Effect of UV-B irradiation on interspecific competition between Ulva pertusa and Grateloupia filicina

We report the effect of UV-B irradiation (9.6 kJ m^?2 day^?1) on interspecific competition between two species of macroalgae, Ulva pertusa (U) and Grateloupia filicina (G), in co-culture. Growth of U. pertusa and G. filicina was inhibited by UV-B irradiation in mono-culture and specific growth rate (μ) declined as a result. Interspecific competition between U. pertusa and G. filicina was closely related to the initial weights when co-cultured. When initial ratios of U. pertusa (U) to G. filicina (G) were U:G=1.2:1 and 1:1, U. pertusa was the dominant algae. When the initial U:G ratio was 1:1.2, G. filicina was competitively dominant in the earlier stage, but U. pertusa grew faster, superseding G. filicina in the later stage. At initial ration U:G = 1:1.4, G. filicina was predominant. Under UV-B irradiation, the competitive ability of G. filicina was weakened and the interspecific competitive balance favored U. pertusa, which suggests that G. filicina was more sensitive to UV-B irradiation. We also probed the potential allelopathic effects between the two species, which led to mutual growth inhibition.     

Effects of UV-B irradiation on isoforms of antioxidant enzymes and their activities in red alga Grateloupiafilicina （Rhodophyta）

Macroalgae in a littoral zone are inevitably exposed to UV-B irradiance.We analyzed the effects of UV-B on isoenzyme patterns and activities of superoxide dismutase(SOD),peroxidase(POX),catalase(CAT),and ascorbate peroxidase(APX) of red algae Grateloupia filicina(Lamour.) C.Agardh.The activities of SOD,CAT,and APX changed in response to UV-B in a time- and dose-dependent manner.POX activity increased significantly under all three UV-B treatments.The enzymatic assay showed three distinct bands of SODⅠ(Mn-SOD),SODⅡ(Fe-SOD),and SODⅢ(CuZn-SOD) under a low(Luv) and medium(Muv) dose of UV-B irradiation,while SODⅠ and SODⅢ activities decreased significantly when exposed to a high dose of UV-B irradiation(Huv).The activity of POX isoenzymes increased significantly after exposure to UV-B,which is consistent with the total activity.In addition,a clear decrease in activity of CATIV was detected in response to all the three doses of UV treatments.Some bands of APX isoenzyme were also clearly influenced by UV-B irradiation.Correspondingly,the daily growth rate declined under all the three exposure doses,and was especially significant under Muv and Huv treatments.These data suggest that,although the protection mechanisms of antioxidant defense system are partly inducible by UV-B to prevent the damage,G.filicina has incomplete tolerance to higher UV-B irradiation stress.     

Effects of dietary supplementation of Ulva pertusa and non-starch polysaccharide enzymes on gut microbiota of Siganus canaliculatus

Fishes represent the highest diversity of vertebrates; however, our understanding of the compositions and functions of their gut microbiota is limited. In this study, we provided the first insight into the gut microbiota of the herbivorous fish Siganus canaliculatus by using three molecular ecology techniques based on the 16 S r RNA genes(denaturing gradient gel electrophoresis, clone library construction, and highthroughput Illumina sequencing), and the Illumina sequencing technique is suggested here due to its higher overall coverage of the total 16 S r RNA genes. A core gut microbiota of 29 bacterial groups, covering 99.9% of the total bacterial community, was found to be dominated by Proteobacteria and Firmicutes in fish fed three dif ferent diets with/without the supplementation of U lva pertusa and non-starch polysaccharide(NSP) enzymes(cellulase, xylanase, and β-glucanase). Diverse potential NSP-degrading bacteria and probiotics(e.g., R uminococcus, Clostridium and Lachnospiraceae) were detected in the intestine of the fish fed U. pertusa, suggesting that these microorganisms likely participated in the degradation of NSPs derived from U. pertusa. This study supports our previous conclusion that U. pertusa-based diets are suitable for the production of S. canaliculatus with lower costs without compromising quality.     

Preparation of polysaccharides in different molecular weights from Ulva pertusa Kjellm （Chorophyta）

As molecular weight controls the biological activities of polysaccharides, screening the optimal molecular weight of polysaccharides is important in drug research and application. In this study, hydrogen peroxide was employed as oxidant, and temperature, reaction time, and concentration of polysaccharides and hydrogen peroxide were examined for their effects on the preparation of polysaccharides in different molecular weights from Ulva pertusa. Our experiment suggested that the optimal degradation concentrations for polysaccharides and hydrogen peroxide were 2.5% (w/v) and 8.0% (v/v), respectively. The range of degradation measured by relative viscosity was mainly controlled by temperature and time. Results revealed that 35℃ was the optimal temperature for obtaining low-degradation samples, and 50℃ was the most favorable temperature to accelerate the reaction to yield highly-degraded samples. Four samples in different molecular weights A, B, C and D were finally prepared. The controllability was evaluated by the relative standard deviation (RSD) of relative viscosity, and the peak molecular weights and the polydispersity indexes (Mw/Mn) of molecular weights were measured by high performance gel permeation chromatography (HPGPC).     

