Comparison of 1980 Lake Huron,Georgian Bay - North Channel surveillance data with historical data

A statistical regionalization procedure was used to delineate significantly (p 0.10) different areas, for a variety of surveillance parameters measured in 1980 in Lake Huron and Georgian Bay-North Channel. The analyses performed were compared with similar analyses done on 1971 (Lake Huron) and 1974 (Georgian Bay-North Channel) data. The regions produced from the 1980 analyses compared favourably with the 1971 and 1974 analyses. Significant (p 0.01) increases in NO₃NO₂-N and RSiO₂ were observed for Lake Huron between the 1971 and 1980 data sets. Significant (p 0.01) increases in NO₃NO₂-N and significant (p 0.01) decreases in TP and chlorophyll a were observed for Georgian Bay-North Channel between the 1974 and 1980 data sets.     

The benthic macro-algae of Georgian Bay,the North Channel and their drainage basin

Thirty-nine subgeneric taxa of macroalgae have been collected from 83 sites in Georgian Bay, the North Channel and their drainage basin. There were 15 species in the Bay and Channel and 32 species in streams, rivers and impoundments in the basin. Only 8 of the Bay and Channel species were also found in the watershed. Cladophora glomerata was the most important species in Georgian Bay and the North Channel, having an estimated 640 × 10³ m² cover and 19 × 10⁴ kg fresh weight standing crop. However, this species was largely concentrated on the southwestern shorelines of these water bodies. Its distribution along the northeastern shoreline appears to be limited by total ion and phosphorus levels. Chara globularis/vulgaris was the subdominant taxon in Georgian Bay and the North Channel with an estimated 70 × 10³ m² cover and 15 × 10³ kg fresh weight biomass. This species was more widely distributed than C. glomerata. No other taxon contributed significantly to the standing crop including the frequently occurring Ulothrix zonata, Zygnema spp. and Spirogyra spp. The maximum benthic macroalgal biomass was estimated to be approximately 10% of the phytoplankton biomass.     

A comparison of the effectiveness of sea lamprey control in Georgian Bay and the North Channel of Lake Huron

The sea lamprey control program in the Great Lakes has effectively reduced the abundance of sea lamprey, and, in conjunction with appropriate fishery management practices, has contributed to the restoration of valuable stocks of fish — particularly the salmonids. Sea lamprey producing tributaries of Lake Huron have been treated with lampricide on a continuing basis since 1966, and indications of decreasing abundance of sea lamprey have been evident since 1969. Control of sea lamprey has been more successful in Georgian Bay than in North Channel, as shown by the numbers of spawning phase animals captured in assessment devices, and by the incidence of lamprey-inflicted wounds on fish. The St. Marys River — the only known uncontrolled sources of recruitment to parasitic sea lamprey populations of Lake Huron — is suspected of being the cause of the higher levels of sea lamprey abundance observed in the northwest part of the lake.     

A fish kill of massive proportion in Kuwait Bay, Arabian Gulf, 2001: the roles of bacterial disease, harmful algae, and eutrophication

In August and September 2001, Kuwait Bay, a semi-enclosed embayment of the Arabian Gulf, experienced a massive fish kill involving over >2500 metric tons of wild mullet (Liza klunzingeri), due to the bacterium Streptococcus agalactiae. In the Bay, this event was preceded by a small fish kill (100–1000 dead fish per day) of gilthead sea bream (Sparus auratus) in aquaculture net pens associated with a bloom of the dinoflagellate Ceratium furca. Sea bream were found to be culture positive for S. agalactiae, but did not show any visible signs of disease. Unusually warm temperatures (up to 35 °C) and calm conditions prevailed during this period. As the wild fish kill progressed, various harmful algae were observed, including Gymnodinium catenatum, Gyrodinium impudicum, and Pyrodinium bahamense var. compressum. Cell numbers of G. catenatum and G. impudicum exceeded 10⁶ l⁻¹ in some locations. All fish tested below the limits of detection for paralytic shellfish poisoning (PSP) and brevetoxins. Clams (Circe callipyga) were positive for PSP but at levels below regulatory limits. Nutrient concentrations, both inorganic and organic, were highly variable with time and from site to site, reflecting inputs from sewage outfalls, the aquaculture operations, a high biomass of decomposing fish, and other sources. It is hypothesized that many factors contributed to the initial outbreak of the bacterial disease, including unusual warm and calm conditions. The same factors, as well as enriched nutrient conditions, also apparently were conducive to the subsequent HAB outbreaks. The detection of PSP, while below regulatory limits, warrants further monitoring to protect human health.     

