Phylogeography of the marine macroalga Sargassum hemiphyllum (Phaeophyceae,Heterokontophyta) in northwestern Pacific

Sargassum hemiphyllum is commonly found in Japan and Korea, with a variety, var. chinense, that is found distributed in the southern Chinese coast. We previously reported distinct genetic differentiation between the two taxa based on the PCR‐RFLP data of plastid RubiscoL‐S spacer. The present study aims at elucidating the phylogeographic pattern of S. hemiphyllum based on more markers in the nuclear and extranuclear genomes, with a view to reveal the occurrence of hybridization. The two allopatrically distributed taxa were found to be genetically distinct in nuclear ITS2, plastidial Rubisco (Rbc) and mitochondrial TrnW_I (Trn) spacers. Their divergence was postulated to be attributable to the vicariant event which resulted from the isolation of the Sea of Japan during the late Miocene (6.58–11.25 Mya). Divergence within both S. hemiphyllum and the chinense variety was observed based on Trn spacer, while the divergence in S. hemiphyllum was further confirmed in Rbc spacer. This divergence appears to correspond to the separation of the Japanese populations between the Sea of Japan and the Pacific that occurred around 0.92–2.88 Mya (the early Pleistocene). The presence of an ITS2 clone resembling var. chinense sequences in a Japanese population of S. hemiphyllum (JpNS) raises the possibility of the introgression of var. chinense individuals into S. hemiphyllum population. Compared to that between S. hemiphyllum and the chinense variety, hybridization among the Japanese and Korean populations of S. hemiphyllum is highly probable as all these individuals share a pool of nuclear ITS2 sequences, possibly attributable to incomplete concerted evolution of ITS2.     

The effect of wrack composition and diversity on macrofaunal assemblages in intertidal marine sediments

Wrack (dead, washed-up seaweed and seagrass) buried in soft substrata may increase the organic content and alter the physical structure of sediments. These effects may influence the composition and structure of macrofaunal assemblages in the sediment. Such influences can be expected to vary according to the type and amount of wrack as well as the presence of invasive seaweeds in the wrack. In this study, we deliberately buried different amounts of the invasive species Sargassum muticum in isolation or mixed to the native species Ulva sp. and Fucus vesiculosus, in two intertidal sandflats to test some hypotheses about the response of macrofaunal assemblages. We tested whether (1) diversity of detritus (i.e. different mixtures), and (2) the amount of detritus of S. muticum influenced the composition and the relative abundance of macrofaunal assemblages. We also assessed whether the sediment organic carbon and the biomass of benthic microalgae varied depending on the diversity of detritus and the amount of detritus of S. muticum. Finally, we tested if these effects of wrack were consistent across sites. Results indicated that buried wrack affected the composition and structure of macrofaunal assemblages in short-term (i.e. 4 weeks), but there were no differences depending on detritus diversity or the amount of S. muticum. In addition, sediment organic matter and microalgal biomass were not affected by the addition of wrack. They instead varied greatly among small spatial scales (i.e. plots). Wrack composition or abundance of the invasive species S. muticum played thus a small role in shaping the structure of macrofaunal assemblages or the biomass of benthic microalgae in these intertidal sediments, probably because these sediments are frequently affected by various inputs of organic matter and benthic assemblages are already adapted to organically enriched sediments.     

PHOTOSYSTEM II QUANTUM YIELDS AND XANTHOPHYLL-CYCLE PIGMENTS OF THE MACROALGA SARGASSUM NATANS (PHAEOPHYCEAE): RESPONSES UNDER NATURAL SUNLIGHT

