Mycosporine-like amino acids (MAAs) profile of a rice-field cyanobacterium Anabaena doliolum as influenced by PAR and UVR

The mycosporine-like amino acid (MAA) profile of a rice-field cyanobacterium, Anabaena doliolum, was studied under PAR and PAR + UVR conditions. The high-performance liquid chromatographic analysis of water-soluble compounds reveals the biosynthesis of three MAAs, mycosporine-glycine (lambda (max) = 310 nm), porphyra-334 (lambda (max) = 334 nm) and shinorine (lambda (max) = 334 nm), with retention times of 4.1, 3.5 and 2.3 min, respectively. This is the first report for the occurrence of mycosporine-glycine and porphyra-334 in addition to shinorine in Anabaena strains studied so far. The results indicate that mycosporine-glycine (monosubstituted) acts as a precursor for the biosynthesis of the bisubstituted MAAs shinorine and porphyra-334. Mycosporine-glycine was under constitutive control while porphyra-334 and shinorine were induced by UV-B radiation, indicating the involvement of UV-regulated enzymes in the biotransformation of MAAs. It seems that A. doliolum is able to protect its cell machinery from UVR by synthesizing a complex set of MAAs and thus is able to survive successfully during the summer in its natural brightly lit habitats.     

MAA Synthesis and Accumulation in Polar Macroalgae are Controlled by Abiotic Factors

Mycosporine‐like amino acids (MAAs) are regarded as powerful sunscreens protecting the algae against harmful UV radiation. The MAA protection efficiency was tested in algal samples by measuring the optimum quantum yield of photosynthesis using photosystem II fluorescence. It could be demonstrated that the recovery of photosynthesis after exposure to enhanced UV radiation is faster in individuals with high MAA content. MAAs can be synthesized in several polar macroalgae in response to different radiation conditions. Although MAA induction patterns are very species‐specific, some similarities can be found. Field studies indicate that plants from different growth habitats providing distinct radiation climate can be grouped into three physiological categories depending on their MAA content. The first group (I) includes mainly deep‐water species, typically lacking MAAs. The second group (II), algal species found in a broad range of water depths (eu‐ and sublittoral), which are able to flexibly synthesize and accumulate MAAs. The third group (III) includes supra‐ and eulittoral taxa, which always contain high MAA concentrations. In laboratory studies, we showed that taxa of group II and III responded in three different ways based on MAA accumulation when exposed to different radiation conditions (PAR, PAR + UVA, PAR + UVA + UVB). Either they: (a) exhibit highest total MAA concentration under the full artificial spectrum; (b) increase their MAA concentration after exposure to PAR and PAR + UVA or (c) MAA concentration declines after exposure to the full spectrum. Our studies have indicated that when coupled with UVR, exposure to temperature fluctuations ranging from 0 to 10 °C also affect MAA biosynthesis.     

SYNTHESIS OF MYCOSPORINE-LIKE AMINO ACIDS IN CHONDRUS CRISPUS (FLORIDEOPHYCEAE) AND THE CONSEQUENCES FOR SENSITIVITY TO ULTRAVIOLET B RADIATION

