Redescription of Vorticella oceanica Zacharias, 1906 (Ciliophora: Peritrichia) with notes on its host, the marine planktonic diatom Chaetoceros coarctatum Lauder,1864

The late-spring quantitative relationship between epiphyton and macroinvertebrates was analyzed on the basis of units of colonizable plant surface of Typha angustifolia, Phragmites australis and Nuphar lutea (floating leaves) in the shallow euthrophic Lake Loosdrecht (the Netherlands), with a high seston load. The non-predatory chironomid larvae (Glyptotendipes viridis, Endochironomus albipennis, Pentapedilum sordens, Cricotopus sylvestris agg.) dominated among the macroinvertebrate taxa, controlling the diversity and resemblance of macroinvertebrate assemblages. There was a gradient in functional feeding groups among the chironomids from continuous filtering of the seston to prevailing utilization of epiphyton. We found no direct relationship between the total macroinvertebrate abundance and the epiphyton mass on the plants surface. We attribute this to the filter feeding-strategy of the most abundant species, Glyptotendipes viridis, that utilizes seston in the eutrophicated lake.     

Macrophytes and flood plain water dynamics in the River Danube ecotone research region (Austria)

In the ecotone research region of the Danube in Austria (Man-and-the-Biosphere (MaB)- project 5/21, Austrian Academy of Science) the macrophytes are one of the most important groups of organisms investigated. The species composition and the plant mass in hydrologically dynamic, and in predominantly stagnant sections of a system of lateral branches and sloughs were studied. This study showed that areas protected from frequent disturbance by floods had a greater number of species and higher biomass of aquatic macrophytes. Some species were shown to be evenly distributed throughout the branch system, whereas other species tended to form rare, but large singular patches. A set of new data elaboration techniques enabled us to describe the distribution pattern of the aquatic vegetation in this large branch system of the River Danube.     

Development of fish communities in lakes after biomanipulation

Biomanipulation measures in the Netherlands are usually a combination of a drastic fish stock reduction and an introduction of pike fingerlings. In three small shallow lakes (Noorddiep, Bleiswijkse Zoom and Zwemlust) these measures resulted in a clear water state and the development of macrophytes. After the measures the fish community developed differently because of the new physical and biological conditions. Results of lake Noorddiep and lake Bleiswijkse Zoom showed that the fish community became more divers. Bream and carp became less dominant and were partly replaced by roach and perch. The importance of the main predator pike-perch was strongly reduced and replaced by pike and perch. The share of piscivorous fish in the total fish stock increased at all sites. The recruitment of young-of-the-year was similar or even higher in the clear overgrown areas than in the turbid water before the measures, but the recruitment of young-of-the-year to older fish differed between the species. Predation by pike and perch could not control the young-of-the-year cyprinids, but their predation may have contributed to the shift from bream to roach, because of selective predation on bream in the open water, while roach was hiding in the vegetation. The macrophytes provide new refugia and feeding conditions that favour roach and perch, but offer relatively poor survival conditions for bream and carp.     

Shifts in macrophyte species composition as a result of eutrophication and pollution in Dutch transboundary streams over the past decades

The catchment areas of transboundary streams in the Netherlands have been subject to increasing agricultural and industrial activities over the past decades. To evaluate the effects of these activities on the aquatic vegetation, a study has been carried out in 28 Dutch transboundary lowland streams. Recent data on distribution of 58 aquatic plant species and their growth forms were compared with historical data and were correlated with abiotic variables. Most of these streams lost species that are characteristic for streams and are sensitive to turbidity, eutrophication and pollution (e.g. Potamogeton alpinus, P. polygonifolius, P. densus, Ranunculus peltatus ssp. heterophyllus, Callitriche stagnalis and Myriophyllum alterniflorum.) Species, not common in streams but tolerant to turbidity, eutrophication or pollution (e.g. Potamogeton trichoides, Elodea nuttallii) appeared in many streams or increased in abundance. There was also a shift in growth forms: submerged species decreased or were replaced by emergent/floating-leaved species. Correspondence analysis was carried out to study the relation between the observed changes and the abiotic characteristic of the streams. The magnitude of the shift in species composition was positively correlated with the PO₄ ^3- concentration and pH (which was highly correlated with Cd²⁺) of the water. This leads to the hypothesis that increased input of sewage, agricultural and industrial water causes a change in species composition and main growth forms of aquatic plant species in lowland streams.     

