Ascoseira Research Articles

Synthesis of hybrid nanoflowers using extract of Ascoseira mirabilis, a large brown parenchymatous macroalga endemic to the Antarctic Ocean, as the organic component and evaluation of their antimicrobial, catalytic, and antioxidant activities

Synthesis of hybrid nanoflowers using extract of Ascoseira mirabilis, a large brown parenchymatous macroalga endemic to the Antarctic Ocean, as the organic component and evaluation of their antimicrobial, catalytic, and antioxidant activities

Studies toward the comprehension of fungal-macroalgae interaction in cold marine regions from a biotechnological perspective

In marine ecosystems, macroalgae are the habitat for several microorganisms, fungi being among them. In the Antarctic benthic coastal ecosystem, macroalgae play a key role in organic matter cycling. In this study, 13 different macroalgae from Potter Cove and surrounding areas were sampled and 48 fungal isolates were obtained from six species, four Rhodophyta Ballia callitricha, Gigartina skottsbergii, Neuroglossum delesseriae and Palmaria decipiens, and two Phaeophyceae: Adenocystis utricularis and Ascoseira mirabilis. Fungal isolates mostly belonged to the Ascomycota phylum (Antarctomyces, Cadophora, Cladosporium, Penicillium, Phialocephala, and Pseudogymnoascus) and only one to the phylum Mucoromycota. Two of the isolates could not be identified to genus level, implying that Antarctica is a source of probable novel fungal taxa with enormous bioprospecting and biotechnological potential. 73% of the fungal isolates were moderate eurypsychrophilic (they grew at 5–25 °C), 12.5% were eurypsychrophilic and grew in the whole range, 12.5% of the isolates were narrow eurypsychrophilic (growth at 15–25 °C), and Mucoromycota AUe4 was classified as stenopsychrophilic as it grew at 5–15 °C. Organic extracts of seven macroalgae from which no fungal growth was obtained (three red algae Georgiella confluens, Gymnogongrus turquetii, Plocamium cartlagineum, and four brown algae Desmarestia anceps, D. Antarctica, Desmarestia menziesii, Himantothallus grandifolius) were tested against representative fungi of the genera isolated in this work. All extracts presented fungal inhibition, those from Plocamium cartilagineum and G. turquetii showed the best results, and for most of these macroalgae, this represents the first report of antifungal activity and constitute a promising source of compounds for future evaluation.

Superoxide dismutase and ascorbate peroxidase genes in Antarctic endemic brown alga Ascoseira mirabilis (Ascoseirales, Phaeophyceae): data mining of a de novo transcriptome

Abstract The Antarctic endemic brown alga Ascoseira mirabilis is physically and physiologically well adapted to the extreme polar environment. To better understand the molecular strategies associated with stress adaptation, the transcriptome of A. mirabilis was sequenced, and its antioxidant enzyme genes were identified and compared with other algae. A total of 126,576 unigenes with a mean length of 734 bp and N50 of 1174 bp was assembled from the transcriptome data. Phylogenetic analysis revealed that dramatic evolutionary changes had occurred in the brown algal superoxide dismutases (SODs) and class I peroxidases that were not consistent with the phylogeny of the species. Fe/Mn SODs are more prevalent in brown algae than in red and green algae. Two additional Fe-SODs in A. mirabilis were phylogenetically closely related to those of green algae, but not to those in other brown algae. We also identified three A. mirabilis ascorbate peroxidase (APx) genes that had a different origin from other brown algal APxs. The SOD and APx genes specifically identified in A. mirabilis will be crucial for understanding the evolution of the algal antioxidant enzymes that contribute to ecological success under extreme environmental conditions in the Antarctic region.

