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Macrocystis pyrifera is a major habitat forming kelp in coastal ecosystems of temperate regions of the northern and southern hemispheres. We investigated the seasonal occurrence of adult sporophytes, morphological characteristics, and reproductive phenology at two sites within a wave-protected harbour and two wave-exposed sites in southern New Zealand every 3–4 months between 2012 and 2013. Seasonality in reproduction was assessed via the number of sporophylls, the occurrence of sori on sporophylls, and non-sporophyllous laminae (fertile pneumatocyst-bearing blades and fertile apical scimitars), meiospore release, and germination. We found that M. pyrifera was present and reproductive year-round in three of the four sites, and patterns were similar for the wave-exposure conditions. Sori were found on pneumatocyst-bearing blades and apical scimitars in addition to the sporophylls, and viable meiospores were released from all three types of laminae. Morphological variations between sites with different wave exposure indicate that sporophytes from wave-protected sites have bigger blades and holdfasts and are longer than those from wave-exposed sites. We discuss the implications of these biological variables for the ecology of M. pyrifera inhabiting different wave exposure environments in southern New Zealand.

Macrocystis pyrifera is a major habitat forming kelp in coastal ecosystems of temperate regions of the northern and southern hemispheres. We investigated the seasonal occurrence of adult sporophytes, morphological characteristics, and reproductive phenology at two sites within a wave-protected harbour and two wave-exposed sites in southern New Zealand every 3-4 months between 2012 and 2013. Seasonality in reproduction was assessed via the number of sporophylls, the occurrence of sori on sporophylls, and non-sporophyllous laminae (fertile pneumatocyst-bearing blades and fertile apical scimitars), meiospore release, and germination. We found that M. pyrifera was present and reproductive year-round in three of the four sites, and patterns were similar for the wave-exposure conditions. Sori were found on pneumatocyst-bearing blades and apical scimitars in addition to the sporophylls, and viable meiospores were released from all three types of laminae. Morphological variations between sites with different wave exposure indicate that sporophytes from wave-protected sites have bigger blades and holdfasts and are longer than those from wave-exposed sites. We discuss the implications of these biological variables for the ecology of M. pyrifera inhabiting different wave exposure environments in southern New Zealand.

Short-term effects of pCO2 (700–380 ppm; High carbon (HC) and Low carbon (LC), respectively) and nitrate content (50–5 µM; High nitrogen (HN) and Low nitrogen (LN), respectively on photosynthesis were investigated in Ulva rigida (Chlorophyta) under solar radiation (in-situ) and in the laboratory under artificial light (ex-situ). After six days of incubation at ambient temperature (AT), algae were subjected to a 4 °C temperature increase (AT+4 °C) for 3 d. Both in-situ and ex-situ maximal electron transport rate (ETRmax) and in situ gross photosynthesis (GP), measured by O2 evolution, presented highest values under HCHN, and lowest under HCLN, across all measuring systems. Maximal quantum yield (Fv/Fm), and ETRmax of photosystem (PS) II [ETR(II)max] and PSI [ETR(I)max], decreased under HCLN at AT+4 °C. Ex situ ETR was higher than in situ ETR. At noon, Fv/Fm decreased (indicating photoinhibition), whereas ETR(II)max and maximal non-photochemical quenching (NPQmax) increased. ETR(II)max decreased under AT+ 4 °C in contrast to Fv/Fm, photosynthetic efficiency (α ETR) and saturated irradiance (EK). Thus, U. rigida exhibited a decrease in photosynthesis under acidification, changing LN, and AT+4 °C. These results emphasize the importance of studying the interaction between environmental parameters using in-situ versus ex-situ conditions, when aiming to evaluate the impact of global change on marine macroalgae.

Resilience and biochemical response to predicted future North Atlantic Ocean temperature conditions (+2 °C of current seasonal observations) and different light conditions were investigated in four commercially valuable macroalgae that naturally inhabit different shore levels (Ascophyllum nodosum, Fucus serratus, Laminaria digitata and Palmaria palmata). Increased irradiances had a positive effect on growth rates of the intertidal species (Ascophyllum. nodosum and Fucus serratus). Growth and chlorophyll contents of Laminaria digitata were most strongly impacted by temperature, but its fatty acid contents and composition were more strongly controlled by light. Neither changes in light nor temperature affected growth of Palmaria palmata although biochemical composition was highly sensitive to temperature. Pigments and polyunsaturated fatty acids exhibited a correlated response in the brown canopy-forming macroalgae, with decreasing concentrations with increasing light conditions. By integrating growth and changes in biochemical composition, new production of essential and commercially relevant biomolecules was evaluated, Effects of individual and combined environmental factors on growth and key biochemical composition were linked to the specific acclimation potential of macroalgae from different habitats. Results demonstrate that future global change will not only impact on coastal food webs but also has likely impacts on sustainable production of algal biomass and high-value compounds due to changes in productivity and biochemical composition under anticipated future environmental regimes.