The induction and protective role of the UV-absorbing compounds known as mycosporine-like amino acids (MAAs) were examined in sublittoral Chondrus crispus Stackh. transplanted for 2 weeks in the spring and summer to shallow water under three irradiance conditions: PAR (photosynthetically active radiation; 400–700 nm), PAR + UVA (PAR + 320– 400 nm), PAR + UVA + UVB (PAR + UVA + 280– 320 nm). Sublittoral thalli collected around Helgoland, North Sea, Germany, from 6 m below the mean low water of spring tides contained less than 0.1 mg·g⁻¹ dry weight (DW) total MAAs, whereas eulittoral samples contained over 1 mg·g⁻¹ DW. Transplantation to shallow water led to the immediate synthesis of three MAAs in the following temporal order: shinorine (λ_max 334 nm), asterina (λ_max 330 nm), and palythine (λ_max 320 nm), with the shinorine content peaking and then declining after 2 days (exposure to 100 mol photons·m⁻²). Maximum total MAA content (2 mg·g⁻¹ DW) also occurred after 2 days of induction, exceeding the content normally found in eulittoral samples. Furthermore, the relative proportion of the different MAAs at this time was different than that in eulittoral samples. After 2 days the total content declined to the eulittoral value, with palythine as the principal MAA. Similar data were obtained for all treatments, indicating that MAA synthesis in C. crispus was induced by PAR and not especially stimulated by UV radiation. The ability of photosystem II (PSII) to resist damage by UVB was tested periodically during the acclimation period by exposing samples to a defined UVB dose in the lab. Changes in chlorophyll fluorescence (F_v/F_m and effective quantum yield, φ_II) indicated that PSII function was inhibited during the initial stage of acclimation but gradually improved with time. No difference among screening treatments was detected except in spring for the samples acclimating to PAR + UVA + UVB. In this treatment F_v/F_m and φ_II were significantly lower than in the other treatments. During the first week of each experiment, growth rates were also significantly reduced by UVB. The reductions occurred despite maximum MAA content, indicating an incomplete protection of photosynthetic and growth-related processes.     

Natural ultraviolet radiation and photosynthetically active radiation induce formation of mycosporine-like amino acids in the marine macroalga Chondrus crispus (Rhodophyta)

The UV-absorbing mycosporine-like amino acids (MAAs) are hypothesized to protect organisms against harmful UV radiation (UVR). Since the physiology and metabolism of these compounds are unknown, the induction and kinetics of MAA biosynthesis by various natural radiation conditions were investigated in the marine red alga Chondrus crispus collected from Helgoland, Germany. Three photosynthetically active radiation (PAR, 400–700 nm) treatments without UVR and three UV-A/B (290–400 nm) treatments without PAR were given. Chondrus crispus collected from 4–6 m depth contained only traces of the MAA palythine. After 24 h exposure to 100% ambient PAR, traces of three additional MAAs, shinorine, palythinol and palythene, were detected, and their concentrations increased strongly during a one-week exposure to all PAR treatments. The concentration of all MAAs varied directly with PAR dose, with palythine and shinorine being four- to sevenfold higher than palythinol and palythene. Likewise, naturally high doses of both UV-A and UV-B resulted in a strong accumulation of all MAAs, in particular shinorine. While shinorine accumulation was much more stimulated by UVR, the content of all other MAAs was more affected by high PAR, indicating an MAA-specific induction triggered by UVR or PAR. Received: 24 September 1997 / Accepted: 17 December 1997     

Antarctic krill (Euphausia superba) acquire a UV-absorbing mycosporine-like amino acid from dietary algae

We hypothesised that Antarctic krill acquire UV-absorbing mycosporine-like amino acids (MAAs) from dietary algae, which produce MAAs in response to ultraviolet (UV) irradiation. To test this hypothesis, we grew cultures of Phaeocystis antarctica that had been grown under either photosynthetically active radiation (PAR, 400-750 nm) plus UV irradiation (UVR, 280-400 nm), or else PAR-only. Algae grown under PAR-only produced high concentrations of porphyra-334, whereas additional UVR caused formation of high concentrations of mycosporine-glycine:valine and lower concentrations of porphyra-334. Krill were fed with either of these two cultures on eight occasions over 63 days. A third group was starved for the duration of the experiment. Animals were analysed after 36 and 63 days for MAA content. Remaining animals from all treatments were starved for a further 35 days and analysed to examine MAA retention characteristics. Our findings are that krill acquired different MAAs from dietary algae depending on the light conditions under which the algae were grown. Specifically, krill fed algae grown under PAR-only had higher concentrations of porphyra-334 than starved krill. Conversely, krill fed algae grown under PAR with additional UVR had high body concentrations of mycosporine-glycine:valine. MAA concentrations in starved krill remained static throughout the experiment. However, long term starvation (35 days) caused levels of certain acquired MAAs to decline. From this we can infer that MAA concentrations in krill are dependent on the MAA content of phytoplankton, and therefore the algae's response to UV exposure. This has implications for transfer of MAAs through marine trophic webs.     

