Environmental heterogeneity and productivity drive the assemblage of benthic diatom:a case study of the Three Gorges Reservoir

Dam construction has a critical effect on river ecosystems in the world,resulting in a rapid decline in biodiversity and ecosystem health.However,the effect of dam construction on the assemblage pattern of benthic diatoms remains unclear.The benthic diatoms assemblages in the tributary backwater area of the Three Gorges Reservoir(TGR)were investigated under low water level(LWL)and high water level(HWL)conditions.Results show that Discostella stelligera,Nitzschia palea,and Craticula subminuscula were dominant species in LWL,while Achnanthidium minutissimum and Nitzschia dissipata were dominant in HWL.Furthermore,environmental variables,productivity parameters,diversity indices,and community similarity were found significantly different between LWL and HWL periods.The Mantel test indicated that both environmental and spatial factors had significant effects on diatom communities in backwater area,while productivity was also a key driving force in LWL.The variation partitioning analysis(VPA)further demonstrated that environment factors could explain the largest variance of diatom assemblages in HWL(9%)and LWL(11%),followed by spatial factors.The relative importance of productivity to diatom community was significantly enhanced in LWL,but only a slight effect was found in HWL.These results indicate that the diatom assemblages were shaped by both environmental filtering and spatial factors.The relative importance of spatial factors depended on the degree of productivity.Therefore,the homogenization of diatom communities due to environmental disturbance,e.g.eutrophication and dam building,is the underlying mechanism in assembling the benthic diatoms.

STUDIES ON CULTURE CONDITIONS OF BENTHIC DIATOMS FOR FEEDING ABALONE Ⅲ. EFFECTS OF IRON AND SILICON NUTRIENTS AND OF ORTHOGONAL COMBINATIONS OF NITROGEN,PHOSPHORUS,IRON AND SILICON ON GROWTH RATE

Effects of iron and silicon nutrients and of orthogonal combinations of nitrogen, phosphorus, iron and silicon on the growth rate of three benthic diatoms were studied by using an in situ OD measurement method. The results of monofactor tests of ironand silicon shawed that Fe-EDTA was bettef than ferric citrate in the culture of these diatoms;that the favourable concentration of Fe-EDTA was about 0.5 mg/L of Fe and that of silicate was 2.5 mg/L of Si or more.The orthogonal test showed that the optimal concentration ratios(mg/L)of nitrogen, phosphorus, iron and silicon were: 5. 0: 0. 25: 0.5: 2. 0 for Cocconeis scutellum var. parva; 2.5: 1.0: 1.0: 2.0 for Amphora coffeaeformis; and 5.0: 0. 15: 0.5: 2.0 for N. mollis.

Distribution patterns of benthic diatoms during summer in the Niyang River,Tibet,China

The aim of this study was to investigate the distribution, density, community structure and biodiversity characteristics of benthic diatoms, and to analyze whether differences in species composition and abundance exist in different regions of the Niyang River, Tibet. Among the 157 taxa observed in 15 sampling sites in the main river and tributary, most were casual species (>100), the relative abundance of the genera Achnanthes and Fragilaria was 67% of the total relative abundance. Achnanthes minutissima was the most important species and dominated the whole river reaches (average relative abundance was 30%); the average diatom densities were 7.4 × 105 cell/cm2 at all sites, and increased slowly from the upper section to downriver. The significant indicator taxa with higher relative abundance were Achnanthes biasolettiana (18.0%) and Fragilaria arcus (18.2%), Fragilaria capucina var. vaucheriae (31.2%), Fragilaria construens var. venter (11.3%) and Cymbella affinis (11.0%) in the upper, tributary and mid-river sections, respectively. Achnanthes minutissima was the most abundant species (56%) in the downriver section. Biodiversity indices showed a gradual decrease from the up-to down-river section, and dominant species were more abundant in the upper and mid-river sections than in the downriver section. A two-way indictor species analysis (TWINSPAN) of diatom composition clearly showed four different groups, namely the upper, mid, lower and tributary sections. Detrended correspondence analysis (DCA) supported the results of TWINSPAN, and the characteristics of site distribution and species composition in the Niyang River supported the spatial structure of diatom assemblages. This study indicates that bio-assessment programs utilizing benthic diatoms could clearly benefit lotic water with regional stratification.

