Phlorotannin Content Research Articles

Lack of Physiological Depth Patterns in Conspecifics of Endemic Antarctic Brown Algae: A Trade-Off between UV Stress Tolerance and Shade Adaptation?

A striking characteristic of endemic Antarctic brown algae is their broad vertical distribution. This feature is largely determined by the shade adaptation in order to cope with the seasonal variation in light availability. However, during spring-summer months, when light penetrates deep in the water column these organisms have to withstand high levels of solar radiation, including UV. In the present study we examine the light use characteristics in parallel to a potential for UV tolerance (measured as content of phenolic compounds, antioxidant activity and maximum quantum yield of fluorescence) in conspecific populations of four Antarctic brown algae (Ascoseira mirabilis, Desmarestia menziesii, D. anceps and Himantothallus grandifolius) distributed over a depth gradient between 5 and 30 m. The main results indicated that a) photosynthetic efficiency was uniform along the depth gradient in all the studied species, and b) short-term (6 h) exposure to UV radiation revealed a high tolerance measured as chlorophyll fluorescence, phlorotannin content and antioxidant capacity. Multivariate analysis of similarity indicated that light requirements for photosynthesis, soluble phlorotannins and antioxidant capacity are the variables determining the responses along the depth gradient in all the studied species. The suite of physiological responses of algae with a shallower distribution (A. mirabilis and D. menziesii) differed from those with deeper vertical range (D. anceps and H. grandifolius). These patterns are consistent with the underwater light penetration that defines two zones: 0–15 m, with influence of UV radiation (1% of UV-B and UV-A at 9 m and 15 m respectively) and a zone below 15 m marked by PAR incidence (1% up to 30 m). These results support the prediction that algae show a UV stress tolerance capacity along a broad depth range according to their marked shade adaptation. The high contents of phlorotannins and antioxidant potential appear to be strongly responsible for the lack of clear depth patterns in light demand characteristics and UV tolerance.

Constitutive or Inducible Protective Mechanisms against UV-B Radiation in the Brown Alga Fucus vesiculosus? A Study of Gene Expression and Phlorotannin Content Responses.

A role as UV sunscreens has been suggested for phlorotannins, the phenolic compounds that accumulate in brown algae in response to a number of external stimuli and take part in cell wall structure. After exposure of the intertidal brown alga Fucus vesiculosus to artificial UV-B radiation, we examined its physiological responses by following the transcript level of the pksIII gene encoding a phloroglucinol synthase, likely to be involved in the first step of phlorotannins biosynthesis. We also monitored the expression of three targeted genes, encoding a heat shock protein (hsp70), which is involved in global stress responses, an aryl sulfotransferase (ast), which could be involved in the sulfation of phlorotannins, and a vanadium bromoperoxidase (vbpo), which can potentially participate in the scavenging of Reactive Oxygen Species (ROS) and in the cross-linking and condensation of phlorotannins. We investigated whether transcriptional regulation of these genes is correlated with an induction of phlorotannin accumulation by establishing metabolite profiling of purified fractions of low molecular weight phlorotannins. Our findings demonstrated that a high dose of UV-B radiation induced a significant overexpression of hsp70 after 12 and 24 hours following the exposure to the UV-B treatment, compared to control treatment. The physiological performance of algae quantified by the photosynthetic efficiency (Fv/Fm) was slightly reduced. However UV-B treatment did not induce the accumulation of soluble phlorotannins in F. vesiculosus during the kinetics of four weeks, a result that may be related to the lack of induction of the pksIII gene expression. Taken together these results suggest a constitutive accumulation of phlorotannins occurring during the development of F.vesiculosus, rather than inducible processes. Gene expression studies and phlorotannin profiling provide here complementary approaches to global quantifications currently used in studies of phenolic compounds in brown algae.

