Optimal number of Fucus vesiculosus samples to differentiate between sites affected by distinct levels of heavy metal contamination

The presence of trace elements in marine habitats is a serious environmental problem which increasingly affects ecosystem and human health. The use of macroalgae as contamination biomonitors represents a valuable alternative approach to traditional physicochemical methods. The present study was carried out to determine the optimal number of samples of Fucus vesiculosus needed to detect statistically significant differences in the mean concentrations of Al, As, Cd, Co Cr, Cu, Fe, Hg, Ni, Pb, Zn, N and δ15N between two sampling sites affected by different levels of contamination. For this purpose, we plotted the density distributions of the concentrations of the different elements and examined the local variability at three sites. For sites with mean concentrations differing by more than 30 %, 20 samples were sufficient to detect significant differences for all of the elements, except Cr. The proposed methodology could be used in other studies in the absence of specific research on each species and region.

Estimating intertidal seaweed biomass at larger scales from quadrat surveys

The amount of macroalgal biomass is an important ecosystem variable. Estimates can be made for a sampled area or values can be extrapolated to represent biomass over a larger region. Typically biomass is scaled-up using the area multiplied by the mean: a non-spatial method. Where algal biomass is patchy or shows gradients, non-spatial estimates for an area may be improved by spatial interpolation. A separate issue with scaling-up biomass estimates is that conventional confidence intervals based on the standard error (SE) of the sample may not be appropriate. The issues around interpolation and confidence intervals were examined for three fucoid species using data from 40 × 0.25 m-2 quadrats thrown in a 0.717 ha sampling plot on the shore of Galway Bay. Despite evidence of spatial autocorrelation, interpolation did not appear to improve estimates of the total plot biomass of Fucus serratus and F. vesiculosus. In contrast, interpolated estimates for Ascophyllum nodosum had less error than those based on the non-spatial method. Bootstrapped confidence intervals had several benefits over those based on the SE. These benefits include the avoidance of negative confidence limits at low sample sizes and no assumptions of normality in the data. If there is reason to expect strong patchiness or a gradient of biomass in the area of interest, interpolation is likely to produce more accurate estimates of biomass than non-spatial methods. Development of methodologies for biomass would benefit from more definition of local and regional gradients in biomass and their associated covariates.

Forecast climate change conditions sustain growth and physiology but hamper reproduction in range-margin populations of a foundation rockweed species

Intensifying environmental changes due to climate change affect marine species worldwide. Herein, we experimentally tested if the combination of forecasted warming and hyposalinity adversely affected growth, receptacle formation, and photosynthesis of three marginal populations of the brown alga Fucus from the northern Baltic Sea. Growth was not impaired by the projected consequences of climate change but genotypes varied in their responses, suggesting existence of genetic variation in phenotypic plasticity. Climate change further prevented receptacle formation, implying that Fucus fail to reproduce sexually. Photosynthesis was not affected by climate change but varied among populations. Our results show that Fucus populations photosynthesized, grew, and survived well under the projected climate change but their sexual reproduction ceased. This suggests that the marginal populations tested herein are resilient to future conditions but only if asexual reproduction enables them to proliferate.

Differentiation in fitness-related traits in response to elevated temperatures between leading and trailing edge populations of marine macrophytes

The nature of species distribution boundaries is a key subject in ecology and evolution. Edge populations are potentially more exposed to climate-related environmental pressures. Despite research efforts, little is known about variability in fitness-related traits in leading (i.e., colder, high latitude) versus trailing (i.e., warmer, low latitude) edge populations. We tested whether the resilience, i.e. the resistance and recovery, of key traits differs between a distributional cold (Greenland) and warm (Portugal) range edge population of two foundation marine macrophytes, the intertidal macroalga Fucus vesiculosus and the subtidal seagrass Zostera marina. The resistance and recovery of edge populations to elevated seawater temperatures was compared under common experimental conditions using photosynthetic efficiency and expression of heat shock proteins (HSP). Cold and warm edge populations differed in their response, but this was species specific. The warm edge population of F. vesiculosus showed higher thermal resistance and recovery whereas the cold leading edge was less tolerant. The opposite was observed in Z. marina, with reduced recovery at the warm edge, while the cold edge was not markedly affected by warming. Our results confirm that differentiation of thermal stress responses can occur between leading and trailing edges, but such responses depend on local population traits and are thus not predictable just based on thermal pressures.

Bladder wrack (Fucus vesiculosus) as a multi-isotope bio-monitor in an urbanized fjord of the western Baltic Sea

The spatial variations in the elemental and stable carbon, nitrogen, and sulphur isotope composition of bladder wrack (Fucus vesiculosus) growing along the shore line of the semi-enclosed urbanized Kiel Fjord (western Baltic Sea) was investigated at more than 60 sites. The analyses of the carbon-nitrogen-sulphur (CNS) stoichiometry and C and N stable isotope signature of F. vesiculosus displayed substantial differences between the north-western and the south-eastern parts of the Kiel Fjord. Different size classes displayed in part differences in C:N and C:S ratios, and the carbon isotope composition, reflecting the impact of the boundary conditions during growth. Whereas the sulphur isotope composition was controlled by the assimilation of seawater sulphate, the carbon isotope composition reflected the difference in the composition of surface waters. The δ15N values of the organic tissue tend to be an integrated monitor of anthropogenic impacts on the fjord. Results are compared to the composition of surface waters.