Water quality assessment of benthic diatom communities for water quality in the subalpine karstic lakes of Jiuzhaigou,a world heritage site in China

Jiuzhaigou, characterized by its magnificent waterscapes and subalpine karstic features, is both a World Heritage Site and a World Biosphere Reserve in southwestern China. In recent years, this unique ecosystem has shown signs of stress due to increasing tourism activities within the reserve. The various routine methods, which monitor physical and chemical properties, do not fully reflect water quality in the subalpine and alpine lakes, while the indicators using aquatic organisms to evaluate the water quality or status of the subalpine lakes are poorly reported. Thus, in this study, benthic diatoms from multiple habitats in Jiuzhaigou were sampled and assessed for water quality monitoring. Canonical Correspondence Analysis(CCA) showed that the canonical coefficients for elevation, water temperature and total nitrogen on the first Canonical Correspondence Analysis axis were-0.84, 0.78 and-0.53, respectively, environmental variables associated with the distribution patterns of benthic diatoms. The dominance of diatom taxa indicative of nutrient enrichment indicates a clear trend toward eutrophication in the Pearl Shoal and Colorful Lake, two of the sites mostly visited by tourists. It was observed that the effect of the type of substratum on diatom community composition is not significant in subalpine lakes. The most dominant species in Jiuzhaigou lakes are the genera Achnanthes, Fragilaria, Cymbella, Cocconeis, Diatoma and Denticula. In combination with dominant and sensitive species in the benthic diatom communities, CCA and CA methods can be used to evaluate the impact of human activities on subalpine karstic lakes. The dominance of diatom taxa is indicative of nutrient enrichment and the results of CCA and CA indicate a clear trend toward eutrophication in the Pearl Shoal and Colorful Lake, two of the sites mostly visited by tourists.

STUDIES ON CULTURE CONDITIONS OF BENTHIC DIATOMS FOR FEEDING ABALONE I.EFFECTS OF TEMPERATURE AND LIGHT INTENSITY ON GROWTH RATE

Effects of temperature and light intensity on the groWth rate of four species of benthic diatoms for feeding abalone were studied by using a novel method (in situ optical density measurement)which was simple, convenient, fast, accurate and reliable for determining biomass of benthic algae. The results showed that the favourable temperature and light intensity were as follows: for Amphora coffeaeformis, 30℃, 18 W/m2 for Cocconeis scutellum var. parv. 18℃, 20 W/m2; for Navicula Corymbosa, 18℃. 12.4 W/m2;for Navicula mollis, 24℃, 6 W/m2.

Biomass,species composition and diversity of benthic diatoms in mangroves of the Houyu Bay,China

The biomass, species composition and diversity of benthic diatom assemblages in mud-flat soils in Kandelia candel (L.) Druce communities with and without vegetation were studied seasonally at the Houyu Bay in Fuding City, Fujian Province, China. A total of 103 taxa were identified (including varieties). Eighty-four taxa were found in the mud-flat with vegetation and 74 taxa in the mud-flat without vegetation, while the biomass was large in January and April and decreased from July to October. The most abundant species in the mud-flat with vegetation are Nitzschia cocconeiformis, Gyrosigma scalproides and N. fasciculata, compared with G. scalproides and N. obtusa var. scalpelliformis in the mud-flat without vegetation. High H' values at 2 sites during all seasons suggest that diatom assemblages in the sediments of the Houyu Bay represent an original environment. Multi-dimensional scaling of diatom assemblages from mud-flats with and without vegetation shows that a slight seasonal change and only a single association occur in the mangroves.

