Production Of Mycosporine-like Amino Acids Research Articles

Effect of UV-B Radiation and Desiccation Stress on Photoprotective Compounds Accumulation in Marine Leptolyngbya sp.

Increased awareness regarding the harmful effects of ultraviolet (UV)-B radiation has led to the search for new sources of natural UV-B protecting compounds. Mycosporine-like amino acids are one of such promising compounds found in several organisms. Cyanobacteria are ideal organisms for isolation of these compounds due to their compatibility and adaptability to thrive under harsh environmental conditions. In the following investigation, we report the production of shinorine in Leptolyngbya sp. isolated from the intertidal region. Based on the spectral characteristics and liquid chromatography-mass spectrometry analysis, the UV-absorbing compound was identified as shinorine. To the best of our knowledge, this is the first report on the occurrence of shinorine in Leptolyngbya sp. We also investigated the effect of artificial UV-B radiation and periodic desiccation on chlorophyll-a, total carotenoids, and mycosporine-like amino acids (MAAs) production. The UV-B radiation had a negative effect on growth and chlorophyll concentration, whereas it showed an inductive effect on the production of total carotenoids and MAAs. Desiccation along with UV-B radiation led to an increase in the concentration of photoprotective compounds. These results indicate that carotenoids and MAAs thus facilitate cyanobacteria to avoid and protect themselves from the deleterious effects of UV-B and desiccation.

Production of Mycosporine-Like Amino Acids from Gracilaria vermiculophylla (Rhodophyta) Cultured Through One Year in an Integrated Multi-trophic Aquaculture (IMTA) System.

This study evaluates the production of biomass and mycosporine-like amino acids (MAAs) throughout the year in Gracilaria vermiculophylla (Rhodophyta) collected in Ria de Aveiro (Portugal). The algae were grown in outdoor tanks in seawater with the addition of fishpond effluents under two different water flows (100 and 200Lh-1) in an integrated multi-trophic aquaculture (IMTA) system (tanks 1200L; 1.5m2) and different algal densities (3, 5, and 7kgm-2). MAA content in IMTA seaweeds was significantly affected by the interaction of time and stocking density, but not by the water flow. The highest MAA content was observed in April (about 3.13mgg-1 DW) followed by May (1.79mgg-1 DW). Seaweed biomass productivity was higher in May (372.06gDWm-2week-1) than in April (353.40gDWm-2week-1). Four MAAs were identified by HPLC and electrospray ionization mass spectrometry (ESI-MS) in G. vermiculophylla: Porphyra-334, Shinorine, Palythine and Asterina-330. The highest levels of Porphyra-334 and Shinorine were reached from November to January and the Palythine + Asterina-330 from April to August. Taking into account the average biomass and MAA production of G. vermiculophylla growing in this IMTA system (8.56g of MAA in 18m2 culture along 8months; 35.5% produced in April), a total amount of 71.33gMAAyear-1 could be produced in this system by scaling up to 100m2. MAAs could be further used as photoprotector and antioxidant compounds in cosmetic products.

Spring production of mycosporine-like amino acids and other UV-absorbing compounds in sea ice-associated algae communities in the Canadian Arctic

