Submerged macrophyte vegetation and the European Water Framework Directive: assessment of status and trends in shallow,alkaline lakes in the Netherlands

The submerged macrophyte vegetation of lakes created after enclosing former estuaries, situated in the central and south-western part of the Netherlands, has been monitored annually from 1992 onwards. Between 1992 and 2004, pronounced changes in overall cover and species composition of the submerged vegetation have occurred, resulting from changes of water quality and morphology in the lakes. In most cases vegetation cover and species diversity increased or remained stable, with the exception of two lakes in the southwest part of the country. Abundance and species composition were assessed according to the requirements of the EU Water Framework Directive, using the assessment procedure proposed to assess macrophytes in natural water bodies in the Netherlands. The assessment procedure included calculation of the ‘ecological quality ratio’ (EQR) for each of eleven water bodies in each of 13 years, based on transect monitoring data. The EQR indicating Good Ecological Status for Macrophytes was achieved in only three of the lakes. The consequences of hydromorphological modifications, and measures necessary to achieve the desired condition are discussed. Nutrient concentrations should be reduced further, while additional management measures are necessary to improve conditions for macrophytes.     

The influence of physical factors and ornithogenic products on plant and arthropod abundance at an Inland Nunatak group in Antarctica

Summary Robertskollen is a group of geologically similar nunataks in western Dronning Maud Land, Antarctica, with breeding colonies of snow petrels Pagodroma nivea at some of the nunataks. Transects determining macro-plant structure and cover were conducted along an a priori determined bird-influence gradient to assess the relative importance of ornithogenic products and physical factors on plant assemblages. Fine-scale (intra-transect) dispersion patterns of plants were determined primarily by physical factors affecting water availability (i.e. the amount of drift-snow available and the effects of shelter and shade on evaporation rates). Coarse-scale (inter-transect) analysis of plant dispersion patterns, however, showed significant responses along the bird-influence gradient, with consistent responses between nunataks. Plant cover was directly related to bird-influence, but was depressed within bird colonies, apparently due to excessive nutrient enrichment. Mites (Acari) were the only arthropods recorded at Robertskollen and total mite abundance was related to plant cover, although specific responses varied. Thallus diameters of the abundant lichen Umbilicaria decussata decreased with decreasing bird influence, suggesting that nutrients limit plant growth away from bird colonies. Soil concentrations of major plant nutrients, N, P and K, were significantly greater close to bird colonies. We conclude that nutrients in ornithogenic products have direct causal effects on the abundance and dispersion of the biota of inland Antarctic nunataks, and that the effects of nutrient enrichment are detectable at different spatial scales from the effects of physical factors.     

Effects of temperature on spring bloom dynamics of epilithic diatom communities in the Gulf of Bothnia

Abstract. In order to forecast consequences of climatic changes for littoral algae in coastal ecosystems, the effects of temperature increase on spring bloom dynamics of epilithic diatom communities were studied in two ways: (1) Communities were compared from sites receiving different amounts of cooling water discharge from a nuclear power plant. (2) Communities from the exceptionally warm spring of 1989 were compared with those from the same sites in the preceding normal years. The studies were carried out in and around the Forsmark Biotest Basin, an artificial waterbody that receives brackish cooling water from the Forsmark nuclear power plant on the Swedish east coast. Species composition and biomass data from 200 epilithic diatom samples taken in the period January-May from 1983 to 1989 were analysed. Multiple regression analysis was used to show the responses of diatom cover, community diversity and abundances of individual taxa to water temperature and other environmental factors. Constrained ordination (CCA) was used to display the relationship of overall community composition to environment. Increased water temperature resulted in higher biomass through a chain of ecological effects. Strong reduction of ice cover was crucial in this chain, resulting in reduced loss of diatom cells by reduced abrading and higher primary production by higher availability of light, nutrients and substrate. The conclusion is that large blooms of fast-growing epilithic diatoms in large colonies can occupy the niche that emerges when the ice-free season is prolonged in the northern Baltic Sea and areas similar in salinity and climatic conditions. Dramatic species shifts may only be expected if the winter ice cover is totally absent.     