The dynamics and ecology of exotic tropical species in floating plant mats: Lake Naivasha,Kenya

The floating water fern Salvinia molesta has occurred in Lake Naivasha since the early 1960s and during this period has obstructed fishing activities and navigation. In recent years the extent of Salvinia has declined markedly. Since 1988, a second floating weed, Eichhornia crassipes (water hyacinth), has colonised the lake. Salvinia formed large mats around the edges, bays and lagoons and had very few plant or invertebrate species associated with it. Mats of E. crassipes, however, support a greater abundance and variety of animal and plant species, which shows a relationship with mat size. This seems to have facilitated plant succession but without a zonation typical of the classic hydroseral sequence for the lake.     

Seasonal changes in composition and biomass of epiphytic algae on the macrophyte Ranunculus penicillatus in a chalk stream,with estimates of production,and observations on the epiphytes of Cladophora glomerata

The epiphytic algae on surfaces of the macrophyte Ranunculus penicillatus (Dumort.) Bab. var. calcareus (R. W. Butcher) C. D. K. Cook and on Cladophora glomerata (L.) Kütz growing in the River Itchen at Otterbourne near Southampton were studied between February 1984 and June 1985. The river at this site has a mean flow rate of 0.33 m s^–1, and is about 16 m wide and on average 20 cm deep, with a discharge ranging through the year between 0.34 and 2.46 m³ s^–1. The pH of the river varies little around 8.2, with a mean alkalinity of 236 mg HCO _inf3 ^sup1 l^–1, because of its origin from chalk springs. Ranunculus grows throughout the year, with peaks of biomass in spring and autumn. It forms a very large surface for attachment of epiphytes, and covers on average 40% of the stream bed. Numbers of epiphyte cells removed from Ranunculus ranged through the year between 52 × 10³ and 271 × 10³ cells mm^–2 stream floor, with maximum numbers in April, and a secondary peak in October. This pattern partly reflects fluctuations in the biomass of Ranunculus; the number of cells per unit area of plant surface showed a broader spring peak and lower fluctuations in other seasons. Diatoms formed 65 to 98% of these epiphyte cells, with chlorophytes reaching their peak (10%) in summer and cyanophytes (25%) in autumn. Estimates of biomass of these epiphytic forms, derived from measurements of chlorophyll c, indicate a range between 30 and 100 g dry weight m^–2 of weed bed. Colonisation studies showed that the algae grow and reproduce throughout the year, with a mean generation time of about 5 days, suggesting an annual production of about 3 kg dry weight m^–2 of weed bed, which makes epiphytic algae the principal primary producers in the stream. The numbers and biomass of epiphytic algae on Cladophora are considerably less.The species of epiphytic algae found on Ranunculus were generally similar to those growing on Cladophora, and to epilithic algae on pebbles of the stream bed, but different species were dominant on the different substrata. Algal cells in the water column were all derived from benthic habitats, although their relative abundance was very different.     

Field ecology of freshwater macroalgae in pools and ditches,with special attention to eutrophication

A review is presented on the occurrence of macroalgae in dune pools, ditches and moorland pools in The Netherlands, which were studied in the period 1980–1987. There are clear effects of eutrophication on biomass as well as on species composition. A general trend is that under mesotrophic or moderately eutrophic conditions, the filamentous macroalgae form a diversified component of the primary producers in shallow water bodies. Especially spore forming genera asSpirogyra andOedogonium can be represented with up to about 20 species per site. In hardwater ditches alsoVaucheria is an important component, especially the sediment dwellingVaucheria dichotoma. Under distinctly eutrophic conditions dense floating algal masses contain only one or a few species asCladophora glomerata, Enteromorpha intestinalis, Hydrodictyon reticulatum. Under hypertrophic conditions the water surface is covered by dense blanketing mats of duckweeds in summer and autumn. Besides trophic factors, other factors as alkalinity and chloride concentration play a role in species composition. The results are discussed in the framework of water quality assessment of polder waters and possible applications for water purification or use as manuring substance. The need for experimental ecophysiological studies is underlined.     