Our understanding of the physiological mechanisms that allow marine photoautotrophs to thrive in a high light environment is limited. The pelagic phaeophyte, Sargassum natans (L.) Gaillon, exists at the air–sea interface and often is exposed to high irradiances. During a cruise in the Gulf of Mexico, aggregates of S. natans were collected and maintained in a shipboard incubator under natural sunlight. In vivo fluorescence and pigmentation dynamics were assessed over two daily cycles to characterize the photophysiological responses of this taxon to varying irradiance (i.e. overcast and sunny conditions). The relative proportion of the photosynthetic carotenoid, violaxanthin, to the photoprotective carotenoid, zeaxanthin, decreased during daylight hours. This mirrored the dynamics in the maximum quantum yield for stable charge separation at photosystem II (F_V/F_M[variable fluorescence/maximum fluorescence]), which decreased (relative to predawn levels) by 50%–60% during periods of sustained bright light and recovered to predawn values 3 h after sunset. The ratio of de-epoxidized to epoxidized components of the xanthophyll-cycle pigment pool (violaxanthin, zeaxanthin) was associated with energy dissipation activity within the pigment bed. The operational quantum yield for photosystem II activity (φ_IIe) was substantially lower than F_V/F_M due to both a decreased probability that absorbed photons reached open reaction centers and to the induction of nonphotochemical fluorescence quenching (which was rapidly reversible). Bright light also affected the rate of electron flow from the reaction center chlorophyll through to the secondary electron acceptor, quinone B (Q_B); specifically, single turnover decay curves indicated that the proportion of Q_B bound to the D1–D2 complex in photosystem II decreased during the protracted periods of bright light. Kautsky curves suggested that the relative proportion of inactive light-harvesting complexes also increased during periods of bright light. Taken together, these findings suggest that S. natans can tolerate high irradiances by down-regulating its quantum yield during the day, decreasing its functional absorption coefficient through the uncoupling of light-harvesting complexes, and decreasing the efficiency with which absorbed light is utilized. These cellular responses appear to be driven by the absolute flux of light and not by an endogenous rhythm, which is phased to a particular time of day.     

IMPACT OF THE INVASIVE SEAWEED SARGASSUM MUTICUM (PHAEOPHYTA) ON AN INTERTIDAL MACROALGAL ASSEMBLAGE1

The impact of the invasive seaweed Sargassum muticum (Yendo) Fensholt on a low intertidal macroalgal assemblage was assessed at a semiexposed rocky shore in northern Spain between 2002 and 2004. Sargassum muticum plants were removed from the mature macroalgal assemblage and from those occurring along the successional process of the assemblage. Biomass, richness, diversity, and percentage cover of macroalgae in experimental plots were compared with unmanipulated controls. The effect of S. muticum removal on the macroalgal assemblage more than 2 years after the beginning of the experiment was negligible. Moreover, no differences between treatments were detected in the general patterns of succession. Only significant differences in S. muticum abundance were detected between treatments at the end of the experiment. We suggest that the low abundance of S. muticum at this intertidal level and its pseudoperennial life cycle may limit competition with native macroalgae. However, long‐term removal experiments may be a more indicator of the impact of S. muticum at the upper limit of its vertical distribution.     

FUNCTIONAL-MORPHOLOGICAL RELATIONSHIPS IN SARGASSUM POLYCERATIUM (PHAEOPHYTA): PHENOTYPIC AND ONTOGENETIC VARIABILITY IN APPARENT PHOTOSYNTHESIS AND DARK RESPIRATION1

Phenotypic and ontogenetic changes in apparent photosynthesis and dark respiration for Sargassum polyceratium Mont. were related to the differential allocation of resources into blades, stems, vesicles, and fertile branches as well as anatomical parameters of surface area, volume, and blade density from a population in the Content Keys, Florida. Three divergent phenotypes were evaluated during four phases of ontogeny: maximum growth (October), peak reproduction (December), senescence (April), and stasis (July). Photosynthetic and respiratory rates changed throughout the year, at different stages of morphogenesis, and among different phenotypes. Photosynthesis was highest during active growth, decreased during reproduction and senescence, and was lowest during stasis. In contrast, respiration was higher during peak reproduction and stasis. Temporal, phenotypic, and ontogenetic changes in apparent photosynthesis were best explained by interactions among anatomical features, growth stages, and source-sink relationships of metabolic reserves and pigments. Surface area: volume (SA:V) ratios played a secondary role. Photosynthetic performance of mature axes decreased with the allocation of resources away from blades to air bladders and fertile branches. Apparent productivity and development of fertile branches on phenotypes were not correlated. High respiratory rates, SA:V ratios, blade areas, and low blade densities occurred on developing axes and were consistent with adaptations to low light fields. Sargassum polyceratium, because of its morphological differentiation, is a relatively complex, physiologically variable alga.     