The increasing use of seaweeds in European cuisine led to cultivation initiatives funded by the European Union. Ulva lactuca, commonly known as sea lettuce, is a fast growing seaweed in the North Atlantic that chefs are bringing into the local cuisine. Here, different strains of Arctic U. lactuca were mass-cultivated under controlled conditions for up to 10 months. We quantified various chemical constituents associated with both health benefits (carbohydrates, protein, fatty acids, minerals) and health risks (heavy metals). Chemical analyses showed that long-term cultivation provided biomass of consistently high food quality and nutritional value. Concentrations of macroelements (C, N, P, Ca, Na, K, Mg) and micronutrients (Fe, Zn, Co, Mn, I) were sufficient to contribute to daily dietary mineral intake. Heavy metals (As, Cd, Hg and Pb) were found at low levels to pose health risk. The nutritional value of Ulva in terms of carbohydrates, protein and fatty acids is comparable to some selected fruits, vegetables, nuts and grains.

Exposure to seaweed-derived iodine through the consumption of macroalgae can positively and negatively influence human health, depending on whether adequate (150 μg day−1) or excessive quantities are ingested. Following harvest, macroalgal material typically undergoes certain processing procedures involving washing, dehydration, rehydration (soaking) and cooking (boiling) before it is consumed. In this study, we assessed iodine in edible brown (Alaria esculenta), red (Palmaria palmata) and green (Ulva intestinalis) macroalgae and quantified the iodine loss during processing. Freshly collected A. esculenta contained higher quantities of iodine (670 μg (g dw)−1) than P. palmata (97 μg (g dw)−1) and U. intestinalis (92 μg (g dw)−1), implying that only 0.2–1.6 g dw of freshly harvested algae contain the recommended daily intake level. Washing (10 min in deionised water) and dehydration (air-, oven- and freeze-drying) at low irradiances only marginally affected iodine levels, suggesting that gentle preservation techniques prevent iodine loss. By contrast, rehydration (1–24 h soaking in deionised water) significantly reduced iodine: by 62 % in A. esculenta, by 15 % in P. palmata and by 10 % in U. intestinalis. The iodine levels of all three species decreased further upon boiling (20 min in deionised water). Despite a considerable, but species-specific, loss of iodine during processing, all macroalgae still contained iodine at 66 to 165 μg (g dw)−1 after rehydration and subsequent boiling. Our results indicate that both raw and processed macroalgae can be considered as a rich source of iodine and thus their consumption may influence human health and nutrition.

This study represents a large-scale investigation into iodine contents in three commercially important and edible seaweed species from the North Atlantic: the brown algae Saccharina latissima and Alaria esculenta, and the red alga Palmaria palmata. Variability among and within species were explored in terms of temporal and spatial variations in addition to biomass source. Mean iodine concentration in bulk seaweed biomass was species-specific: Saccharina > Alaria > Palmaria. Iodine contents of Saccharina biomass were similar between years and seasons, but varied significantly between sampling locations and biomass sources. In Alaria and Palmaria, none of the independent variables examined contributed significantly to the small variations observed. Our data suggest that all three species are rich sources of iodine, and only 32, 283, or 2149 mg dry weight of unprocessed dry biomass of Saccharina, Alaria, or Palmaria, respectively, meets the recommended daily intake levels for most healthy humans.