鄱阳湖湿地优势植物枯落物的分解速率及碳、氮、磷释放动态特征

植物枯落物分解对生态系统碳通量和养分循环有至关重要的作用,这一过程主要由3个相互作用的因素决定,即化学(枯落物理化特性)、物理(气候和环境)以及生物(参与枯落物分解的微生物和无脊椎动物)因素。在气候和立地环境条件相同的情况下,枯落物质量是制约分解的内在因素。在鄱阳湖湿地开展了野外定位观测实验,采用分解袋技术研究了鄱阳湖湿地优势植物芦苇(Phragmite)、南荻(Triarrhena lutarioriparia)和薹草(Carex.cinerascens Kükenth)枯落物分解速率及碳(C)、氮(N)、磷(P)元素释放动态特的征差异性。结果表明,在0—150 d内三种植物枯落物的干物质分解速率和残留率以及碳相对归还指数(CRRI)、氮相对归还指数(NRRI)、磷相对归还指数(PRRI)差异性都极其显著。在0—150 d内分解速率都是芦苇的最大,薹草的次之,南荻最小。分解进行150 d后,芦苇、南荻和薹草枯落物干物质残留率依次约为56.57%、67.99%和60.88%,CRRI依次约为57.44%、34.58%和41.75%,NRRI依次约为50.71%、-22.66%、和23....     

Reshaping the Ecology of Invading Populations of Hemlock Woolly Adelgid, Adelges tsugae (Homoptera: Adelgidae), in Eastern North America

Hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae), is native to Japan where it is an innocuous inhabitant of Tsuga diversifolia Masters and T. sieboldii Carriere throughout their natural growing areas. Native adelgid populations are regulated by host resistance and natural enemies, in particular the oribatid mite, Diapterobates humeralis (Hermann) and the coccinellid beetle, Pseudoscymnus tsugae Sasaji and McClure. Invading populations of A. tsugae in western North America on T. heterophylla Sargent and T. mertensiana Carriere are mainly regulated by host resistance. However, invading populations in eastern North America attain damaging levels on T. canadensis (L.) Carriere and T. caroliniana Engelmann and are regulated mainly by weather and negative density-dependent feedback mechanisms related to host deterioration. Although A. tsugae is only passively dispersed by wind, birds, forest-dwelling mammals and humans, it is spreading at an alarming rate and is sufficiently cold hardy to threaten the existence of the two eastern hemlock species throughout their natural ranges. The current hope for suppressing invading populations of hemlock woolly adelgid in eastern North America lies with the exotic predator, P. tsugae. Extensive laboratory studies of the biology and predatory ability of P. tsugae revealed that it feeds on all life stages of its prey, that its multivoltine life cycle is well synchronized with that of the adelgid, and that it has great potential for biological control. We have reared and released nearly 130,000 adults of P. tsugae in forests in Connecticut, New Jersey and Virginia during the past four years. P. tsugae has reproduced, dispersed, overwintered and reduced densities of hemlock woolly adelgid by 47–88% in only five months on release branches at these sites. Current studies are investigating the long-term ability of P. tsugae to regulate invading populations of A. tsugae in eastern North America.     

我国北方岩溶泉域刚毛藻的系统发育及形态学研究

脆弱刚毛藻(Cladophora fracta)是一种大型丝状绿藻,生境分布广泛。然而,对于岩溶泉域分布的刚毛藻研究较少,它们的遗传多样性、生物地理亲缘性和生理特性都有待于深入研究。该研究对我国北方地区五个典型岩溶泉域的50个脆弱刚毛藻样本进行了形态学和分子系统学描述。主要研究目标:(1)对我国北方地区五个典型岩溶泉的刚毛藻生境进行描述;(2)根据形态学特征和分子序列对藻体进行鉴定;(3)探究生境对藻体生理特性的影响。结果表明:基于SSU和LSU序列的结果,发现所分析的50株刚毛藻个体为同一种,同时还发现了13个不同的核糖体基因型。基于SSU和LSU的系统发育树,刚毛藻属均未能形成单系分支,分布在三个不同的分支上。13个样本基因型在SSU和LSU树中的位置相似,与Cladophora vagabunda有很高的序列同源性,但是形态特征却差异很大。从显微结构结果来看,五个岩溶泉域采集到的刚毛藻在细胞直径上无显著差异,藻体的形态特征与脆弱刚毛藻相一致。但是,岩溶泉域采集的藻体细胞直径比文献报道中在湖泊和河流中采集的脆弱刚毛藻直径要大。另外,仅在两个地点(XA和ST)采集的标本中发现有假根状分枝。因此,基于形态学和分子序列的结果,将这五个泉域的刚毛藻鉴定为脆弱刚毛藻(Cladophora fracta)。     