Early Embryogenesis of Brown Alga Fucus vesiculosus L. is Characterized by Significant Changes in Carbon and Energy Metabolism

Brown algae have an important role in marine environments. With respect to their broad distribution and importance for the environment and human use, brown algae of the order Fucales in particular became a model system for physiological and ecological studies. Thus, several fucoids have been extensively studied for their composition on the molecular level. However, research of fucoid physiology and biochemistry so far mostly focused on the adult algae, so a holistic view on the development of these organisms, including the crucial first life stages, is still missing. Therefore, we employed non-targeted metabolite profiling by gas chromatography coupled to mass spectrometry to create a non-biased picture of the early development of the fucoid alga Fucus vesiculosus. We found that embryogenic physiology was mainly dominated by a tight regulation of carbon and energy metabolism. The first dramatic changes of zygote metabolism started within 1 h after fertilization, while metabolism of 6-9 days old embryos appeared already close to that of an adult alga, indicated by the intensive production of secondary metabolites and accumulation of mannitol and citric acid. Given the comprehensive description and analysis we obtained in our experiments, our results exhibit an invaluable resource for the design of further experiments related to physiology of early algal development.

Reciprocal transplants support a plasticity-first scenario during colonisation of a large hyposaline basin by a marine macro alga

BACKGROUND

Establishing populations in ecologically marginal habitats may require substantial phenotypic changes that come about through phenotypic plasticity, local adaptation, or both. West-Eberhard's "plasticity-first" model suggests that plasticity allows for rapid colonisation of a new environment, followed by directional selection that develops local adaptation. Two predictions from this model are that (i) individuals of the original population have high enough plasticity to survive and reproduce in the marginal environment, and (ii) individuals of the marginal population show evidence of local adaptation. Individuals of the macroalga Fucus vesiculosus from the North Sea colonised the hyposaline (≥2-3‰) Baltic Sea less than 8000 years ago. The colonisation involved a switch from fully sexual to facultative asexual recruitment with release of adventitious branches that grow rhizoids and attach to the substratum. To test the predictions from the plasticity-first model we reciprocally transplanted F. vesiculosus from the original population (ambient salinity 24‰) and from the marginal population inside the Baltic Sea (ambient salinity 4‰). We also transplanted individuals of the Baltic endemic sister species F. radicans from 4 to 24‰. We assessed the degree of plasticity and local adaptation in growth and reproductive traits after 6 months by comparing the performance of individuals in 4 and 24‰.

RESULTS

Branches of all individuals survived the 6 months period in both salinities, but grew better in their native salinity. Baltic Sea individuals more frequently developed asexual traits while North Sea individuals initiated formation of receptacles for sexual reproduction.

CONCLUSIONS

Marine individuals of F. vesiculosus are highly plastic with respect to salinity and North Sea populations can survive the extreme hyposaline conditions of the Baltic Sea without selective mortality. Plasticity alone would thus allow for an initial establishment of this species inside the postglacial Baltic Sea at salinities where reproduction remains functional. Since establishment, the Baltic Sea populations have evolved adaptations to extreme hyposaline waters and have in addition evolved asexual recruitment that, however, tends to impede local adaptation. Overall, our results support the "plasticity-first" model for the initial colonisation of the Baltic Sea by Fucus vesiculosus.

Bioaccumulation of Hg, Cd and Pb by Fucus vesiculosus in single and multi-metal contamination scenarios and its effect on growth rate

Results of 7-days exposure to metals, using environmentally realistic conditions, evidenced the high potential of living Fucus vesiculosus to remove Pb, Hg and Cd from contaminated salt waters. For different contamination scenarios (single- and multi-contamination), ca 450 mg L-1 (dry weight), enable to reduce the concentrations of Pb in 65%, of Hg in 95% and of Cd between 25 and 76%. Overall, bioconcentration factors ranged from 600 to 2300. Elovich kinetic model described very well the bioaccumulation of Pb and Cd over time, while pseudo-second-order model adjusted better to experimental data regarding Hg. F. vesiculosus showed different affinity toward studied metals, following the sequence order: Hg > Pb > Cd. Analysis of metal content in the macroalgae after bioaccumulation, proved that all metal removed from solution was bound to the biomass. Depuration experiments reveled no significant loss of metal back to solution. Exposure to contaminants only adversely affected the organism's growth for the highest concentrations of Cd and Pb. Findings are an important contribute for the development of remediation biotechnologies for confined saline waters contaminated with trace metal contaminants, more efficient and with lower costs than the traditional treatment methods.

Nutrients influence the thermal ecophysiology of an intertidal macroalga: multiple stressors or multiple drivers?