Nuclear DNA content estimations and nuclear development patterns in Antarctic macroalgae

Nuclear DNA content of marine macroalgae is known for only about a 3% of the globally known taxa, and so far, the only available data concerning marine Antarctic macroalgae refer to the Phaeophyceae Ascoseira mirabilis and Desmarestia antarctica. As these data can be useful for species delimitation when combined with other taxonomical information, we aimed to expand the available number of measurements in the understudied Antarctic seaweed flora. To address this, we measured the nuclear DNA content of 12 Antarctic marine algae (seven Rhodophyceae and five Phaeophyceae). Nuclear DNA analyses were carried out by spectrofluorimetry and image analysis from samples conserved in Carnoy, using DAPI as DNA marker. For ten of these taxa, our values represent the first estimations to date. The nuclear DNA content estimates obtained for the Antarctic red algae examined vary between 2C = 0.38 pg in Gigartina skottsbergii and 2C = 1.63 pg in Neuroglossum delesseriae. In brown algae, the values range from 2C = 0.18 pg in both Desmarestia antarctica and Desmarestia menziesii to 2C = 0.96 pg in Phaeurus antarcticus. Furthermore, this study allowed us to identify nuclear developmental patterns for the first time in two Antarctic seaweeds (Ballia callitricha and Neuroglossum delesseriae).

Extraction of sterols in brown macroalgae from Antarctica and their identification by liquid chromatography coupled with tandem mass spectrometry

This study reports for the first time the extraction and quantification of sterols in six species of brown macroalgae from Antarctica: Adenocystis utricularis, Ascoseira mirabilis, Cystosphaera jacquinotii, Desmarestia anceps, Desmarestia antarctica, and Himantothallus grandifolius. Ultrasound irradiation was used as a promotor to extract sterols from algal biomass. The extracts were analyzed by high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for sterol quantization (ergosterol, brassicasterol, fucosterol, β-sitosterol, campesterol, cholesterol, and stigmasterol). In general, fucosterol was the most abundant (6.60 to 48.13 mg kg−1), followed by β-sitosterol (5.29 to 16.49 mg kg−1), stigmasterol (2.69 to 14.84 mg kg−1) in five of the six examined algae. The sterol campesterol was found in lower concentrations (0.07 to 0.15 mg kg−1) in all studied samples.

Stress tolerance of Antarctic macroalgae in the early life stages

Early life stages of macroalgae, especially from polar species, can be highly vulnerable to physical stressors, leading to important consequences for the fate of the whole population in scenarios of changing environmental variability. In the present study, tolerance to UV and temperature stress, as measured by rapid adjustment of photochemistry, Fv/Fm, and photosynthetic characteristics based on P-E curves (ETRmax, α and Ek), was assessed in the early life stages of six Antarctic macroalgal species from eulittoral (Pyropia endiviifolia, Iridaea cordata, Adenocystis utricularis and Monostroma hariotii) and sublittoral (Ascoseira mirabilis and Gigartina skottsbergii). Reproductive cells of eulittoral species showed the highest light demands (Ek >45 μmol photon m−2 s−1) when compared to those from sublittoral species (Ek 30 % inhibition in Fv/Fm in the same condition. Enhanced temperature (7 and 12 °C) improved the tolerance of I. cordata compared to 2 °C, but exacerbated the detrimental effects of UV on A. mirabilis. Results showed that photosynthetic characteristics varied among reproductive cells of different species, reflecting the vertical zonation of parental thalli. Otherwise, these differences appear to underlie biogeographical and evolutionary components. In addition, UV tolerance was modulated by temperature increase, while temperature increase, in turn, ameliorated the detrimental effects of stress treatments in some eulittoral species (I. cordata tetraspores). In sublittoral A. mirabilis gametangia, temperature exacerbated the reduction of photosynthetic efficiency.

