Udo Nitschke

A new HPLC method for the detection of iodine applied to natural samples of edible seaweeds and commercial seaweed food products.

Rich in micronutrients and considered to contain high iodine levels, seaweeds have multiple applications as food/supplements and nutraceuticals with potential health implications. Here, we describe the development and validation of a new analytical method to quantify iodine as iodide (I(-)) using an isocratic HPLC system with UV detection; algal iodine was converted to I(-) via dry alkaline incineration. The method was successfully applied to 19 macroalgal species from three taxonomic groups and five commercially available seaweed food products. Fesh kelps contained highest levels, reaching >1.0% per dry weight (DW), but concentrations differed amongst thallus parts. In addition to kelps, other brown (Fucales: ∼ 0.05% DW) and some red species (∼ 0.05% DW) can also serve as a rich source of iodine; lowest iodine concentrations were detected in green macroalgae (∼ 0.005% DW), implying that quantities recommended for seaweed consumption may require species-specific re-evaluation to reach adequate daily intake levels.

Connecting marine productivity to sea-spray via nanoscale biological processes: Phytoplankton Dance or Death Disco?

Bursting bubbles at the ocean-surface produce airborne salt-water spray-droplets, in turn, forming climate-cooling marine haze and cloud layers. The reflectance and ultimate cooling effect of these layers is determined by the spray’s water-uptake properties that are modified through entrainment of ocean-surface organic matter (OM) into the airborne droplets. We present new results illustrating a clear dependence of OM mass-fraction enrichment in sea spray (OMss) on both phytoplankton-biomass, determined from Chlorophyll-a (Chl-a) and Net Primary Productivity (NPP). The correlation coefficient for OMss as a function of Chl-a increased form 0.67 on a daily timescale to 0.85 on a monthly timescale. An even stronger correlation was found as a function of NPP, increasing to 0.93 on a monthly timescale. We suggest the observed dependence is through the demise of the bloom, driven by nanoscale biological processes (such as viral infections), releasing large quantities of transferable OM comprising cell debris, exudates and other colloidal materials. This OM, through aggregation processes, leads to enrichment in sea-spray, thus demonstrating an important coupling between biologically-driven plankton bloom termination, marine productivity and sea-spray modification with potentially significant climate impacts.

Chlorophyll a fluorescence responses of temperate Phaeophyceae under submersion and emersion regimes: a comparison of rapid and steady-state light curves

The potential of algae to acclimate to environmental stress is commonly assessed using chlorophyll a fluorescence, with changes in parameters of photosynthesis versus irradiance (P/E) curves measured either as rapid light curves (RLC) or steady-state light curves (LC). Here, effects of emersion on primary photosynthesis of four brown macroalgae (Ascophyllum nodosum, Fucus serratus, Sargassum muticum, Laminaria digitata) were compared by applying both RLC and LC. When LC were used, photosynthetic performance was enhanced during emersion in A. nodosum and F. serratus as shown by increases in qP, rETRmax and Ek. By contrast, emersion had no impact on photosynthetic parameters of S. muticum and L. digitata. Relative changes in the NPQ–rETR relationship were reduced in A. nodosum, F. serratus and S. muticum, but remained unaffected in L. digitata. As none of the species developed their potential NPQmax, corresponding values could not be determined from RLC. Using RLC, observed photosynthetic performance of F. serratus and L. digitata was reduced upon emersion, whilst values for NPQmax were enhanced. Only results derived from LC provide evidence for a potential physiological adaptation of brown macroalgae to their natural habitat; it is recommended using the LC protocol to detect environmental impacts on photosynthesis.

Molecular iodine (I2) emission from two Laminaria species (Phaeophyceae) and impact of irradiance and temperature on I2 emission into air and iodide release into seawater from Laminaria digitata.

Kelps of the genus Laminaria accumulate iodine at high concentrations, but the iodine retaining capacity can be affected by emersion and physiological stress. In this study, I2 emission into the atmosphere from Laminaria digitata and Laminaria hyperborea was compared under controlled low irradiances and temperatures. The two species exhibited different I2 emission rates as blades of L. digitata emitted I2 at rates five times higher than those from newly-grown blades (current growth season) of L. hyperborea. I2 emission was not detectable from old blades (previous growth season) of L. hyperborea. Additionally, effects of irradiance and temperature on both I2 emission into air and net I(-) release into seawater where assessed for L. digitata while monitoring photo-physiological parameters as stress indicators. Irradiances between 30 and 120 μmol photons m(-2) s(-1) had only marginal effects on both I2 emission and I(-) release rates, but physiological stress, indicated by photoinhibition, was observed. The results suggest that the irradiances applied here were not stressful enough to impact on the iodine release. By contrast, at elevated temperatures (20 °C), photoinhibition was accompanied by an increase in I2 emission rates, but net I(-) release rates remained similar at 10-20 °C. High I2 emission rates into air and I(-) release into seawater observed from L. digitata underpin the fundamental function of this kelp as mediator of coastal iodine fluxes.