Urbanization of coastlines is leading to increased introduction of nutrients from the terrestrial environment to nearshore habitats. While such nutrient influxes can be detrimental to coastal marine organisms due to increased eutrophication and subsequent reduced oxygen, they could also have positive effects (i.e., increased food availability) on species that are nitrogen-limited such as macroalgae. Nutrient enrichment in this environment thus has the potential to counteract some of the negative impacts of increasing temperatures, at least for some species. Characterizing the physiological response of organisms to simultaneous changes in multiple drivers such as these is an important first step in predicting how global climate change may lead to ecological responses at more local levels. We evaluated how nutrient enrichment (i.e., nitrogen availability) affected the growth of Fucus vesiculosus, a foundational macroalgal species in the North Atlantic rocky intertidal zone, and found that nutrient-enriched algal blades showed a significant increase in tissue growth compared to individuals grown under ambient conditions. We further quantified net photosynthesis by ambient and nutrient-enriched tissues at saturating irradiance over a range of temperature conditions (6-30°C). Respiration was unaffected by nutrient treatment; however, there was a significant increase in photosynthetic oxygen production for nutrient-enriched tissue compared to ambient, but only at elevated (≥18°C) temperatures. This study contributes to a growing body of literature showing the complexity of responses to changes in multiple drivers, and highlights the importance of studying the impacts of global climate change within the context of more local environmental conditions.

Dynamics of cell wall assembly during early embryogenesis in the brown alga Fucus

Zygotes from Fucus species have been used extensively to study cell polarization and rhizoid outgrowth, and in this model system cell wall deposition aligns with the establishment of polarity. Monoclonal antibodies are essential tools for the in situ analysis of cell wall glycans, and here we report the characteristics of six monoclonal antibodies to alginates (BAM6-BAM11). The use of these, in conjunction with monoclonal antibodies to brown algal sulfated fucans, has enabled the study of the developmental dynamics of the Fucus zygote cell walls. Young zygotes are spherical and all alginate epitopes are deposited uniformly following cellulose deposition. At germination, sulfated fucans are secreted in the growing rhizoid wall. The redistribution of cell wall epitopes was investigated during treatments that cause reorientation of the growth axis (change in light direction) or disrupt rhizoid development (arabinogalactan-protein-reactive Yariv reagent). Alginate modeling was drastically impaired in the latter, and both treatments cause a redistribution of highly sulfated fucan epitopes. The dynamics of cell wall glycans in this system have been visualized in situ for the first time, leading to an enhanced understanding of the early developmental mechanisms of Fucus species. These sets of monoclonal antibodies significantly extend the available molecular tools for brown algal cell wall studies.

Arabinogalactan proteins have deep roots in eukaryotes: identification of genes and epitopes in brown algae and their role in Fucus serratus embryo development

Arabinogalactan proteins (AGPs) are highly glycosylated, hydroxyproline-rich proteins found at the cell surface of plants, where they play key roles in developmental processes. Brown algae are marine, multicellular, photosynthetic eukaryotes. They belong to the phylum Stramenopiles, which is unrelated to land plants and green algae (Chloroplastida). Brown algae share common evolutionary features with other multicellular organisms, including a carbohydrate-rich cell wall. They differ markedly from plants in their cell wall composition, and AGPs have not been reported in brown algae. Here we investigated the presence of chimeric AGP-like core proteins in this lineage. We report that the genome sequence of the brown algal model Ectocarpus siliculosus encodes AGP protein backbone motifs, in a gene context that differs considerably from what is known in land plants. We showed the occurrence of AGP glycan epitopes in a range of brown algal cell wall extracts. We demonstrated that these chimeric AGP-like core proteins are developmentally regulated in embryos of the order Fucales and showed that AGP loss of function seriously impairs the course of early embryogenesis. Our findings shine a new light on the role of AGPs in cell wall sensing and raise questions about the origin and evolution of AGPs in eukaryotes.

A macroalgal germling bioassay to assess biocide concentrations in marine waters

A bioassay method using the early life stages (germlings) of macroalgae was developed to detect toxicity of anti-fouling paint biocides. A laboratory based bioassay using Ulva intestinalis and Fucus spiralis germlings was performed with 4 common anti-fouling biocides (tributyltin (TBT), Irgarol 1051, Diuron and zinc sulphate), over a range of environmentally relevant concentrations (0.0033-10 μg l(-1)). Comparison between the two species showed that germlings of U. intestinalis were better adapted for in-situ monitoring, as germlings of F. spiralis appeared to be too robust to display sufficient growth differences. The response of U. intestinalis germling growth appeared to reflect environmental biocide concentrations. Overall the developed method showed potential for the assessment of the sub-lethal effects of anti-fouling biocides on the early developmental stages of U. intestinalis.