Seaweeds are increasingly used in European cuisines due to their nutritional value. Many algal constituents, such as polyphenols, are important antioxidants and thus considered beneficial to humans. However, many seaweed species can accumulate heavy metals and exhibit potential health risks upon ingestion. We investigated temporal and spatial variations in polyphenol and heavy metal (As, Cd, Hg, Pb) concentrations of three edible seaweed species. The brown algae Saccharina latissima and Alaria esculenta, and the red alga Palmaria palmata were sourced from natural populations and aquaculture in the NE Atlantic and processed as bulk biomass mimicking industrial scales. The mean polyphenol content was species-specific (Alaria > Saccharina > Palmaria), and highest in winter (for Alaria and Saccharina) and spring (for Palmaria); inter-annual and spatial variations were marginal. Heavy metal concentrations varied between species and depended on collection site, but seasonal variations were minimal. Our data suggest that all three species are good sources of antioxidants, and the heavy metal concentrations are below the upper limits set by the French recommendation and the EU Commission Regulation on contaminants in foodstuffs. A health risk assessment indicated that consumption of these seaweed species poses a low risk for humans with regard to heavy metals. However, an EU-wide regulation on maximal concentration of heavy metals in seaweeds should be established.

Laminaria digitata forms locally extensive and ecologically important kelp beds in northern temperate regions. Its sporophytes retain large quantities of iodine which, when released into seawater (as iodide, I−) and into air (as molecular iodine, I2), have the potential to contribute significantly to coastal iodine biogeochemical processes. Here, standing crop of a living L. digitata bed and biomass of degrading kelp deposited near the high tide mark were quantified in western Ireland (53°09′25″N, 09°06′58″W) in summer 2011. Measurements revealed an average of 17 living individuals m−2, accounting for 0.6 (kg dw) m−2, and the biomass of degrading kelp averaged 0.05 (kg dw) m−2. We further investigated the iodine-retention capacity of L. digitata and the effect of degradation. Under controlled conditions, I− release into seawater and I2 emission into air depended on the physiological state of L. digitata. Fresh and “healthy” phylloids absorbed I− from seawater with I2 emission rates reaching 27 nmol (g dw)−1 h−1. After 4 days of degradation, I2 emission rates were enhanced by a factor of 3.1. Over 29 days of submersed degradation, ~4.7 μmol I− (g dw)−1 were released into seawater, a process which could trigger iodine recycling in coastal areas. Combined field and laboratory data suggest that living L. digitata sporophytes possess an I2 emission capacity of ~16 μmol m−2 h−1, whilst emersed degrading kelp contributes 1–5 μmol m−2 h−1 to coastal atmospheric I2 during summer. This study provides evidence that not only living but also degrading kelp acts as driver of coastal iodine fluxes.

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.

Three macroalgal species belonging to Chlorophyta (Ulva rigida), Rhodophyta (Ellisolandia elongata) and Phaeophyceae (Heterokontophyta; Cystoseira tamariscifolia), natu- rally growing at the same shore level and representing 3 morpho-functional groups, were exposed to short-term changes in temperature under different carbon and nitrogen regimes. Experiments were conducted in outdoor tanks at 4 combinations of carbon and nitrogen levels under reduced solar radiation. In vivo chl a fluorescence parameters and pigment contents were monitored to assess diurnal physiological responses and potential for recovery. Strong fluctuations in chl a flu- orescence parameters, but not in chl a content, were observed in response to diurnal variation in solar radiation and light climate within the tanks; sensitivity varied between algal species and, in some cases, depended on the carbon and nitrogen regime. Nitrogen uptake was similarly high in U. rigida and E. elongata and lowest in C. tamariscifolia. In U. rigida and E. elongata, chl a con- centrations decreased after high-carbon treatments. Effective photosystem II quantum efficiency was reduced in all species at noon, and lowest in C. tamariscifolia. The results highlight the com- plexity of physiological short-term acclimations which were most likely linked to biochemical changes at the cellular level. Long-term experiments are required in future for more comprehen- sive investigation of the observed interactive effects of the different environmental parameters.