鄱阳湖湿地灰化苔草生长季氮磷含量与储量的变化

湿地植物在营养元素生物地球化学循环过程中起着重要作用,研究植物氮磷元素的吸收、分配和积累特征对于正确理解氮磷循环关键过程及其生态作用具有重要意义。基于野外实地观测和室内实验分析,研究了鄱阳湖淡水湿地灰化苔草春草生长季内不同部位生物量、氮磷含量及氮磷储量的动态变化。结果表明:在生长季内,灰化苔草各部位生物量随时间推移而增加,地上部分生物量在各生长期均高于地下部分,地下部分生物量积累速率相对稳定,而地上部分和总体平均积累速率表现为生长前期高于生长后期;各部位氮磷含量经历了先减少再增加的变化过程,其中地上部分氮元素在灰化苔草生长的中后期显著高于地下部分,而磷元素在中前期两者差异更为显著;生物量与氮磷储量均呈显著正相关,是灰化苔草氮磷储量动态变化的主导因子,氮磷元素主要储存在灰化苔草的地上部分;研究期间灰化苔草平均氮磷比介于3.32—3.83之间,按营养限制理论进行判断,氮元素可能是灰化苔草生长的限制性营养因子。     

The recent palaeolimnology of Lake Nicholls,Mount Field National Park,Tasmania

Analyses were carried out for diatoms, spherical carbonaceous particles, and magnetic minerals on a short sediment core from a small cirque lake, Lake Nicholls, in the Mount Field National Park, south-west Tasmania.Catchment disturbance is not evident from the fairly constant sediment accumulation rates and magnetic analyses of the sediment record. However, there is evidence for a low level of atmospheric contamination during the industrial period, which reaches a maximum at the present time, but is less than in many areas of north-west Europe. Changes in the diatom assemblages recorded in the sediment core are likely to be related to factors, other than catchment change or atmospheric contamination, such as the response of within lake processes to climate change.Several diatom taxa found in the cores cannot presently be assigned to known species. Although some of these may later be identified following this preliminary study, it seems highly likely that freshwater lakes in south-west Tasmania contain a number of new and perhaps endemic taxa.     

Distribution and ecology of Demospongiae from the circalittoral of the islands of the Aegean Sea (Eastern Mediterranean)

Size-selective predation by fish is often considered to be a primary driver of seasonal declines in large-bodied Daphnia populations. However, large Daphnia commonly exhibit midsummer extinctions in ponds lacking planktivorous fish. A number of empirical and theoretical studies suggest that resource competition and its interaction with nutrient enrichment may determine variable dominance by large Daphnia. Low resource levels may favor competitive dominance by small-bodied taxa while large Daphnia may be favored under high resource conditions or following a nutrient/productivity pulse. Nutrient enrichment may also influence the strength of invertebrate predation on Daphnia by affecting how long vulnerable juveniles are exposed to predation. We investigated these hypotheses using an in situ mesocosm experiment in a permanent fishless pond that exhibited seasonal losses of Daphnia pulex. To explore the effects of nutrient enrichment, Daphnia plus a diverse assemblage of small-bodied zooplankton were exposed to three levels of enrichment (low, medium, and high). To explore the interaction between nutrient enrichment and invertebrate predation, we crossed the presence/absence of Notonecta undulata with low and high nutrient manipulations. We found no evidence of competitive reversals or shifts in dominance among nutrient levels, Daphnia performed poorly regardless of enrichment. This may have been due to shifts in algal composition to dominance by large filamentous green algae. Notonecta had significant negative effects on Daphnia alone, but no interaction with nutrient enrichment was detected. These results suggest that Daphnia are not invariably superior resource competitors compared to small taxa. Though predators can have negative effects, their presence is not necessary to explain poor Daphnia performance. Rather, abiotic conditions and/or resource-based effects are probably of greater importance.     