Nitrogen availability limits phosphorus uptake in an intertidal macroalga

Nutrients such as nitrogen (N) and phosphorus (P) limit primary productivity, and recent anthropogenic activities are changing the availability of these nutrients, leading to alterations in the type and magnitude of nutrient limitation. Recent work highlights the potential for N and P to interact to limit primary production in terrestrial and freshwater systems. However, mechanisms underlying co-limitation are not well described. Documentation of ambient nutrient levels and tissue nutrients of the intertidal macroalga Fucus vesiculosus for 2 years in the southern Gulf of Maine, USA, indicates that N availability may be impacting the ability of F. vesiculosus to access P, despite relatively high ambient P concentrations. To experimentally validate these observations, F. vesiculosus individuals were enriched with N or P for 6 weeks, followed by an uptake experiment to examine how the interactions between these nutrients affected macroalgal N and P uptake efficiency. Results illustrate that exposure of seaweed to different nutrient regimes influenced nutrient uptake efficiency. Notably, seaweeds enriched with N displayed the highest P uptake efficiency at low, biologically relevant, P concentrations. Our results confirm that N availability may be mediating the ability of primary producers to access P. These interactions between limiting nutrients have implications for not only the growth and functioning of primary producers who rely directly on these nutrients but also the entire communities that they support.

Spatial and temporal dynamics of fucoid populations (Ascophyllum nodosum and Fucus serratus): a comparison between central and range edge populations

Persistence of populations at range edges relies on local population dynamics and fitness, in the case of geographically isolated populations of species with low dispersal potential. Focusing on spatial variations in demography helps to predict the long-term capability for persistence of populations across the geographical range of species' distribution. The demography of two ecological and phylogenetically close macroalgal species with different life history characteristics was investigated by using stochastic, stage-based matrix models. Populations of Ascophyllum nodosum and Fucus serratus were sampled for up to 4 years at central locations in France and at their southern range limits in Portugal. The stochastic population growth rate (λ(s)) of A. nodosum was lower and more variable in central than in southern sites whilst for F. serratus this trend was reversed with λ(s) much lower and more variable in southern than in central populations. Individuals were larger in central than in southern populations for both species, which was reflected in the lower transition probabilities of individuals to larger size classes and higher probability of shrinkage in the southern populations. In both central and southern populations elasticity analysis (proportional sensitivity) of population growth rate showed that fertility elements had a small contribution to λ(s) that was more sensitive to changes in matrix transitions corresponding to survival. The highest elasticities were found for loop transitions in A. nodosum and for growth to larger size classes in F. serratus. Sensitivity analysis showed high selective pressure on individual growth for both species at both locations. The results of this study highlight the deterministic role of species-specific life-history traits in population demography across the geographical range of species. Additionally, this study demonstrates that individuals' life-transitions differ in vulnerability to environmental variability and shows the importance of vegetative compared to reproductive stages for the long-term persistence of populations.

Physical factors driving intertidal macroalgae distribution: physiological stress of a dominant fucoid at its southern limit

Climate change is driving species range shifts worldwide. However, physiological responses related to distributional changes are not fully understood. Oceanographers have reported an increase in ocean temperature in the northwest Iberian Peninsula that is potentially related to the decline in some cold-temperate intertidal macroalgae in the Cantabrian Sea, namely Fucus serratus. Low tide stress could also play a role in this decline. We performed one mensurative (in situ) and two manipulative (in culture) experiments designed to evaluate the interactive effects of some physical factors. The first experiment analysed field response to low tide stress in marginal (mid-Cantabrian Sea and northern Portugal) versus central (Galicia) populations of F. serratus. Then a second experiment was performed that utilized either harsh or mild summer conditions of atmospheric temperature, irradiance, humidity, and wind velocity to compare the responses of individuals from one marginal and one central population to low tide stress. Finally, the combined effect of sea temperature and the other factors was evaluated to detect interactive effects. Changes in frond growth, maximal photosynthetic quantum yield (F(v)/F(m)), temperature, and desiccation were found. Three additive factors (solar irradiation, ocean and air temperatures) were found to drive F. serratus distribution, except under mildly humid conditions that ameliorated atmospheric thermal stress (two additive factors). Mid-Cantabrian Sea temperatures have recently increased, reaching the inhibitory levels suggested in this study of F. serratus. We also expect an additive secondary contribution of low tide stress to this species decline. On the northern Portugal coast, ocean warming plus low tide stress has not reached this species' inhibition threshold. No significant differential responses attributed to the population of origin were found. Mechanistic approaches that are designed to analyse the interactive effects of physical stressors may improve the levels of confidence in predicted range shifts of species.

Prezygotic barriers to hybridization in marine broadcast spawners: reproductive timing and mating system variation

