Irina M. Yakovleva

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 (λmax 334 nm), asterina (λmax 330 nm), and palythine (λmax 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 (Fv/Fm and effective quantum yield, φII) 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 Fv/Fm and φII 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.

Dynamics of lipid and fatty acid composition of shallow-water corals under thermal stress: an experimental approach

Coral bleaching induces changes in lipid and fatty acid composition that result in low lipid content, reducing the likelihood of coral survival. Species-specific differences in the metabolism of lipid reserves may contribute to the differential resistance of corals under acute heat exposures. Here, we examined the dynamics of lipids and fatty acid abundance in corals subjected to short-term heat stress. The stony corals Acropora intermedia, Montipora digitata, and the soft coral Sinularia capitalis all showed a 60–75% decline in both storage and structural lipids. However, S. capitalis and M. digitata exhibited no significant change in the percentages of structural lipids (i.e., polar lipids and sterols) until they had lost 90–95% of their endosymbionts, whereas A. intermedia showed a rapid decline in structural lipids after a 50% loss of symbionts. After a 90–95% loss of symbionts under heat stress, all three corals showed a relative depletion of polyunsaturated fatty acids that had symbiont biomarkers, suggesting that polyunsaturated fatty acids were translocated from the symbiont to the coral host tissue.

Diversity of fatty acid composition of symbiotic dinoflagellates in corals: Evidence for the transfer of host PUFAs to the symbionts

High diversity of fatty acid (FA) composition of endosymbiotic dinoflagellates of the Symbiodinium group (zooxanthellae) isolated from different cnidarian groups has been found. To explain this diversity, FA composition of the total lipids of pure symbiont fractions (SF) and host cell tissue fractions (HF) isolated from one hydrocoral, two soft coral, and seven hard coral species inhabiting the shallow waters of the South China Sea (Vietnam) were compared. Symbiodinium phylogenetic clade designation for each SF was also determined, however, the relationship between the clade designation and FA composition of Symbiodinium was not found. The profiles of marker polyunsaturated FAs (PUFAs) of symbionts (18:4n-3, 18:5n-3, 20:5n-3) did not depend on taxonomic designation of the host and reflected only a specimen-specific diversity of the SF lipids. Several FAs such as 20:0, C24 PUFAs, 22:5n-6, and 18:2n-7 concentrated in HF lipids but were also found in SF lipids. For ten cnidarian species studied, the principal components analysis of total FAs (27 variables) of the symbiotic fractions was performed. The clear division of the symbiotic dinoflagellates according to the host systematic identity was found on a subclass level. This division was mainly caused by the FAs specific for the host lipids of each cnidarian subclasses such as hard corals, soft corals, and hydrocorals. Thus, the coral hosts affect the FA profile of their symbionts and cause the diversity of FA composition of Symbiodinium. The transfer of FAs from the coral host to their symbiotic dinoflagellates and modulation of PUFA biosynthesis in symbionts by the host are considered as possible reasons of the diversity studied.

An AFLP-based survey of genetic diversity and relationships of major farmed cultivars and geographically isolated wild populations of Saccharina japonica (Phaeophyta) along the northwest coasts of the Pacific

Abstract The genetic diversity and relationships of six representative cultivars and six geographically isolated wild populations of Saccharina japonica along the northwest coasts of the Pacific Ocean were investigated using AFLP markers. A total of 547 bands were generated across all samples by ten primer combinations. At the cultivar or population level, the percentage of polymorphic loci (P), gene diversity (H), and Shannon’s information index (I) was highest in Dalian population (P 59.05%; H 0.2057; I 0.3062) and lowest in Lianjiang cultivar (P 9.87%; H 0.0331; I 0.0497). At the species level, P, H, and I were 85.01%, 0.1948, and 0.3096, respectively. Unique bands were detected in all the six wild populations, with Dalian being the most. In comparison, only Yanza cultivar possessed one unique band. The GST value was 0.6226 and the gene flow (Nm) was 0.1515, indicating strong genetic differentiation among cultivars and populations. Two UMPGA dendrograms were constructed based on the Dice similarity coefficients among individuals and on genetic distances among cultivars and populations, which generally revealed three major clades corresponding to three countries. Analysis of molecular variance revealed that a larger proportion (60.21%) of the total genetic variation was attributable to differences among cultivars and populations. The Mantel test suggested that genetic differentiation was positively correlated with geographic distance (r = 0.7962, P = 0.011) in the six wild populations, agreeing with the isolation by distance model. On the whole, low to moderate genetic diversity within cultivars and populations (except Dalian population) and high genetic differentiation among cultivars and populations were detected.

