An experimental analysis of lunule function in the sand dollar Mellita quinquiesperforata

Coefficients of lift and drag for fifty lunulate sand dollars [Mellita quinquiesperforata (Leske 1778)], poised over a flat, sandy surface, were determined at seven different air stream velocities. Coefficients of static friction were obtained experimentally on level sand in standing water. Critical velocity, at which a sand dollar would be dislodged, is defined as that current velocity in which the force of drag is equal to the product of residual weight (i.e. weight-lift) and the coefficient of static friction. Small individuals have lower critical velocities than large ones: 26 cm s^?1 and 43 cm s^?1 for individuals 48 and 94 mm in diameter, respectively. Measurements were repeated for 20 of the controls, their lunules smoothly filled with modelling clay, and 20 from which lunule spines were removed. In every case, blocking the lunules decreased critical velocity, by an average of 15%; this was shown to be statistically significant (P>0.01). Removal of spines, which partially occlude the lunules, significantly (P>0.01) increased critical velocity by an average of 13%. Direct measurements in a water tunnel showed that calculated values of critical velocity were slightly too high, but otherwise confirmed the role of the lunules. Allometric analysis showed that as sand dollars increase in size, the distances of the lunules from the center of the disk increase less rapidly than the radii. A principal components' analysis of profile measurements of nine species indicated that lunulate and non-lunulate sand dollars are quite different in form. Lunulate species tend to be thinedged, flat-domed and larger in diameter. Some alternative ideas of lunule function are discussed and it is shown that there are no allometric or experimental data to support any of the suggested feeding hypotheses.     

Reproductive cycles in two populations of the Pacific sand dollar Dendraster excentricus

East Pacific swimming crabs are poorly known ecologically. We trawled samples along 4 estuarine-continental shelf transects to provide information on the population structure and species composition of portunids along environmental stress gradients. Portunids comprised almost 99% of the benthic crabs. Callinectes toxotes dominates the freshest estuarine areas, but is replaced by C. arcuatus in estuary mouth and shallow-shelf samples. Deeper shelf samples are dominated by Euphylax robustus and Portunus sper. Great numbers of E. dovii, a pelagic species, were taken on the shelf; their size distribution implies intraspecific competition. Evidence is given that differences in salinity tolerance account for differential landward limits, but competition, predation by fishes, increased fouling and decreased available food exclude eurytopic species from physicochemically equable shelf waters.     

不同土壤提取物对人参种子生长的化感效应及其化学组成

采用甲醇提取法提取新林地土、人参根际土以及栽培人参(Panax ginseng)、西洋参(Panax quinquefolius)的老参地土.每种土壤提取物设6个质量浓度梯度,以研究不同土壤提取物在特定质量浓度下对人参种子胚根和胚轴生长的化感效应,每种处理设3次重复.试验结果表明,与对照相比,人参根际土提取物对人参种子生长的化感效应最强,老参地土提取物对人参种子生长的化感效应次之,新林地土提取物对人参种子生长的化感效应最弱.经GC-MS分析,分别从6种土壤提取物中检测到1425种数量不等的化合物组分,其中苯胺类物质、酚酸及其衍生物被报道在其它植物上有化感活性,可能参与对人参种子的生理性毒害作用.     

Larval abundance and recruitment of the sand dollar Dendraster excentricus in Monterey Bay,California, USA

Seasonal abundance of planktonic larvae of the sand dollar Dendraster excentricus was determined in Monterey Bay, California, USA. Larvae were counted from two offshore stations and also over a coastal sand dollar bed, and these data were compared with settlement in the sand dollar bed, with adult population structure and with adult reproductive condition. These measurements were made during the period July 1978 to October 1980 and in October 1981. Sand dollar larvae were most abundant in the plankton during the summer, a period when phytoplankton productivity tended to be high and currents were relatively slow and variable. In some years, small-scale current variations appeared to prevent many larvae in the open bay from reaching the nearshore sand dollar beds; however, in other years, massive shoreward transport of the larvae evidently did occur, since the adult population in the sand dollar bed exhibited a mode in size, indicating a large settlement. A comparison of settled individuals in 1980 and the adult size-frequency distribution in 1981 gives an estimated mortality rate of 88% yr^-1 for early juveniles of D. excentricus.     