The Seasonal Succession of Biotic Communities in Wetlands of the Tropical Wet-and-Dry Climatic Zone: I. Physical and Chemical Causes and Biological Effects in the Pantanal of Mato Grosso,Brazil

The tropical wet-and-dry climatic zone is characterized by aquatic environments that cover extensive areas during part of the year and shrink to small standing water bodies or rivers with minimal water levels during the dry seasons. Even in the small permanent water bodies, the conditions fluctuate radically during each annual cycle. While there are often strong currents in the water courses during the high water periods, most aquatic habitats are strictly lentic during the dry seasons. Studies conducted in the Pantanal of Mato Grosso, one of the largest wetlands of the world, revealed major features of changes in physical and chemical parameters during the annual cycle. The general features of the climate include a hot, rainy period usually lasting from late October through late April, a cool, dry period from late April through late August, and a hot, dry period from late August through late October. Considerable year to year variations are encountered in the dates of onset and end of the various seasons, however. Four annual periods are recognized according to the water level in the Pantanal. Generally, the concentrations of dissolved inorganic substances are very low and stable during the high water period and variable and usually high in the remaining standing water bodies when much of the region has dried out. The amount of mineral nutrients increases as the water level rises during the early rainy season but decreases again as the aquatic macrophyte populations develop. Some of the reasons for the many short-term changes in mineral nutrient concentrations and the roles of the various aquatic communities are discussed. The results presented will serve as a basis for subsequent studies on the seasonal succession of the flora and fauna.     

Colony sound facilitates sexual and agonistic activities in royal penguins

A unique playback system was used to exaggerate continuously the number of calls heard in royal penguin, Eudyptes schlegeli, colonies to determine whether social facilitation increases a female's exposure to both sexual and agonistic activities, a process that could influence the timing of reproduction in colonies. We also determined whether the source of colony sound or the phase of the breeding cycle influenced the facilitation of sexual or agonistic activities. The system recorded and then played a new 12-min colony sound sample every 24 min throughout the first four phases of the breeding cycle. Because each broadcast was unique, this playback system avoids the possibility of habituation and can modify the acoustic environment in social groups for extended periods of time. The activities of penguins in control colonies (with no playback) were compared with those in colonies that heard samples derived from either their own or a different colony. Colony sound facilitated both sexual and agonistic activities from male and female royal penguins during all four phases of the cycle that we examined. Playbacks from the perceiver's own colony facilitated a greater response than sound originating from a different colony. Studies comparing egg-laying dates in colonies exposed continuously to the sounds of agonistic activities with those in control colonies, or colonies exposed continuously to the sounds of sexual activities are now needed to determine whether the facilitation of agonistic activities opposes the effects of social stimulation on the hormonal changes leading to ovulation in colony-dwelling birds. Copyright 2000 The Association for the Study of Animal Behaviour.     

The surfaces of colonies of Mycobacterium species studied in the scanning electron microscope

The study of the morphology of the surface of several mycobacterial species differing in their pathogenicity by the methods of scanning and transmission electron microscopy has revealed that cells in such colonies and micrococlonies are associated and form one common layer of medium electron density. The cells in this layer are sharply outlined. The cover on the surface of mycobacterial colonies, revealed in this investigation, ensures the stability of mycobacteria in the environment and their resistance to the action of various chemical and physical factors.     

Positive interactions between desert granivores: localized facilitation of harvester ants by kangaroo rats