STUDIES ON CULTURE CONDITIONS OF BENTHIC DIATOMS FOR FEEDING ABALONE Ⅱ. EFFECTS OF SALINITY pH, NITROGENOUS AND PHOSPHATE NUTRIENTS ON GROWTH RATE

Effects of salinity , pH, nitrogenous and phosphate nutrients on the growth rate of four species of benthic diatoms were studied by using the method of in situ optical density measurement . The optimal culture conditions for the four species of diatoms are as follows: for Amphora coffeaeformis , s 35 ; pH 8.5; N03 -N 1.54, NH4-N, 7.0; CO (NH2)2-N, 2.5 (mg/L); PO43--P 1.13 (mg/L) ; for Cocconeis scutellum var parva , s 30 ; pH 8.5 ; NO3-N 3.08, NH4+-N 3.5, CO(NH2)2-N 5.0 (mg/L); pO43-－P0.283 (mg/L), for Navicula corymbosa s 25; pH 8.0; N03- －N 1.54, NH4+ -N 3.5, CO(NH2)2-N 5.0(mg/L); PO43-－P0.565 (mg/L), for Navicula mollis , s 25 ; pH 8.0; NO3- － 1.54 NH4+ - N 1.75, CO(NH2)2 -N 1.25 (mg/L), P043-－P 0.141(mg/L).

Benthic diatom community response to metal contamination from an abandoned Cu mine:Case study of the Gromolo Torrent(Italy)

Environmental contamination has become a global problem of increasing intensity due to the exponential growth of industrialization. One main debated issue is the metal contamination of rivers receiving Acid Mine Drainage(AMD) from active/abandoned mines. In order to assess the quality of lotic systems, diatoms are commonly used, as their assemblage modifies on the basis of changes in environmental parameters. Benthic diatom changes were analyzed along the metal-impacted Gromolo Torrent(Liguria, NW Italy) with the aim of understanding the effects of input from the abandoned Libiola Cu mine. The results support the hypothesis that metals from AMD lead to massive changes in diatoms, resulting in low biological diversity and in a shift of dominance, passing from the genera Cymbella and Cocconeis to more tolerant and opportunistic species, such as Achnanthidium minutissimum and Fragilaria rumpens. The high concentrations of labile metals, measured through Diffusion Gradients in Thin-films(DGT) immediately downstream of the two AMD inputs in the torrent, corresponded to a sudden decrease in the presence of diatoms, indicating the possible reaching of acute toxic levels. In particular,A. minutissimum dominated the mining area and was positively correlated with Cu and Zn;whereas F. rumpens bloomed downstream of this area, where the metal content was diluted,and was positively correlated with As and Pb. Finally, an important abundance of Nitzschia palea and teratological forms of A. minutissimum and F. rumpens were observed downstream from the mine, indicating that metals may have an important impact on diatoms up to the torrent mouth.

Deformity frequencies of benthic marine diatoms associated with contaminated sediments in Hong Kong

The relationship between contaminated sediments and deformity frequencies for benthic diatoms was the subject of this study. There were two basic types of diatom deformities observed in this study of Tolo Harbour diatoms: 1. Diatoms with deformed cell wall morphology and 2. diatoms with deformed ornamentation. Deformed individuals of Fragilaria capucina and Achananthes hauckiana Grun. displayed external cell wall deformities while deformed individuals of Diatoma displayed deformities in valve ornamentation. Abnormal cell morphology was used as an indicator of a degraded ecosystem. There was a significant correlation( P <0.05, r s=0.652) between sediment toxicity as reflected by the microtox test and benthic diatom diversity. Species diversity and species richness levels at the twelve sites were closely correlated with one another and inversely correlated with sediment toxicity as reflected by our microtox results( r s=0.809, P <0.01). The microtox test for acute toxicity was correlated ( P <0.05) with diatom species richness. The deformity frequencies and microtox tests were not significantly correlated. This lack of correlation was expected as in numerous laboratory studies, toxic substances were not necessarily mutagenic. The use of diatom deformity frequencies as a means of assessing the mutagenic/teratogenic impacts of anthropogenic substances on a marine benthic diatom community necessitates the enumeration of a large number of diatoms making this method extremely labor intensive.