The effect of ultraviolet radiation on photosynthesis and ultraviolet-absorbing substances in the endemic Arctic macroalga Devaleraea ramentacea (Rhodophyta)

In field studies conducted at the Kongsfjord (Spitsbergen), the effect of filtered natural radiation conditions (solar without ulraviolet [UV]-A+UV-B, solar without UV-B, solar) on photosynthesis and the metabolism of UV-absorbing mycosporine-like amino acids (MAAs) in the marine red alga Devaleraea ramentacea have been studied. While solar treatment without UV-A+UV-B did not affect photosynthesis during the course of a day, solar without UV-B and the full solar spectrum led to a strong inhibition. However, after offset of the various radiation conditions, all algae fully recovered. Isolates collected from different depths were exposed in the laboratory to artificial fluence rates of photosynthetic active radiation (PAR), PAR+UV-A, and PAR+UV-A+UV-B. The photosynthetic capacity was affected in accordance with the original sampling depth, i.e. shallow-water isolates were more resistant than algae from deeper waters, indicating that D. ramentacea is able to acclimate to changes in irradiance. Seven different UV-absorbing MAAs were detected in this alga, namely mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol, and palythene. The total amount of MAAs continuously decreased with increasing collecting depth when sampled in mid June, and algae taken in late August from the same depths contained on average 30–45% higher MAA concentrations, indicating a seasonal effect as well. The presence of increasing MAA contents with decreasing depth correlated with a more insensitive photosynthetic capacity under both UV-A and UV-B treatments. Populations of D. ramentacea collected from 1 m depth, with one fully exposed to solar radiation and the other growing protected as understorey vegetation underneath the kelp Laminaria saccharina, exhibited quantitatively different MAA compositions in the apices. The exposed seaweeds contained 2.5-fold higher MAA values compared with the more shaded algae. Moreover, the exposed isolates showed a strong tissue gradient in MAAs, pigments, and proteins. The green apices contained 5-fold higher MAA contents than the red bases. Transplantation of D. ramentacea from 2 m depth to the surface induced the formation and accumulation of MAAs after 1 week exposure to the full solar spectrum. Control samples which were treated with the solar spectrum without UV-A+B or with solar without UV-B showed unchanged MAA contents, indicating a strong UV-B effect on MAA metabolism. All data well supported the suggested physiological function of MAAs as natural UV sunscreens in macroalgae.     

UV‐radiation effects on photosynthesis and photoprotection in gametophytic and sporophytic stages of the freshwater red alga Kumanoa ambigua (Rhodophyta,Batrachospermales)

The aim of this study was to analyze the photosynthetic performance of gametophytic and sporophytic (‘Chantransia’) stages of Kumanoa ambigua in culture under UV radiation. We hypothesized that both life history stages of K. ambigua would exhibit different photosynthetic responses to UVR exposure. Experiments were performed under three conditions: (i) photosynthetically active radiation (PAR) only (400–700 nm), P control; (ii) PAR + UVA (320–700 nm), PA treatment; and (iii) PAR + UVA + UVB (280–700 nm), PAB treatment. The photosynthetic parameters were measured as in vivo chlorophyll a fluorescence. Differences were found between life stages, observing higher values of NPQ and effective quantum yields (ΔF/F_m′) under UVA and PAR in gametophytes compared to sporophytes. One type of mycosporine‐like amino acid (MAA) was detected in the gametophyte in all treatments, but not in the ‘Chantransia’ stage. The increased photosynthetic performance for some parameters and the presence of MAA in gametophyte suggest that it is less sensitive to UV radiation, particularly UVA, in comparison to sporophyte under culture conditions. This approach is relevant for a better understanding of the adaptation and physiological acclimation of freshwater Rhodophyta to varying light climates in terms of global changes.     