Unadapted behaviour of native,dominant ant species during the colonization of an aggressive,invasive ant

Among the factors driving the invasive success of non-indigenous species, the “escape opportunity” or “enemy release” hypothesis argues that an invader’s success may result partly from less resistance from the new competitors found in its introduced range. In this study, we examined competitive interactions between the little fire ant Wasmannia auropunctata (Roger) and ant species of the genus Pheidole in places where both are native (French Guiana) and in places where only species of Pheidole are native (New Caledonia). The experimental introduction of W. auropunctata at food resources monopolized by the Pheidole species induced the recruitment of major workers only for the Guianian Pheidole species, which were very effective at killing Wasmannia competitors. In contrast, an overall decrease in the number of Pheidole workers and no recruitment of major workers were observed for the New Caledonian species, although the latter were the only ones able to kill the Wasmannia workers. These results emphasize the inappropriate response of native dominant New Caledonian species to W. auropunctata and, thus, the importance of enemy recognition and specification in the organization of ant communities. This factor could explain how invasive animal species, particularly ants, may be able to successfully invade species-rich communities.     

The role of phosphatases in the metabolism of Peridinium cinctum,from Lake Kinneret

The annual algal bloom (February–June) in Lake Kinneret consists almost entirely of the dinoflagellatePeridinium cinctum f.westii (Dinophyceae). To clarify the role of phosphatases in the alga, experiments were carried out using cells from culture or from the lake. In culture, as the external ambient orthophosphate (Pi) concentration decreased, alkaline phosphatase activity increased (and to some extent acid phosphatase activity, as well). Hot water extractable P decreased, although molybdate reactive phosphorus (MRP) appeared to be utilized in preference to the non-MRP component of this pool. Alkaline phosphatase inPeridinium collected from the lake as well as cells grown in culture under a high (3–6 mg l^–1) ambient Pi concentration in both continuous light and a 12:12 light-dark cycle, showed a diurnal fluctuation in activity. These results, together with previous observations suggest that the phosphatases inPeridinium are controlled by changes in intracellular phosphorus levels (other than the hot water extractable pool) and/or by other metabolic processes not directly involved in P nutrition.     

Effects of filamentous algae and deposited matter on the survival of Fucus vesiculosus L. germlings in the Baltic Sea

As a result of increased nutrient levels in the Baltic Sea during thepast 50 years, mass developments of filamentous algae have become a commonfeature along the Swedish east coast and deposition of organic matter has alsoincreased. To test whether these two factors have any effects on the early lifestages of Fucus vesiculosus a number of laboratory andfield studies were conducted. The amount of epilithic and epiphytic filamentousalgae on F. vesiculosus and the amount of deposited matterin the littoral zone were quantified during the two reproductive periods ofF. vesiculosus, early summer (May–June) and lateautumn (September–October). Both filamentous algae (Cladophoraglomerata) and deposited matter (introduced either before or aftersettlement of fertilized eggs) were shown to significantly decrease the numberof surviving germlings. The survival of germlings seeded on stones withfilamentous algae, or seeded on culture dishes concurrently with the lowestconcentration of deposited matter (0.1 g dm^–2),was 5% or less. In the field, the amount of filamentous algae was significantlyhigher during F. vesiculosus summer reproduction, whereasthe amount of deposited matter collected in traps was significantly higherduring the period of autumn reproduction. The greatest biomass of filamentousalgae was observed at sheltered sites. Based on the negative effects offilamentous algae and deposited matter on Fucusrecruitmentand the observation of local and seasonal differences in abundance offilamentous algae and deposition, we suggest that the prerequisites for thesurvival of either summer or autumn-reproducing populations of F.vesiculosus in the Baltic Sea may differ locally.     

