Phycodrys Rubens Research Articles

A Warmer Arctic Compromises Winter Survival of Habitat-Forming Seaweeds

Continuous winter darkness at a latitude of 79°N was simulated in cultures of four species of Arctic seaweeds at 3 and 8°C. The laminarians Saccharina latissima and Alaria esculenta, and the rhodophytes Phycodrys rubens and Ptilota gunneri were monitored for 4 months in total darkness and after 1 week following light return in early spring, under controlled laboratory conditions. Biomass loss during darkness was enhanced by the high temperature in all species. At 8°C, the two laminarians were unable to resume growth upon re-illumination. Alaria esculenta showed new blade production by the end of the dark period, but only at 3°C. In all species, the photosynthetic ability was sustained, not suspended, during the whole dark period. P. rubens exhibited lower photosynthetic potential at 8°C than at 3°C during the darkness period, but it was able to recover its O2 evolving potential upon re-illumination, as P. gunneri and S. latissima did, but the latter only at 3°C. The reactivation of photosynthesis seemed to involve photosystem II over photosystem I, as 7 d of photoperiod after the prolonged darkness was not enough to fully recover the PAM-related photosynthetic parameters. Only small changes were recorded in the internal chemical composition (total C, total N, carbohydrates, proteins, and lipids), but species-specific differences were observed. Unlike subarctic areas with an operating photoperiod along the year, a warmer polar night might pose a limit to the ability of multi-year seaweeds to occupy the new ice-free illuminated areas of the Arctic coasts, so that newcomers will potentially be restricted to the spring-summer season.

A whole-plant specimen of the marine macroalga Pterigophycos from the Eocene of Bolca (Veneto, N-Italy)

Uncalcified macroalgae are generally rare as fossils, and hence their past diversity and evolutionary history remain poorly resolved. The Bolca area in northern Italy has yielded abundant adpression fossils of Eocene macroalgae. However, the vast majority of specimens are detached blades and blade portions. Here, we present an almost complete thallus of the macroalga Pterigophycos from Bolca that consists of a squat holdfast from which leaf-like blades up to 30 cm long extend. Each blade has a midrib extending over its entire length. Proximally the lamina forms a narrow rim on each side of the midrib, but becomes wider and lobed in the lower mid-portion. In the upper three quarters of the blade the lamina consists of spathulate or wedge-shaped segments. Pterigophycos blades have certain features in common with the present-day Phycodrys rubens, Delesseria sanguinea (both Ceramiales, Rhodophyta), Undaria pinnatifida, and Egregia menziesii (both Laminariales, Phaeophyceae); however, the systematic affinity of the fossil remains unresolved. The fossil is suggestive of intraspecific variability in blade morphology, and thus contests the historic view that there are several different species of Pterigophycos in the Bolca flora.

Transfer of the monospecific genus Nienburgella (Delesseriaceae, Rhodophyta) to Phycodrys, based on morphological and molecular evidence

The genus Phycodrys is characterized by having a Phycodrys-type apical organization, a well-developed central midrib with paired lateral veins, monostromatic areas between the veins, four-celled carpogonial branches with two groups of sterile cells, and a cystocarp with a large fusion cell and short-catenated carposporangia. In contrast, the monospecific genus Nienburgella has a faint midrib, a mostly polystromatic blade without lateral veins, bilaterally isometric second-order cell row length, and Phycodrys-like apical growth and cystocarp. Nothing is known about Nienburgella’s procarp. We collected several specimens of Nienburgella angusta from the East Sea of South Korea and noticed that they resemble Phycodrys radicosa. We compared these two species using morphological and molecular phylogenetic analyses. Our results revealed that both species are closely related to one another than to other taxa in the tribe Phycodryeae, and that Nienburgella angusta procarp developmental pattern is the same as the one observed in Phycodrys rubens, the generitype species of Phycodrys. Thallus structure (mono- or polystromatic) was species-delimiting but not genus-delimiting. Bilateral second-order cell row isometry occurs in other Phycodrys species, including the type species. Therefore, we propose transferring the species Nienburgella angusta as well as the monospecific genus Nienburgella to Phycodrys.