De-eutrophication of effluent wastewater from fish aquaculture by using marine green alga Ulva pertusa

The de-eutrophication abilities and characteristics of Ulva pertusa, a marine green alga, were investigated in Qingdao Yihai Hatchery Center from spring to summer in 2005 by analyzing the dynamic changes in NH+4, NOˉ3, NO2ˉ as well as the total dissolved inorganic nitrogen (DIN). The results show that the effluent wastewater produced by fish aquaculture had typical eutrophication levels with an average of 34.3 μmol L-1 DIN. This level far exceeded the level IV quality of the national seawater standard and c...     

Comparative Studies on Phosphorus Uptake and Growth Kinetics of the Microalga Tetraselmis subcordiformis and the Macroalga Ulva pertusa

Short-term uptake experiments and long-term semicontinuous culture experiments were performed under the condition of phosphorus (P) limitation to estimate and compare the P uptake and growth kinetics of the microalga Tetraselmis subcordiformis and the macroalga Ulva pertusa. Two new parameters, the maximum specific uptake rate (Vm^sp) and the maximal growth efficiency (β), are introduced to achieve uniformity for the comparison of nutrient uptake and growth efficiency between microalgae and macroalgae. T. subcordiformis possesses 3 times lower half saturation uptake constant, 4 times higher maximal growth rate and 20 times higher maximum specific uptake rate than U. pertusa, while U. pertusa possesses 4 times higher maximal growth efficiency than T. subcordiformis.     

De-eutrophication of effluent wastewater from fish aquaculture by using marine green alga Ulva pertusa

The de-eutrophication abilities and characteristics of Ulva pertusa, a marine green alga, were investigated in Qingdao Yihai Hatchery Center from spring to summer in 2005 by analyzing the dynamic changes in NH ₄ ⁺ , NO ₃ ^? , NO ₂ ^? as well as the total dissolved inorganic nitrogen (DIN). The results show that the effluent wastewater produced by fish aquaculture had typical eutrophication levels with an average of 34.3 μmol L^?1 DIN. This level far exceeded the level IV quality of the national seawater standard and could easily lead to phytoplankton blooms in nature if discarded with no treatment. The de-eutrophication abilities of U. pertusa varied greatly and depended mainly on the original eutrophic level the U. pertusa material was derived from. U. pertusa used to living in low DIN conditions had poor DIN removal abilities, while materials cultured in DIN-enriched seawater showed strong de-eutrophication abilities. In other words, the de-eutrophication ability of U. pertusa was evidently induced by high DIN levels. The de-eutrophication capacity of U. pertusa seemed to also be light dependent, because it was weaker in darkness than under illumination. However, no further improvement in the de-eutrophication capacity of U. pertusa was observed once the light intensity exceeded 300 μmol M² S^?1. Results of semi-continuous wastewater replacement experiments showed that U. pertusa permanently absorbed nutrients from eutrophicated wastewater at a mean rate of 299 mg/kg fresh weight per day (126 mg/kg DIN during the night, 173 mg/kg in daytime). Based on the above results, engineered de-eutrophication of wastewater by using a U. pertusa filter system seems feasible. The algal quantity required to purify all the eutrophicated outflow wastewater from the Qingdao Yihai Hatchery Center into oligotrophic level I clean seawater was also estimated using the daily discharged wastewater, the average DIN concentration released and the de-eutrophication capacity of U. pertusa.     

Effect of CO2 enrichment on competition between Skeletonema costatum and Heterosigma akashiwo

We investigated the effect of CO₂ enrichment and initial inoculum density on competition between Skeletonema costatum and Heterosigma akashiwo, two common algae seen in algal blooms. The initial inoculum density (0.2×10⁴, 0.4×10⁴, 0.8×10⁴ cells/ml) had a significant effect on population growth and competition between H. akashiwo and S. costatum. The time required for population growth to reach the exponential growth phase and stationary phase decreased significantly as the initial density increased. When the two species were cultured together, S. costatum tended to outcompete H. akashiwo, especially when present at higher initial ratios. CO₂ enrichment (5 000 μl/L CO₂) increased the maximum population density and carrying capacity of H. akashiwo but decreased these measures for S. costatum. Thus, CO₂ enrichment favored the growth of H. akashiwo over S. costatum.     