Responses of Antarctic Iridaea cordata (Rhodophyta) tetraspores exposed to ultraviolet radiation

In Antarctica ozone depletion is highest during spring, coinciding with the reproduction of many seaweed species. Propagules are the life-stage of an alga most susceptible to environmental perturbations. Therefore, fertile thalli of Iridaea cordata (Turner) Bory (Rhodophyta) were collected in the eulittoral of King George Island (Antarctica) to examine spore susceptibility to ultraviolet radiation (UVR). In the laboratory, freshly released tetraspores were exposed to photosynthetically active radiation (PAR) (400–700 nm), PAR+UV-A (320–700 nm) or PAR+UV-A+UV-B (280–700 nm). Photosynthetic efficiency was measured during 1–8 h of exposure and after 48 h of recovery. Additionally, mycosporine-like amino acids (MAAs) and DNA damage were determined. Saturating irradiance of photosynthesis of freshly released tetraspores was 57 µmol photons m⁻² s⁻¹. Exposure to increasing fluence of PAR reduced photosynthetic efficiency. UVR further decreased the photosynthetic efficiencies of the tetraspores but spores were able to recover completely after UVR exposure and 2 days post-cultivation under low PAR. DNA damage was minimal and lesions were effectively repaired under photoreactivating light. Concentrations of the MAAs shinorine and palythine were higher in tetraspores treated with UVR than in spores only exposed to PAR. Generally, the tetraspores show a good UV tolerance. This flexible response of the tetraspores of this species to changing radiation conditions enables the alga to grow along a considerable depth gradient from the sublittoral to the eulittoral where they can be exposed to enhanced UVBR under conditions of stratospheric ozone depletion.     

Porphyra-334, a potential natural source for UVA protective sunscreens.

The mycosporine-like amino acid (MAA), porphyra-334 (lambda(max) = 334 nm; epsilon = 42,300 M(-1) cm(-1)), was isolated from the aquatic cyanobacterium Aphanizomenon flos-aquae (AFA) and its structure was verified by spectroscopic methods. The UVA absorption properties of the crude methanolic extract were determined against two commercial sun care products in terms of mean critical wavelength, mean UVA/UVB ratios and UVA protection category (Boots the Chemists, Ltd.). The crude methanolic extract from AFA exhibited maximum UVA protection comparable to that determined for Boots SPF 4.     

Differential responses of tetrasporophytes and gametophytes of Mazzaella laminarioides (Gigartinales,Rhodophyta) under solar UV radiation

The effects of solar UV radiation on mycosporine‐like amino acids (MAAs), growth, photosynthetic pigments (Chl a, phycobiliproteins), soluble proteins (SP), and C and N content of Mazzaella laminarioides tetrasporophytes and gametophytes were investigated. Apical segments of tetrasporophytes and gametophytes were exposed to solar radiation under three treatments (PAR [P], PAR+UVA [PA], and PAR+UVA+UVB [PAB]) during 18 d in spring 2009, Punta Arenas, Chile. Samples were taken after 2, 6, 12, and 18 d of solar radiation exposure. Most of the parameters assessed on M. laminarioides were significantly influenced by the radiation treatment, and both gametophytes and tetrasporophytes seemed to respond differently when exposed to high UV radiation. The two main effects promoted by UV radiation were: (i) higher synthesis of MAAs in gametophytes than tetrasporophytes at 2 d, and (ii) a decrease in phycoerythrin, phycocyanin, and SPs, but an increase in MAA content in tetrasporophytes at 6 and 12 d of culture. Despite some changes that were observed in biochemical parameters in both tetrasporophytes and gametophytes of M. laminarioides when exposed to UVB radiation, these changes did not promote deleterious effects that might interfere with the growth in the long term (18 d). The tolerance and resistance of M. laminarioides to higher UV irradiance were expected, as this intertidal species is exposed to variation in solar radiation, especially during low tide.     