Effect of solar irradiance on lipids of the green alga Ulva fenestrata Postels et Ruprecht

Abstract We examined variations in lipid composition of the marine green alga Ulva fenestrata grown under different irradiance conditions (80% of incident photosynthetically active radiation [PAR] and 24% PAR). The ratio of storage lipids (triacylglycerol) to major structural chloroplast lipids (glycolipids and phosphatidylglycerol) was influenced considerably by the irradiance. Triacylglycerol predominated in U. fenestrata exposed to 80% PAR (58.7±1.7% of total lipids). In contrast, when the alga was grown at 24% PAR, the amount of monogalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and phosphatidylglycerol increased two to three and a half times compared to algae cultivated at 80% PAR. The content of digalactosyldiacylglycerol and betaine lipid in U. fenestrata showed little dependence on light intensity. Each lipid class had a characteristic fatty acid composition. However, the relative proportions of fatty acids present in triacylglycerol, monogalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol did not depend on irradiance conditions. The variation in fatty acid composition of digalactosyldiacylglycerol and phosphatidylglycerol and changes in the amounts of lipids were responsible for the differences in total fatty acid composition of U. fenestrata among light intensities. The most sensitive to the change in quantity of incident light were the 16:4n-3 and 16:0 acids. The highest level of 16:4n-3 acid was detected in algae grown under 24% PAR, whereas 16:0 acid was highest at 80% PAR. However, the total lipid content in the algae was relatively constant at different light intensities (5.0±1.0 mg/g fresh weight at 80% PAR and 5.2±1.1 mg/g at 24% PAR). These results suggest that changes in lipid composition of U. fenestrata can be considered as a mechanism of adaptation and survival of thalli subjected to variations in solar irradiance.

Biosynthesis of polyunsaturated fatty acids in zooxanthellae and polyps of corals

The fatty acid (FA) composition of zooxanthellae, polyp tissue, and intact colonies was determined in soft coral Sinularia sp. and hard coral Acropora sp. Analysis of the distribution of polyunsaturated fatty acids (PUFAs) among the zooxanthellae and the host organism showed that 18: 3n-6 and C18–22 PUFAs of the n-3 series (18: 4n-3, 20: 5n-3, 22: 5n-3, and 22: 6n-3) were mainly synthesized by the zooxanthellae and that C20–22 PUFAs of the n-6 series (20: 3n-6, 20: 4n-6, and 22: 4n-6) were synthesized in the polyp tissue. Soft coral polyps were able to synthesize tetracosapolyenoic FAs (24: 5n-6 and 24: 6n-3) and 18: 2n-7, their zooxanthellae synthesized C16 PUFAs (16: 2n-7, 16: 3n-4, and 16: 4n-1). It is supposed that the biosynthesis of 16: 2n-7 in Sinularia sp. and 18: 3n-6 in Acropora sp. is catalyzed by Δ6 desaturase. The relatively even distribution of three FAs (18: 2n-6, 18: 3n-6, and 16: 2n-7) among lipids of zooxanthellae and coral polyps indicates the possible transport of these FAs between symbionts and the host organism.

Ontogenetic change in the abundance of mycosporine-like amino acids in non-zooxanthellate coral larvae

Although mycosporine-like amino acids (MAAs) have been extensively investigated in reef-building corals, the sources of these MAAs and the process of their interconversion remain a topic of interest. Here we examined ontogenetic change in the abundance of MAAs in planula larvae of the spawning scleractinian coral Goniastrea retiformis in the absence of zooxanthellae and other dietary input. In order to examine the potential contribution of prokaryotes in the synthesis of MAAs in animal tissue, one group of larvae were treated with the antibiotic rifampicin. High concentrations of MAAs (mycosporine-glycine, shinorine, palythinol, asterina-330), were present in the asymbiotic eggs and adults; however, no MAAs were present in the endosymbiotic zooxanthellae. We documented a steady decline in the total MAA concentrations through time in larvae treated with rifampicin; however, in the absence of antibiotic there was a significant increase in the concentration of MAAs, driven by a sharp increase in the abundance of shinorine and palythinol between day 3 and 7. Our results suggest that MAA synthesis and conversion in G. retiformis larvae occurred in the absence of symbiotic zooxanthellae, and indicate a possible contribution of prokaryotes associated with the animal tissue to these processes.