Sympatric assemblages of congeners with incomplete reproductive barriers offer the opportunity to study the roles that ecological and non-ecological factors play in reproductive isolation. While interspecific asynchrony in gamete release and gametic incompatibility are known prezygotic barriers to hybridization, the role of mating system variation has been emphasized in plants. Reproductive isolation between the sibling brown algal species Fucus spiralis, Fucus guiryi (selfing hermaphrodite) and Fucus vesiculosus (dioecious) was studied because they form hybrids in parapatry in the rocky intertidal zone, maintain species integrity over a broad geographic range, and have contrasting mating systems. We compared reproductive synchrony (spawning overlap) between the three species at several temporal scales (yearly/seasonal, semilunar/tidal, and hourly during single tides). Interspecific patterns of egg release were coincident at seasonal (single peak in spring to early summer) to semilunar timescales. Synthesis of available data indicated that spawning is controlled by semidiurnal tidal and daily light-dark cues, and not directly by semilunar cycles. Importantly, interspecific shifts in timing detected at the hourly scale during single tides were consistent with a partial ecological prezygotic hybridization barrier. The species displayed patterns of gamete release consistent with a power law distribution, indicating a high degree of reproductive synchrony, while the hypothesis of weaker selective constraints for synchrony in selfing versus outcrossing species was supported by observed spawning in hermaphrodites over a broader range of tidal phase than in outcrossers. Synchronous gamete release is critical to the success of external fertilization, while high-energy intertidal environments may offer only limited windows of reproductive opportunity. Within these windows, however, subtle variations in reproductive timing have evolved with the potential to form ecological barriers to hybridization.

Phenotypic variation in sexually and asexually recruited individuals of the Baltic Sea endemic macroalga Fucus radicans: in the field and after growth in a common-garden

BACKGROUND

Most species of brown macroalgae recruit exclusively sexually. However, Fucus radicans, a dominant species in the northern Baltic Sea, recruits new attached thalli both sexually and asexually. The level of asexual recruitment varies among populations from complete sexual recruitment to almost (> 90%) monoclonal populations. If phenotypic traits have substantial inherited variation, low levels of sexual activity will decrease population variation in these traits, which may affect function and resilience of the species. We assessed the level of inherited variation in nine phenotypic traits by comparing variation within and among three monoclonal groups and one group of unique multilocus genotypes (MLGs) sampled in the wild.

RESULTS

Of the nine phenotypic traits, recovery after freezing, recovery after desiccation, and phlorotannin content showed substantial inherited variation, that is, phenotypic variation in these traits were to a large extend genetically determined. In contrast, variation in six other phenotypic traits (growth rate, palatability to isopod grazers, thallus width, distance between dichotomies, water content after desiccation and photochemical yield under ambient conditions) did not show significant signals of genetic variation at the power of analyses used in the study. Averaged over all nine traits, phenotypic variation within monoclonal groups was only 68% of the variation within the group of different MLGs showing that genotype diversity does affect the overall level of phenotypic variation in this species.

CONCLUSIONS

Our result indicates that, in general, phenotypic diversity in populations of Fucus radicans increases with increased multilocus genotype (MLG) diversity, but effects are specific for individual traits. In the light of Fucus radicans being a foundation species of the northern Baltic Sea, we propose that increased MLG diversity (leading to increased trait variation) will promote ecosystem function and resilience in areas where F. radicans is common, but this suggestion needs experimental support.

Adaptation to high light irradiances enhances the photosynthetic Cu2+ resistance in Cu2+ tolerant and non-tolerant populations of the brown macroalgae Fucus serratus

The relationship between light acclimation and Cu(2+) tolerance was studied in two populations of Fucus serratus known to be naturally non-tolerant and tolerant to Cu(2+). Acclimation to high irradiances increased the photosynthetic tolerance to Cu(2+). The xanthophyll cycle was apparently not involved in protecting the photosynthetic apparatus against Cu(2+) toxicity, as results showed that Cu(2+) did not induce dynamic photoinhibition. The higher photosynthetic Cu(2+) resistance of high light algae did not result in increased growth. The excess energy acquired by high light-adapted algae appeared to be utilized in Cu(2+) defense mechanisms in the Cu(2+) non-tolerant population. The polyphenol content of the algae was reciprocal to the Cu(T) content, suggesting that polyphenol may be the primary Cu(2+) defense of non-tolerant low light algae, acting through secretion and extracellular chelating of Cu(2+), while the compounds do not seem to be involved in the primary Cu(2+) tolerance mechanism in Cu(2+) tolerant algae.

Experimental confirmation of multiple community states in a marine ecosystem

Small changes in environmental conditions can unexpectedly tip an ecosystem from one community type to another, and these often irreversible shifts have been observed in semi-arid grasslands, freshwater lakes and ponds, coral reefs, and kelp forests. A commonly accepted explanation is that these ecosystems contain multiple stable points, but experimental tests confirming multiple stable states have proven elusive. Here we present a novel approach and show that mussel beds and rockweed stands are multiple stable states on intertidal shores in the Gulf of Maine, USA. Using broad-scale observational data and long-term data from experimental clearings, we show that the removal of rockweed by winter ice scour can tip persistent rockweed stands to mussel beds. The observational data were analyzed with Anderson's discriminant analysis of principal coordinates, which provided an objective function to separate mussel beds from rockweed stands. The function was then applied to 55 experimental plots, which had been established in rockweed stands in 1996. Based on 2005 data, all uncleared controls and all but one of the small clearings were classified as rockweed stands; 37% of the large clearings were classified as mussel beds. Our results address the establishment of mussels versus rockweeds and complement rather than refute the current paradigm that mussel beds and rockweed stands, once established, are maintained by site-specific differences in strong consumer control.