Comparative chloroplast genomes of Ulva prolifera and U. linza (Ulvophyceae) provide genetic resources for the development of interspecific markers

Journal of Oceanology and Limnology - The green seaweeds Ulva linza and U. prolifera are closely related species. They usually co-occur widely and have important ecological significance as primary...     

舌状蜈蚣藻Grateloupia livida(Harv.)Yamada生殖器官的研究

本种为我国南方常见一种经济红藻。藻体直立,叶片窄带状,单条或叉状,全缘或有小育枝,体下部淅细成柄状。藻体不中空。我们发现它在生殖器官发育过程中也出现三个新特徵:1、少数果胞枝与助细胞可在同一的生殖枝丛中形成,2、少数果胞枝枝丛中可出现2个果胞枝;3、少数助细胞枝丛中可出现2个助细胞。     

Antimicrobial Activity of Ulva reticulata and Its Endophytes

Seaweeds are known to exhibit various antimicrobial properties,since it harbours an enormous range of indigenous bioactive compounds.The emergence of drug resistant strains has directed to the identification of prospective metabolites from seaweed and its endophytes,thereby exploiting the properties in resisting bacterial diseases.The current study was aimed to assess the antimicrobial activity of extracts obtained from Ulva reticulate,for which metabolites of Ulva reticulata and its endophytes were extracted and assessed against human pathogens like Staphylococcus aureus,Escherichia coli,Pseudomonas aeruginosa,Salmonella typhi,and Bacillus subtilis.It was observed that the hexane extract of isolate VITDSJ2 was effective against all the tested pathogens but a significant inhibition was observed for Staphylococcus aureus and Escherichia coli.Further,Gas chromatography coupled with Mass spectroscopy(GC-MS) revealed the existence of phenol,3,5-bis(1,1-dimethylethyl) in the crude hexane extract which is well-known to possess antibacterial activity.The effective isolate VITDSJ2 was identified to be the closest neighbour of Pseudomonas stutzeri by phenotypic and genotypic methods.The crude extracts of the seaweed Ulva reticulata was also screened for antibacterial activity and the hexane extract was effective in showing inhibition against all the tested pathogens.The compound in the crude extract of Ulva reticulata was identified as hentriacontane using GC-MS.The extracts obtained from dichloromethane did not show significant activity in comparison with the hexane extracts.Hence the metabolites of Ulva reticulata and the bacterial secondary metabolites of the endophytes could be used in the treatment of bacterial infections.     

Experimental study on the interspecific interactions between the two bloom-forming algal species and the rotifer Brachionus plicatilis

The interspecific interactions between the rotifer Brachionus plicatilis and two harmful algal blooms (HAB) species were investigated experimentally by single culture method. B. plicatilis population and the growth of the two algae were compared at different algal cell densities. The results demonstrated that the B. plicatilis obtained sufficient nutrition from Prorocentrum donghaiense to support net population increase. With exposure to 2.5×10⁴ cells mL⁻¹ of P. donghaiense, the number of B. plicatilis increased faster than it did when exposed to other four algal densities (5, 10, 15 and 20 ×10⁴ cells mL⁻¹), and the increase rate of B. plicatilis population (r) at this algal density was 0.104 ± 0.015 rd⁻¹. Cell densities of P. donghaiense decreased due to the grazing of B. plicatilis. In contrast, Heterosigma akashiwo had an adverse effect on B. plicatilis population and its growth was largely unaffected by rotifer grazing. In this case, B. plicatilis population decreased and H. akashiwo grew at a rate similar to that of the control.     

Structural analysis and anti-complement activity of polysaccharides extracted from Grateloupia livida (Harv.) Yamada