Effect of storage time on phlorotannin content and antioxidant activity of six Sargassum species from Nhatrang Bay, Vietnam

The phlorotannin content and the total antioxidant, reducing power and DPPH free-radical-scavenging activities in relation to postharvest storage time of six Sargassum species (Sargassum mcclurei, Sargassum polycystum, Sargassum oligocystum, Sargassum serratum, Sargassum aquifolium, and Sargassum denticarpum) commonly found growing in the tropical marine area of Nhatrang, Khanhhoa Province, Viet Nam, were investigated. The results showed that phlorotannin content with total antioxidant and reducing power activity, and DPPH free radical scavenging of Sargassum aquifolium species were the highest, corresponding to 6.770 ± 0.001 mg phlorotannin g−1 DW, 6.1290 ± 0.0200 mg ascorbic acid g−1 DW, 19.7210 ± 0.0300 mg FeSO4 g−1 DW and 76.28 ± 0.20 % of 25 μg DPPH mL−1 extract. The change (decline) of phlorotannin content with antioxidant activities in Sargassum polycystum occurs the fastest. The storage time of the algae descends in the following species order such as S. oligocystum > S. mcclurei, S. aquifolium > S. serratum > S. denticarpum > S. polycystum.

Comparison of different techniques for the preservation and extraction of phlorotannins in the kelp Lessonia spicata (Phaeophyceae): assays of DPPH, ORAC-PGR, and ORAC-FL as testing methods

Preservation, storage, and safe transport of samples are key factors affecting brown algal phlorotannin (phenolics) quantification, their extraction yield, and antioxidant activity. This is especially relevant when field sampling is carried out in remote areas. The objective of the present study was to evaluate and compare five preservation (frozen control, freeze-dried, silica-dried, oven-dried, and air-dried) and two extraction methods (“rapid” and “traditional” extraction) of phlorotannins in the kelp Lessonia spicata (former Lessonia nigrescens). The antioxidant power of the samples treated with the different drying methods was compared through three different in vitro antioxidant assays: 2,2-diphenyl-1-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) methods, employing fluorescein (ORAC-FL) and pyrogallol red (ORAC-PGR) as target molecules. The results of the testing methods indicated that freeze-drying afforded the best extraction yields of phlorotannins (18–30 % higher than control using frozen material) whereas concentrations from samples dried in silica and oven averaged between 17 and 20 % lower than control. The antioxidant activity of phlorotannins measured using the DPPH test decreased significantly in samples kept dried compared to that in control, with activities varying from 65 (freeze-dried) to 21 % (air-dried). Accordingly, with ORAC-PGR and ORAC-FL indexes, sample preservation employing silica-drying or air-drying caused a high decrease of the antioxidant activity of polyphenols. No differences in both total phlorotannin concentration and antioxidant activity between the two extraction methods were found.

Combined Effects of Temperature and Nutrient Enrichment on Palatability of the Brown Alga Sargassum yezoense (Yamada) Yoshida & T. Konno

Global warming is predicted to strengthen marine plant-herbivore interactions. However, little is known about the effect of temperature on palatability and the associated chemical composition of marine macroalgae. To study the effects of physiological stress caused by the warm water temperatures and nutrient-poor conditions that occur during summer, we cultured the brown alga Sargassum yezoense at three different temperatures (16°C, 22°C, and 28°C) in both nutrient-enriched and non-enriched media. We then compared phlorotannin (i.e., defensive compounds) and nitrogen concentrations of S. yezoense as well as consumption rate by the sea urchin Hemicetrotus pulcherrimus among the treatment groups. No effect of culture temperature on phlorotannin and ni-trogen concentrations or consumption rate was detected. Nutrient enrichment resulted in decreased phlorotannin concentration and increased nitrogen concentration. Although nutrient enrichment did not affect consumption rate, a positive correlation between nitrogen concentration and consumption rate was detected. In contrast, there was no correlation between phlorotannin concentration and consumption rate. These results suggested that palatability of S. yezoense to H. pulcherrimus might not be affected by elevated temperature but that it could increase with nutrient enrichment.

Improved antioxidant activities of brown seaweed Ecklonia radiata extracts prepared by microwave-assisted enzymatic extraction