Glacial and depth influence on sublittoral macroalgal standing stock in a high-Arctic fjord

The motivation behind this study is the progression of global warming, which severely affects the entire Arctic and could have effects on macroalgal assemblages. Three sampling sites were located at different distances to glacier fronts to study the effect of glacial exposure on macroalgal community composition and standing stock. In addition, the variability between two depths (5 and 10 m) was investigated. The subtidal communities at each site and depth were dominated by brown macroalgae of the order Laminariales, which made up over 95% of the macroalgal biomass and at least 65% of the macroalgal abundance at each site. The mean macroalgal species richness and abundance were reduced at glacially impacted sites, but the differences were not statistically significant. The community structure based on abundance data varied between the clear and glacially exposed sites due to the higher abundances of Laminaria digitata, Phycodrys rubens and Alaria esculenta at the clear site and Saccharina latissima at the glacial sites. The biomass structure did not vary between sites. The kelp biomass distribution between depths was patchy and dependent on water properties. The maximum biomass was observed at the depth of 10 m at the clear site, while it was observed at shallower depths at the glacial sites. As deglaciation proceeds, new seabed areas are uncovered, and the number of ice-free days grows, creating favourable conditions for macroalgal expansion. However, due to increased turbidity close to the glacier fronts, decreases in species richness, abundance and biomass of macroalgae are likely to occur, as well as the reorganization of the community structure. Such changes may intensify with continued Arctic warming. The hypothesis about reduction of macrophyte abundance and biomass due to the glacial impact was not supported by our data.

Plant Part Age and Size Affect Sessile Macrobenthic Assemblages Associated with a Foliose Red Algae Phycodrys rubens in the White Sea

Facilitation by foundation species commonly structures terrestrial and marine communities. Intraspecific variation in individual properties of these strong facilitators can affect the whole suite of the dependent taxa. Marine macroalgae often act as ecosystem engineers, providing shelter and substrate for numerous associated organisms. Epibiosis of foliose red algae, however, remains underexplored, especially in the high latitudes. Here we studied sessile macrobenthic assemblages associated with a foliose red algae Phycodrys rubens in the White Sea (66° N) shallow subtidal, and the effect of individual plant properties on their structure. The blades of P. rubens develop annually, and it is possible to tell the young (usually larger) plant parts from the old ones. We hypothesized that epibenthic community structure depends on plant part age and size. We examined epibiosis on 110 plants at two sites, and the results generally supported our hypotheses. Old plant parts were several times smaller, and had higher total cover than young parts. Sponges strongly dominated the epibiosis on old parts, and young parts were dominated by polychaetes and bryozoans. Plant part surface area negatively correlated with total cover on young parts, while on old parts the relatioship was location-specific. On young parts the relative abundance of a polychaete Circeis armoricana increased with surface area, and the proportion of sponges decreased. The patterns indicate that epibenthic community structure is linked to the demography of an ecosystem engineer.

Diversity and structure of epibenthic communities of the red algae zone in the White Sea

At high latitudes, the marine transitional zone between the highly productive kelp communities and the devoid of vegetation deep-waters is occupied mainly by number of red algae species, both encrusting and cespitose, which associate with rich and diverse fauna. However, zoologists and botanists never scrutinized these communities in equal manner up to present. We investigated the transition red algae zone in the White Sea in summer 2016 and 2017 using scuba equipment. The photic depth is limited to 18–23 m at different locations. Sessile species prevail among 315 epibenthic organisms in species number ( ~ 80%) and biomass ( ~ 90%). Communities of the red algae zone are rich in species (from 54 to 177). The most distinct differences were observed between the communities of Kandalaksha and Onega Bays. Vertical heterogeneity of the red algae zone was revealed; at most locations, Rhodophyta predominate in the upper subzone and Cirripedia predominate in the lower parts of the red algae zone. At the investigated depths, shallow-water and deep-water sets of species were defined. Interspecific spatial interactions between sessile organisms are revealed: 72.2 ± 3.5% of them were recorded as epibionts, and 29.1 ± 2.5% were registered as basibionts. These interactions provide evidence of the increase of species diversity: 32.7 ± 6.8% of sessile taxa were recorded exclusively as epibionts. Algae Phycodrys rubens, Odonthalia dentata, and Coccotylus truncatus, ascidian Styela rustica, barnacles Balanus crenatus, Verruca stroemia, and polychaete Pista maculata are foundation species, each supporting multi-level suites (up to four levels) of dependent species.