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 541:91-104 (2015) - DOI: https://doi.org/10.3354/meps11540 Spring production of mycosporine-like amino acids and other UV-absorbing compounds in sea ice-associated algae communities in the Canadian Arctic Ashley Elliott1, C. J. Mundy1, Michel Gosselin2, Michel Poulin3, Karley Campbell1, Feiyue Wang1,* 1Center for Earth Observation Science, Department of Environment and Geography, University of Manitoba, Winnipeg, MB R3T 2N2, Canada 2Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski, Rimouski, QC G5L 3A1, Canada 3Research and Collections Division, Canadian Museum of Nature, Ottawa, ON K1P 6P4, Canada *Corresponding author: feiyue.wang@umanitoba.ca ABSTRACT: Marine phytoplankton are known to produce mycosporine-like amino acids (MAAs) for protection against UV radiation. To assess whether the same strategy applies to sea ice-associated communities, MAAs were measured in algal communities associated with surface melt ponds, sea ice (bottom 3 cm), sea ice-water interface below melt ponds, and underlying seawater in a coastal bay of the Canadian Arctic Archipelago during the spring melt transition from snow-covered to melt pond-covered sea ice. Six UV-absorbing compounds (UVACs) were detected as the spring melt progressed, 3 of which are identified to be shinorine, palythine, and porphyra-334. A fourth UVAC (U1) is most likely palythene. The molecular identities of the other 2 UVACs, U2 and U3, which have an absorption maximum of 363 and 300 nm, respectively, remain to be structurally elucidated. The highest UVAC nominal concentrations were observed in the 3 cm bottom ice under thin snow-covered sites just prior to complete snowmelt. Normalization to chlorophyll a content revealed that the greatest contribution to UV absorption from biota was associated with melt ponds that are exposed to the highest light intensity. These results confirm that Arctic sea ice-associated communities are capable of producing photoprotectants and that spatial and temporal variations in MAA and other UVAC synthesis are affected by snow cover and UV radiation exposure. KEY WORDS: Mycosporine-like amino acids · Sea ice community · Ultraviolet radiation · Photoprotection · Arctic Ocean · Algae Full text in pdf format PreviousNextCite this article as: Elliott A, Mundy CJ, Gosselin M, Poulin M, Campbell K, Wang F (2015) Spring production of mycosporine-like amino acids and other UV-absorbing compounds in sea ice-associated algae communities in the Canadian Arctic. Mar Ecol Prog Ser 541:91-104. https://doi.org/10.3354/meps11540 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 541. Online publication date: December 15, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Effects of Light and Salinity Stresses in Production of Mycosporine-Like Amino Acids by Gymnodinium catenatum (Dinophyceae).

Mycosporine-like amino acids (MAAs) were analyzed in a Portuguese Gymnodinium catenatum strain when transferred to high salinity and high light conditions. Total MAA concentrations increased progressively between 30 and 36 psu, attaining at 36 psu 2.9-fold the 30 psu treatment. When abruptly transferred to solar light in an outdoor shadowed location, MAA concentration increased steadily along the day for most compounds. After 8h, mycosporine-glycine, palythene and M-319 attained or surpassed 25-fold their initial concentration, while M-370 only attained 4-fold concentration. When transferred from halogen to fluorescent light, polar MAAs such as shinorine and porphyra-334, increased until day two and then declined, while M-370 increase slowly, becoming the dominant compound from the profile after 1week. These experiments put into evidence the relation of palythene with M-319, which was further identified as its acid degradation product, palythine. Acid degradation of M-370 originated M-324, while M-311 seems to be the precursor of M-370. Under high salinity and high light conditions chain formation was altered toward shorter chains or solitary cells. This alteration can represent a morphological stress sign, which in the natural environment could affect average population speed during daily vertical migrations.

O-Methyltransferase is shared between the pentose phosphate and shikimate pathways and is essential for mycosporine-like amino acid biosynthesis in Anabaena variabilis ATCC 29413.

The parent core structure of mycosporine-like amino acids (MAAs) is 4-deoxygadusol, which, in cyanobacteria, is derived from conversion of the pentose phosphate pathway intermediate sedoheptulose 7-phosphate by the enzymes 2-epi-5-epivaliolone synthase (EVS) and O-methyltransferase (OMT). Yet, deletion of the EVS gene from Anabaena variabilis ATCC 29413 was shown to have little effect on MAA production, thus suggesting that its biosynthesis is not exclusive to the pentose phosphate pathway. Herein, we report how, using pathway-specific inhibitors, we demonstrated unequivocally that MAA biosynthesis occurs also via the shikimate pathway. In addition, complete in-frame gene deletion of the OMT gene from A. variabilis ATCC 29413 reveals that, although biochemically distinct, the pentose phosphate and shikimate pathways are inextricably linked to MAA biosynthesis in this cyanobacterium. Furthermore, proteomic data reveal that the shikimate pathway is the predominate route for UV-induced MAA biosynthesis.