Control of grazing by light availability via light-dependent, wound-induced metabolites: The role of reactive oxygen species

Light may influence grazing through its effect on grazers or by influencing the physiology and biochemistry of primary producers. It has recently been established that reactive oxygen species (ROS) produced by a wounded macroalga depend on light via photosynthetic electron transport. Since ROS can act as both chemical messengers and toxins, it is hypothesized that the light-dependence of wound-induced ROS can have ecological consequences for plant–herbivore interactions. Through spin trapping and electron paramagnetic resonance, this study shows that wounded Ascoseira mirabilis produced ROS that were correlated with A. mirabilis wounding in light but not dark conditions. In feeding assays where sympatric amphipods consumed palatable macroalgae in the presence of wounded A. mirabilis, amphipod consumption was correlated with A. mirabilis wounding in light but not dark conditions. The nonlinear effect of ROS on grazing suggests that in ecology, as in physiology, low levels of ROS may act as messengers while high levels are toxic.

UV Sensitivity of Vegetative and Reproductive Tissues of Two Antarctic Brown Algae is Related to Differential Allocation of Phenolic Substances.

UV sensitivity of the vegetative and reproductive tissues of two Antarctic brown macroalgae was compared. Photosynthesis as well as the content and localization of phenolic substances were determined. Responses to UV radiation were quantified as chlorophyll fluorescence (Fv /Fm ). Ascoseira mirabilis showed high UV tolerance, while in Cystosphaera jacquinotii Fv /Fm decreased by 15-21%, the receptacles being more tolerant than the vegetative blades. The phlorotannin contents showed an opposite pattern: the soluble fraction dominated in C.jacquinotii while in A.mirabilis the insoluble fraction was more abundant. Soluble phlorotannins were higher in the reproductive than in vegetative tissues in both species. Images of tissue cross-sections under violet-blue light excitation confirmed a high allocation of phenolic compounds (as blue autofluorescence) in C.jacquinotii, both in reproductive and vegetative blades. The allocation and proportions of the soluble and insoluble phlorotannins could be related with the observed UV tolerance of the vegetative and reproductive tissues.

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.

Effects of increased seawater temperature on UV tolerance of Antarctic marine macroalgae

Cold-adapted Antarctic marine macroalgae have different physiological strategies to tolerate the ultra- violet (UV) radiation at low seawater temperatures around 0 °C. The warming of Antarctica's coasts driven by global climate change may alter the physiology such to influence their UV tolerance. This study examined the interactive effects of different seawater temperatures (2 vs. 7 °C) and UV radiation on the physiological performance (primary photochemistry: F v /F m , soluble and insoluble phlorotan- nins, radical scavenging capacity) of seven macroalgae, which are dominant in Antarctic coastal ecosystems. Four brown and three red macroalgae, collected from Fildes Bay (King George Island, South Shetland Islands) in January/ February, were exposed to 6 h of UV/temperature stress, followed by a 16-h recovery. The brown macroalgae Des- marestia menziesii and Ascoseira mirabilis showed the highest UV tolerance at 2 °C, followed by Desmarestia anceps, and the rhodophytes Iridaea cordata, Tremato- carpus antarcticus, and Palmaria decipiens. Himanto- thallus grandifolius (Phaeophyceae) was sensitive to UV radiation at 2 °C. At 7 °C, UV tolerance was improved in UV-sensitive macroalgae probably due to a more efficient damage repair of the photosynthetic apparatus. Tempera- ture, however, did not modulate UV tolerance in D. anceps,

Reactive oxygen species as a marine grazing defense: H2O2 and wounded Ascoseira mirabilis both inhibit feeding by an amphipod grazer

Marine macroalgae can release reactive oxygen species (ROS) upon wounding and grazing. Here we address the potential role of ROS in herbivore defense. We performed feeding assays in the presence of varying concentrations of hydrogen peroxide (H2O2), a common type of ROS. H2O2 inhibited feeding by a marine amphipod grazer, Gondogeneia antarctica, over broad levels of concentration, and its potency was strongly dependent on its rate of decay in natural seawater. Because it is possible that the inhibitory levels of H2O2 are encountered in the vicinity of a sympatric macroalgal wound, we suggest that H2O2 has the potential to act as a direct anti-grazing defense in marine ecosystems. Since some sympatric macroalgae release a burst of non-H2O2 ROS, we also performed experiments to evaluate the role of these naturally-produced ROS on sympatric grazers. The presence of wounded Ascoseira mirabilis (which releases a burst of non-H2O2 ROS after wounding) during a feeding assay inhibited feeding of G. antarctica compared to the presence of intact A. mirabilis. These data are consistent with a role for ROS as a direct anti-herbivore defense in nature. However, the data are also consistent with hypotheses that involve other putative activated anti-grazing defenses.