Diatom diet selectivity by early post-larval abalone Haliotis diversicolor supertexta under hatchery conditions

Benthic diatoms constitute the primary diet of abalone during their early stages of development.To evaluate the dietary preferences of early post-larval abalone,Haliotis diversicolor supertexta,we analyzed the gut contents of post-larvae that settled on diatom films.We compared the abundance and species diversity of diatom assemblages in the gut to those of the epiphytic diatom assemblages on the attachment films,and identified 40 benthic diatom species in the gut contents of post-larvae 12 to 24 d after settlement.The most abundant taxa in the gut contents were Navicula spp.,Amphora copulate,and Amphora coffeaeformis.Navicula spp.accounted for 64.0% of the cell density.In the attachment films,we identified 110 diatom species belonging to 38 genera.Pennate diatoms were the dominant members including the species Amphiprora alata,Cocconeis placentula var.euglypta,Cylindrotheca closterium,Navicula sp.2,and A.coffeaeformis.Nano-diatoms(<20 μm in length) accounted for a considerable proportion of the total species number and cell density of the diatom assemblages in the gut contents and on the films.This suggests that nano-diatoms are important to the efficient production of abalone seed.The difference of the composition and abundance of diatoms between in the guts and on the biofilms suggests that early post-larval grazing was selective.An early post-larval abalone preferred nano-diatoms and the genera Navicula and Amphora during the month after settlement.

Response of benthic algae to environmental conditions in an urban lake recovered from eutrophication, China

Benthic algae communities dominate the primary production in littoral zone of shallow lake.To tmderstand the long-term effect of alteration in the composition of benthic algae community assemblage in such as a lake in China,we analyzed the benthic algae developments and indicators in the Donghu Lake in Wuhan,central China in 2004 and 2014.We compared the benthic algae biomass,compositions,and species richness of aquatic macrophytes and the changes of primary physicochemical parameters.The results show that in the 10-year period,chl a and conductivity declined significantly but nutrient level of the whole lake remained largely stable.The benthic algae biomass doubled and the relative proportion of green algae increased,whereas the benthic diatom ratio decreased.The benthic diatom assemblages and taxa differed in a number of ways,showing more epiphytic diatom species,and the relative abundance and species richness changed markedly.The number of aquatic macrophyte species increased from 3 in 2004 to 15 in 2014,presenting a remarkable recovery from previous eutrophication conditions.The changes of water level,chl a,and conductivity played a crucial role in governing aquatic macrophytes re-colonization in the littoral zones in the period.The ecological characteristics of littoral benthic diatoms reflect habitat coupling as indicated by redundancy analysis.Therefore,the close link between benthic algae and macrophyte recovery demonstrates that the benthic algae metrics are much more useful than nutrient levels to quantify the process of restoration in the lake.

Environmental change and its effects on inter-decadal variations of diatom production, species composition and frustule dissolution in a coastal marginal sea

The implications of climate change during the second half of the 20 th century have been reported throughout the world. Although marginal seas are sensitive to climate change and anthropogenic impacts, relatively little attention has been given to the South East Asian marginal seas. Thus, to bridge this gap in knowledge, a sediment core was collected from the coastal areas of the Leizhou Peninsula in the South China Sea(SCS) to study the inter-decadal climate change and its consequences using diatom species composition as a proxy record. Diatom absolute abundance varied from 2 300 to 68 000 and averaged 16 000 valves per gram of dry weight(v/gdw). The fractional dissolution index(Fi) was usually below 0.5, which indicates low to moderate preservation of diatom valves at coastal area of the SCS. At the inter-decadal time scale, total diatom abundance was high for the period after 1972, which coincided with 1) increased percentage of planktonic diatom abundance and Fi; 2) emergence and dominance of high productivity indicative cosmopolitan species such as T halassionema nitzschioides and Paralia sulcata(their relative abundance increased from <1.5% to >7% for the period before and after 1972, respectively); 3) decreased relative abundance of the small-sized eutrophication indicative species, C yclotella striata, from 70% to 40%. This study reveals that variations in the abundance of diatoms preserved in the sediment was a function of both production and dissolution/preservation of diatom valves, which in turn was intimately connected to the prevailing environmental/climatic conditions. In conclusion, these data reveal the existence of substantial changes in the coastal SCS in response to the 1970 s climate shift that was recorded in dif ferent parts of the world.