Can bottom ice algae tolerate irradiance and temperature changes?

Sea ice algae are significant primary producers of the ice-covered marine environment, growing under typically cold, dim conditions. During ice break-up they are released to the water column, where temperatures can be several degrees higher and irradiance can increase by orders of magnitude. To determine how sea ice algae respond to such rapid changes, we carried out incubations to examine their tolerance to environmentally realistic levels of change in temperature and PAR, as expressed by photosynthetic response and production of mycosporine-like amino acids (MAAs). The algae were also exposed to a broader range of temperatures, to evaluate their potential to function in warmer seas in the event, for instance, of anthropogenic transfer to locations further north. When subjected to PAR (0–100μmolm−2s−1) at ecologically relevant temperatures (−1°C, 2°C, 5°C), the algae showed tolerance, indicated by a lack of decline in the quantum efficiency of photosystem II (PSII). The data show that bottom ice algae can tolerate increasing temperature and PAR comparable to the changes experienced during and after sea ice melt. MAA production increased at higher PAR and temperature. At ambient PAR levels, increased temperatures resulted in lower ϕPSII. However, as PAR levels were increased, higher temperature reduced the level of stress as indicated by higher ϕPSII values. This result suggests, for the first time in sea ice algal studies, that higher temperatures can ameliorate the negative effects of increased PAR. Exposure to much higher temperatures suggested that the algae were capable of retaining some photosynthetic function at water temperatures well above those currently experienced in some of their Antarctic habitats. However, when temperature was gradually increased past 14°C, the photosystems started to become inactivated as indicated by a decrease in quantum yield, suggesting that the algae would not be viable if transferred to lower latitude cold temperate areas.

Analysis of proteins involved in the production of MAA׳s in two Cyanobacteria Synechocystis PCC 6803 and Anabaena cylindrica.

Mycosporine- like amino acids (MAAs) are small (<400Da), colourless, water soluble compounds composed of cyclohexenone or cyclohexinimine chromophere conjugated with the nitrogen substituent of amino acid or its amino alcohol. These compounds are known for their UV- absorbing role in various organisms and seem to have evolutionary significance. The biosynthesis of MAAs is presumed to occur via the first part of shikimate pathway. In the present work two cyanobacteria Synechocystis PCC 6803 and Anabaena cylindrica were tested for their ability to synthesize MAAs and protein involved in the production of MAAs. It was found that protein sequence 3-phosphoshikimate 1-carboxyvinyltransferase is involved in producing mycosporine glycine in Synechocystis PCC 6803 and 3-dehydroquinate synthase is involved for producing shinorine in Anabaena cylindrica. Phylogenetic and bioinformatic analysis of Mycosporine like amino acid producing protein sequence of both cyanobacterial species Synechocystis PCC 6803 and Anabaena cylindrica provide a useful framework to understand the relationship of the different forms and how they have evolved from a common ancestor. These products seem to be conserved but the residues are prone to variation which might be due the fact that different cyanobacteria show different physiological process in response of Ultraviolet stress.