Vegetation of the red algal belt of the White Sea (European Arctic, Russia)

In 2016–2018, during the summer period, the first detail studies of the red algal belt of the White Sea were carried out time with SCUBA diving at the Chupa Inlet, near the Cape Kartesh, and at the Kolvitsa Inlet (the Kandalaksha Bay), in the vicinity of Sonostrov Island (the White Sea Basin) and Bolshoy Zhuzhmuy Island (the Onega Bay). The upper boundary of the red algal belt lies at a depth of about 7 m, and the lower boundary, at a depth of about 20 m. In the White Sea, the algae distribution in the lower part of the photic zone depends on the geomorphological structure of the bottom and on the composition of the accompanying sedentary fauna, so the lower boundary may vary in the depth range from 14 down to 23 m. In total, 87 species of algae belonging to the three large taxonomic groups have been registered: Chlorophyta (13), Phaeophyceae (33), and Rhodophyta (41). Significant richness of the species composition, vertical zoning, and a variety of phytocoenoses of the red algal belt in different parts of the White Sea have been found. Phytocoenoses of the red algal belt refer to three associations: ass. Odonthalia dentata(–Pseudolithoderma extensum), ass. Phycodrys rubens+Coccotylus truncatus(–Pseudolithoderma extensum), and ass. Lithothamnion glaciale. Nineteen species of macrophytes were the most common and characteristic representatives of the red algal belt, including thirteen species of red algae, four species of brown algae, and two species of green algae. It has been found that abundant and characteristic species of the red algal belt have an additional edificatory function in the studied phytocoenoses, being the consorts that carry rich epiflora and form favorable conditions for increasing the species diversity of algae in the lower phytal zone. The observed rapid shrinkage of the depth range of the kelp and red algal belts, as well as the changes in the vertical distribution of some other algal species in the White Sea, require specific attention concerning altering of their habitat conditions.

Species composition and structure of macrophytobenthos in the lower part of the photic zone of the Kolvitsa inlet (Kandalaksha Bay, White Sea)

The Kolvitsa inlet of the Kandalaksha Bay is a poorly studied part of the White Sea. Sampling was carried out in intertidal and subtidal (using diving equipment) zones from 15 to 21 July 2016. Fifty species of macroalgae were found: 9 species of Chlorophyta, 18 species of Phaeophyceae, and 23 species of Rhodophyta. First records of Choreocolax polysiphoniae and Coccotylus hartzii in the Kandalaksha Bay are reported. The red algal zone at the Kolvitsa inlet extends at the depths from 7 to 17–18 m. Zonation and phytocoenoses with high species richness at the red algal belt were discovered. Community of Odonthalia dentata inhabits the depth of 7–8 m and includes 31 species of seaweeds with their average biomass 282.1 ± 37.6 g/m2; the height of vegetation is 20 cm; Coccotylus truncatus and Polysiphonia stricta are subdominants. Community of C. truncatus inhabits the depths from 8–9 to 11–12 m and includes 35 species of seaweeds with their average biomass 157.4 ± 92.2 g/m2; the height of vegetation is 10 cm; P. stricta, O. dentata and Phycodrys rubens are subdominants. Community of C. truncatus and P. rubens inhabits the depths from 11–12 to 14–15 m and includes 26 species of seaweeds with their average biomass 41.9 ± 1.1 g/m2; the height of vegetation is 5–6 cm; Euthora cristata is a subdominant. Few species of red cortical calcareous algae inhabit the depths from 15 to 18 m. Thirty two epiphytic algae were found. Secondary holdfasts on the erect filaments of Polysiphonia stricta were detected as a specific adaptation for attachment to basiphytes. Most of the epiphytes grow on three species mainly. C. truncatus may be considered as consorcium forming inside the phytocoenoses of the lower part of the photic zone because the biomass of its epiphytes is comparable with that of seaweeds on the ground in the same community.