Decadal variations in diatoms and dinoflagellates on the inner shelf of the East China Sea, China

Diatoms and dinoflagellates are two major groups of phytoplankton that flourish in the oceans, particularly in coastal zone and upwelling systems, and their contrasting production have been reported in several world seas. However, this information is not available in the coastal East China Sea(ECS). Thus, to investigate and compare the decadal trends in diatoms and dinoflagellates, a sediment core, 47-cm long, was collected from the coastal zone of the ECS. Sediment chlorophyll-a(Chl-a), phytoplankton-group specific pigment signatures of diatoms and dinoflagellates, and diatom valve concentrations were determined. The sediment core covered the period from 1961 to 2011 AD. The chlorophyll-a contents ranged from 2.32 to 73 μg/g dry sediment(dw) and averaged 9.81 μg/g dw. Diatom absolute abundance ranged from 29 152 to 177 501 valve/gram(v/g) dw and averaged 72 137 v/g dw. Diatom valve and diatom specific pigment marker concentrations were not significantly correlated. Peridinin increased after the 1980 s in line with intensified use of fertilizer and related increases in nutrient inputs into the marine environment. The increased occurrence of dinoflagellate dominance after the 1980 s can be mostly explained by the increase in nutrients. However, the contribution of dinoflagellates to total phytoplankton production(Chl-a) decreased during the final decade of this study, probably because of the overwhelming increase in diatom production that corresponded with the construction of the Three Gorges Dam(TGD) and related light availability. Similarly, the mean ratio of fucoxanthin/peridinin for the period from 1982 to 2001 was 6% less than for 1961 to 1982, while the ratio for 2001 to 2011 was 45.3% greater than for 1982 to 2001. The decadal variation in the fucoxanthin/peridinin ratio implies that dinoflagellate production had been gradually increasing until 2001. We suggest that the observed changes can be explained by anthropogenic impacts, such as nutrient loading and dam construction.

Feeding and Growth Characteristics of a Diatom-Feeding Flagellate Isolated from the Bottom Sediment of Onagawa Bay, Northeastern Japan

In recent years, several marine heterotrophic nanoflagellates have been reported to feed on diatoms much larger than themselves. However, very little is known about the grazer-prey relationships between heterotrophic nanoflagellates and diatoms in aquatic ecosystems. A diatom-feeding flagellate was discovered in the bottom sediment of OnagawaBay. It fed and proliferated on diatoms, especially Skeletonema costatum sensu lato. This study determined growth and ingestion rates of the flagellate on Skeletonema costatum s.l. under laboratory conditons. Its grazing pressure on the sinking flux of S. costatum s.l. was calculated by combining field data. Specific growth rate of the flagellate increased with increasing prey concentration. The maximum specific growth rate was 0.79 d–1 and maximum ingestion rate of the flagellate was 0.66 ng·C·grazer–1·d–1. Calculated grazing pressure of the flagellate on S. costatum s.l. flux was up to 25.6%. The results imply that the flagellate has a considerable grazing impact on S. costatum s.l. flux at least in a restricted season of the year. Therefore, the present study suggests that this benthic flagellate plays an important role in pelagic-benthic coupling inOnagawaBay.

中国曲丝藻属新记录种——温泉曲丝藻(Achnanthidium thermalis)

底栖硅藻是水体生态系统中的重要初级生产者,由于其对环境具有敏感性,可用做水体生态系统的指征生物,因此底栖硅藻生物多样性调查工作尤为重要。本研究于乌梁素海的底栖硅藻调查中发现了中国曲丝藻属新记录种—温泉曲丝藻(Achnanthidium thermalis Rabenhorst)。结合光学显微镜和电子显微镜进行观察,发现该种具备曲丝藻属基本特征,又因其具有中央区两侧线纹不对称,仅一侧线纹延伸至壳缘的特征,我们将其鉴定为温泉曲丝藻。进一步分析电子显微镜下该种特征,发现其具有典型的双列线纹,而曲丝藻属的常见种类线纹特征通常为单列线纹。依照分类依据,将其鉴定为温泉曲丝藻。