Ultraviolet-B Wavelengths Regulate Changes in UV Absorption of Cleaner Fish Labroides dimidiatus Mucus

High-energy wavelengths in the ultraviolet-B (UVB, 280-315 nm) and the UVA (315-400-nm) portion of the spectrum are harmful to terrestrial and aquatic organisms. Interestingly, UVA is also involved in the repair of UV induced damage. Organisms living in shallow coral reef environments possess UV absorbing compounds, such as mycosporine-like amino acids, to protect them from UV radiation. While it has been demonstrated that exposure to UV (280-400 nm) affects the UV absorbance of fish mucus, whether the effects of UV exposure vary between UVB and UVA wavelengths is not known. Therefore, we investigated whether the UVB, UVA, or photosynthetically active radiation (PAR, 400-700 nm) portions of the spectrum affected the UV absorbance of epithelial mucus and Fulton’s body condition index of the cleaner fish Labroides dimidiatus. We also compared field-measured UV absorbance with laboratory based high-performance liquid chromatography measurements of mycosporine-like amino acid concentrations. After 1 week, we found that the UV absorbance of epithelial mucus was higher in the UVB+UVA+PAR treatment compared with the UVA+PAR and PAR only treatments; after 2 and 3 weeks, however, differences between treatments were not detected. After 3 weeks, Fulton’s body condition index was lower for fish in the UVB+UVA+PAR compared with PAR and UVA+PAR treatments; furthermore, all experimentally treated fish had a lower Fulton’s body condition index than did freshly caught fish. Finally, we found a decrease with depth in the UV absorbance of mucus of wild-caught fish. This study suggests that the increase in UV absorbance of fish mucus in response to increased overall UV levels is a function of the UVB portion of the spectrum. This has important implications for the ability of cleaner fish and other fishes to adjust their mucus UV protection in response to variations in environmental UV exposure.     

EFFECTS OF ULTRAVIOLET‐A RADIATION AND NUTRIENT AVAILABILITY ON THE CELLULAR COMPOSITION OF PHOTOPROTECTIVE COMPOUNDS IN GLENODINIUM FOLIACEUM (DINOPHYCEAE)1

The photoprotective response in the dinoflagellate Glenodinium foliaceum F. Stein exposed to ultraviolet‐A (UVA) radiation (320–400 nm; 1.7 W · m²) and the effect of nitrate and phosphate availability on that response have been studied. Parameters measured over a 14 d growth period in control (PAR) and experimental (PAR + UVA) cultures included cellular mycosporine‐like amino acids (MAAs), chls, carotenoids, and culture growth rates. Although there were no significant effects of UVA on growth rate, there was significant induction of MAA compounds (28 ± 2 pg · cell^?1) and a reduction in chl a (9.6 ± 0.1 pg · cell^?1) and fucoxanthin (4.4 ± 0.1 pg · cell^?1) compared to the control cultures (3 ± 1 pg · cell^?1, 13.3 ± 3.2 pg · cell^?1, and 7.4 ± 0.3 pg · cell^?1, respectively). In a second investigation, MAA concentrations in UVA‐exposed cultures were lower when nitrate was limited (P < 0.05) but were higher when phosphate was limiting. Nitrate limitation led to significant decreases (P < 0.05) in cellular concentration of chls (chl c₁, chl c₂, and chl a), but other pigments were not affected. Phosphate availability had no effect on final pigment concentrations. Results suggest that nutrient availability significantly affects cellular accumulation of photoprotective compounds in G. foliaceum exposed to UVA.     

Living in the intertidal zone - seasonal effects on heterosides and sun-screen compounds in the red alga Bangia atropurpurea (Bangiales)

The seasonal patterns of daylength and ultraviolet radiation (UVB and UVA) at Williamstown, Victoria, Australia were measured (October 1995-May 1996) and are considered in relation to levels of heterosides (soluble sugar compounds: D-isofloridoside, floridoside and L-isofloridoside) and sun-screen compounds (mycosporine-like amino acids: MAAs) in the intertidal red alga Bangia atropurpurea. UVB peaked in December-January at 2.2-2.4 W m(-2) and UVA also peaked at 70 W m(-2) in the same period. Total heteroside concentrations were highest (1230-1900 mmol kg(-1) dry weight) during November-December with floridoside and D-isofloridoside being 90% of the total. In late February through mid-April total heteroside contents were lower (315-905 mmol kg(-1) dry weight) with L-floridoside being as much as 34% of the total indicating a seasonal effect. Total MAAs varied from 3.4 to 7.1 mg g(-1) dry weight (mean 4.9 mg g(-1) dry weight) with both highest and lowest levels occurring in February. Porphyra-334 constituted 83 to 97% of this total with asterina-330, palythine and palythinol being 3-17%. Although maximum MAA concentrations did not show any significant parallel with the peak UV values, the quantitative data point to Bangia cells over the course of the seasons always loaded up with these photoprotective compounds.     