Studies on the water extracts of medicinal plants grown in copper mining areas and their antioxidant effects

High copper (Cu) accumulation in medicinal plants might favor lipid peroxidation and hence affect antioxidant responses. This effect was studied by determining antioxidant activities in the water extracts of medicinal plants from Cu mining impact site and compared with control samples. Antioxidant activities of the extracted medicinal plants were assayed by measuring (1) total phenolic and flavonoid contents, (2) diphenyl-1-picrylhydrazyl (DPPH)^? free radical scavenging activity, and (3) inhibition capacities of lipid peroxidation. The total phenolic as well as total flavonoid contents of the mining impact samples and control samples are not significantly different. However, inhibition of lipid peroxidation capacities was significantly less (12–60%) for mining impact samples as reflected by the IC₅₀ values. These anomalies were attributed to high concentrations of Cu (2–4-fold higher) in mining impact samples as measured by inductively coupled plasma mass spectrometry. A positive correlation was observed between Cu levels and IC₅₀ values for the inhibition of lipid peroxidation for mining impact samples.     

Fertilisation, embryogenesis and larval development in the tropical intertidal sand dollar Arachnoides placenta in response to reduced seawater pH

We examined the response of the tropical sand dollar Arachnoides placenta to reduced seawater pH in experiments spanning ca. 50 % of the planktonic larval duration. A. placenta inhabits intertidal sandy beaches where we observed a minimum in situ pH range 0.06 pH units (pH 8.10–8.16). The responses of gametes and larvae to seawater pH were tested in vitro in ambient (pH 8.14, pCO₂ = 525.7 μatm, total alkalinity = 2,651 μmol kg soln^?1) and three reduced pH seawater treatments (7.8–7.0). Percentage fertilisation decreased significantly with decreasing pH across a range of sperm/egg ratios (4:1 up to 4,000:1). A. placenta reached the advanced pluteus stage in 4 days, and during this time, we saw no difference in survival rate of larvae between the ambient (67 %) and pH 7.79 (72 %) treatments. Four-day survival was, however, reduced to 44 and 11 % in the pH 7.65 and 7.12 treatments, respectively. Larval development and morphometrics varied among pH treatments. Embryos reared in pH 7.12 exhibited arrested development. Larvae reared at pH 7.65 showed delayed development and greater mortality compared with those reared at pH 7.79 and 8.14. When larval morphometrics are compared among larvae of the same size, differences in larval width and total arm length between pH treatments disappear. These results suggest that variation in larval size among the three highest pH treatments at a given time are likely the result of slower development and apparent shrinkage of surviving larvae and not direct changes in larval shape. There were no differences in the percentage inorganic content (a proxy for calcification) in larvae reared in either an ambient or a pH 7.7 treatment. The responses of fertilisation and development to decreased pH/increased pCO₂ in A. placenta are within the range of those reported for other intertidal and subtidal echinoid species from colder latitudes.     

Chemical defense in the eggs and embryos of antarctic sea stars (Echinodermata)

Fifteen species of reproductively mature echinoderms (11 sea stars, 3 sea urchins, 1 sea cucumber) were collected from McMurdo Sound, Antarctica, during austral spring and summer of 1985 and 1986; eggs and embryos were obtained, and were tested for ichthyonoxicity using the common marine killifishFundulus grandis as a model predator. Chemical deterrents occurred in the large, yolky eggs of the pelagic lecithotrophic sea starPerknaster fuscus and the planktotrophic sea starPorania antarctica. Brooded embryos of the sea starsDiplasterias brucei andNotasterias armata were also noxious. Significant ichthyonoxicity was not detected in the remaining 7 species of sea stars, 3 sea urchins, and 1 sea cucumber. Chemical deterrents were generally effective at concentrations below a single egg or embryo per agar test-pellet. Although chemicals found in these eggs and embryos are noxious to an allopatric fish, they may not be noxious to sympatric fish.     