Seaweeds are important sources of bioactive compounds with potential use in functional foods and nutraceutical products. This study aims to investigate the extraction efficiency of phlorotannins and antioxidant compounds of a South Australian brown seaweed Ecklonia radiata by enzymatic and microwave-assisted enzymatic extraction in order to evaluate their uses as potential functional food ingredients. A selected group of carbohydrases (Viscozyme, Celluclast, and Ultraflo) and proteases (Alcalase, Neutrase, and Flavourzyme) has been applied to improve the extraction efficiency, alone and intensified with microwave heating, using conventional acid-base and water extractions as controls. The antioxidant activities of the extracts were evaluated using both ferric reducing ability of plasma (FRAP) and oxygen radical absorbance capacity (ORAC) assays. Significantly higher yields in total phlorotannin content (TPC) and antioxidant activities of the extracts were achieved by enzymatic and microwave-assisted enzymatic extraction. Microwave-assisted Viscozyme extraction for 5 to 30 min was the most effective process with an extraction yield achieved of 52 %. The extract had a TPC of 4.4 g phloroglucinol equivalents (PGE).100 g−1 dry weight (DW) and antioxidant activities of 29.7 mmol FeSO4 equivalents.100 g−1 DW and 740.1 μmol Trolox equivalents (TE).g−1 DW. In contrast, the conventional acidic extraction for 24 hours resulted in a TPC of 3.4 g PGE.100 g−1 DW and antioxidant activities of 21.1 mmol FeSO4 equivalents.100 g−1 DW and 512.4 μmol TE.g−1 DW. Extracts of brown seaweed E. radiata have potential for use in value-added products for nutritional purposes, using the microwave-assisted enzymatic extraction techniques.

Climate change impacts on overstory Desmarestia spp. from the western Antarctic Peninsula

This study examines climate change impacts (increased temperature and pCO2) on canopy-forming Desmarestia anceps and D. menziesii from the western Antarctic Peninsula during the austral summer–winter of 2013. These are ecologically important species that play a role functionally equivalent to kelp forests in this region. Two-way factorial microcosm experiments with treatments reflecting near-future ocean conditions were run with these species and include increased temperature alone (3.5 °C × pH 8.0), reduced pH alone (1.5 °C × pH 7.6), and both factors combined (3.5 °C × pH 7.6). Phlorotannin concentration, chlorophyll a concentration, growth, and photosynthetic parameters (slope to saturation of photo centers (α), saturating irradiance (Ek), maximum electron transport rate (ETRmax), and maximum quantum yield of photosystem II (Fv/Fm)) were used to assess the physiological responses of the individuals to the different climate change treatments. Few significant impacts were observed: In D. menziesii,Ek at the midpoint (after 39 days) was significantly higher in the 3.5 °C × pH 7.6 treatment and phlorotannin concentration was significantly higher in the 1.5 °C × pH 7.6 treatment than others at the end point of the experiment (79 days). All individuals in the experiment grew quickly through the midpoint, but growth declined thereafter. The photosynthetic apparatus of these species acclimated to microcosm conditions, and photo-physiological parameters changed between initial, midpoint, and end point measurements. Results indicate that D. menziesii is the more sensitive of the two species and that climate change factors can have a synergistic effect on this species. However, neither species responds negatively to climate change factors at the level of change used in this study, though the observed shifts in phlorotannin concentration and photosynthetic characteristics may have an unforeseen impact on the community dynamics in this geographic area.

Methyl jasmonate enhances phlorotannin production in the brown seaweed Ecklonia cava

Ecklonia cava is a brown seaweed widely distributed on the coasts of Korea and Japan and is used as food ingredient, animal feed, fertilizer, and medicine. E. cava contains a variety of compounds including carotenoids, fucoidans, and phlorotannins that play diverse biological and ecological roles. The marine algal polyphenols, the phlorotannins, found only in the brown algae have greater potential antioxidant activity than the polyphenols from terrestrial plants. Considering their significance in industrial applications, it would be beneficial to develop a simple method that can enhance amounts of phlorotannins in such algae. By adding 2 μM methyl jasmonate (MeJA) to the postharvest culture for 24 h, the crude phlorotannin content was increased by 156 %. The contents of individual phlorotannins, such as dieckol, phlorotannin 974A, phlorotannin 974B, and phlorofucofuroeckol-A were also increased by approximately 224, 176, 227, and 181 %, respectively. Additionally, MeJA treatment significantly enhanced the viability of E. cava tissue, suggesting that MeJA may prevent postharvest decay, at least in the short term.