The relative contributions of diet and associated microbiota to the accumulation of UV‐absorbing mycosporine‐like amino acids in the freshwater copepod Boeckella antiqua

1. Mycosporine‐like amino acids (MAAs) are ubiquitous compounds in aquatic organisms that are usually considered sunscreens that protect them from harmful ultraviolet radiation. Given that virtually all animals lack the metabolic pathways to synthesise MAAs de novo, they must acquire them either from their diet or from microorganisms living in close association. In freshwater copepods, accumulation of MAAs is stimulated by exposure to ultraviolet and/or visible radiation. 2. A 2 × 2 factorial experiment was performed to assess the contributions of dietary and microbial sources of MAAs in the freshwater copepod Boeckella antiqua. The treatments consisted of two different diets: an MAA‐free diet, including only Chlamydomonas reinhardtii, and an MAA‐rich diet, including both C. reinhardtii and Peridinium inconspicuum, crossed with two antibiotic treatments, with and without chloramphenicol. Treatment with chloramphenicol was intended to inhibit the development of bacteria associated with the copepods. 3. MAA concentration in B. antiqua was affected by the experimental conditions: (i) exposure to artificial PAR + UVR stimulated the accumulation of several MAAs (up to 62% increase in total MAA concentration with respect to the initial concentration); (ii) the presence of chloramphenicol in the culture media reduced the MAA concentration in copepods fed an MAA‐free diet; (iii) in the absence of chloramphenicol, copepods fed the MAA‐rich diet had significantly higher total MAA concentration than those fed the MAA‐deficient diet; but (iv) dietary supplementation with an MAA‐rich algae in the presence of chloramphenicol failed to significantly increase total MAA concentration. 4. Analysis of profiles from denaturing gradient gel electrophoresis (DGGE) showed that the prokaryotic community associated with the copepods was affected by chloramphenicol. Dendograms constructed from digitalised DGGE images consistently grouped the antibiotics treatments separately from the initial samples and the treatments without antibiotics. Two band positions were exclusive to treatments without antibiotics. 5. We conclude that when offered an MAA‐rich diet, B. antiqua may accumulate a proportion of MAAs from diet. However, we suspect that in the absence of an MAA‐rich dietary source (as in its natural habitat), virtually all MAAs present in B. antiqua are produced by copepod‐associated prokaryotes.     

SENSITIVITY OF ANTARCTIC UROSPORA PENICILLIFORMIS (ULOTRICHALES,CHLOROPHYTA) TO ULTRAVIOLET RADIATION IS LIFE‐STAGE DEPENDENT1

The sensitivity of different life stages of the eulittoral green alga Urospora penicilliformis (Roth) Aresch. to ultraviolet radiation (UVR) was examined in the laboratory. Gametophytic filaments and propagules (zoospores and gametes) released from filaments were separately exposed to different fluence of radiation treatments consisting of PAR (P = 400–700 nm), PAR + ultraviolet A (UVA) (PA, UVA = 320–400 nm), and PAR + UVA + ultraviolet B (UVB) (PAB, UVB = 280–320 nm). Photophysiological indices (ETR_max, E_k, and α) derived from rapid light curves were measured in controls, while photosynthetic efficiency and amount of DNA lesions in terms of cyclobutane pyrimidine dimers (CPDs) were measured after exposure to radiation treatments and after recovery in low PAR; pigments of propagules were quantified after exposure treatment only. The photosynthetic conversion efficiency (α) and photosynthetic capacity (rETR_max) were higher in gametophytes compared with the propagules. The propagules were slightly more sensitive to UVB‐induced DNA damage; however, both life stages of the eulittoral inhabiting turf alga were not severely affected by the negative impacts of UVR. Exposure to a maximum of 8 h UVR caused mild effects on the photochemical efficiency of PSII and induced minimal DNA lesions in both the gametophytes and propagules. Pigment concentrations were not significantly different between PAR‐exposed and PAR + UVR–exposed propagules. Our data showed that U. penicilliformis from the Antarctic is rather insensitive to the applied UVR. This amphi‐equatorial species possesses different protective mechanisms that can cope with high UVR in cold‐temperate waters of both hemispheres and in polar regions under conditions of increasing UVR as a consequence of further reduction of stratospheric ozone.     