In vitro agonistic and antagonistic endocrine disrupting effects of organic extracts from waste water of different treatment processes

Effluents from wastewater treatment plant （WWTP） have been reported to have a broad spectrum of endocrine disrupting compounds （EDCs）. The majority of studies have focused on the occurrence of estrogenic activity, while ignoring nuclear hormone receptors （NRs） pathways. In the present study, a battery of in vitro yeast bioassays and a cell bioassay, including antagonistic and agonistic effects on estrogen receptor （ER）, androgen receptor （AR）, progesterone receptor （PR）, estrogen- related receptor （ERR） and aryl hydrocarbon receptor （AHR）, were conducted to evaluate the removal efficien- cies of EDCs by different treatment processes of a WWTP located in Beijing. Estrogenic, anti-estrogenic, anti- androgenic, anti-progesteronic, anti-ERR and the activa- tion of AHR activities were detected in samples from all treatment processes and the receiving water. The concen- tration of estrogenic contaminants with estradiol （E2） equivalent concentrations ranged from 0.82 x 10-9 to 3.54 x 10 9g Ee_EQ.L-1. The concentration of anti-estrogenic contaminants with 4-hydroxytamoxifen （4-OHT） equiva- lent concentrations ranged from 1.24 × 10-6 to 2.36 x 10-6 g 4-OHT-EQ.L-1. The concentration of anti-androgenic contaminants ranged from 2.21 x 10-s to 3.52 × 10-6g flutamide-EQ. L-1. The concentration of anti-progesteronic contaminants ranged from 3.15 x 10^-5 to 2.71 x 10^-4g RU486-EQ. L-1. The concentration of anti-ERR contami- nants ranged from 7.09 x 10-5 to 6.50 x 104 g 4-OHT-EQ × L^-10. The concentration of AHR activators ranged from 1.7 × 10-10 to 3.4 × 10^-10g TCDD-EQ-L-1. These processes including secondary clarifier, coagulation, as well as coal and sand filtration could eliminated 67.2% of estrogenic contaminants, 47.0% of anti-estrogenic contaminants, 98.3% of anti-androgenic contaminants, 88.4% of anti- progesteronic contaminants, 65.4% of anti-ERR contami- nants and 46.9% of AHR activators. WWTP effluents contain multiple receptor disruptors may have very complex adverse effects on exposed organisms.     

航道疏浚泥悬浮液对黑鲷胚胎的发育及仔鱼摄食生长的影响

采用静水试验法,温度在20℃左右,并保持试验用水溶解氧为饱和溶氧的60%,用疏浚泥悬浮液与过滤海水按等对数间距稀释成4个体积浓度水平(1:2、1:10、1:50、1:200),同时以过滤海水为对照组,每一个浓度组设3个平行样本,对人工养殖的黑鲷Spaptls macrocephalus鱼卵和仔鱼进行毒性试验.试验结果表明:疏浚泥悬浮液对鱼卵孵化有一定影响,但不显著.仔鱼的全长和体重的增长与悬浮液浓度的变化并无十分明显的对应关系,只有当水体中的悬浮液达到一定浓度时,才显现出对仔鱼生长的影响作用.在仔鱼摄食过程中,悬浮液对全长生长产生的抑制或影响作用不显著,但高浓度的悬浮液则对体重增长产生了一定的抑制性,不过这是一种短暂性的影响,随着时间的延长,其作用逐渐减弱或消失.     