형질전환 미세조류의 고주파 처리 배양을 통한 MAA 생산량 증가

Mycosporine-like 아미노산(MAAs)은 UV 흡수물질이며, 다양한 해양생물들은 MAAs의 합성과 축적을 통하여 환경자외선의 직 간접적인 영향을 감소시키는 기능을 진화시켜 왔다. 이 연구에서는 미세조류, Chlamydomonas hedleyi에 포도당 전달 단백질인 Glucose transporter 1(Glut-1) 유전자를 pCAM1303 벡터에 도입한 형질전환체를 제작하여, 형질전환체의 바이오매스를 최대로 증가시킬 수 있는 최적의 Glucose 농도와 NH4Cl농도를 결정하고, 고주파(Radiofrequency) 발생장치를 활용한 바이오매스 증가와 함께 MAA를 대량 생산할 수 있는 배양 조건을 확립하였다. 연구결과 고주파 처리를 통한 형질전환 미세조류는 4.13 mg/L(MAAs/DCW)으로 3.23 mg/L(MAAs/DCW)의 고주파 처리 없이 배양한 형질전환체보다 효율이 증가하였다. 이러한 결과는 자외선 A 흡수물질을 인위적으로 증폭시킬 수 있어서, 대량배양한 후 MAAs물질을 분리 및 정제하여 피부자극성이 없는 친환경적인 자외선 차단 화장품 산업화에 크게 기여할 수 있음을 의미한다. In sea water, microalgae are exposed to a range of critical environmental conditions. Microalgae are protected from UV-A radiation due to the presence of mycosporine like amino acids(MAAs). Owing to the UV-A absorption properties of MAAs, they are used widely as a UV protecting ingredient in cosmetics. Therefore, there is a need to increase the production yield of MAAs. This study investigated the production yield of MAAs in transformed microalgae by radiofrequency(RF) exposure. Initially, the Glut-1 gene was transformed to Chlamydomonas hedleyi microalgae as a glucose transporter. The biomass was enhanced after Glut-1 gene transformation. In addition, the MAAs production yield was increased during large scale production in bioreactors due to the RF treatment. Therefore, purified extracts of MAAs can be used as a sun block material in the cosmetic industrial field.

Discovery of gene cluster for mycosporine-like amino acid biosynthesis from Actinomycetales microorganisms and production of a novel mycosporine-like amino acid by heterologous expression.

Mycosporines and mycosporine-like amino acids (MAAs), including shinorine (mycosporine-glycine-serine) and porphyra-334 (mycosporine-glycine-threonine), are UV-absorbing compounds produced by cyanobacteria, fungi, and marine micro- and macroalgae. These MAAs have the ability to protect these organisms from damage by environmental UV radiation. Although no reports have described the production of MAAs and the corresponding genes involved in MAA biosynthesis from Gram-positive bacteria to date, genome mining of the Gram-positive bacterial database revealed that two microorganisms belonging to the order Actinomycetales, Actinosynnema mirum DSM 43827 and Pseudonocardia sp. strain P1, possess a gene cluster homologous to the biosynthetic gene clusters identified from cyanobacteria. When the two strains were grown in liquid culture, Pseudonocardia sp. accumulated a very small amount of MAA-like compound in a medium-dependent manner, whereas A. mirum did not produce MAAs under any culture conditions, indicating that the biosynthetic gene cluster of A. mirum was in a cryptic state in this microorganism. In order to characterize these biosynthetic gene clusters, each biosynthetic gene cluster was heterologously expressed in an engineered host, Streptomyces avermitilis SUKA22. Since the resultant transformants carrying the entire biosynthetic gene cluster controlled by an alternative promoter produced mainly shinorine, this is the first confirmation of a biosynthetic gene cluster for MAA from Gram-positive bacteria. Furthermore, S. avermitilis SUKA22 transformants carrying the biosynthetic gene cluster for MAA of A. mirum accumulated not only shinorine and porphyra-334 but also a novel MAA. Structure elucidation revealed that the novel MAA is mycosporine-glycine-alanine, which substitutes l-alanine for the l-serine of shinorine.