Effects of simultaneous increase in temperature and ocean acidification on biochemical composition and photosynthetic performance of common macroalgae from Kongsfjorden (Svalbard)

Increased temperature and ocean acidification are two main factors threatening Arctic coastal ecosystems. To explore the consequences of increased average temperature and ocean acidification in Kongsfjorden, the performance of six common species of macroalgae, the chlorophyte Monostroma arcticum, the rhodophytes Phycodrys rubens, and Ptilota plumosa, and the phaeophytes Alaria esculenta, Desmarestia aculeata and Saccorhiza dermatodea, was tested after 9 days of culture at 4 and 10 °C in combination with current (ca. 390 ppmv) and future (1000 ppmv) levels of atmospheric CO2 under solar radiation in summer. Temperature affected mainly the photosynthetic performance as measured by PAM fluorescence, particularly the initial slope (α) of ETR curves, the light saturation parameter (E k ), and F v /F m values, as well as the protein content, especially in the phaeophytes. On the other hand, CO2 affected mainly the internal accumulation of carbohydrates and lipids. The C:N balance was largely unaffected. External carbonic anhydrase activity was not inhibited at high CO2, and nitrate reductase activity remained unaffected. The resulting growth rate was not altered by treatments in three out of the six species studied. On the other hand, P. rubens showed a positive effect of increasing temperature, D. aculeata was negatively influenced by CO2, and S. dermatodea was positively affected by CO2. Significant interactions between CO2 and temperature were found in 20 % of the analyses. Whether additive or synergistic, the co-occurrence of a higher temperature with other stressors such as elevated CO2 increases the probability of community changes by modifying the performance of these species.

Thermo-chemical behaviour and chemical product formation from Polar seaweeds during intermediate pyrolysis

Fundamental analytical pyrolysis studies of biomass from Polar seaweeds, which exhibit a different biomass composition than terrestrial and micro-algae biomass were performed via thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass-spectrometry (Py-GC/MS). The main reason for this study is the adaptation of these species to very harsh environments making them an interesting source for thermo-chemical processing for bioenergy generation and production of biochemicals via intermediate pyrolysis.Several macroalgal species from the Arctic region Kongsfjorden, Spitsbergen/Norway (Prasiola crispa, Monostroma arcticum, Polysiphonia arctica, Devaleraea ramentacea, Odonthalia dentata, Phycodrys rubens, Sphacelaria plumosa) and from the Antarctic peninsula, Potter Cove King George Island (Gigartina skottsbergii, Plocamium cartilagineum, Myriogramme manginii, Hymencladiopsis crustigena, Kallymenia antarctica) were investigated under intermediate pyrolysis conditions.TGA of the Polar seaweeds revealed three stages of degradation representing dehydration, devolatilization and decomposition of carbonaceous solids. The maximum degradation temperatures Prasiola crispa were observed within the range of 220–320°C and are lower than typically obtained by terrestrial biomass, due to divergent polysaccharide compositions. Biochar residues accounted for 33–46% and ash contents of 27–45% were obtained.Identification of volatile products by Py-GC/MS revealed a complexity of generated chemical compounds and significant differences between the species. A widespread occurrence of aromatics (toluene, styrene, phenol and 4-methylphenol), acids (acetic acid, benzoic acid alkyl ester derivatives, 2-propenoic acid esters and octadecanoic acid octyl esters) in pyrolysates was detected. Ubiquitous furan-derived products included furfural and 5-methyl-2-furaldehyde. As a pyran-derived compound maltol was obtained by one red algal species (P. rubens) and the monosaccharide d-allose was detected in pyrolysates in one green algal (P. crispa). Further unique chemicals detected were dianhydromannitol from brown algae and isosorbide from green algae biomass. In contrast, the anhydrosugar levoglucosan and the triterpene squalene was detected in a large number of pyrolysates analysed.

Specific epibacterial communities on macroalgae: phylogeny matters more than habitat

Epibacterial communities on thalli of the algal species Fucus serratus, Fucus vesiculo- sus, Laminaria saccharina, Ulva compressa, Delesseria sanguinea and Phycodrys rubens were analysed using 16S ribosomal RNA gene-based DGGE. Individuals of all species were collected in the Kiel Fjord (Baltic Sea) and in the rocky intertidal of Helgoland (North Sea). DGGE gels as well as cluster and multidimensional scaling analysis based on the DGGE band patterns of the epibacterial community showed significant differences between the epibacterial communities on the investigated algal species both in the Baltic and North Seas. Epibacterial communities differed less between regions than between host species, and were more similar on closely related host species. Results give the first evidence for lineage-specific bacterial associations to algal thalli. Furthermore, the results suggest that these algal species may control their epibiotic bacterial communities.