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.

Photosynthetic performance, DNA damage and repair in gametes of the endemic Antarctic brown alga Ascoseira mirabilis exposed to ultraviolet radiation

Abstract Stress physiology on the reproductive cells of Antarctic macroalgae remained unstudied. Ascoseira mirabilis is endemic to the Antarctic region, an isolated ecosystem exposed to extreme environmental conditions. Moreover, stratospheric ozone depletion leads to increasing ultraviolet radiation (280–400 nm) at the earth's surface, thus it is necessary to investigate the capacity of reproductive cells to cope with different UV irradiances. This study is aimed to investigate the impact of exposure to different spectral irradiance on the photosynthetic performance, DNA damage and gamete morphology of the A. mirabilis. Gametangia, gametes and zygotes of the upper sublittoral brown alga A. mirabilis were exposed to photosynthetically active radiation (PAR = P; 400–700 nm), P + UV‐A radiation (UV‐A, 320–400 nm) and P + UV‐A + UV‐B radiation (UV‐B, 280–320 nm). Rapid photosynthesis versus irradiance curves of freshly released propagules were measured. Photosynthetic efficiencies and DNA damage (in terms of cyclobutane pyrimidine dimers) were determined after 1, 2, 4 and 8 h exposure as well as after 2 days of recovery in dim white light. Saturation irradiance (Ik) in freshly released propagules was 52 μmol photons m−2 s−1. Exposure for 1 h under 22 μmol photons m−2 s−1 of PAR significantly reduced the optimum quantum yield (Fv/Fm), suggesting that propagules are low light adapted. Furthermore, UVR significantly contributed to the photoinhibition of photosynthesis. Increasing dose as a function of exposure time additionally exacerbated the effects of different light treatments. The amount of DNA damage increased with the UV‐B dose but an efficient repair mechanism was observed in gametes pre‐exposed to a dose lower than 5.8 × 103 J m−2 of UV‐B. The results of this study demonstrate the negative impact of UV‐B radiation. However, gametes of A. mirabilis are capable of photosynthetic recovery and DNA repair when the stress factor is removed. This capacity was observed to be dependent on the fitness of the parental sporophyte.

Biological and environmental characterization of marine macroalgal assemblages in Potter Cove, South Shetland Islands, Antarctica

Abstract We describe the macroalgal assemblages in Potter Cove and their distribution by depth, substratum, irradiation, nutrients, salinity, water temperature and light period. We determined groups by using K-means, the Hellinger index and the maximum Calinski-Harabasz pseudo-F-statistic as stopping rule. Indicator species were assessed with the IndVal index. Relationships between groups and environmental factors were determined by correspondence analysis, and results were validated by a canonical correspondence analysis of species and environment. To compare the group biodiversities we used species richness and diversity indices and abundance biomass comparisons curves. Analysis with incidence data discriminated one shallow Iridaea assemblage and one deep Himantothallus assemblage. Analysis using biomass discriminated three facies, the first in the upper zone (Iridaea cordata, Monostroma hariotii, Adenocystis utricularis, Enteromorpha bulbosa), the second (Desmarestia menziesii, D. antarctica, Ascoseira mirabilis, Curdiea racovitzae, Gigartina skottsbergii, Kallymenia antarctica, Neuroglossum delesseriae, Phaeurus antarcticus, Gymnogongrus turquetii) at intermediate depth and the third (H. grandifolius, D. anceps, Georgiella confluens, Ballia callitricha, Plocamium cartilagineum), coincident with the deep qualitative assemblage, was found in a less disturbed environment. The difference in species composition between the groups was mainly related to depth as an environmental variable. The high specific diversity at intermediate depths can be explained by the presence of patches in different successional stages caused by iceberg scouring.