Photoprotective function of mycosporine-like amino acids in a bipolar diatom (Porosira glacialis): evidence from ultraviolet radiation and stable isotope probing

This study investigated the synthesis of photoprotective compounds by Bacillariophyceae (Porosira glacialis) in real time using a 13C tracer. Our results show a relationship between the net production rates of mycosporine-like amino acids (MAAs) and photoprotective pigments such as diadinoxanthin (DD). After 24 h, the total carbon uptake rate of P. glacialis was higher when exposed to photosynthetically active radiation (PAR) than when exposed to ultraviolet radiation (UVR). However, with time, the total carbon uptake rate and turnover rate of P. glacialis exposed to UVR increased to the point where the net production rate of MAAs under UVR was higher than that of P. glacialis exposed to PAR. The differences in MAA and DD production rates and carbon uptake indicate the production of MAA and DD as a defense strategy in response to UV-induced damage. The results of this study provide insight into the synthetic pathways of photoprotective compounds and the carbon cycle within P. glacialis cells and reveal contrasting patterns in the production of MAAs and xanthophyll compounds such as DD over time.

Production of mycosporine-like amino acids by phytoplankton under ultraviolet radiation exposure in the Sub-Antarctic Zone south of Tasmania

Production of mycosporine-like amino acids by phytoplankton under ultraviolet radiation exposure in the Sub-Antarctic Zone south of Tasmania

Production of mycosporine-like amino acids of in situ phytoplankton community in Kongsfjorden, Svalbard, Arctic

The spatial distribution of UV-absorbing compounds (mycosporine-like amino acids, MAAs), was investigated by comparing the phytoplankton community structures in the inner and outer waters of the Kongsfjorden inlet, which is located in arctic Svalbard. Thalassiosira sp. and Phaeocystis sp. were dominant in the outer waters of the Kongfjorden inlet, demonstrating high chlorophyll a (chl a) concentrations and low MAA concentrations in the outer bay waters. However, Kongsfjorden Bay was dominated by Phaeocystis sp. and demonstrated high MAA concentrations despite low chl a concentrations. The carbon fixation rate at a station located inside Kongsfjorden Bay (T05) was significantly photo-inhibited by UV radiation, demonstrating higher production rates of MAA and chl a than at a station (B09) in outer bloom waters. Additionally, the turnover rates of individual MAAs were faster inside the Kongsfjorden Bay than in the outside waters. As a result, the natural phytoplankton community demonstrated different UV adaptation mechanisms according to the phytoplankton species, in this case, Thalassiosira sp. vs. Phaeocystis sp. It is possible to understand real-time changes for newly photosynthesized MAAs as UV-absorbing compounds in the natural phytoplankton community. This takes place via determination of in situ MAA production rates using 13C tracer and High Performance Liquid Chromatography (HPLC) combined with an isotope ratio mass spectrometer (irMS).

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.

Seasonal changes of antioxidant and oxidative parameters in the coralPocillopora capitataon the Pacific coast of Mexico

AbstractThe physiological responses of the coralPocillopora capitatato environmental conditions common in winter and summer were studied in 2007 during February–March (winter) and June–July (summer) at La Boquita reef (Manzanillo, Colima, Mexico). Shallow and deep sampling stations were established at different distances from a small jetty built next to the Juluapan Lagoon. We analyzed superoxide radicals () and lipid peroxidants (TBARS); the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione‐S‐transferase (GST); chlorophylla(Chla), zooxanthellae density (ZD); and mycosporine‐like amino acids (MAAs). Our results showed that the, TBARS, CAT, GST, MAAs, and Chla,levels were significantly higher in summer (P &lt; 0.05); no seasonal difference was found for GPx, GR or ZD. We found significant differences (P &lt; 0.05) in winter only for Chlaand ZD at shallow sites and, in contrast, forat deeper sites. The results of this study indicate that increasing temperature and radiation associated with seasonal changes (from winter to summer), the efficiency of the enzymes GST, CR and GPX, and the production of MAAs together form a powerful mechanism forP. capitatato offset the detrimental effects of environmental change.

