h) were performed, incubating plankton communities under white, green and blue light respectively, with and without addition of 2 nM Fe. Pigment ratios were affected by iron addition only to a minor extent. The pigment composition as dictated by the light conditions was similar for both the iron-enriched and the unamended bottles. Upon iron addition, phytoplankton auto-fluorescence, as estimated by flow cytometry, decreased markedly, indicating iron stress of the endemic phytoplankton community. It was concluded that iron did not control chromatic adaptation via the pigment composition, but exerted a clear effect on the efficiency of electron transfer

Low temporal variation in the intact polar lipid composition of North Sea coastal marine water reveals limited chemotaxonomic value

Temporal variations in the abundance and composition of intact polar lipids (IPLs) in North Sea coastal marine water were assessed over a one-year seasonal cycle, and compared with environmental parameters and the microbial community composition. Sulfoquinovosyldiacylglycerol (SQDG) was the most abundant IPL class, followed by phosphatidylcholine (PC), phosphatidylglycerol (PG) and diacylglyceryl-(N,N,N)-trimethylhomoserine (DGTS) in roughly equal concentrations, and smaller amounts of phosphatidylethanolamine (PE). Although the total concentrations of these IPL classes varied substantially throughout the year, the composition of the IPL pool remained remarkably constant. Statistical analysis yielded negative correlations between IPL concentrations and dissolved inorganic nutrient concentrations, but no changes in the overall planktonic IPL composition due to nutrient limitation were observed. Significant correlations between SQDG, PC, PG and DGTS concentrations and chlorophyll a concentrations and algal abundances indicated that eukaryotic primary producers, in particular Phaeocystis globosa, were the predominant source of IPLs at this site. However, while IPL concentrations in the water were closely tied to total algal abundances, the rapid succession of different algal groups blooming throughout the year resulted in only minor shifts in the IPL composition. Principal component analysis showed that the IPLs were derived from multiple sources, and that no IPL species could be exclusively assigned to a particular algal taxa or (cyano)bacteria. Thus, the most commonly occurring IPLs appear to have limited chemotaxonomic potential, highlighting the need to use targeted assays of more specific biomarker IPLs

Co-variance of dissolved Fe-binding ligands with phytoplankton characteristics in the Canary Basin

Dissolved Fe and ligand concentrations and the Fe-binding strength of the organic ligands were measured in samples from the upper water column (150 m) of the oligotrophic waters of the Canary Basin (eastern North Atlantic Ocean). Concentrations of major nutrients, phytoplankton abundance and photosynthetic characteristics were also measured in the same samples. The concentrations of dissolved Fe and dissolved organic ligands were low with mean values of 0.31 ± 0.18 nM Fe and 1.79 ± 0.73 nEq of M Fe (n = 47), respectively. The conditional binding constant varied between 10^19.8–10^22.7 (n = 47). The largest variation with depth in the ligand concentrations (between 4.78 and 1.1 nEq of M Fe) was observed in the upper layer, above the Deep Chlorophyll Maximum (DCM located between 80 and 100 m), with high surface values in stations at 18 and 34. At the DCM where Fe was depleted, the ligand concentrations were still relatively high showing the same trend with depth as the amount of phytoplankton cells. Here 62% of the vertical variation in ligand concentrations can be explained by parameters describing phytoplankton cell abundance or biomass and orthosilicic acid concentration, which could reflect diatom growth. Ligand concentrations below the maximum of the DCM (n = 4) showed good linear positive relationships with the total phytoplankton biomass as well as with 2 out of 4 distinguished groups of phytoplankton (Synechococcus and pico-eukaryote I). In the maximum of the DCM and below this maximum the phytoplankton origin of the dissolved organic ligands of Fe is very probable. Data suggest a release of ligands by cell lysis and not by an active production. However, the origin in the surface layer is more difficult to explain. Although the amount of phytoplankton cells in the surface layer is reduced, it is still ~ 25% of the cell concentration observed in the DCM. High concentrations of organic ligands could then be a remnant of past blooms or present production under nutrient depleted conditions. Input of Sahara dust can be another source of ligands.

Physiological responses of three species of marine pico-phytoplankton to ammonium, phosphate, iron and light limitation

Experiments were conducted with three species of marine pico-phytoplankton: Synechococcus sp. (CCMP 839), Pelagomonas calceolata (CCMP 1756) and Prasinomonas capsulatus (CCMP 1617) in order to collect physiological parameters for pico-phytoplankton to be utilised in Ocean Biogeochemical Climate Models. The main parameters to follow the effects of ammonium, phosphate, iron and light limitation were cell growth rates (µ), half saturation constants for growth (Km), N, P and Fe quota (per cell or per mol C), and photochemical quantum efficiency (Fv/Fm). The nitrate and phosphate limitation experiments demonstrated that the small phytoplankton species could grow at low N and P concentrations. Km values were in the micro-molar (NH4+) and sub-micro-molar (PO43-) range. N and P quota were in the femto-molar range per cell and varied from nutrient-deplete to nutrient-replete conditions. Fv/Fm values were only adversely affected at the lowest N and P concentrations in these experiments. In the Fe limitation experiments, it was shown that all three species were adversely affected only at extremely low Fe concentrations. Iron chelating agents had to be added to force the species in Fe limitation till ultimately growth stopped. Km values with respect to dissolved Fe were in the femto-molar range. Fe quota were in the low zepto-molar (10-21 M) range per cell, and varied considerably from Fe limiting to Fe replete growth conditions. Fv/Fm values diminished only at the lowest iron concentrations. In the light limitation experiments, growth rates and photochemical quantum efficiencies were adversely affected only at irradiance levels below 10 µmol photons m-2 s-1. These results indicate that the pico-phytoplankton species will hardly ever be completely stopped in their growth by NH4+, PO43-, Fe or light (separately) under natural conditions.

Biological interactions in enclosed phytoplankton communities including Alexandrium catenella

1 page, figures, tablesPeer reviewe

Phaeocystis blooms and nutrient enrichment in the continental coastal zones of the North sea

With increasing frequency over the past 20 years, generally during the second half of June, Dutch and German beaches were covered with a massive layer, up to 2 m thick, of the alga Phaeocystis pouchetii. Increased anthropogenic inputs of nutrients, unbalanced in favour of nitrogen and phosphorus with respect to silica, promoted these conditions and reinforced the tendency of Phaeocystis to develop temporary, explosive blooms. These blooms caused a decrease in food resources for zooplankton, and increased deposition of organic material to the bottom, accumulation of organic material (dissolved or in the form of foam), and emission of volatile sulphur compounds. Means of control were unclear but it was possible that the food, cosmetic, textile and pharmaceutical industries could exploit the Phaeocystis mucus.SCOPUS: NotDefined.jinfo:eu-repo/semantics/publishe