Assessing species richness of macrofauna associated with macroalgae in Arctic kelp forests (Hornsund, Svalbard)

Kelp beds support diverse and productive benthic coastal ecosystems and are often perceived as cold water analogs of tropical coral reefs, yet the levels of species richness in polar regions have remained largely unexplored. The present study aims to assess the magnitude of macrozoobenthic species richness associated with the macroalgae in an Arctic kelp forest. The study was conducted in Hornsund, a high latitude Arctic fjord off west Spitsbergen (76–77°N). A total of 403 samples (i.e., individual algae) were collected by scuba divers at three sites located along the fjord axis at varying depths (5–10 m). The most common invertebrate species and the sample species richness (mean 11.5 species per sample) were consistent among the most common algal species (Laminaria digitata, Saccharina latissima,Alaria esculenta, Desmarestia aculeta, Odonthalia dentata, Phycodrys rubens). Fauna associated with overstory kelps was concentrated on the holdfasts. A total of 208 species were identified; Bryozoa, Polychaeta and Hydrozoa yielded the highest numbers of species (70, 52 and 37, respectively). The non-parametric Chao2 estimator of true species richness gave an estimate of 259 species (with 95% confidence intervals from 234 to 308). Despite the high sampling effort, the total species richness was not captured. This may stem from the high level of rarity within the fauna associated with kelps; 38% of the species occurred only in one or two samples. The studied fauna was much less diverse than similar assemblages surveyed at lower latitudes. The high numbers of species and the common occurrence of colonial forms (Bryozoa, Hydrozoa) in the current study show that these taxa cannot be omitted in macrobenthic diversity surveys performed within kelp habitats.

Ultraviolet-B-Induced Cyclobutane-pyrimidine Dimer Formation and Repair in Arctic Marine Macrophytes¶

The significance of ultraviolet-B radiation (UVBR: 280–315 nm)–induced DNA damage as a stress factor for Arctic marine macrophytes was examined in the Kongsfjord (Spitsbergen, 78°55.5′N, 11°56.0′E) in summer. UVBR penetration in the water column was monitored as accumulation of cyclobutane-pyrimidine dimers (CPD) in bare DNA. This showed that UVBR transparency of the fjord was variable, with 1% depths ranging between 4 and 8 m. In addition, induction and repair kinetics of CPD were studied in several subtidal macrophytes obtained from the Kongsfjord (5–15 m). Surface exposure experiments demonstrated CPD accumulation in Palmaria palmata, Devaleraea ramentacea, Phycodrys rubens, Coccotylus truncatus and Odonthalia dentata. In artificial light, field collected material of P. palmata, D. ramentacea, P. rubens and Laminaria saccharina showed efficient CPD repair, with only 10% of the artificially induced CPD remaining after 5 h. No significant differences in repair rate were observed among these species. CPD repair was slower or absent in O. dentata, C. truncatus and Monostroma arcticum, indicating that fast repair mechanisms such as photolyase were not continuously expressed in these species. CPD repair rates were not directly related to the vertical distribution of algae in the water column and to the reported UV sensitivity of the examined species. Dosimeter incubations showed that maximal exposure to DNA damaging wavelengths was low for all examined species. Furthermore, most species collected below the 1% depth for DNA damage displayed efficient CPD repair, suggesting that UVBR-induced CPD currently impose a minor threat for mature stages of these species growing in the Kongsfjord, Spitsbergen.

Enzymatic defences against photooxidative stress induced by ultraviolet radiation in Arctic marine macroalgae