Foliose algal assemblages and deforested barren areas: phlorotannin content, sea urchin grazing and holdfast community structure in the Aleutian dragon kelp, Eualaria fistulosa

In the Aleutian Archipelago, two distinct organizational states of kelp forest communities exist, foliose algal assemblages and deforested barren areas. The canopy-forming kelp Eualaria fistulosa can be found in both states, although it is much less abundant in the deforested state. In contrast, sea urchins also occur in both states, but they are considerably more abundant in the deforested state. This study determined whether the protective phlorotannin content in E. fistulosa sporophylls that originated in foliose algal assemblages would differ from those that originated in deforested areas. We also examined sea urchin grazing rates on these sporophylls to determine whether there were any differences in grazing rates related to the origin of the sporophylls. Next, we determined whether taxon richness and abundance of E. fistulosa holdfast communities would differ depending on the origin of the holdfast. Our results showed that sporophylls that were collected in barren areas generally had higher phlorotannin content than sporophylls found in foliose algal assemblages, although phlorotannin content varied across the study area. Grazing rates on sporophyll tissue and holdfast community structure did not differ between foliose algal assemblages and barren areas. These results show that phlorotannin content is greatest in areas under high grazing pressure and that phlorotannins may possibly protect E. fistulosa and the holdfast communities from being grazed in barren areas.

Phenolic-rich extracts from the edible seaweed, ascophyllum nodosum, inhibit α-amylase and α-glucosidase: Potential anti-hyperglycemic effects

Different extracts of the edible seaweed, Ascophyllum nodosum, were compared for their ability to inhibit α-amylase and effectiveness was linked to phenol and apparent phlorotannin contents. After solid phase extraction, phenolic-enriched extracts retained potent α-amylase inhibition [IC50 ~ 0.05 µg GAE/mL], whereas phlorotannin-rich sub-fractions were threefold less potent. Potency could be restored by re-addition of the wash fraction suggesting synergy between tannin and non-tannin components. The phenolic-rich extract and the phlorotannin-rich fraction inhibited α-glucosidase equally effectively (IC50 ~ 10 µg GAE/mL). Co-incubation of the tannin-rich fraction with acarbose reduced the concentration of acarbose required for effective inhibition of both amylase and glucosidase. That pre-incubation of amylase with the tannin-rich fraction markedly improved but the addition of BSA reduced inhibitory effectiveness suggested that phlorotannins inhibit amylase, but not glucosidase, through a protein-binding mechanism. The use of phlorotannins in combination with acarbose for postprandial glycemic control in type-2 diabetics is discussed.

Jeju seaweeds suppress lipopolysaccharide-stimulated proinflammatory response in RAW 264.7 murine macrophages

To investigate the anti-inflammatory effects of Jeju seaweeds on macrophage RAW 264.7 cells under lipopolysaccharide (LPS) stimulation. Ethyl acetate fractions were prepared from five different types of Jeju seaweeds, Dictyopteris divaricata (D. divaricata), Dictyopteris prolifera (D. prolifera), Prionitis cornea (P. cornea), Grateloupia lanceolata (G. lanceolata), and Grateloupia filicina (G. filicina). They were screened for inhibitory effects on proinflammatory mediators and cytokines such as nitric oxide (NO), prostaglandin E2, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6). Our results revealed that D. divaricata, D. prolifera, P. cornea, G. lanceolata, and G. filicina potently inhibited LPS-stimulated NO production (IC50 values were 18.0, 38.36, 38.43, 32.81 and 37.14 µg/mL, respectively). Consistent with these findings, D. divaricata, D. prolifera, P. cornea, and G. filicina also reduced the LPS-induced and prostaglandin E2 production in a concentration-dependent manner. Expectedly, they suppressed the expression of inducible NO synthase and cyclooxygenase-2 at the protein level in a dose-dependent manner in the RAW 264.7 cells, as determined by western blotting. In addition, the levels of TNF-α and IL-6, released into the medium, were also reduced by D. divaricata, D. prolifera, P. cornea, G. lanceolata, and G. filicina in a dose-dependent manner (IC50 values for TNF-α were 16.11, 28.21, 84.27, 45.52 and 74.75 µg/mL, respectively; IC50 values for IL-6 were 37.35, 80.08, 103.28, 62.53 and 84.28 µg/mL, respectively). The total phlorotannin content was measured by the Folin-Ciocalteu method and expressed as phloroglucinol equivalents. The content was 92.0 µg/mg for D. divaricata, 151.8 µg/mg for D. prolifera, 57.2 µg/mg for P. cornea, 53.0 µg/mg for G. lanceolata, and 40.2 µg/mg for G. filicina. Thus, these findings suggest that Jeju seaweed extracts have potential therapeutic applications for inflammatory responses.