Dissolved organic carbon reduces the toxicity of copper to germlings of the macroalgae, Fucus vesiculosus

This study investigates the effects of waterborne copper exposure on germling growth in chemically defined seawater. Germlings of the macroalgae, Fucus vesiculosus were exposed to a range of copper and dissolved organic carbon (DOC as humic acid) concentrations over 14 days. Germling growth was found to be a sensitive indicator of copper exposure with total copper (TCu) and labile copper (LCu) EC(50) values of approximately 40 and 20 microg/L, respectively, in the absence of added DOC. The addition of DOC into the exposure media provided germlings with protection against copper toxicity, with an increased TCu EC(50) value of 117.3 microg/L at a corrected DOC (cDOC from humic acid only) concentration of 2.03 mg/L. The LCu EC(50) was not affected by a cDOC concentration of 1.65 mg/L or less, suggesting that the LCu concentration not the TCu concentration was responsible for inhibiting germling growth. However, at a cDOC concentration of approximately 2mg/L an increase in the LCu EC(50) suggests that the LCu concentration may play a role in the overall toxicity to the germlings. This is contrary to current understanding of aquatic copper toxicity and possible explanations for this are discussed.

A tip-high, Ca(2+) -interdependent, reactive oxygen species gradient is associated with polarized growth in Fucus serratus zygotes

We report the existence of a tip-high reactive oxygen species (ROS) gradient in growing Fucus serratus zygotes, using both 5-(and 6-) chloromethyl-2',7'-dichlorodihydrofluorescein and nitroblue tetrazolium staining to report ROS generation. Suppression of the ROS gradient inhibits polarized zygotic growth; conversely, exogenous ROS generation can redirect zygotic polarization following inhibition of endogenous ROS. Confocal imaging of fluo-4 dextran distributions suggests that the ROS gradient is interdependent on the tip-high [Ca(2+)](cyt) gradient which is known to be associated with polarized growth. Our data support a model in which localized production of ROS at the rhizoid tip stimulates formation of a localized tip-high [Ca(2+)](cyt) gradient. Such modulation of intracellular [Ca(2+)](cyt) signals by ROS is a common motif in many plant and algal systems and this study extends this mechanism to embryogenesis.

AUREOCHROME, a photoreceptor required for photomorphogenesis in stramenopiles

A blue light (BL) receptor was discovered in stramenopile algae Vaucheria frigida (Xanthophyceae) and Fucus distichus (Phaeophyceae). Two homologs were identified in Vaucheria; each has one basic region/leucine zipper (bZIP) domain and one light-oxygen-voltage (LOV)-sensing domain. We named these chromoproteins AUREOCHROMEs (AUREO1 and AUREO2). AUREO1 binds flavin mononucleotide via its LOV domain and forms a 390-nm-absorbing form, indicative of formation of a cysteinyl adduct to the C(4a) carbon of the flavin mononucleotide upon BL irradiation. The adduct decays to the ground state in approximately 5 min. Its bZIP domain binds the target sequence TGACGT. The AUREO1 target binding was strongly enhanced by BL treatment, implying that AUREO1 functions as a BL-regulated transcription factor. The function of AUREO1 as photoreceptor for BL-induced branching is elucidated through RNAi experiments. RNAi of AUREO2 unexpectedly induces sex organ primordia instead of branches, implicating AUREO2 as a subswitch to initiate development of a branch, but not a sex organ. AUREO sequences are also found in the genome of the marine diatom Thalassiosira pseudonana (Bacillariophyceae), but are not present in green plants. AUREOCHROME therefore represents a BL receptor in photosynthetic stramenopiles.

Interactions between wave action and grazing control the distribution of intertidal macroalgae

Canopy-forming macroalgae are key species on temperate rocky shores. However, there is a lack of understanding of how the relative balance of physical and biological factors controls the establishment and persistence of intertidal macroalgae. Here we present an integrated study of the relative importance of wave-induced forces and grazing for the recruitment and survival of the canopy-forming intertidal macroalgae Fucus vesiculosus and F. spiralis. A set of overtopped breakwaters provided a nearly unconfounded gradient in wave exposure between seaward and landward sides. A biomechanical analysis was performed based on empirical measurements of maximum drag forces in breaking waves, a model of long-term maximum wave height, and the breaking stress of Fucus spp. The estimated maximum flow speed (7-8 m/s) on the seaward side of the breakwaters was predicted to completely dislodge or prune Fucus spp. larger than approximately 10 cm, while dislodgment was highly unlikely on the landward side for all sizes. Experimental transplantation of Fucus spp. supported the biomechanical analysis but also suggested that mechanical abrasion may further limit survival in wave-exposed locations. Experimental removal of the limpet Patella vulgata, which was the principal grazer at this site, resulted in recruitment of Fucus spp. on the seaward side. We present a model of limpet grazing that indicates that limpet densities >5-20 individuals/m2 provide a proximate mechanism preventing establishment of Fucus spp., whereas wave action >2 m/s reduces persistence through dislodgment and battering. In a conceptual model we further propose that recruitment and survival of juvenile Fucus spp. are controlled indirectly by wave exposure through higher limpet densities at exposed locations. This model predicts that climate change, and in particular an increased frequency of storm events in the northeast Atlantic, will restrict fucoids to more sheltered locations.