The activities of the antioxidant enzymes superoxide dismutase (SOD), glutathione reductase (GR), ascorbate peroxidase (APX) and catalase (CAT), as well as the content of the antioxidant compound ascorbic acid, were determined in five green, seven red and ten brown macroalgal species from the Kongsfjord (Spitsbergen, Svalbard, Norway). In general, higher antioxidant enzyme activities and a higher content of ascorbic acid were measured in green algae in comparison to red and brown algae. Species from the eulittoral and upper sublittoral (Acrosiphonia penicilliformis, Monostroma arcticum, Chaetomorpha linum, Chaetomorpha melagonium, Devaleraea ramentacea, Palmaria palmata) showed higher antioxidant enzyme activities compared to species from the lower sublittoral, indicating a more efficient biochemical protection in algae exposed to higher stress conditions in the field. The activity of GR was stimulated by artificial ultraviolet radiation in the green alga M. arcticum, and in the red algae Coccotylus truncatus and Phycodrys rubens after 84 h under continuous exposure. GR activity was even higher when the UV exposure was followed by incubation in darkness for 24 h, indicating a higher elimination rate of toxic oxygen radicals under these conditions. D. ramentacea, P. palmata and A. penicilliformis did not show any significant effect of UV radiation on CAT, APX and SOD activities after 8 days of culture under laboratory conditions. However, a significant reduction in activities of GR and SOD was observed in A. penicilliformis when solar UV radiation was cut off by selective filter foils in the field, indicating a lower oxidative stress in the absence of UV radiation. Overall, the ecological success of macroalgae in the eulittoral and upper sublittoral is supported by an enhanced oxygen-reactive scavenging system, allowing fast acclimation to the changes in environmental radiation conditions.

Long-term effects of ultraviolet radiation on growth and photosynthetic performance of polar and cold-temperate macroalgae

Long-term effects of artificial ultraviolet radiation (UV) and natural solar radiation on growth and photosynthetic activity, as measured by chlorophyll fluorescence, were investigated in 13 different polar and cold-temperate macroalgal species. Isolates of five different species from the Arctic and Antarctic were exposed to different light treatments of photosynthetically active radiation (PAR), PAR+UVA and PAR+UVA+UVB. Eight different species collected on the island of Helgoland, North Sea, Germany, were studied in the laboratory and under natural solar radiation conditions. Increase in fresh weight and changes in photosynthetic performance were monitored over a period of 3–4 weeks. The sublittoral polar species, particularly the Antarctic red algal species Gymnogongrus antarcticus and G. turquetii, the Arctic cold-temperate brown alga Alaria esculenta and, very drastically, the Arctic-endemic Laminaria solidungula, exhibited strong inhibiting effects of artificial UVB radiation on growth. In the cold-temperate sublittoral growth of the red algae Phycodrys rubens and, to a lesser extend, Membranoptera alata was substantially inhibited by UV radiation. In contrast, eulittoral species, e.g. Fucus serratus, did not show any differences in growth with respect to artificial irradiation conditions, with or without UV radiation. In the laboratory, some individuals of the green alga Codium fragile exhibited strong morphological changes of the whole thallus, particularly under UVB exposure. In the experimental outdoor set up, growth of most of the algal species was already inhibited by the full solar UV waveband, but, apart from Polyides rotundus, no additional UVB effect could be detected. Changes of in vivo fluorescence were not always consistent with the measurable changes in growth rate, indicating that physiological processes leading to an inhibition of growth may act independently of changes in photosynthetic activity. For the polar species, a general correlation between the natural vertical distribution in the field and the individual sensitivity towards UV radiation was indicated, while for eulittoral species from Helgoland no clear relationship was found. The obtained results show that measuring growth is a good ecological parameter to monitor long-term effects of UV radiation on single macroalgal species and the possible resulting changes of whole algal communities in coastal ecosystems.

Temperature dependence of UV radiation effects in Arctic and temperate isolates of three red macrophytes

The temperature dependence of UV effects was studied for Arctic and temperate isolates of the red macrophytes Palmaria palmata, Coccotylus truncatus and Phycodrys rubens. The effects of daily repeated artificial ultraviolet B and A radiation (UVBR: 280–320 nm, UVAR: 320–400 nm) treatments were examined for all isolates at 6, 12 and 18 °C by measuring growth, optimal quantum yield of PSII (Fv/Fm) and cyclobutane-pyrimidine dimer (CPD) accumulation. Furthermore, possible ecotypic differences in UV sensitivity between Arctic and temperate isolates were evaluated. Large species-specific differences in UV sensitivity were observed for all parameters: the lower subtidal species C. truncatus and P. rubens were highly sensitive to the UV treatments, whereas P. palmata, which predominantly occurs in the upper subtidal zone, was not affected by these treatments. Only minor differences were found between Arctic and temperate isolates, suggesting that no differences in UV sensitivity have evolved in these species. Relative growth rates were temperature-dependent, whereas species-specific UV effects on growth rates were relatively independent of temperature. In contrast, the species-specific decrease in Fv/Fm and its subsequent recovery were temperature-dependent in all species. UV effects on Fv/Fm were lower at 12 and 18 °C compared with 6 °C. In addition, UV effects on Fv/Fm decreased in the course of the experiment at all temperatures, indicating acclimation to the UV treatments. CPDs accumulated during the experiment in both isolates of P. rubens, whereas CPD concentrations remained low for the other two species. CPD accumulation appeared to be independent of temperature. The results suggest that summer temperatures occurring in temperate regions facilitate repair of UV-induced damage and acclimation to UV radiation in these algae compared with Arctic temperatures. Because the differences in UV effects on Fv/Fm, growth and CPD accumulation were relatively small over a broad range of temperatures, it was concluded that the influence of temperature on UV effects is small in these species.