Polysaccharides were extracted from Grateloupia livida(Harv.) Yamada using hot water(extracted product denoted WGW) and then degraded in dilute sulfuric acid(degraded product denoted WGWD). The degraded mixture was then separated into four fractions through anion exchange chromatography on 2-diethylaminoethanol(DEAE)-Bio-Gel Agarose FF gel. Electrospray ionization collision-induced dissociation tandem mass spectrometry(ESI-CID-MS/MS) was performed to elucidate the structural features of all fractions. In combination with nuclear magnetic resonance spectroscopy(NMR)and infrared spectroscopy(IR) data, the major polysaccharide structures were concluded to be μ-carrageenan and κ-carrageenan. μ-Carrageenan usually has a backbone of alternating 1,3-linked β-D-galactopyranose residues sulfated at C-4 and 1,4-linked a-D-galactopyranose residues sulfated at C-6, while κ-carrageenan consists of alternating 1,3-linked β-D-galactopyranose residues sulfated at C-4 and 1,4-linked a-D-3,6-anhydrogalactopyranose residues. Trace v-carrageenan, composed of 1,3-linked β-D-galactopyranose residues sulfated at C-4 and 1,4-linked a-D-galactopyranose residues sulfated at C-2 and C-6, was also detected. Furthermore, the polysaccharide had a backbone comprising 1,3-linked β-D-galactopyranose and1,4-linked α-L-galactopyranose sulfated at C-6, which is the agarose precursor. The hydroxy groups in the galactopyranose were partially substituted by methyl and pyruvic acid acetal(PA) groups. The anticomplementary activities of WGW and its derivatives against classical pathways were measured. The native polysaccharides in WGW had higher activities, while the derivatives had much weaker activities. This indicated that the molecular weight and sulfate content were important factors affecting the anti-complement activity.     

Interspecific competition and allelopathic interaction between Karenia mikimotoi and Dunaliella salina in laboratory culture

Algal allelopathy is a manifold ecological/physiological phenomenon that is focused on chemical interactions and autotoxicity. We investigated the allelopathic interactions between Karenia mikimotoi and Dunaliella salina in laboratory cultures based on diff erent temperature(15°C, 20°C, and 25°C) and lighting(40, 80, and 160 μmol/(m~2 ·s)) conditions. The growth of D. salina in bi-algae culture(1:1 size/density) was significantly restrained. The results of cell-free filtrate culture indicate that direct cell-tocell contact was not necessary in interspecific competition. Further experimental results demonstrated that allelochemicals released from K. mikimotoi were markedly influenced by both temperature( P =0.013) and irradiance( P =0.003), resulting in diff erent growth characteristics of D. salina in filtrate mediums. Compared with the plateau period, K. mikimotoi exudates in the exponential phase had a stronger short-term inhibition eff ect on D. salina in normal conditions. A clear concentration-dependent relationship was observed in the eff ect of allelochemicals released from K. mikimotoi with low-promoting and high-repressing eff ects on D. Salina in a short time-scale. In addition, allelopathic substances remain stable and eff ective under high temperature and pressure stress. Many flocculent sediments adhering with D. salina cells were observed in all filtrate mediums, while the quantity and color depended on the original culture conditions.     

Effects of iron and humic acid on competition between Microcystis aeruginosa and Scenedesmus obliquus revealed by HPLC analysis of pigments

Iron is a vital micro nutrient for growth of bloom-forming Microcystis aeruginosa and competition with other algae,and its availability is affected by humic acid.The effect of iron and humic acid on growth and competition between M.aeruginosa and Scenedesmus obliquus was assessed.The results showed the growth of M.aeruginosa and S.obliquus in mono-cultures was inhibited by humic acid at low iron concentrations(0.01 mg/L);the maximum inhibition ratios were 67.84% and 38.31%,respectively.The inhibition of humic acid on the two species was significantly alleviated when iron concentrations were1.00 mg/L,with the maximum inhibition rate reduced to 5.82% for M.aeruginosa and to 23.06% for S.obliquus.S.obliquus was the dominant species in mixed cultures,and the mutual inhibition between M.aeruginosa and S.obliquus at low iron concentration was greater than that at high iron concentration.The inhibition of S.obliquus on M.aeruginosa was reduced at low iron concentrations;it increased at high iron concentrations,as concentrations of humic acid rose.     

Molecular Grouping of Grateloupia Tissues Collected Along Chinese Coast and Microsatellite Diversity Analysis of G. asiatica

Genus Grateloupia is one of the most speciose genera in family Halymeniales. It is also one of the sources for natural materials, food and medicine. With different environments, Grateloupia change their morphological characteristics, making their morphological identification very difficult. In addition, few of the species diversity in this genus has been described before. In this study, phylogenetic analysis based on rbc L gene sequence was employed to group Grateloupia collected from three locations along Chinese coast. The microsatellites were also used to evaluate their genetic diversity. In total, the tissue parts of 6 putative species were collected from G. asiatica, G. livida, G. lanceolate, G. catenata, G. turuturu and G. filicina. In order to evaluate their genetic diversity and then conserve them better, 40 microsatellites available for Grateloupia were used to evaluate their genetic diversity, and 11 microsatellites were found to be applicable to determine the genetic diversity of G. asiatica. It was found that the genetic diversity of G. asiatica around Qingdao was very rich. We suggested that the species of genus Grateloupia should be identified based on rbc L phylogenetic analysis before the diversity evaluation with microsatellites. The microsatellites should be developed for each species of Grateloupia so that their genetic diversity can be evaluated appropriately.     