四种植物提取物的杀螺效果研究

福寿螺是我国华南地区一种危害十分严重的外来入侵生物。采用分布广泛的四种植物：水蜈蚣（Kyllinga brevifolia Rottb.）、红花酢浆草（Oxalis corymbosa DC）、红叶乌桕（Euphorbia cotinifolia L.）和辣蓼草（Polygonum flaccidum Meissn.）作为原料,在实验室内通过人工研磨方法提取植物体内的有效成分作为药剂,分别对福寿螺幼螺进行室内毒杀及刺激其上爬的效果研究。结果表明：水蜈蚣提取物的杀螺效果不明显,而红花酢浆草、红叶乌桕、辣蓼草等三种植物提取物具有较好的杀螺效果。72h的毒性实验表明,这三种植物提取物在质量浓度为400mg·L-1时,均能全部杀死福寿螺幼螺;其中,红花酢浆草的杀螺效果最强,质量浓度为100mg·L-1时的杀螺率就达到80%,200mg·L-1的质量浓度下已能全部杀死福寿螺,红叶乌桕在200mg·L-1质量浓度时的杀螺率为56.67%,而在此质量浓度下辣蓼草仅为26.67%。另外,提取物刺激福寿螺上爬实验结果表明,红花酢浆草和红叶乌桕均有刺激福寿螺向上爬的作用,且红花酢浆草刺激作用稍强于红叶乌桕。综合杀螺和刺激福寿螺上爬作用的效果,可以得出在控制福寿螺上红花酢浆草和红叶乌桕是比较理想的备选植物。     

Seasonal and diel variation in movement rhythms of sand dollar, Peronella lesueuri (Valenciennes 1841), in Cockburn Sound, Western Australia

Rates and direction of movement in the sand dollar Peronella lesueuri were measured in summer and winter in Cockburn Sound, a large coastal embayment in south-western Australia. P. lesueuri was found to have a diurnal activity pattern throughout the year and had a greater movement rate in the summer (mean of 5.3 cm h^?1, day; 3.9 cm h^?1, night) than in the winter (mean of 2.7 cm h^?1, day; 2.0 cm h^?1, night). Seasonal change in temperature and physiological requirements by the sand dollar are the most likely reason for the seasonal differences. Reasons for diurnal variation were not clear. Direction of movement was found to be random at both times of the year. Based on these movement rates, one sand dollar can bioturbate an approximate area of 0.1 m² day^?1 and 36.4 m² year^?1. At a conservative density estimate of 0.5 sand dollars per m² it takes approximately 20 days for the sand dollars to rework the entire area of the sediments in the habitats they occupy.     

鼠尾藻和鸭毛藻水提液对三角褐指藻的抑制作用

调查了鼠尾藻Sargassum thunbergii和鸭毛藻Symphyocladia latiuscula水提液对三角褐指藻Phaeodactylum tricornutum 生长的抑制作用.结果表明,海藻水提液明显抑制三角褐指藻生长,并且这种抑制作用来自藻体活性物质(化感物质);鼠尾藻和鸭毛藻的化感物质既溶于水也溶于乙醇,随时间可能被三角褐指藻消耗尽或发生降解,因而抑制作用减弱以至消失,最大抑制发生在接种4 d.鼠尾藻和鸭毛藻水提液抑制三角褐指藻生长的半效应质量浓度(EC_(50,96h))分别为4.37g·L~(-1)和3.59g·L~(-1),暗示三角褐指藻对鸭毛藻水提液抑制的反应更敏感.     

Ecological effects of cultivation on the machair sand dune systems of the Outer Hebrides, Scotland

The machair sand dune systems of the Outer Hebrides of Scotland are a unique habitat, which is rare within both a global and European context. Unusually, the machair habitat also represents an agricultural resource that is very important to the Hebridean people, having been subject to both grazing and cultivation throughout the historical period. Following designation as an Environmentally Sensitive Area (ESA) in 1988, the machairs of South Uist have been studied with the aim of understanding the links between agricultural practice and their plant community and ecosystem dynamics. This research focused primarily on the effects of cultivation practices and their role in maintaining plant species richness and community and ecosystem stability. Within two carefully selected areas, the successional plant communities of machair at different stages of recovery following ploughing and cultivation of cereals and potato patches or ‘lazy beds’ were identified at both a macro- and micro-level. Investigations of the vegetation recovery processes on turves taken from newly ploughed land indicated that the initial stages of recolonization are characterized primarily by rapid vegetative reproduction and growth, although re-vegetation by seeds is also an important factor. The implications of these findings for the long-term management of machair plant communities are discussed and in particular the need to maintain old cultivation practices such as shallow ploughing. The need for more detailed research into both seed banks and seed rain and into processes of vegetative reproduction is stressed. Nomenclature: Clapham et al. (1981) and Stace (1991, 1997) for vascular plants; Hubbard (1984) for grasses; Pankhurst & Mullin (1991) for the regional flora; Dobson (1992) for lichens; Watson (1981) for mosses and liverworts.     