CORRIGENDUM

Journal of PhycologyVolume 36, Issue 5 p. 975-975 Free Access CORRIGENDUM First published: 31 January 2003 https://doi.org/10.1046/j.1529-8817.2000.03657.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat The following references were missing from Ingo Maier's book review of Algae by L. E. Graham and L. Wilcox in the August 2000 issue (36:788–9): References Cavalier-Smith, T. & Chao, E. E. 1996. 18S rRNA sequence of Heterosigma carterae (Raphidophyceae), and the phylogeny of heterokont algae (Ochrophyta). Phycologia 35: 500– 10. Clayton, M. 1987. Isogamy and a fucalean type of life history in the Antarctic brown alga Ascoseira mirabilis (Ascoseirales, Phaeophyta). Bot. Mar. 30: 447– 54. Volume36, Issue5October 2000Pages 975-975 ReferencesRelatedInformation

Feeding ecology of the Antarctic herbivorous gastropod Laevilacunaria antarctica Martens

The grazing activity of the Antarctic prosobranch gastropod Laevilacunaria antarctica on macroalgae was investigated in order to evaluate its position in the shallow water food web of Potter Cove, King George Island, Antarctica. From 12 abundant macroalgal species tested in feeding experiments, L. antarctica avoided only three species, the brown algae Ascoseira mirabilis, Phaeurus antarcticus, and Himantothallus grandifolius, significantly. The gastropod can be classified as a general feeder on macroalgae in the rocky intertidal and shallow waters of Potter Cove. Comparative grazing experiments showed that epiphytic diatoms contribute about 2/3 to the total diet of L. antarctica. Mean abundance and biomass of the snails in this area were 292.0±135.3 (S.D.) ind m −2 and 1.549±1.021 (S.D.) g AFDW m −2, respectively. The total consumption of macroalgae by the population of L. antarctica in Potter Cove is estimated to be 118 kJ m −2 year −1. This alone, however, is not sufficient to sustain the standing stock of gastropods in the investigation area. Grazing experiments showed that feeding on macroalgae which carry epiphytic diatoms is about three times higher than on macroalgae without epiphytes. It is therefore concluded that the population of L. antarctica in Potter Cove is maintained by consumption of both epiphytic diatoms and macroalgae. Feeding experiments showed that chemical compounds of macroalgae are not active in a chemical defense against grazing of L. antarctica. It is therefore discussed that structural characteristics of the algae can explain the low grazing rate of L. antarctica on some macroalgal species. Various models explaining macroalgal–herbivore relationships based on functional groups of algae are considered. The predictions on the feeding of L. antarctica derived from these functional form models in many cases correspond with the results derived from feeding experiments in this study. They are, however, inconsistent regarding grazing on or avoidance of some algal species and thereby obscure important information on special adaptations of organisms, e.g. L. antarctica, in macroalgal–herbivore interactions.

Seasonal changes in C, N and major organic compounds and their significance to morpho-functional processes in the endemic Antarctic brown alga Ascoseira mirabilis

The seasonal and intra-thallus variations in the contents of C, N, proteins and amino acids, as well as in the storage carbohydrates mannitol and laminaran, were measured in the endemic Antarctic brown alga Ascoseira mirabilis between September and February and related to seasonal changes in dark respiration and photosynthesis. Carbon contents between 31 and 37% DW were relatively constant throughout these months and no variations were detected among thallus regions. Nitrogen contents, by contrast, were higher in September/October (3.1% DW) and decreased in January and February (1.8% DW). In general, the basal regions had the lower N contents. Proteins reached maximum values of 13% DW in November and February and were inversely correlated to photosynthesis (net Pmax). The amino acid content was also higher in October and November (maxima close to 10% DW), but low between December and February (close to 5% DW), probably related to a seasonal pattern of N allocation in the alga. The storage carbohydrates mannitol and laminaran exhibited inverse seasonal changes: low mannitol values close to 5% DW in September were coupled with high laminaran contents varying between 7 and 15% DW. The existence of high laminaran contents in the distal blade region during September and February suggests that this compound was effectively accumulated in this region. The low P/R ratios in spring and the existence of a significant relationship between mannitol content and seasonal photosynthetic activity in the basal region appear to support the hypothesis of a possible utilization of carbohydrates to power growth in A. mirabilis.