纤毛虫与藻类共生关系的研究现状与展望

纤毛虫与藻类的共生关系在水体环境中广泛存在并有着重要的生态功能。文章回顾了国内外纤毛虫与藻类共生研究的发展历程,主要介绍了纤毛虫与藻类共生的生态功能,以及显微观察与分子生物学技术在纤毛虫与藻类共生研究中的应用;阐述了包括草履虫与小球藻共生关系建立的4个过程及其互作机制、红色中缢虫与隐藻的共生关系、宿主与共生体之间的互作等内容;提出了纤毛虫与藻类共生研究中亟待解决的科学问题,包括草履虫食物泡膜(digestive vacuole, DV)与围藻膜(perialgal vacuole, PV)发挥作用的分子机制、红色中缢虫与隐藻共生关系的建立过程、红色中缢虫在共生过程中的功能作用等,并展望未来的研究方向。     

Lack of relationship between gliding cyanobacteria and filamentous gliding heterotrophic eubacteria: comparison of 16S rRNA catalogues of Spirulina,Saprospira, Vitreoscilla,Leucothrix, and Herpetosiphon

Spirulina platensis and Spirulina maxima were characterized by 16S ribosomal RNA oligonucleotide cataloguing. Both species are highly related. They fall into the main group of the cyanobacteria, showing a remote relationship to Nostoc, Fischerella, Aphanocapsa, and also to Prochloron. Low similarity coefficients were found between the Spirulina species and certain organotrophic and sulfide oxidizing bacteria, viz. Saprospira grandis, Vitreoscilla stercoraria, Leucothrix mucor, Herpetosiphon aurantiacus, and Beggiatoa leptomitiformis, respectively. This result does not support the classical hypothesis that certain filamentous gliding bacteria are apochlorotic cyanobacteria.     

Field ecology of the ochratoxin A-producing Penicillium verrucosum: Survival and resource colonisation in soil

A field experiment was conducted to elucidate the survival of P. verrucosum in infested bulk soil(T1) and infested soil with waste grain (T2). The infested soil and reference soil (T3) was filled into steel cylinders, which were buried and sampled 13 times during a period from October 1994 to March 1996.The abundance of P. verrucosum and indigenous soil fungi were assessed by dilution plating on a selective and diagnostic medium (DYSG). Kernel infection was examined in T2. According to our results, P. verrucosum seems well adapted to survival in arable soil and little affected by indigenous fungi. During the first autumn and winter the grain caused a proliferation of P. verrucosum while its abundance in bulk soil was more constant except for a decrease in February 95, which is ascribed to frost/thaw alternations. In T2, P. verrucosum initially infected more than 50% of the kernels but during the first few months it was ousted by other fungi. A hypothesis regarding waste grain as the natural niche for the fungus in the field was therefore partly rejected. A gradual decrease in the abundance of P. verrucosum in soil during spring, a die-off in the dry summer and aproliferation during the second winter were found in both T1 and T2. Our results cannot provide the reason for the increase during the second winter. On an overall basis, however, they show that P. verrucosum can survive in the field, proliferate on soil organic matter and probably become an integral part of the soil ecosystem. This may constitute a risk of grain contamination when given appropriate environmental conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Control of phosphorus loading and flushing as restoration methods for Lake Veluwe,The Netherlands

As a result of high nutrient loading Lake Veluwe suffered from an almost permanent bloom of the blue-green algaOscillatoria agardhii Gomont. In 1979, the phosphorus loading of the lake was reduced from approx. 3 to 1 g P.m^–2.a^–1. Moreover, since then the lake has been flushed during winter periods with water low in phosphorus. This measure aimed primarily at interrupting the continuous algal bloom. The results of these measures show a sharp decline of total-phosphorus values from 0.40–0.60 mg P.l^–1 (before 1980) to 0.10–0.20 mg P.l^–1 (after 1980). Summer values for chlorophylla dropped from 200–400 mg.m^–3 to 50–150 mg.m^–3.The increase in transparency of the lake water was relatively small, from summer values of 15–25 cm before the implementation of the measures to 25–45 cm afterwards. The disappointing transparency values may be explained by the decreasing chlorophylla and phosphorus content of the algae per unit biovolume. Blue-green algae are gradually loosing ground. In the summer of 1985 green algae and diatoms dominated the phytoplankton for the first time since almost 20 years. To achieve the ultimate water quality objectives (transparency values of more than 100 cm in summer), the phosphorus loading has to be reduced further.