Enrichment and purification of marine polyphenol phlorotannins using macroporous adsorption resins

Phlorotannins are one of the most important bioactive polyphenols; however, their purification using chromatographic methods has not been explored. Here, we studied purification of phlorotannins from the crude phlorotannin extract (CPhE) of the brown seaweed Ecklonia cava using macroporous adsorption resins. For purification of phlorotannins, four resins (HP-20, SP-850, XAD-7HP, and XAD-2) were screened. Among them, HP-20 resin showed the highest adsorption and desorption capacities. In static adsorption tests, the adsorption capacity of HP-20 increased with increasing temperature (25–45°C). Optimal conditions for the dynamic experiments can be summarized as follows: total phlorotannin content (TPhC) in loading solution: 1.5mg PGE/mL, processing volume: 4 BV, flow rate: 1mL/min, temperature: 45°C, desorption solvent: 40% ethanol solution. After purification, TPhC (452mg PGE/g) and arsenic (180μg/g) of CPhE increased and decreased to 905mg PGE/g and 48μg/g, respectively. Recovery rate of phlorotannins from CPhE was 92%.

The physiological state of intertidal brown seaweeds Fucus serratus Linnaeus, 1753 and Fucus distichus Linnaeus, 1767 cultivated on a biofiltration system in the Barents Sea

The physiological parameters (growth rate, specific area, photosynthesis rate, metabolic activity of cells, contents of photosynthetic pigments, dry matter, and soluble phlorotannins) of the intertidal brown seaweeds Fucus serratus and F. distichus cultivated in the Barents Sea for oil biofiltration purposes were investigated. The possibility of their existence submerged to a 5 m depth is shown. The duration of the survival of the plants in the absence of a tide cycle depended on the degree of fouling and the presence of phytophages. For long-term growth of seaweeds on vertical ropes, fucoids need to be subjected to periodic desiccation.

LPS-induced NO inhibition and antioxidant activities of ethanol extracts and their solvent partitioned fractions from four brown seaweeds

The nitric oxide inhibitory (NOI) and antioxidant (ABTS and DPPH radical scavenging effects with reducing power) activities of the ethanol (EtOH) extracts and solvent partitioned fractions from Scytosiphon lomentaria, Chorda filum, Agarum cribrosum, and Desmarestia viridis were investigated, and the correlation between biological activity and total phenolic (TP) and phlorotannin (TPT) content was determined by PCA analysis. The yield of EtOH extracts from four brown seaweeds ranged from 2.6 to 6.6% with the highest yield from D. viridis, and the predominant compounds in their solvent partitioned fractions had medium and/or less polarity. The TP and TPT content of the EtOH extracts were in the ranges of 25.0–44.1 mg GAE/g sample and 0.2–4.6 mg PG/g sample, respectively, which were mostly included in the organic solvent partitioned fractions. Strong NOI activity was observed in the EtOH extracts and their solvent partitioned fractions from D. viridis and C. filum. In addition, the EtOH extract and its solvent partitioned fractions of D. viridis exhibited little cytotoxicity to Raw 264.7 cells. The most potent ABTS and DPPH radical scavenging capacity was shown in the EtOH extracts and their solvent partitioned fractions from S. lomentaria and C. filum, and both also exhibited strong reducing ability. In the PCA analysis the content of TPT had a good correlation with DPPH (r = 0.62), ABTS (r = 0.69) and reducing power (r = 0.65), however, an unfair correlation was observed between the contents of TP and TPT and NOI, suggesting that the phlorotannins might be responsible for the DPPH and ABTS radical scavenging activities.

Optimization of the microwave-assisted extraction of phlorotannins from Saccharina japonica Aresch and evaluation of the inhibitory effects of phlorotannin-containing extracts on HepG2 cancer cells