Responses to food web manipulation in a shallow waterfowl lake

The effects of fish stock reduction have been studies in 3 Dutch lakes (Lake Zwemlust, Lake Bleiswijkse Zoom and Lake Noorddiep) and 1 Danish lake (Lake Væng) during 4–5 years. A general response id described. The fish stock reduction led in general to a low fish stock, low chlorophyii-a, high transparency and high abunuance of macrophytes. Large Daphnia became abundant, but their density decreased, due to food limitation and predation by fish. The total nitrogen concentration became low due to N-uptake by macrophytes and enhanced denitrification. In Lake Bleiswijkse Zoom the water transparency deteriorated and the clear water state was not stable. The fish stock increased and the production of young fish in summer was high. lear water occurred only in spring. Large daphnids were absent in summer and the macrophytes decreased.In Lake Zwemlust, Lake Væng and Lake Noorddiep the water remained clear during the first five years. In summer of the sixth year (1992) transparency decreased in Lake Zwemlust (with high P-concentration of 1.0 mg P l^-1). Also in Lake Væng (with a low nutrient concentration of 0.15 mg P.^-1) a short term turbid stage (1.5 month) occurred in summer 1992 after a sudden collapse of the macrophytes. Deterioration of the water quality seems to start in summer and seems related to a collapse in macrophytes. At a low planktivorous fishstock (e.g. Lake Væng)thhe duration of the turbid state is shorter. than in presence of a high planktivorous fish biomass (e.g. Lake Zwemlust, and later years of Lake Bleiswijkse Zoom).     

Vertical structure of seed banks and the impact of depth of burial on recruitment in two temporary marshes

The structure of the seed bank (including Chara oospores), in relation to depth within the sediment and disturbance, was studied in two Rhône delta temporary marshes for two years. The seeds of all species were concentrated in the top 2 cm of sediment with very low numbers beeing found below 4 cm. When an exclosure eliminated disturbances of the sediment by animals, the vertical repartition of seeds at site 2 was more pronounced than outside the exclosure.In experiment 1, the emergence capacity of seeds from different depths and buried under layers of sterile equivalent to those in the field was measured. Depending of the species, 22 to 98% of the seeds germinated from unburied seeds in the top 2 cm. Only 1% of the oospores of Chara (from site 2) at 2 to 4 cm depth in the sediment emerged.In experiment 2, surface seed bank samples were placed under 0, 2 or 4 cm sterile sediment depth. The samples contained numerous recent seeds and the emergence percentage reached 41% (for Ruppia maritima). Only the seeds of Zannichellia spp failed to germinate from a depth of 2 cm or more. The emergence percentage from 2 cm depth or more was always lower than at the surface. These experiments showed that both burial and ageing of seeds decrease germination capacity.The majority of the active seeds located at the surface germinate when the marsh is flooded. Seeds located between 2 and 4 cm can be brought back to the surface by disturbances and play the role of a reserve involved in maintenance of populations that go without seed production for one or some years.     