Fatty acid composition of Arctic and Antarctic macroalgae: indicator of phylogenetic and trophic relationships

The fatty acid composition of 6 Arctic and 14 Antarctic macroalgae species (Rhodo- phyta, Phaeophyta and Chlorophyta) from Kongsfjorden (west Spitsbergen, Arctic) and King George Island (Antarctic Peninsula) was investigated. The macroalgae were cultivated in nutrient-enriched seawater at low temperatures (0 to 5°C) and light conditions similar to natural irradiance. The most abundant fatty acids in the Arctic and Antarctic Rhodophyta were generally 20:5(n-3) and 16:0. The Arctic Palmaria palmata and the Antarctic Audouinella purpurea were characterised by very high proportions of 20:5(n-3) (67.3 and 60.3%, respectively). Other important fatty acids were 16:1(n-7) and 20:4(n-6). Two species were dominated by 20:4(n-6) (Phycodrys rubens, 35.3% and Delesseria lancifolia, 31.1%). In Ptilota gunneri and Rhodymenia subantarctica, 16:1(n-7) accounted for 39.9 and 32.7%, respectively. In the Phaeophyta, the major polyunsaturated fatty acids were 18:4(n-3), 20:5(n-3) and 20:4(n-6) followed by 18:3(n-3) and 18:2(n-6). The principal saturated fatty acid was 16:0. A high percentage of the uncommon monounsaturated fatty acid 16:1(n-5) (11.1%) was found in Desmarestia muelleri sporophytes. Their gametophytes exhibited only traces of this component, but instead had double the amount of 18:2(n-6) and 18:3(n-3). The Arctic chlorophyte Prasiola crispa and the Antarctic Lambia antarctica had fatty acid compositions dominated by the polyunsaturated fatty acids 18:3(n-3) and 18:2(n-6). In L. antarctica, 18:1(n-7) was present at higher levels than 18:2(n- 6). The clear differences in fatty acid compositions of these 3 taxa are probably due to their different evolutionary position. The high proportions of 20:5(n-3) in the Rhodophyta reflect a 'marine'-like character and hence the phylogenetically oldest lineage. The Chlorophyta comprise the most 'mod- ern' group and this is supported by primarily C18 unsaturated fatty acids typical of the vegetative tissue of higher plants. The fatty acid composition of the Phaeophyta support their intermediate posi- tion. The clear differences between the macroalgal taxa, and also variations between species, make fatty acids a potential tracer for studies of food-web interactions.

Ultraviolet-B-induced cyclobutane-pyrimidine dimer formation and repair in Arctic marine macrophytes.

The significance of ultraviolet-B radiation (UVBR: 280-315 nm)-induced DNA damage as a stress factor for Arctic marine macrophytes was examined in the Kongsfjord (Spitsbergen, 78 degrees 55.5'N, 11 degrees 56.0'E) in summer. UVBR penetration in the water column was monitored as accumulation of cyclobutane-pyrimidine dimers (CPD) in bare DNA. This showed that UVBR transparency of the fjord was variable, with 1% depths ranging between 4 and 8 m. In addition, induction and repair kinetics of CPD were studied in several subtidal macrophytes obtained from the Kongsfjord (5-15 m). Surface exposure experiments demonstrated CPD accumulation in Palmaria palmata, Devaleraea ramentacea, Phycodrys rubens, Coccotylus truncatus and Odonthalia dentata. In artificial light, field collected material of P. palmata, D. ramentacea, P. rubens and Laminaria saccharina showed efficient CPD repair, with only 10% of the artificially induced CPD remaining after 5 h. No significant differences in repair rate were observed among these species. CPD repair was slower or absent in O. dentata, C. truncatus and Monostroma arcticum, indicating that fast repair mechanisms such as photolyase were not continuously expressed in these species. CPD repair rates were not directly related to the vertical distribution of algae in the water column and to the reported UV sensitivity of the examined species. Dosimeter incubations showed that maximal exposure to DNA damaging wavelengths was low for all examined species. Furthermore, most species collected below the 1% depth for DNA damage displayed efficient CPD repair, suggesting that UVBR-induced CPD currently impose a minor threat for mature stages of these species growing in the Kongsfjord, Spitsbergen.