Coastal iodine emissions. 1. Release of I2 by Laminaria digitata in chamber experiments

Tidally exposed macroalgae emit large amounts of I(2) and iodocarbons that produce hotspots of iodine chemistry and intense particle nucleation events in the coastal marine boundary layer. Current emission rates are poorly characterized, however, with reported emission rates varying by 3 orders of magnitude. In this study, I(2) emissions from 25 Laminaria digitata samples were investigated in a simulation chamber using incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS). The chamber design allowed gradual extraction of seawater to simulate tidal emersion of algae. Samples were exposed to air with or without O(3) and to varying irradiances. Emission of I(2) occurred in four distinct stages: (1) moderate emissions from partially submerged samples; (2) a strong release by fully emerged samples; (3) slowing or stopping of I(2) release; and (4) later pulses of I(2) evident in some samples. Emission rates were highly variable and ranged from 7 to 616 pmol min(-1) gFW(-1) in ozone-free air, with a median value of 55 pmol min(-1) gFW(-1) for 20 samples.

Does the lack of mannitol accumulation in an isolate of Rhodella maculata (Rhodellophyceae, Rhodophyta) from the brackish Baltic Sea indicate a stressed population at the distribution limit?

The unicellular red alga Rhodella maculata Evans is reported for the first time from the central Baltic Sea (habitat salinity 5 psu). To evaluate whether this Baltic isolate is locally adapted to the brackish environment, its salt stress response was compared with a marine isolate (33 psu) by measuring growth rates, photosynthetic performance and the concentration of the osmolyte mannitol as a function of changing salinity between 1 and 60 psu. The brackish Baltic isolate grew between 5 and 40 psu, a narrower salinity range than in the marine isolate (1–60 psu). The marine isolate of R. maculata showed adaptations to an intertidal habitat with fluctuating salinities rather than to stable salinity conditions. The cells of the marine isolate performed a pronounced regulation of primary photosynthesis via non-photochemical quenching (NPQ), and accumulation of mannitol was involved in osmotic acclimation as intracellular concentrations increased considerably with rising salinities from 1 to 180 µmol g−1 dry weight. At its habitat salinity (5 psu), the brackish isolate achieved only 39% of the growth rate measured at 33 psu; when exposed to higher salinities it lacked the ability to carry out substantial NPQ regulation, and it did not accumulate mannitol. However, when cultured at 33 psu for more than three months, the Baltic isolate showed a considerably improved salinity response in the higher salinity range (33–60 psu). Thus, the Baltic Sea isolate of R. maculata does not seem to be locally adapted to its brackish environment, and should be regarded as a stressed population at its distributional limit.

Coastal iodine emissions: part 2. Chamber experiments of particle formation from Laminaria digitata-derived and laboratory-generated I2

Laboratory studies into particle formation from Laminaria digitata macroalgae were undertaken to elucidate aerosol formation for a range of I(2) (0.3-76 ppb(v)) and O(3) (<3-96 ppb(v)) mixing ratios and light levels (E(PAR) = 15, 100, and 235 μmol photons m(-2) s(-1)). No clear pattern was observed for I(2) or aerosol parameters as a function of light levels. Aerosol mass fluxes and particle number concentrations, were, however, correlated with I(2) mixing ratios for low O(3) mixing ratios of <3 ppb(v) (R(2) = 0.7 and 0.83, respectively for low light levels, and R(2) = 0.95 and 0.98, respectively for medium light levels). Additional experiments into particle production as a function of laboratory-generated I(2), over a mixing ratio range of 1-8 ppb(v), were conducted under moderate O(3) mixing ratios (∼24 ppb(v)) where a clear, 100-fold or greater, increase in the aerosol number concentrations and mass fluxes was observed compared to the low O(3) experiments. A linear relationship between particle concentration and I(2) was found, in reasonable agreement with previous studies. Scaling the laboratory relationship to aerosol concentrations typical of the coastal boundary layer suggests a I(2) mixing ratio range of 6-93 ppt(v) can account for the observed particle production events. Aerosol number concentration produced from I(2) is more than a factor of 10 higher than that produced from CH(2)I(2) for the same mixing ratios.

Variability in iodine in temperate seaweeds and iodine accumulation kinetics of Fucus vesiculosus and Laminaria digitata (Phaeophyceae, Ochrophyta)

The biogeochemistry of iodine in temperate coastal ecosystems is largely mediated by macroalgae, which act as a major biological sink and source of iodine. Their capacity to accumulate, retain and release iodine has been associated with abiotic and biotic stressors, but quantitative information is limited. We evaluated the seasonal iodine retention capacity of eleven macroalgal species belonging to different systematic groups, collected from two sites in Ireland. Iodine accumulation and retention were then further quantified in Fucus vesiculosus and Laminaria digitata in relation to I− concentrations in seawater and temperature. In general, iodine contents were ~101–102 μmol · (g dw)−1 for Laminariales, 100–101 μmol · (g dw)−1 for Fucales, 10−1–100 μmol · (g dw)−1 for Rhodophyta, and 10−1 μmol · (g dw)−1 for Chlorophyta. Typically, algal iodine contents were above average in winter and below average in summer. Iodine accumulation in F. vesiculosus and L. digitata depended on I− availability and followed the Michaelis‐Menten kinetic. The ratio of maximum accumulation rate to half accumulation coefficient (ρmax: Kt) was 2.4 times higher for F. vesiculosus than for L. digitata, suggesting that F. vesiculosus was more efficient in iodine accumulation. Both species exhibited a temperature‐dependent net loss of iodine, and only an exposure to sufficient external I− concentrations compensated for this loss. This study revealed that both environmental (e.g., I− in seawater, temperature) and organismal (e.g., the status of the iodine storage pool) variables determine retention and variability in iodine in temperate seaweeds.