Submerged vascular plants and water chemistry in the coastal marsh Albufera de Mallorca (Balearic Islands)

Ten species of aquatic macrophytes have been analyzed for seven environmental variables by means of a significance test. A synthetic view has been obtained through a cluster analysis for species and a principal component analysis for 17 variables which form the multidimensional space where we project the species habitats. Myriophyllum spicatum L., Najas marina L., Potamogeton crispus L., Potamogeton pectinatus L. and Zannichellia pedunculata Reichenb. are widely distributed in the Albufera. Ceratophyllum submersum L. and Ruppia maritima L. var. brevirostris Ag. are considered stenoic. The tolerance of Ceratophyllum submersum to salts is significantly low and that of Ruppia cirrhosa (Petagna) Grande and Ruppia maritima var. brevirostris significantly high. Ceratophyllum submersum has a significantly negative distribution with regard to chlorophyll a and phosphate concentrations. Ceratophyllum demersum L. and C. submersum primarily occur in nitrate-rich waters whereas Ruppia cirrhosa primarily occurs in low nitrate waters.     

Biological effects of salinity gradient reversals in a southeast African estuarine lake

St Lucia Lake on the north coast of Natal, South Africa, has an area of 325 km² and is the largest estuarine complex in Africa. It consists of a 20 km tidal channel, averagingca. 400 m in width, linking the sea with the non-tidal lake which is H-shaped with a maximum length ofca. 40 km and width ofca. 20 km. Except during flood periods the depth of the lake does not exceed 2 m. The salinity gradient depends on evaporation, the configuration of the mouth and on the input of fresh water from four rivers which discharge into the northern and western areas of the lake. If fresh water input is high, the lake and much of the channel may be fresh. An intermediate stage features a normal salinity gradient while a third stage shows a reversed salinity gradient with salinities in excess of 100‰ in the upper reaches of the system. Changing salinities have marked effects on the biota. Aquatic macrophytes show cycles of appearance and disappearance depending on salinity tolerance and the presence of dormant stages. The resident benthic faunal species go through cycles of range expansion and contraction depending on prevailing salinities and recolonisation by dispersal phases. To date salinities in the southern part of the lake have approached, but not exceeded, lethal levels and this has therefore acted as a reservoir area. Catchment degradation and water abstraction are anticipated to exacerbate future salinity extremes. This has resulted in concern for the long term viability of this Ramsar site which has major southern African populations of hippopotamus and crocodile, provides breeding sites for South African Red Data water bird species and plays an important nursery role for marine fish and penaeid prawns.     

灵芝液态发酵胞内外多糖结构特征及其活性研究进展

灵芝是一味传统的中药材,具有很高的药用价值,多糖是其主要的活性成分之一,可从其子实体、孢子粉、发酵菌丝体和胞外液中获得。近年来,从灵芝菌丝体和胞外液中发现的多糖越来越得到研究者们的关注。本文从发酵培养基成分及发酵条件对灵芝胞内外多糖的影响、灵芝胞内外多糖的结构、灵芝胞内外多糖生物活性3个方面进行综述,为发酵来源灵芝多糖的开发利用提供科学理论依据。     

MICROBIAL COLONIZATION ON NATURAL AND ARTIFICIAL MACROPHYTES IN A PHOSPHORUS-LIMITED,HARDWATER LAKE1

Epiphyte communities in a phosphorus-limited hard-water lake were compared over a 14-week period from Potamogeton illinoensis and structurally similar artificial plants of different leaf ages. Artificial plants were serially incubated in the lake to simulate the age of natural leaves. The physiognomy of loosely attached epiphytes appeared similar on the two substrata. Algal cell number and biovolume were 15-fold and 17-fold higher, respectively, on artificial leaves early in the growing season, but total algal density gradually became similar on natural and artificial plants. In contrast, the taxonomic composition of loosely attached algae became increasingly distinct, and mean cell biovolume on natural leaves was twice that on artificial leaves. Adnate epiphytes on both substrata developed from sparse populations of bacteria on new leaves to a community of diatoms, blue-green algae and numerous bacteria on mature and senescent leaves. Adnate community succession on natural leaves in late senescence/death differed from that on artificial leaves colonized for comparable periods in having (1) a marked increase in filamentous blue-green algae, (2) a subsequent decrease in all algae, and (3) a final fungi-dominated stage. The trends in colonization indicate that macrophytes in this oligotrophic lake provided a distinct habitat from that of artificial substrata for epiphytes throughout the growing season.