Stylonema alsidii is a non-florideophycean red alga of a simple morphology and has recently classified as cosmopolitan, suggesting a pronounced physiological ability to successfully colonise new coastal habitats. As for most non-florideophycean red algae, understanding of the general ecology and physiology of this species is, to date, limited. Here, we report S. alsidii from the low-salinity Baltic Sea (habitat salinity: ~ 25 SA) for the first time. We compared its salinity stress response with that of a marine isolate (habitat salinity: ~ 35 SA) by measuring growth, chlorophyll a (chl a) fluorescence responses, photo-protection capabilities (via NPQ) and low molecular weight carbohydrates (LMWCs) under hypo- and hypersaline conditions. S. alsidii appeared to be a euryhaline species; either isolate grew in a wide salinity range from 5 to 60 SA and exhibited a growth maximum at full marine 33 SA. In the marine S. alsidii, the maximum photosystem II (PSII) efficiency (Fv/Fm), the light saturation coefficient of photosynthesis (Ek) and NPQ mechanism were maximal at a full marine salinity, but reduced after exposure to hypo- and hypersaline stress. By contrast, PSII functioning and NPQ mechanisms of the Baltic isolate remained enhanced at low salinities and, thus, reflected an optimised physiological performance at local salinity regimes. However, the results may not allow a differentiation of salinity ecotypes and isolate-specific salinity stress responses could be a result of phenotypic plasticity. The heteroside digeneaside and the polyol sorbitol were the only detectable LMWCs in S. alsidii. In contrast to digeneaside, sorbitol appeared to be involved in processes of osmotic acclimation; this polyol was accumulated with increasing salinities by a factor of 5 (marine isolate) to 10 (Baltic isolate) and, thus, probably functions as organic osmolyte. Euryhaline growth and photosynthesis due to pronounced photo-protective capabilities and the regulation of sorbitol enables S. alsidii to colonise habitats exhibiting large salinity fluctuations (intertidal zones) and along salinity gradients (Baltic Sea) and, thus, can contribute to the wide distribution of this species.

Based on the results of a pilot study in 2007, which found high mixing ratios of molecular iodine (I2) above the intertidal macroalgae (seaweed) beds at Mweenish Bay (Ireland), we extended the study to nine different locations in the vicinity of Mace Head Atmospheric Research Station on the west coast of Ireland during a field campaign in 2009. The mean values of I2 mixing ratio found above the macroalgae beds at nine different locations ranged from 104 to 393 ppt, implying a high source strength of I2. Such mixing ratios are sufficient to result in photochemically driven coastal new-particle formation events. Mixing ratios above the Ascophyllum nodosum and Fucus vesiculosus beds increased with exposure time: after 6 h exposure to ambient air the mixing ratios were one order of magnitude higher than those initially present. This contrasts with the emission characteristics of Laminaria digitata, where most I2 was emitted within the first half hour of exposure. Discrete in situ measurements (offline) of I2 emission from ambient air-exposed chamber experiments of L. digitata, A. nodosum and F. vesiculosus substantially supported the field observations. Further online and time-resolved measurements of the I2 emission from O3-exposed macroalgal experiments in a chamber confirmed the distinct I2 emission characteristics of A. nodosum and F. vesiculosus compared to those of L. digitata. The emission rates of A. nodosum and F. vesiculosus were comparable to or even higher than L. digitata after the initial exposure period of ~20–30 min. We suggest that A. nodosum and F. vesiculosus may provide an important source of photolabile iodine in the coastal boundary layer and that their impact on photochemistry and coastal new-particle formation should be reevaluated in light of their longer exposure at low tide and their widespread distribution.

Tidally exposed macroalgae emit large amounts of I2 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, I2 emissions from 25 Laminaria digitata samples were investigated in a simulation chamber using incoherent broadbandcavity-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 O3 and to varying irradiances. Emission of I2 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 I2 release; and (4) later pulses of I2 evident in some samples. Emission rates were highly variable and ranged from 7to 616 pmol min−1 gFW−1 in ozone-free air, with a median value of 55 pmol min−1 gFW−1 for 20 samples.

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) (

The effect of salinity on growth, photosynthetic performance and osmotic acclimation was investigated in the eulittoral red algal species Bangiopsis subsimplex (Stylonematophyceae). The strain grew in a broad salinity range between 1 and 70 psu showing optimum growth between 10 and 50 psu. The saturation point Ik of the photosynthesis irradiance curves ranged between 153 and 83 μmol photons m −2 s −1 at all salinities and indicates an adaptation of B. subsimplex to moderate radiation conditions. Adjustments on the photosynthetic level (non-photochemical quenching) were sufficient to prevent damage to the photosynthetic apparatus as Fv/Fm values were constantly high (N0.7) even when grown at the most hypo- and hypersaline conditions. As main low molecular weight carbohydrates, B. subsimplex contains the heteroside digeneaside and the polyol sorbitol. Digeneaside concentration was low and almost unchanged after hypersaline treatment (b20 μmol g −1 DW), i.e. it did not play a role in osmotic acclimation. By contrast, sorbitol levels increased linearly from 150 to 380 μmol g −1 DW with increasing salinities between 5 and 60 psu, indicating its important function as an osmolyte and compatible solute under hypersaline conditions. The data presented are consistent with the natural habitat of B. subsimplex, i.e. the upper eulittoral zone. © 2007 Elsevier B.V. All rights reserved.