UVR defense mechanisms in eurytopic and invasive Gracilaria vermiculophylla (Gracilariales, Rhodophyta)

The invasive success of Gracilaria vermiculophylla has been attributed to its wide tolerance range to different abiotic factors, but its response to ultraviolet radiation (UVR) is yet to be investigated. In the laboratory, carpospores and vegetative thalli of an Atlantic population were exposed to different radiation treatments consisting of high PAR (photosynthetically active radiation) only (P), PAR+UV-A (PA) and PAR+UV-A+UV-B (PAB). Photosynthesis of carpospores was photoinhibited under different radiation treatments but photosystem II (PSII) function was restored after 12 h under dim white light. Growth of vegetative thalli was significantly higher under radiation supplemented with UVR. Decrease in chlorophyll a (Chl a) under daily continuous 16-h exposure to 300 μmol photons m(-2) s(-1) of PAR suggests preventive accumulation of excited chlorophyll molecules within the antennae to minimize the generation of dangerous reactive oxygen species. Moreover, an increase in total carotenoids and xanthophyll cycle pigments (i.e. violaxanthin, antheraxanthin and zeaxanthin) further suggests effective photoprotection under UVR. The presence of the ketocarotenoid β-cryptoxanthin also indicates protection against UVR and oxidative stress. The initial concentration of total mycosporine-like amino acids (MAAs) in freshly-released spores increased approximately four times after 8-h laboratory radiation treatments. On the other hand, initial specific MAAs in vegetative thalli changed in composition after 7-day exposure to laboratory radiation conditions without affecting the total concentration. The above responses suggest that G. vermiculophylla have multiple UVR defense mechanisms to cope with the dynamic variation in light quantity and quality encountered in its habitat. Beside being eurytopic, the UVR photoprotective mechanisms likely contribute to the current invasive success of the species in shallow lagoons and estuaries exposed to high solar radiation.     

AMMONIUM AND UV RADIATION STIMULATE THE ACCUMULATION OF MYCOSPORINE‐LIKE AMINO ACIDS IN PORPHYRA COLUMBINA (RHODOPHYTA) FROM PATAGONIA,ARGENTINA1

The combined effects of ammonium concentration and UV radiation on the red alga Porphyra columbina (Montagne) from the Patagonian coast (Chubut, Argentina) was determined using short‐term (less than a week) experimentation. Discs of P. columbina were incubated with three ammonium concentrations (0, 50, and 300 μM NH₄Cl) in anilluminated chamber (PAR=300 μmol photons·m^?2·s^?1, UVA=15 W·m^?2, UVB=0.7 W·m^?2) at 15°C. Algae incubated at 300 μM ammonium showed a significant increase (P<0.05) in the concentration of mycosporine‐like amino acids (MAAs) compared with the initial value or with the other ammonium treatments. The increase of MAAs was, however, a function of the quality of irradiance received, with a higher increase in samples exposed to UVA compared with UVB (29% and 5% increase, respectively). However, UVB radiation was more effective in inducing MAA synthesis per unit energy received by the algae. Samples exposed to PAR only had an intermediate increase in MAA concentration of 16%. Chl a concentration decreased through the incubation with the greatest decrease at high ammonium concentration. Phycobiliprotein (BP) decreased through time with the smallest decrease occurring at high ammonium concentration. Photoinhibition (as a decrease of optimal quantum yield) was significantly greater under nitrogen‐deprived conditions than that under replete ammonium levels. Maximal gross photosynthesis (GP_max), as oxygen evolution, and maximal electron transport rate (ETR_max), as chl fluorescence, increased with the ammonium concentration. Positive relationships between maximal GP or ETR and pigment ratios (BP/chl a and MAAs/chl a) and negative relationships with chl a concentration were found.     