无毒防污涂料表面底栖硅藻附着评价的实验方法

在实验室培养了底栖硅藻目标附着生物,利用显微镜、图像处理技术等实验研究了底栖硅藻在低表面能无毒防污涂层上的附着面积分数,并测定了附着底栖硅藻的叶绿素a值。研究结果表明,文中提出的海洋生物附着评价实验方法科学有效,并且附着底栖硅藻的叶绿素a值与其在无毒防污涂层上的附着面积分数成反比。

两种海洋底栖硅藻的培养条件研究

对春夏季节采集于中国海南琼海鲍鱼场的底栖硅藻进行分离纯化,对得到的亚历山大菱形藻(Nitzschia alexand-rina)和矮小卵形藻(Cocconeis diminuta)两种底栖硅藻进行了单因子最佳培养条件的实验研究.培养两种底栖硅藻的营养盐最佳浓度、盐度、光照强度、温度条件分别为:亚历山大菱形藻:NO3--N 2.5 mg/L,PO33--P 0.5 mg/L,Fe-EDTA-Fe 0.1mg/L,SiO23-Si 0.5 mg/L,35,5 500 lx,30℃.矮小卵形藻:NO3--N 2.5 mg/L,PO43--P 1.5 mg/L,Fe-EDTA-Fe 0.1 mg/L,SiO32--Si 0.5 mg/L,30,3 300 lx,30℃.实验结果表明:两种底栖硅藻所需的NO3--N的浓度较前人报道的其他硅藻培养的实验结果偏低且影响不大,其他营养盐成分铁、硅、磷对硅藻生长有较大影响;基础生态因子温度、盐度和光照影响也较大,温度对这两种硅藻的生长影响最为显著.本研究数据拟对鲍苗种生产中饵料底栖硅藻培养起参考作用.

干露和冷藏对坛紫菜及杂藻存活与生长的影响

将人工养殖的坛紫菜叶状体及与其有生长竞争关系的5种大型杂藻——肠浒苔、条浒苔、孔石莼、真江蓠、水云以及卵形藻等进行干露和冷藏实验．结果表明，坛紫菜叶状体干露至含水率10％～15％后直接培养，其成活率在99％以上，增重率与未经干露组的相比无显著差异；大型杂藻干露后含水率低于25％时则全部死亡；坛紫菜叶状体含水率为10％～15％时，在低温-20℃冷藏30d后进行培养，成活率达99％～100％，当含水率低于10％时，其成活率低于30％；坛紫菜叶状体含水率高于或低于10%～15％时进行低温冷藏，均会影响其成活率及冷藏后培养时的藻体增重率；与坛紫菜叶状体冷藏相同天数的大型杂藻，其死亡率达到100％；干露和冷藏可以有效地杀死与坛紫菜叶状体有竞争关系的杂藻，并且可以应用于生产以提高坛紫菜产量．

光照和盐度对8种底栖硅藻生长及其生理生化成分的影响

研究了不同光照强度和盐度条件对8种海洋底栖硅藻生长及其生理生化成分的影响.结果表明:8种底栖硅藻生长最适光照强度和盐度不完全相同,其范围分别为1500-5500 lx和25-40;硅藻的理化成分受光照和盐度条件影响也较大,其含量均呈现低-高-低的变化趋势.光照低于1500 lx、盐度低于25或光照、盐度高于最适值时均不利于理化成分的积累,但高于最适光强时利于胞内外总糖的产生;光强高于5500 lx,盐度高于40时,总脂肪含量几乎不增加甚至急剧下降.

温度对8种底栖硅藻生长及其理化成分的影响

考察了不同温度对8种底栖硅藻生长及其理化成分的影响.结果表明:温度低于15℃或高于30℃均不利于细胞生长,同时也不利于胞内理化成分的积累.在15~25℃之间细胞比生长速率及主要理化成分(叶绿素、胞内蛋白和多糖、胞外多糖及总脂肪)含量均可达到最大,而不同藻种的理化成分最大含量也有较大的差异,最高和最低叶绿素含量差值可达8.0 mg/L,胞内蛋白含量差约4.0%多糖含量差约14.0%,总脂肪含量差约为8.0%,胞外多糖浓度含量差约15mg/L.