Interaction Effects of Ambient UV Radiation and Nutrient Limitation on the Toxic Cyanobacterium Nodularia spumigena

Nodularia spumigena is one of the dominating species during the extensive cyanobacterial blooms in the Baltic Sea. The blooms coincide with strong light, stable stratification, low ratios of dissolved inorganic nitrogen, and dissolved inorganic phosphorus. The ability of nitrogen fixation, a high tolerance to phosphorus starvation, and different photo-protective strategies (production of mycosporine-like amino acids, MAAs) may give N. spumigena a competitive advantage over other phytoplankton during the blooms. To elucidate the interactive effects of ambient UV radiation and nutrient limitation on the performance of N. spumigena, an outdoor experiment was designed. Two radiation treatments photosynthetic active radiation (PAR) and PAR +UV-A + UV-B (PAB) and three nutrient treatments were established: nutrient replete (NP), nitrogen limited (-N), and phosphorus limited (-P). Variables measured were specific growth rate, heterocyst frequency, cell volume, cell concentrations of MAAs, photosynthetic pigments, particulate carbon (POC), particulate nitrogen (PON), and particulate phosphorus (POP). Ratios of particulate organic matter were calculated: POC/PON, POC/POP, and PON/POP. There was no interactive effect between radiation and nutrient limitation on the specific growth rate of N. spumigena, but there was an overall effect of phosphorus limitation on the variables measured. Interaction effects were observed for some variables; cell size (larger cells in -P PAB compared to other treatments) and the carotenoid canthaxanthin (highest concentration in -N PAR). In addition, significantly less POC and PON (mol cell(-1)) were found in -P PAR compared to -P PAB, and the opposite radiation effect was observed in -N. Our study shows that despite interactive effects on some of the variables studied, N. spumigena tolerate high ambient UVR also under nutrient limiting conditions and maintain positive growth rate even under severe phosphorus limitation.

The continuity and intensity of ultraviolet irradiation affect the kinetics of biosynthesis, accumulation, and conversion of mycosporine‐like amino acids (MAAs) in the coral Stylophora pistillata

Colonies of Stylophora pistillata unexposed to ultraviolet radiation (UVR) in laboratory aquaria contained minimal amounts of mycosporine‐like amino acids (MAAs). The concentration of MAAs increased rapidly during exposure to broadband UVR, then stabilized between 14 and 28 d of exposure. The four MAAs known to be produced by diverse zooxanthellae (Symbiodinium spp.) in culture were the first to increase in coral colonies, followed by six additional MAAs. Decreases in these four primary MAAs between days 14 and 28 were balanced by stoichiometric increases in the six secondary MAAs, suggesting a precursor‐product relationship. Discontinuing UV exposure caused rapid declines in the concentrations of primary MAAs, while secondary MAAs continued to increase, likely a manifestation of different rates of turnover of the putative enzymes involved in the de novo biosynthesis of primary MAAs and their conversion to secondary MAAs. The continued production of certain MAAs after UV exposure ceased indicates that UV is not required catalytically but is a signal that induces the enzymes of the biosynthetic pathway. Biochemically inhibiting the biosynthesis of primary MAAs after a pool of these MAAs had accumulated did not affect their conversion to secondary MAAs. Doubling the UV irradiance increased the rate of accumulation, first, of primary MAAs and, later, of secondary MAAs. Under normal UV irradiance, the eventual decline in the accumulation rate of primary MAAs was quantitatively explained by their conversion to secondary MAAs. Under doubled UV irradiance, where MAA concentrations were higher, the deceleration of accumulation of primary MAAs was twice as great as the acceleration in secondary MAAs, suggesting a regulation of the de novo biosynthesis of MAAs, perhaps by their own progressive, concentration‐dependent attenuation of UVR.

Mycosporine-like amino acids in Antarctic sea ice algae, and their response to UVB radiation.