Prior exposure to Cu contamination influences the outcome of toxicological testing of Fucus serratus embryos

Brown seaweeds are often employed in single species toxicity testing to study the association between the pollutant and the biota in contaminated marine habitats. We have used Fucus serratus (Phaeophyta) from one Cu resistant and one non-resistant population to evaluate the effect of prior exposure to metal pollution on toxicological endpoints. Analysis of comparative toxicity was conducted for embryo rhizoid elongation and adult relative growth rate (RGR). Algae that had previously been exposed to Cu expressed consistently lower levels of sensitivity to Cu than those that had no history of exposure to the pollutant. For both non-resistant and resistant populations rhizoid length was a more sensitive endpoint than adult RGR. While early life history stages of brown algae are generally regarded as being pollution-sensitive and inhibition of spore and embryo rhizoid elongation is frequently used as endpoints in bioassays, the test results may be affected by prior exposure of the parent algae to the pollutant. We conclude that the effect of prior exposure should be considered when comparing endpoints between studies and when selecting material for future testing.

[Description of the photosynthetic apparatus of Fucus vesiculosus L. in early embryogenesis]

Dynamics of some photosynthetic parameters was studied in gametes, zygotes, and embryos of kelp Fucus vesiculosus L. The following indices were determined at different stages of early development of the seaweed: the contents of pigments and ribulose-1,5-bisphosphate carboxylase/oxygenase, the rates of photosynthesis and dark respiration, and the activities of photosystems I and II. The dynamics of photosynthetic apparatus activity in zygotes and embryos of F. vesiculosus proved to reflect the main physiological processes of its early development.

Photosynthetic responses to Cu2+ exposure are independent of light acclimation and uncoupled from growth inhibition in Fucus serratus (Phaeophyceae)

We have studied the effect of light acclimation on photosynthetic responses and growth during Cu2+ exposure (0-0.84 microM) in the brown seaweed Fucus serratus. Measurements of chlorophyll fluorescence parameters showed that Cu2+ exposure amplified ETR, reduced the chlorophyll content at the cellular level and that there was no effect of light adaptation on the Cu2+ resistance of the algae. In contrast to the inhibitory effects of Cu2+ on chlorophyll fluorescence, O2 evolution and the total content of chlorophyll and carotenoid of the algae was unaffected by Cu2+. We conclude that photoinhibition and perhaps pigment degradation in the meristoderm was compensated for by cells deeper in the thallus with the result that the overall photosynthetic fitness of the algae was maintained. The pronounced inhibitory effects of Cu2+ on algae growth was not a consequence of photoinhibition and could be attributed to direct inhibitory effects on the growth process.

Contents of soluble, cell-wall-bound and exuded phlorotannins in the brown alga Fucus vesiculosus, with implications on their ecological functions

Phlorotannins are ubiquitous secondary metabolites in brown algae that are phenotypically plastic and suggested to have multiple ecological roles. Traditionally, phlorotannins have been quantified as total soluble phlorotannins. Here, we modify a quantification procedure to measure, for the first time, the amount of cell-wall-bound phlorotannins. We also optimize the quantification of soluble phlorotannins. We use these methods to study the responses of soluble and cell-wall-bound phlorotannin to nutrient enrichment in growing and nongrowing parts of the brown alga Fucus vesiculosus. We also examine the effects of nutrient shortage and herbivory on the rate of phlorotannin exudation. Concentrations of cell-wall-bound phlorotannins were much lower than concentrations of soluble phlorotannins; we also found that nutrient treatment over a period of 41 days affected only soluble phlorotannins. Concentrations of each phlorotannin type correlated positively between growing and nongrowing parts of individual seaweeds. However, within nongrowing thalli, soluble and cell-wall-bound phlorotannins were negatively correlated, whereas within growing thalli there was no correlation. Phlorotannins were exuded from the thallus in all treatments. Herbivory increased exudation, while a lack of nutrients had no effect on exudation. Because the amount of cell-wall-bound phlorotannins is much smaller than the amount of soluble phlorotannins, the major function of phlorotannins appears to be a secondary one.