Changes in Growth Rate, Anatomy and Polysaccharide Content of a Sterile Form of Tichocarpus crinitus (Gmel.) Rupr. (Rhodophyta, Tichocarpaceae) Grown under Differing Photon Irradiances in the Sea of Japan, Russia

Abstract Variations in growth rate, thickness of the internal cortical and medullary cell walls, and carrageenan yield of the red alga Tichocarpus crinitus grown under differing irradiances were studied from June to October, when the algae were present in the non-reproductive sterile form. Growth rates were related to irradiance and seasonal patterns in water temperature. The highest growth rate (2.42% d−1) was found in the temperature range 20–24 °C in August. Optimal irradiance was found to be in the range of 10−15% of the incident PAR, i. e. approximately 150−160 μE m−2 s−1 at midday. Irradiance of approximately 90% of the incident PAR induced a large decrease in growth rate plus bleaching and tissue necrosis. The thickness of the cortical cell walls showed large variations between light treatments with high values being found at low irradiances. In contrast, medullary cell walls showed little change in thickness. Phycocolloid yield had the highest value (35.5% DM) in August and the lowest value (11% DM) in October, and was positively related to the growth rate of the algae during the main growing season. Data from 13C-NMR and FTIR spectroscopy indicated that the polysaccharides extracted from the sterile form of T. crinitus were predominantly κ/β bhybrid with λ-type carrageenans. They are localized in the internal cortical tissue of the T. crinitus thalli and their accumulation is negatively correlated with photon irradiance, which leads to non-gelling polysaccharides predominating at low irradiances.

Influence of winter and spring/summer algal communities on the growth and physiology of adjacent scleractinian corals

Abstract The influence of winter and spring/summer mixed algal communities from the low intertidal zone on the growth and physiology of four associated species of scleractinian corals was studied in outdoor culture. Experimental algae and corals came from the fringing reef of Sesoko Island, Okinawa, Japan, where fragments of the corals Acropora hyacinthus, Acropora sp., Porites cylindrica and Pavona divaricata were collected and exposed in aquaria 0.5–1.0 cm above mixed algal associations (AA), consisting of more than 100 species. A 30-day exposure did not show negative influence on algal growth, photosynthesis and respiration for the 4 coral species investigated, in spite of the fact that the AA included algae that are known to be toxic to corals. Moreover, the presence of the spring/winter AA in the aquaria actually stimulated the growth of coral fragments two- to four-fold. The results suggest that even though algal occupancy of the substratum on the fringing reef of Sesoko Island is 90%, it has no negative impact on the growth and physiological state of corals living near the algae. Possible mechanisms of a positive influence of algal communities near, but not in contact with, are organic uptake or enhanced planktonic prey.

Identifying nitrogen sources for macroalgal growth in variously polluted coastal areas of southern Vietnam

Abstract Levels of δ15N and molar C/N ratios were determined for the first time in 73 species of green, brown and red macroalgae at nine sites from differently polluted coastal areas of southern Vietnam in order to identify sources of dissolved inorganic nitrogen (DIN) used by seaweeds for their growth and development. The study sites were provisionally divided into two groups: open coast localities with presumably clear seawater and relatively isolated localities (bays and lagoons) polluted by waste from mariculture and sewage from cities and large villages. The algae collected at “pristine” and polluted sites had on average δ15N signatures of 3.3±0.9‰ and 8.6±1.1‰, respectively. Macroalgae from the west shore of Phu Quoc Island, O Lan Lagoon and Nha Trang Bay assimilated DIN from wastewater enriched with the heavy nitrogen isotope. Among the macroalgae investigated, bioindicators of DIN source were identified. These indicator algae belong mainly to the genera Ulva, Padina, Turbinaria, Gracilaria and Hydropuntia. Analysis of molar C/N ratios in algal tissue showed that thalli collected at “pristine” sites suffered limitation in nitrogen (on average, the C/N ratios=21.6±13.3). In most of the polluted areas, macroalgae were also N limited (on average, the C/N ratios=15.3±8.2).