羊栖菜多糖诱导HL-60细胞凋亡的研究

用MTT法观察羊栖菜多糖(SFPS)在体外抗人白血病HL-60细胞增殖作用;扫描电镜、透射电镜、DNA电泳和流式细胞仪检测HL-60细胞凋亡。结果表明SFPS对HL-60细胞具有显著生长抑制作用,并呈量效和时效关系,药物作用24,36,48,72h的IC_(50)分别为390,362,402,421mg/L;药物浓度为300mg/L和500mg/L作用HL-60细胞后,琼脂糖凝胶电泳显示有凋亡细胞特有的DNA梯状条带,细胞微绒毛减少、染色质固缩、过集,凋亡小体形成;DNA直方图出现亚G_1峰。在一定浓度范围内,SFPS诱导细胞凋亡的作用呈现浓度和时间依赖性,同时G_2/M期细胞比例增多。因此,SFPS抗肿瘤作用与诱导细胞凋亡和G_2/M期细胞阻滞有关。     

Antifouling activity of seaweed extracts on the green alga Enteromorpha prolifera and the mussel Mytilus edulis

Twenty-seven species of common seaweeds from the coast of Korea havebeen screened for antifouling activity. The seaweed extracts were tested inlaboratory assays against the marine fouling green alga Enteromorphaprolifera and the blue mussel Mytilus edulis. Tissue growth, sporesettlement, zygote formation and germlings of the E. prolifera wereinhibited by methanol extracts of the seaweed Ishige sinicola (= I. foliacea) and Sargassum horneri. Spore settlement was stronglyinhibited by using extract concentrations as low as 30 g mL^-1with I. sinicola and 120 g mL^-1 with S. horneri. The repulsive activity of the foot of the mussel was completely inhibited bymethanol extracts of I. sinicola and Scytosiphon lomentaria atconcentrations of 40 g per 10 L drop supplied to eachmussel. These extracts also showed strong antifouling activities onlarval settlement with, respectively, no or only 6% of the spat settlingwhen a test concentration of 0.8 mg mL^-1 was used. This work isthe first stage towards the development of novel antifouling agents frommarine macroalgae.     

基于生境适宜性指数模型的俚岛海黍子生境层级分布

为了深入了解海黍子生境,利用模型对山东俚岛海黍子生境进行适宜性分析,分别选取温度、盐度、水深、浊度、底质、无机氮浓度、磷酸盐浓度和距海藻床距离8种环境因子,通过层次分析法赋值因子权重,结合空间分析方法建立了海黍子HSI模型。利用该模型对山东俚岛近岸海域2018年春、秋两季的环境因子调查结果进行了海黍子生境分析。结果表明: 研究区域内的海黍子海藻床区域主要由极佳生境和适宜生境组成,春季和秋季的分布面积分别占14.2%和18.6%。海黍子生境层级分布随季节而变化,且不同季节的生境层级具有一定的空间重合性。温度和磷酸盐浓度的适宜性变化具有明显的季节性差异,是导致俚岛海黍子HSI季节变化的主要原因。海黍子HSI模型不仅可用于检测海黍子海藻床区域的生境层级分布,还能发现海黍子潜在的适宜生境区域。这为今后开展海黍子资源保护和人工增殖工作提供了科学参考。     

Japan's nationwide long‐term monitoring survey of seaweed communities known as the “Monitoring Sites 1000”: Ten‐year overview and future perspectives

“Monitoring Sites 1000” – Japan's long‐term monitoring survey was established in 2003, based on the Japanese Government policy for the conservation of biodiversity. Ecological surveys have been conducted on various types of ecosystems at approximately 1000 sites in Japan for 15 years now and are planned to be carried out for 100 years. Since 2008, seaweed communities had been monitored at six sites, featuring the kelp (e.g. Saccharina and Ecklonia; Laminariales) and Sargassum (Fucales) communities in the subarctic and temperate regions of Japan. Annual surveys were carried out during the season when these canopy‐forming seaweeds are most abundant. A non‐destructive quadrat sampling method, with permanent quadrats placed along transects perpendicular to the shoreline, was used to determine species composition, coverage, and vertical distribution of seaweeds at these sites; while destructive sampling was done every 5 years to determine biomass. The occurrence of canopy‐forming species Saccharina japonica (var. japonica) and Ecklonia cava have appeared to be stable at the Muroran (southwestern part of Hokkaido Island) and Shimoda (Pacific coast of middle Honshu Island) sites, respectively; whereas the coverage of Ecklonia radicosa (= Eckloniopsis radicosa) at the Satsuma‐Nagashima site in southern part of Kyushu Island was highly variable until its sudden disappearance from the habitat in 2016. Thalli of E. radicosa lost most of their blades through browsing by herbivorous fish, and thus, this may be one of the causes of the decline. A shift in the community structure related to environmental changes had also been observed at some other sites. Pre‐ and post‐disaster data revealed the impact of the 2011 earthquake and tsunami disasters, including a shift in the vertical distribution of Ecklonia bicyclis (= Eisenia bicyclis) to shallower depths at the Shizugawa site in the Pacific coast of northern Honshu Island, due to seafloor subsidence.