Variation in natural selection for growth and phlorotannins in the brown alga Fucus vesiculosus

Directional selection for plant traits associated with resistance to herbivory tends to eliminate genetic variation in such traits. On the other hand, balancing selection arising from trade-offs between resistance and growth or spatially variable selection acts against the elimination of genetic variation. We explore both the amount of genetic variation and variability of natural selection for growth and concentration of phenolic secondary compounds, phlorotannins, in the brown alga Fucus vesiculosus. We measured variation in selection at two growing depths and two levels of nutrient availability in algae that had faced two kinds of past growing environments. Genetic variation was low for growth but high for phlorotannins. The form and strength of selection for both focal traits depended on the past growing environment of the algae. We found strong directional selection for growth rate in algae previously subjected to higher ultraviolet radiation, but not in algae previously subjected to higher nutrient availability. Stabilizing selection for growth occurred especially in the deep growing environment. Selection for phlorotannins was generally weak, but in some past-environment-current-environment combinations we detected either directional selection against phlorotannins or stabilizing selection. Thus, phlorotannins are not selectively neutral but affect the fitness of F. vesiculosus. In particular, there may be a fitness cost of producing phlorotannins, but the realization of such a cost varies from one environment to another. Genetic correlations between selective environments were high for growth but nonexistent for phlorotannins, emphasizing the high phenotypic plasticity of phlorotannin production. The highly heterogeneous selection, including directional, stabilizing, and spatially variable selection as well as temporal change in selection due to responses to past environmental conditions, probably maintains a high amount of genetic variation in phlorotannins. Such variation provides the potential for rapid evolutionary response of phlorotannins under directional selection.

Interactions between auxin transport and the actin cytoskeleton in developmental polarity of Fucus distichus embryos in response to light and gravity

Land plants orient their growth relative to light and gravity through complex mechanisms that require auxin redistribution. Embryos of brown algae use similar environmental stimuli to orient their developmental polarity. These studies of the brown algae Fucus distichus examined whether auxin and auxin transport are also required during polarization in early embryos and to orient growth in already developed tissues. These embryos polarize with the gravity vector in the absence of a light cue. The auxin, indole-3-acetic acid (IAA), and auxin efflux inhibitors, such as naphthylphthalamic acid (NPA), reduced environmental polarization in response to gravity and light vectors. Young rhizoids are negatively phototropic, and NPA also inhibits rhizoid phototropism. The effect of IAA and NPA on gravity and photopolarization is maximal within 2.5 to 4.5 h after fertilization (AF). Over the first 6 h AF, auxin transport is relatively constant, suggesting that developmentally controlled sensitivity to auxin determines the narrow window during which NPA and IAA reduce environmental polarization. Actin patches were formed during the first hour AF and began to photolocalize within 3 h, coinciding with the time of NPA and IAA action. Treatment with NPA reduced the polar localization of actin patches but not patch formation. Latrunculin B prevented environmental polarization in a time frame that overlaps the formation of actin patches and IAA and NPA action. Latrunculin B also altered auxin transport. Together, these results indicate a role for auxin in the orientation of developmental polarity and suggest interactions between the actin cytoskeleton and auxin transport in F. distichus embryos.

Interactions between auxin transport and the actin cytoskeleton in developmental polarity of Fucus distichus embryos in response to light and gravity

Land plants orient their growth relative to light and gravity through complex mechanisms that require auxin redistribution. Embryos of brown algae use similar environmental stimuli to orient their developmental polarity. These studies of the brown algae Fucus distichus examined whether auxin and auxin transport are also required during polarization in early embryos and to orient growth in already developed tissues. These embryos polarize with the gravity vector in the absence of a light cue. The auxin, indole-3-acetic acid (IAA), and auxin efflux inhibitors, such as naphthylphthalamic acid (NPA), reduced environmental polarization in response to gravity and light vectors. Young rhizoids are negatively phototropic, and NPA also inhibits rhizoid phototropism. The effect of IAA and NPA on gravity and photopolarization is maximal within 2.5 to 4.5 h after fertilization (AF). Over the first 6 h AF, auxin transport is relatively constant, suggesting that developmentally controlled sensitivity to auxin determines the narrow window during which NPA and IAA reduce environmental polarization. Actin patches were formed during the first hour AF and began to photolocalize within 3 h, coinciding with the time of NPA and IAA action. Treatment with NPA reduced the polar localization of actin patches but not patch formation. Latrunculin B prevented environmental polarization in a time frame that overlaps the formation of actin patches and IAA and NPA action. Latrunculin B also altered auxin transport. Together, these results indicate a role for auxin in the orientation of developmental polarity and suggest interactions between the actin cytoskeleton and auxin transport in F. distichus embryos.

Stage-dependent sensitivity to ultraviolet radiation in zygotes of the brown alga Fucus serratus

Sensitivity to ultraviolet (UV) radiation (UV-A, lambda = 315-400 nm; plus UV-B, lambda = 280-315 nm) of zygotes of the brown alga Fucus serratus L. (Phaeophyta) has been assessed through effects on growth of developing germlings. Different stages of development were distinguished by considering 5 h periods of time after fertilisation. Both the stage of the zygote and the UV radiation condition significantly affected growth of developing germlings. The negative response of growth rate of early stages of the zygotes to UV radiation seemed to be caused by UV-B rather than UV-A radiation, as the lowest relative growth rates were always estimated for germlings developed from zygotes irradiated with UV-B radiation. As regards the stage of the zygote, those germlings that developed from zygotes irradiated at 5-10 h after fertilisation showed the strongest inhibition of growth compared with the other stages. These results point to polarisation as the most UV-sensitive process during the first 24 h of the development of the zygote. A non-linear relationship between the developmental stage of the zygote and the sensitivity to UV radiation is suggested.