Eye function of Mysidacea (Crustacea) in the northern Baltic Sea

Eye spectral sensitivity, [S(lambda)], was measured in seven northern Baltic mysid species using an electroretinogram technique. Their S(lambda) curves were compared with the spectral distribution of underwater light at their normal habitats. In the littoral species Neomysis integer, Praunus flexuosus and Praunus inermis, the S(lambda) maxima, [S(lambda)(max)], were in the wavelength-bands of 525-535, 505-515 and 520-530 nm respectively. The neoimmigrant species Hemimysis anomala had a S(lambda)(max) around 500 nm and high sensitivity at 393 nm, possibly indicating UV-sensitivity. S(lambda) of the pelagic species Mysis mixta and Mysis relicta sp. II was at about 505-520 nm. M. relicta sp. I from Pojoviken Bay and fresh water humic Lake P??j?rvi had S(lambda)(max) at approximately 550 nm and 570 nm respectively. This is in accordance with a similar long-wavelength shift in light transmittance of the respective waters. The eyes of the latter population were also damaged by strong light. The pontocaspian neoimmigrant H. anomala is clearly adapted to waters transmitting more blue light.     

Distribution of Mycosporine-Like Amino Acids Along a Surface Water Meridional Transect of the Atlantic

The composition and abundance of mycosporine-like amino acids (MAAs) were investigated in the surface waters along a 13,000-km meridional transect (52° N to 45° S) in the Atlantic Ocean (Atlantic Meridional Transect programme: Cruise AMT 18: 4/10/2008-10/11/2008). MAAs were ubiquitous along the transect, although the composition of the MAAs was variable. Highest concentrations were in the far south (below 40° S; MAA >1 μg L(-1)) and in north subtropical equatorial region (NER: 0-25° N; MAA up to 0.8 μg L(-1)). Highest MAA relative to chlorophyll-a occurred in the NER (MAA/chl-a ratio between 2 and 5). MAA/chl-a significantly correlated with the preceding month's mean daily UV dose and with UV-B/UV-A. In the far south, high MAA concentrations coincided with high phytoplankton biomass, high nutrients and a deep mixed layer associated with the austral spring. Here, the phytoplankton community was dominated by micro- and nano-eukaryotes. At the NER, the high MAA/chl-a coincided with low nutrient concentrations, a shallow mixed layer depth (20-70 m) and to a lesser extent to a shallow nitracline (40-90 m). Here, the phytoplankton consisted primarily of picophytoplankton (0-0.2 μm), dominated by the pico-cyanobacteria Synechococcus sp. and Prochlorococcus sp. and by the nitrogen fixing filamentous cyanobacterium Trichodesmium. The low nitrate concentrations (<0.1 μmol L(-1)) at the NER suggest that nitrogen fixation was required for MAA production. Specific MAAs could not easily be assigned to particular groups of phytoplankton and we could not rule out the possibility that MAAs were associated with symbiotic cyanobacteria contained within heterotrophic dinoflagellates or diatoms.     

Differences in photoprotective pigment production between Japanese and Australian strains of Chattonella marina (Raphidophyceae)

Previous studies have shown that isolates of Chattonella marina from Australia and Japan exhibit differences in tolerance to high intensities of visible light. Here we show that the Australian strain of C. marina produces around five times more UV-absorbing mycosporine amino acids (MAAs) than the Japanese strain. This corresponds with 66% increased growth by the Australian strain under UVB exposure compared to no UV exposure. The MAA mycosporine-glycine, which reportedly acts as an antioxidant, was found in high quantity (110 fg cell^-1) in the Australian but was absent in the Japanese strain. In contrast, changes in the concentration of violaxanthin and zeaxanthin per cell were 4.7-4.8 times greater in the Japanese relative to the Australian strain suggesting that the Japanese strain uses a xanthophyll cycle to moderate inhibition by high photosynthetically active radiation (PAR) irradiance. Increased MAA production under high irradiance was also observed in other Australian strains of Chattonella, but not noted in other Japanese strains suggesting ecophenotypic adaptation due to differing environmental conditions.