Ecological effects of cultivation on the machair sand dune systems of the Outer Hebrides, Scotland

The machair sand dune systems of the Outer Hebrides of Scotland are a unique habitat, which is rare within both a global and European context. Unusually, the machair habitat also represents an agricultural resource that is very important to the Hebridean people, having been subject to both grazing and cultivation throughout the historical period. Following designation as an Environmentally Sensitive Area (ESA) in 1988, the machairs of South Uist have been studied with the aim of understanding the links between agricultural practice and their plant community and ecosystem dynamics. This research focused primarily on the effects of cultivation practices and their role in maintaining plant species richness and community and ecosystem stability. Within two carefully selected areas, the successional plant communities of machair at different stages of recovery following ploughing and cultivation of cereals and potato patches or ‘lazy beds’ were identified at both a macro- and micro-level. Investigations of the vegetation recovery processes on turves taken from newly ploughed land indicated that the initial stages of recolonization are characterized primarily by rapid vegetative reproduction and growth, although re-vegetation by seeds is also an important factor. The implications of these findings for the long-term management of machair plant communities are discussed and in particular the need to maintain old cultivation practices such as shallow ploughing. The need for more detailed research into both seed banks and seed rain and into processes of vegetative reproduction is stressed.     

Chemical composition of the slippery epicuticular wax blooms on Macaranga (Euphorbiaceae) ant-plants

Summary. The stems of many Macaranga ant-plants (Euphorbiaceae) are covered by epicuticular wax crystals rendering the surface very slippery for most insects. These wax blooms act as selective barriers protecting the symbiotic ant partners, which are specialized “wax-runners”, against the competition of other ants. Glaucous stems occur almost exclusively among the ant-plants of the genus Macaranga (). We analyzed the cuticular lipids of 16 Macaranga species by GC-MS and investigated the wax crystal morphology using SEM. Presence of crystalline wax blooms was strongly correlated with high concentrations (52%–88%) of triterpenoids. In contrast epicuticular waxes of glossy Macaranga surfaces contained only 0% to 36% of these dominant components. Therefore we conclude that triterpenoids are responsible for the formation of the thread-like Macaranga wax crystals. In all Macaranga ant-plants investigated, the principal components were epitaraxerol and taraxerone accompanied by smaller portions of taraxerol, β-amyrin and friedelin. Only in the case of the non-myrmecophytic M. tanarius did β-amyrin predominate. Moreover, we found that only in M. tanarius, the dense wax crystal lacework is torn into large mosaic-like pieces in the course of secondary stem diameter growth. Both chemical and macroscopic differences may contribute to a reduced slipperiness of M. tanarius stems and appear to be functionally important. The distribution of wax crystals and their composition amongst different sections of the genus suggests that glaucousness is a polyphyletic character within Macaranga. Received 7 October 1999; accepted 3 December 1999     

Inhibitory effects of red algal extracts on larval settlement of the barnacle Balanus improvisus

We examined the chemical antifouling properties of four sublittoral red algae, Chondrus crispus, Delesseria sanguinea, Osmundea ramosissima, and Polyides rotundus, which are all rarely fouled in the field. Two different approaches were used. Firstly, we tested the effects of lipophilic crude extracts on the settlement behaviour of cyprid larvae of the co-existing barnacle Balanus improvisus. Secondly, in a settlement preference experiment, we tested whether B. improvisus cyprid larvae settle on living algae when given a choice between natural algal surfaces and control surfaces. With this procedure, we were able to test both if the algae inhibit recruitment of cyprids, and if this inhibition is a result of chemistry. The settlement of B. improvisus larvae was strongly inhibited at concentrations estimated to be potentially ecologically relevant for all of the tested extracts. However, only C. crispus significantly inhibited settlement in the preference experiment, even though there was also a tendency for settlement inhibition on P. rotundus and O. ramosissima. In contrast, D. sanguinea seemed to stimulate settlement. This contradiction probably resulted from an extraction of metabolites that naturally occur only inside the alga. However, as this study shows, a combination of settlement assays with whole-cell extracts and preference tests of ecologically relevant fouling organisms on natural algal and control surfaces may be a useful procedure to avoid erroneous conclusions regarding natural antifouling roles of compounds based on settlement assays with only whole-cell extracts. Furthermore, this study also shows that production of inhibitory metabolites may explain the low degree of fouling, especially by B. improvisus, on C. crispus.Communicated by L. Hagerman, Helsingør     