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.

Short-term effects of increasing pCO(2); 380 ppm (LC) vs. 700 ppm (HC); at different nitrogen levels; 5 mu M nitrate (LN) vs. 50 mu M (HN); on the contents of protein, mycosporine-like amino acids (MAAs), phenolic compounds and total fatty acids, antioxidant activity, calcification and C: N ratios were analyzed in 3 eulittoral Mediterranean macroalgae with different bio-optical characteristics and carbon assimilation efficiencies: Cystoseira tamariscifolia (Heterokontophyta), Ulva rigida (Chlorophyta) and Ellisolandia elongata (Rhodophyta). After acclimation to different pCO(2) and nitrogen conditions for 6 d, the algae were subjected to a 4 degrees C temperature increase for 3 d. Increasing temperature and pCO(2) produced alterations in the biochemical composition of the 3 macroalgae. Short-term variations of protein levels were observed in U. rigida, with clearly decreased values in the HCLN treatment. In C. tamariscifolia, protein decreased after the temperature increase but only under LC. The interaction of temperature and N affected phenolic compounds only in U. rigida and the content of MAAs in E. elongata. The functional patterns of the 3 macroalgae in response to the pCO(2), nitrogen and temperature regimes may be explained in terms of their bio-optical characteristics and antioxidant activity. The vulnerability and acclimation of the 3 species to the expected variations of climate change factors are discussed.

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.

Iodide (I−) retained by the brown macroalga Laminaria digitata at millimolar levels, possesses antioxidant activities, but the wider physiological significance of its accumulation remains poorly understood. In its natural habitat in the lower intertidal, L. digitata experiences salinity changes and osmotic homeostasis is achieved by regulating the organic osmolyte mannitol. However, I− may also holds an osmotic function. Here, impacts of hypo- and hypersaline conditions on I− release from, and accumulation by, L. digitata were assessed. Additionally, mannitol accumulation was determined at high salinities, and physiological responses to externally elevated iodine concentrations and salinities were characterised by chl a fluorometry. Net I− release rates increased with decreasing salinity. I− was accumulated at normal (35 S A) and high salinities (50 S A); this coincided with enhanced rETRmax and qP causing pronounced photoprotection capabilities via NPQ. At 50 S A elevated tissue iodine levels impeded the well-established response of mannitol accumulation and prevented photoinhibition. Contrarily, low tissue iodine levels limited photoprotection capabilities and resulted in photoinhibition at 50 S A, even though mannitol was accumulated. The results indicate a, so far, undescribed osmotic function of I− in L. digitata and, thus, multifunctional principles of this halogen in kelps. The osmotic function of mannitol may have been substituted by that of I− under hypersaline conditions, suggesting a complementary role of inorganic and organic solutes under salinity stress. This study also provides first evidence that iodine accumulation in L. digitata positively affects photo-physiology.

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 of3 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.

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.

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 E k. 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.

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 mu mol 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.

The emission of molecular iodine (I2) from the stipe, the meristematic area and the distal blade of the brown macroalga Laminaria digitata (Hudson) Lamouroux (Phaeophyceae) was monitored under low light and dark conditions. Photosynthetic parameters were determined to investigate both the extent of stress experienced by different thallus parts and the effects of emersion on photosynthesis. Immediately after air exposure, intense I2 emission was detectable from all thallus parts. I2 emission declined continuously over a period of 180 min following the initial burst, but was not affected by the light regime. The total number of mole of I2 emitted by stipes was approximately 10 times higher than those emitted from other thallus parts. Initial I2 emission rates (measured within 30 min of exposure to air) were highest for stipes (median values: 2,999 and 5,222 pmol g−1 dw min−1 in low light and dark, respectively) and lower, by one order of magnitude, for meristematic regions and distal blades. After exposure to air for between 60 and 180 min, I2 emission rates of all thallus parts were reduced by 70–80%. Air exposure resulted in a decrease of the maximum photosystem II (PSII) efficiency (Fv/Fm) by 3%, and in a 25–55% increase of the effective PSII quantum efficiency (\( \Updelta F/F^{\prime}_{\text{m}} \)); this was caused by a higher fraction of open reaction centres (qP), whereas the efficiency of the latter in capturing energy (\( F^{\prime}_{\text{v}} /F^{\prime}_{\text{m}} \)) remained constant. The results indicate the presence of an iodine pool which is easily volatilised and depleted due to air exposure, even under apparently low stress conditions.