The use of a microwave-assisted extraction (MAE) method for the extraction of phlorotannins from Saccharina japonica Aresch (S. japonica) has been evaluated with particular emphasis on the influential parameters, including the ethanol concentration, solid/liquid ratio, extraction time, extraction temperature, and microwave power. The MAE procedure was optimized using single-factor design and orthogonal array design (OAD). The content of total phlorotannins in S. japonica was determined using a Folin-Ciocalteu (FC) assay. A maximum total phlorotannin content of 0.644 mg of phloroglucinol equivalent per gram of dry weight plant (mg PGE/g DW) was obtained using the optimized model, which included an ethanol concentration of 55%, solid/liquid ratio of 1:8, extraction time of 25 min, irradiation power of 400 W, and temperature of 60°C. Under similar conditions, the application of a conventional extraction method led to a lower phlorotannin yield of 0.585 mg PGE/g WD. These results demonstrated that the MAE approach provided better results for the extraction of phlorotannins from S. japonica and was a promising technique for the extraction of phenolic compounds from S. japonica and other materials. In addition, screening tests for the inhibitory activity showed that the phlorotannin-containing extracts significantly inhibited the growth of human hepatocellular carcinoma cells (HepG2) by inducing their apoptosis. The morphological changes that occurred during cell apoptosis were characterized using Hoechst33258 staining.

Consumption and feeding preference of Echinogammarus marinus on two different algae: Fucus vesiculosus and Ulva intestinalis

Echinogammarus marinus constitutes the most abundant amphipod species in Fucus spp. assemblages from many North Atlantic estuaries. However, there are some doubts about the real use of fucoids by the amphipod. Whilst some studies report the ingestion of Fucus vesiculosus by E. marinus, others suggest that the amphipod preference for fucoids is mostly related to sheltering rather than feeding, due to the high phlorotannin content of brown algae. The purpose of the present work was to disentangle this issue by checking the consumption rate and feeding preference of E. marinus on F. vesiculosus, its preferential habitat, and on Ulva intestinalis, a green algae abundant in the Mondego estuary (Western Coast of Portugal) and usually considered as highly palatable for herbivores.In a 2-stage laboratorial setup, fresh disks of the two types of algae were offered to E. marinus for three days. Consumption rates were estimated from differences between algal and animal initial and final fresh weights using a control correction factor, while preference was tested by differences in algal consumption rates when no choice was offered (stage 1) and when the two algae were offered simultaneously (stage 2).Results showed that E. marinus effectively consumed fresh F. vesiculosus in much higher amounts than U. intestinalis and significantly preferred to consume F. vesiculosus over U. intestinalis. Therefore, feeding habits must be one of the factors related to the close association of the amphipod with F. vesiculosus, although other factors may also be involved (e.g. sheltering).

Polyphenols from Stypopodium zonale (Phaeophyceae): Intrapopulational variation, induction by simulated herbivory, and epibiosis effects

Phlorotannins are exclusive chemical components of brown macroalgae active against herbivores and fouling, but several dynamic aspects of these chemicals remain underexplored or unexplored, such as intra-populational variability, response to wounding damage in tropical macroalgae, and correlation to levels of coverage by epibionts on the macroalgal surface. In this study, we investigated (i) the variation of phlorotannin content in response to artificial damage (induction experiments), (ii) the relationship between phlorotannin contents and epibiosis levels (low, medium, or high percentage of cover on the macroalga Stypopodium zonale), and (iii) the variation of phlorotannins content within-population of this tropical macroalga. Clipping elicited an increase in phlorotannin concentration only after 2 days. In addition, we detected higher phlorotannin concentrations in individuals exposed to low and medium epibiosis coverage and a lower concentration of these chemicals in individuals with a high level of epibiosis. We detected a broad variation in phlorotannin content among S. zonale individuals, from 0.63 to 3.24% (dry weight). These results suggest that the varying levels of phlorotannins found in the tropical macroalga S. zonale may result from different levels of exposure to herbivores in nature. Similarly, our results suggest that S. zonale phlorotannins may be effective antifoulants.

Effects of nutrient enrichment and herbivory on morphology, reproduction and chemical content of Turbinaria conoides (Phaeophyceae)