Chemical composition of rivers and streams in the forest and savanna zones of Nigeria

The aim of this study is to investigate the differences in the chemical conditions of lotic waterbodies in the two major ecosystems in Nigeria, the forest and savanna zones. The forest waters were slightly acidic (mean±SD pH = 6.72±0.58) while the savanna waters were slightly alkaline (pH = 7.11±0.33). The cationic order of dominance in the forest waters was Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ in contrast to Ca²⁺ > Mg²⁺ > Na⁺ > K⁺ in savanna waters. The forest waters were chlorided (typical of coastal and/or marine waters) whereas the savanna waters were carbonated in nature, typical of the worldwide freshwater. Organic carbon was significantly higher in forest waters than in the savanna waters (p < 0.05) while nutrient compounds were significantly higher in savanna waters than in forest waters. The seasonal variation of the chemical parameters was generally more evident in savanna than in forest waters. The differences in water quality between the two major vegetation zones reflect the differences in the biogeochemical processes and nutrient cycling that characterise forest and savanna ecosystems.     

A physically based statistical model of sand abrasion effects on periphyton biomass

The magnitude and frequency of discharge and fine sediment delivery to rivers can influence riverine food webs through the frequency of scour of algae from the streambed. Models that simulate changes in algal biomass are not very accurate for long periods with frequent low-magnitude flow events. During these periods, sand is mobilized over a stable gravel bed and periphyton losses are patchy at the reach scale. At the patch scale, we examine if an established threshold for rapid sand transport is also a periphyton perturbation threshold. We also develop and validate a statistical rock scale periphyton saltation abrasion model (PSAM) to simulate the abrasive effects of sand, transported by a hopping motion called saltation, on post-flow event biomass. Data were collected from 15 riffles of a Canadian Atlantic salmon river. The threshold clearly divided bed patches with high biomass and low transport rates, from those patches with low biomass and high transport rates. A dimensionally balanced PSAM regression model including explained 57% of the variance in post-flow event biomass. The validated model indicates that periphyton biomass decreases with increasing sand transport rates . Biomass was higher if the microscopic algae were protected from abrasion by growing either above the near-bed layer of saltating sand or within a mat containing more resistant macroalgae (e.g. Nostoc). The use of in our models facilitates testing of our findings in other hydro-sedimentary environments because W^* is a dimensionless scaling parameter that is well established in sediment transport literature. New insight is provided regarding modelling local heterogeneity in post-flow event biomass. These developments are essential to enable more accurate assessments of how periphyton biomass will change with the increase in the recurrence frequency of small flow events (and sand supply) associated with urbanization and climate change.     

珠江三角洲城市雨水的化学组成及其成因探讨

于2005—2007年间,基于降水过程监测分析了广州市和珠海市雨水的化学组成。结果表明,广州市雨水的pH值变化于3.32~7.03之间,平均值为4.35,众数约为4.15。珠海市雨水的pH值变化于3.38~6.49之间,平均值为4.51。雨水pH值随降水强度的减弱而降低,这决定于大气中水汽与酸性气体的接触时间。珠江三角洲城市雨水中所含主要离子依次是SO42-、NO3-、NH4＋、Ca2＋、Cl-。雨水的酸化与降水过程密切相关。降雨初期雨水比中后期雨水的pH值高,揭示降雨初期大气中的粉尘颗粒有效中和雨水的酸度。多天连续降水天气对大气尘埃的清洗作用明显,但是持续的SO2和NOx排放更容易使雨水酸化。滨海城市降水初期雨水的电导率上升较快（可以从小于1μS.cm-1上升到20~30μS.cm-1）,随着降水时间的延长雨水的电导率以较慢的速率上升。