Photosynthetic performance of Arctic macroalgae after transplantation from deep to shallow waters.

Transplantation experiments conducted in the Arctic Kongsfjord (Spitsbergen) in summer 1997 investigated the effects of various types of filtered natural radiation (solar, solar without UV-B, solar without UV-A/B) on photosynthesis of various macroalgae. Two brown algal species (Laminaria solidungula, Saccorhiza dermatodea) and four red algal species (Palmaria palmata, Phycodrys rubens, Phyllophora truncata, Ptilota plumosa) were collected from deeper waters, kept in UV-transparent plexiglass tubes wrapped with different spectral cut-off filter foils and positioned at fixed depths in shallow waters for 7-9days. At regular intervals, chlorophyll fluorescence of photosystem II (optimum quantum yield, F v/F m) was determined, as an indicator of photosynthetic performance. The data demonstrate that shallow-water species such as P. palmata are much less affected by natural photosynthetically active radiation (PAR) and UV radiation near the surface than extremely sensitive deep-water species such as Phyc. rubens which exhibited strong decreases in photosynthetic performance, as well as photobleaching of part of the thallus. The other species showed intermediate response patterns. In most species investigated inhibition of photosynthesis was mainly caused by the UV-B wavelengths. Interpretation of the data clearly indicates species-specific tolerances of photosynthesis to ambient solar radiation which can be explained by broad physiological acclimation potentials and/or genetic adaptation to certain (low or high) irradiances. The species-specific photosynthetic performance under radiation stress is in good accordance with the vertical distribution of the macroalgae on the shore.

EFFECTS OF UV‐B‐INDUCED DNA DAMAGE AND PHOTOINHIBITION ON GROWTH OF TEMPERATE MARINE RED MACROPHYTES: HABITAT‐RELATED DIFFERENCES IN UV‐B TOLERANCE

The sensitivity to UV‐B radiation (UVBR: 280–315 nm) was tested for littoral (Palmaria palmata[L.] O. Kuntze, Chondrus crispus Stackhouse) and sublittoral (Phyllophora pseudoceranoides S. G. Gmelin, Rhodymenia pseudopalmata[Lamouroux] Silva, Phycodrys rubens[L.] Batt, Polyneura hilliae[Greville] Kylin) red macrophytes from Brittany, France. Algal fragments were subjected to daily repeated exposures of artificial UVBR that were realistic for springtime solar UVBR at the water surface in Brittany. Growth, DNA damage, photoinhibition, and UV‐absorbing compounds were monitored during 2 weeks of PAR + UV‐A radiation (UVAR) + UVBR, whereas PAR + UVAR and PAR treatments were used as controls. The littoral species showed a higher UV tolerance than the sublittoral species. After 2 weeks, growth of P. palmata and C. crispus was not significantly affected by UVBR, and DNA damage, measured as the number of cyclobutane‐pyrimidine dimers per 106 nucleotides, was negligible. Photoinhibition, determined as the decline in optimal quantum yield, was low and decreased during the course of the experiment, coinciding with the production of UV‐absorbing compounds in these species. In contrast, no UV‐absorbing compounds were induced in the sublittoral species. Growth rates of P. pseudoceranoides and R. pseudopalmata were reduced by 40% compared with the PAR treatment. Additionally, constant levels of DNA damage and pronounced photoinhibition were observed after the UVBR treatments. Growth was completely halted for Phycodrys rubens and Polyneura hilliae, whereas DNA damage accumulated in the course of the experiment. Because Phycodrys rubens and Polyneura hilliae showed the same degree of photoinhibition as the other sublittoral species, it appears that the accumulation of DNA damage may have been responsible for the complete inhibition of growth. The results suggest an important role of DNA repair pathways in determining the UV sensitivity in red macrophytes.