Investigation of the decline of Ulva prolifera in the Subei Shoal and Qingdao based on physiological changes

It has been a scientific consensus that Ulva prolifera green tide that break out annually between May and August in the recent decade off eastern coast of Yellow Sea. To investigate the ecological mechanism of the decline of U. prolifera green tide, we compared the physiological characteristics of U. prolifera samples collected in three stages of the green tide in Subei Shoal north Jiangsu, the initiation point, on May 10(early, the initiation), July 10(middle, the outbreak), and in Taipingjiao, Qingdao on August 10(late, the decline). Compared to the early samples, the middle, and late samples showed a lower chlorophyll content and photosynthetic e fficiency at a higher lipid peroxidation level. The middle and later samples had fewer chloroplasts in the cells of U. prolifera than those in the early samples. In addition, the cells of U. prolifera sampled in the late stage showed ruptured and deformed cell walls. Differences in physiological function were reflected in the growth rate. Both the middle and late U. prolifera samples presented negative growth rates. Correlation analysis results show that the rising temperature was mainly responsible for the local decline of U. prolifera green tide. The high light-intensity that could induce the photoinhibition was also an important factor for the decline. Therefore, U. prolifera population that remained in the Subei Shoal and those that northward drifted to Qingdao experienced the same decline processes: rising temperature and continuous high light conditions in the late phase of green tide reduced the photosynthetic capacity and destroyed the antioxidant system of the thallus, which lead to decrease of biomass. The only difference is that the temperature in the Subei Shoal rose earlier than that in Qingdao; thus, U. prolifera remaining in the Subei Shoal went disappeared first.     

Effects of elevated solar UV-B radiation from ozone depletion on terrestrial ecosystems

In the last three decades much research has been carried out to investigate the biological effects of a thinning stratospheric ozone layer accompanied by an enhanced level of solar ultraviolet-B radiation at the Earth‘s surface.Enhanced UV-B radiation affects ecosystems in many ways directly and indirectly. The responses can be biochemical, physiological, morphological or anatomical, and the direction of the response can vary between different species, communities and ecosystems. In this paper we firstly introduce general concepts, and methods for measuring the ecological effects of UV-B radiaticn. Secondly, we provide an overview interpretation of the effects of enhanced UV-B on terrestrial ecosystems from recent studies.These studies include effects of UV-B on growth and reproduction, composition of communities,competitive balance, decomposition of litter, and interactions with other factors etc. Finally, we recommend future research directions to identify the effects of elevated UV-B radiation on ecosystems in China.     

Screening and isolation of the algicidal compounds from marine green alga Ulva intestinalis

Twenty species of seaweed were collected from the coast of Zhejiang, China, extracted with ethanol, and screened for algicidal activity against red tide microalgae H eterosigma akashiwo and Prorocentrum micans. Inhibitory eff ects of fresh and dried tissues of green alga U lva intestinalis were assessed and the main algicidal compounds were isolated, purifi ed, and identifi ed. Five seaweed species, U. intestinalis, U. fasciata, Grateloupia romosissima, Chondria crassicaulis, and Gracilariopsis lemaneiformis, were investigated for their algicidal activities. Fresh tissues of 8.0 and 16.0 mg/m L of U. intestinalis dissolved in media signifi cantly inhibited growth of H. akashiwo and P. micans, respectively. Dried tissue and ethyl acetate(Et OAc) extracts of U. intestinalis at greater than 1.2 and 0.04 mg/m L, respectively, were fatal to H. akashiwo, while its water and Et OAc extracts in excess of 0.96 and 0.32 mg/m L, respectively, were lethal to P. micans. Three algicidal compounds in the Et OAc extracts were identifi ed as 15-ethoxy-(6z,9z,12z)-hexadecatrienoic acid(I),(6E,9E,12E)-(2-acetoxy- β- D-glucose)-octadecatrienoic acid ester(II) and hexadecanoic acid(III). Of these, compound II displayed the most potent algicidal activity with IC_(50) values of 4.9 and 14.1 μg/m L for H. akashiwo and P. micans, respectively. Compound I showed moderate algicidal activity with IC_(50) values of 13.4 and 24.7 μg/m L for H. akashiwo and P. micans, respectively. These fi ndings suggested that certain macroalgae or products therefrom could be used as ef fective biological control agents against red tide algae.