Distribution of macroalgae and macroalgal communities in gradients of physical conditions in Potter Cove, King George Island, Antarctica

The vegetation of a small fjord and its adjacent open shore was documented by subaquatic video. The distribution of individual species of macroalgae and the composition of assemblages were compared with gradients of light availability, hydrography, slope inclination, substratum, and exposition to turbulence and ice. The sublittoral fringe is usually abraded by winterly ice floes and devoid of large, perennial algae. Below this zone, the upper sublittoral is dominated by Desmarestia menziesii on steep rock faces, where water movements become irregular, or by Ascoseira mirabilis and Palmaria decipiens on weakly inclined slopes with steady rolling water movements. In the central sublittoral above 15 m, where turbulence is still active, Desmarestia anceps is outcompeting all other species on solid substratum, However, the species is not able to persist on loose material under these conditions. Instead, Himantothallus grandifolius may occur. Deeper, where turbulence usually is negligible, Desmarestia anceps also covers loose material. The change of dominance to Himantothallus grandifolius in the deep sublittoral cannot completely be explained at present. Himantothallus grandifolius also prevails in a mixed assemblage under the influence of grounding icebergs. Most of the smaller algae are opportunists with different degrees of tolerance for turbulence, but some apparently need more stable microhabitats and thus are dependent from continuing suppression of competitive large phaeophytes.

Variations in photosynthetic characteristics of the Antarctic marine brown algaAscoseira mirabilisin relation to thallus age and size

Growth, photosynthesis, dark respiration, chlorophyll a (Chl a) content and dry weight were measured in 2- and 3-year-old plants of Ascoseira mirabilis (Ascoseirales), cultivated in the laboratory under changing daylengths which matched the seasonal variations in the Antarctic. Determinations were made in four thallus regions. Growth of A. mirabilis was seasonal, with higher rates in spring. Parameters such as net photosynthesis (P max), photosynthetic efficiency (α), both measured on a fresh weight (FW) basis, and dry weight content, showed significant age- and size-dependent variations. In contrast, no variations were observed in dark respiration, initial light-saturating point of photosynthesis (I k) and Chl a contents. P max had maximum values close to 16·5 μmol O2 g-1 FW h-1 in 2-year-old plants, whereas in 3-year-old plants maximum values of 8 μmol O2 g-1 FW h-1 were determined. The α-values reached maximum rates of 1.4 and 0.6 μmol O2 g-1 FW h-1 (μmol photons m-2 s-1)-1 in 2- and 3-year-old plants,...

Energy contents and organic constituents in Antarctic and south Chilean marine brown algae

The content of proteins, lipids and carbohydrates and the calorific contents in six Antarctic and three south Chilean brown algae were determined. These constitute the first reports of chemical composition in the endemic Antarctic species Cystosphaera jacquinotii, Phaeurus antarcticus and Desmarestia antarctica. There were no marked differences in total energy levels between Antarctic and cold-temperate species (values between 10.6 and 13 kJ g−1 dry weight). However, species such as Adenocystis utricularis showed significantly higher ash-free energy (26.3 kJ), which is explained in terms of morpho-functional differentiation. Ascoseira mirabilis and Phaeurus antarcticus showed high total lipids (2.1–2.2% dry weight) and soluble carbohydrates (5.9 and 3.4% dry weight). In general, algae from Chile had similar energy levels and no obvious differences in organic content could be found.