Mycosporine like amino acids (MAAs) were detected in low concentration in sea ice algae growing in situ at Cape Evans, Antarctica. Four areas of sea ice were covered with plastics of different UV absorption exposing the bottom- ice algal community to a range of UV doses for a period of 15 days. Algae were exposed to visible radiation only; visible + UV radiation; and visible + enhanced UV radiation. MAA content per cell at the start of the experiment was low in snow-covered plots but higher in samples from ice with no snow cover. During the study period, the MAA content per cell reduced in all treatments, but the rate of this decline was less under both ambient UV and visible radiation than under snow covered plots. While low doses of UVB radiation may have stimulated some MAA production (or at least slowed its loss), relatively high doses of UVB radiation resulted in almost complete loss of MAAs from ice algal cells. Despite this reduction in MAA content per cell, the diatoms in all samples grew well, and there was no discernible effect on viability. This suggests that MAAs may play a minor role as photoprotectants in sea ice algae. The unique structure of the bottom ice algal community may provide a self-shading effect such that algal cells closest to the surface of the ice contain more MAAs than those below them and confer a degree of protection on the community as a whole.

Effects of ultraviolet radiation and water motion on the reef coral, Porites compressa Dana: a transplantation experiment

Scleractinian corals have adapted to live in habitats were the level of ultraviolet radiation (UVR, 280–400 nm) is extremely high. The putative photoprotective molecules called mycosporine-like amino acids (MAAs) contained in the corals' tissues absorb UVR and release it harmlessly as heat. MAA concentration in corals is quite plastic and correlates well with UVR dose, but other ecological factors such as water motion may influence MAA production as well. In this study, the effects of ambient UVR and water motion on MAA concentration and several physiological parameters of the reef coral Porites compressa Dana were investigated in a two by two factorial transplantation experiment. Replicate branches from nine morphologically distinct colonies were transplanted from the windward side of Coconut Island (Kaneohe Bay, HI) to a control area on the windward side (ambient water motion) and to an area on the leeward side (low water motion). The transplanted corals were placed under UV-opaque (UVO) or UV-transparent (UVT) filters fixed to the reef. Initially and at 3 and 6 weeks, coral branches were weighed to determine calcification rate and tissues were extracted in methanol for photosynthetic pigment and MAA analysis via high performance liquid chromatography (HPLC). UVR was a significant factor determining MAA concentration. When UVR was screened from the corals' environment, total MAA concentration decreased by 33% over 6 weeks. However, UVR-exposed corals moved to low water motion also decreased MAA levels, while UVR-exposed corals moved to the control area retained initial levels. Photosynthetic pigments and calcification rate were also significantly reduced in corals moved to low water motion. There was no UVR effect on photosynthetic pigments or calcification rate. This study provides evidence that water motion is important for the maintenance of MAAs. However, there were interesting colony-specific patterns in MAA composition and response to the UVR treatment; some colonies had high total concentrations of MAAs in all treatments, while others displayed a pronounced UVR effect. Also, each genotype seemed to have its own signature MAA composition. These findings indicate a genetic (host, zooxanthellae or both) component to UVR resistance in this population of P. compressa.

Seasonal and sex-specific variations in levels of photo-protecting mycosporine-like amino acids (MAAs) in soft corals

This study focusses on the nature and extent of variation in mycosporine-like amino acids (MAAs) in relation to annual cycles in solar radiation, seawater temperature, and reproduction in reef-flat populations of two soft coral species. The results show MAA tissue concentrations in shallow water colonies of Lobophytum compactum and Sinularia flexibilis to be significantly correlated to annual cycles in solar radiation (P<0.0006 and P<0.0005, respectively) and seawater temperature (P<0.0006 and P<0.0004, respectively). Evidence of seasonal cycles in MAA levels in the tissues of shallow-reef invertebrates positively correlating with annual cycles in solar radiation and temperature suggests that they are an integral component of the soft corals' biochemical defence system against high irradiance and/or temperature stress and thus bleaching. This is further corroborated by the higher production of MAAs in females than males prior to spawning (up to 67% and 56% for L. compactum and S. flexibilis, respectively), presumably to provide a high level of protection against irradiance stress for progeny.