SummaryThe effects of nutrient enrichment and herbivory on resource allocation patterns among morphology, reproduction, and chemical content of the brown alga, Turbinaria conoides (J. Agardh) Kützing were tested in the shallow subtidal zone of the Gulf of Thailand. The field experimental design comprised 36 plots (50 × 50 cm2) with and without herbivores, and two nutrient levels. Cages (uncaged and fully caged plots) were used to exclude herbivorous fishes and two nutrients levels were achieved by experimental enrichment above ambient nutrient concentrations. For morphology of Turbinaria, the maximum length (holdfast to frond apex), the width of the base of the stipe, number of blades, holdfast and stipe diameter were measured. Biomass, reproductive output, and tissue nutrient (carbon: nitrogen: phosphorus) content of T. conoides were examined. Phlorotannin concentrations were examined using a modified Folin‐Ciocalteu method. The results showed that herbivory had no effect on morphology, reproduction, or phlorotannin concentrations. This could be due to the structural and morphological deterrents of alga, which might minimize grazing effects from herbivorous fishes. Nutrient enrichment had no effect on morphology and reproduction of T. conoides, possibly due to low nutrient demand in Turbinaria. However, nutrient enrichment did affect phlorotannin concentrations, as phlorotannins in the enriched plots were lower than the ambient plots. These results support, in part, the carbon–nutrient balance hypothesis that states algae will allocate fewer resources to production of anti‐herbivore chemical compounds when enriched with potential growth‐limiting nutrients.

Photosynthetic characteristics and UV stress tolerance of Antarctic seaweeds along the depth gradient

The photosynthetic characteristics through P-E curves and the effect of UV radiation on photosynthesis (measured as rapid adjustment of photochemistry, F v/F m) and DNA damage (as formation of CPDs) were studied in field specimens of green, red and brown algae collected from the eulittoral and sublittoral zone of Fildes Peninsula (King George Island, Antarctic). The content of phenolic compounds (phlorotannins) and the antioxidant activity were also studied in seven brown algae from 0 to 40 m depth. The results indicated that photosynthetic efficiency (α) was high and did not vary between different species and depths, while irradiances for saturation (E k) averaged 55 μmol m−2 s−1 in subtidal and 120 μmol m−2 s−1 in eulittoral species. The studied species exhibited notable short-term UV tolerance along the vertical zonation. In intertidal and shallow water species, decreases in F v/F m by UV radiation were between 0 and 18 %, while in sublittoral algae, decreases in F v/F m varied between 3 and 35 % relative to PAR treatment. In all species, recovery was high averaging 84–100 %. The formation of CPDs increased (15–150 %) under UV exposure, with the highest DNA damage found in some subtidal species. Phlorotannin content varied between 29 mg g−1 DW in Ascoseira mirabilis from 8 m depth and 156 mg g−1 DW in Desmarestia menziesii from 17 m depth. In general, phlorotannin concentrations were constitutively high in deeper sublittoral brown algae, which were correlated with higher antioxidant activities of algal extracts and low decreases in photosynthesis. UV radiation caused a strong decrease in phlorotannin content in the deep-water Himantothallus grandifolius, whereas in D. menziesii and Desmarestia anceps, induction of the synthesis of phlorotannins by UV radiation was observed. The antioxidant activity was in general less affected by UV radiation.

Seasonal fertility and combined effects of temperature and UV-radiation on Alaria esculenta and Laminaria digitata (Phaeophyceae) from Spitsbergen

Global warming and enhanced UV-radiation due to stratospheric ozone depletion could drastically affect Arctic coastal ecosystems. Previous research revealed that the UV-susceptibility and impact of increased UV-radiation on Arctic kelp zoospores are highly variable, potentially due to seasonal acclimation. Accordingly, for a better understanding of climate change effects on Arctic kelp, we need to determine the fertility period of Arctic kelps and to systematically examine the seasonal differences of increased UV-radiation during the fertility period. We examined the fertility period of Laminaria digitata and Alaria hyperborea, by evaluating sorus maturation, zoospore release and germination. Zoospore germination was studied under photosynthetic active radiation (PAR 400–700 nm) and PAR and increased UVAB-radiation (280–700 nm) from July to September at 2 and 7 °C. Furthermore, we tested whether differences in the zoosporic UV-susceptibility were related to the content of UV-screening phlorotannins. The fertility period of A. esculenta is uniform from July to mid-August and ends in September. Within the fertility period, the UV-susceptibility of A. esculenta zoospores was highest at 2 °C and the beginning of July, whereas it was not affected by seasonality at 7 °C. The fertility period of L. digitata starts in late July and lasts at least until September, and no seasonal differences in the UV-susceptibility were found. However, UV-susceptibility was significantly lower at 7 °C. In both species, the zoosporic phlorotannin content did not affect the UV-susceptibility. We conclude that seasonality strongly influences the UV-susceptibility of A. esculenta but at low water temperatures only. Higher seawater temperatures help both species to cope with increasing UV-radiation.