Facilitation, when one species enhances the environment or performance of another species, can be highly localized in space. While facilitation in plant communities has been intensely studied, the role of facilitation in shaping animal communities is less well understood. In the Chihuahuan Desert, both kangaroo rats and harvester ants depend on the abundant seeds of annual plants. Kangaroo rats, however, are hypothesized to facilitate harvester ants through soil disturbance and selective seed predation rather than competing with them. I used a spatially explicit approach to examine whether a positive or negative interaction exists between banner-tailed kangaroo rat (Dipodomys spectabilis) mounds and rough harvester ant (Pogonomyrmex rugosus) colonies. The presence of a scale-dependent interaction between mounds and colonies was tested by comparing fitted spatial point process models with and without interspecific effects. Also, the effect of proximity to a mound on colony mortality and spatial patterns of surviving colonies was examined. The spatial pattern of kangaroo rat mounds and harvester ant colonies was consistent with a positive interspecific interaction at small scales (<10 m). Mortality risk of vulnerable, recently founded harvester ant colonies was lower when located close to a kangaroo rat mound and proximity to a mound partly predicted the spatial pattern of surviving colonies. My findings support localized facilitation of harvester ants by kangaroo rats, likely mediated through ecosystem engineering and foraging effects on plant cover and composition. The scale-dependent effect of kangaroo rats on abiotic and biotic factors appears to result in greater founding and survivorship of young colonies near mounds. These results suggest that soil disturbance and foraging by rodents can have subtle impacts on the distribution and demography of other species.     

Nest site selection of the Kelp gull (Larus dominicanus) in the Beagle Channel, Tierra del Fuego, Argentina

Nest site selection of Kelp gulls Larus dominicanus breeding in Conejo and Bridges islands, Tierra del Fuego, Argentina, was assessed between 14 and 30 December 2005 to describe variability in nest site features and determine variables affecting nest choice. Fourteen microhabitat variables were quantified at 40 nest sites and at 40 random points in each island during the late incubation stage. Nests at the two colonies were placed on different kinds of substrates across areas with varying degrees of cover provided either by rocks or vegetation. Despite the variability observed in nest site features, rock cover and rocky substrates were the main factors determining nest site selection. At Conejo Island, nest sites presented more rock cover, less percentage of vegetation cover and of vegetation debris substrate, and were placed further from the nearest vegetation in comparison to random points. Similarly, gulls at Bridges Island selected nest sites with more rock cover which were placed mainly on rocky and vegetation substrates. This contrasts with results previously obtained in Argentina, which indicated that vegetation is a key factor influencing Kelp gull nest site selection. Over 80% of the nests at both study colonies were placed on the northern slopes of the islands, relatively more protected from the strong prevailing southwest winds, and nests at both colonies tended to be more protected on their southern side either by rocks or vegetation. Results obtained at Tierra del Fuego confirm the plasticity of microhabitat use by Kelp gulls, and their ability to take advantage of nesting sites according to availability and local environmental factors.     

Possible demonstration of multipotential nature of embryonic neural retina by clonal cell culture.

The possible multipotential nature of the neural retina of early chick embryos was examined by the technique of clonal cell culture. Cultures were prepared from cells dissociated from freshly excised neural retinas of 3.5-day-old chick embryos or from cells harvested from primary highdensity cultures. The following four colony types were obtained: colonies differentiating into “lentoid bodies”; colonies with pigment cells; colonies with both “lentoid bodies” and pigment cells; and colonies comprised entirely of unidentifiable cells. Neuronal differentiation occurred frequently in the early stages of culture (up to about 10 days). In some of these neuronal colonies, “lentoid bodies” and, rarely, both “lentoid bodies” and pigment cells differentiated after a further culture period of up to 30 days. Secondary colonies established from primary colonies after 9–10 days demonstrated that these original colonies fell into four different categories: those giving rise to secondary colonies containing only “lentoid bodies,” those giving rise to pigmented colonies only, those developing both lentoid and pigmented colonies, and finally those which gave rise to secondary colonies of all three types, lentoid, pigmented, and mixed colonies. When primary pigmented colonies were recloned at about 30 days after inoculation, the differentiated pigment cells transdifferentiated into lens. Whether multispecific colonies were really of clonal origin or not is discussed. The possible presence of a multipotent progenitor cell able to give rise to multispecific clones in the neural retina of 3.5-day-old chick embryos is suggested. A sequence of differentiation starting from multipotent neural retinal cells to be terminated with lens through the differentiation of neuronal and pigment cells is hypothetically proposed.     

Lentic macroinvertebrate assemblage structure along gradients in spatial heterogeneity, habitat size and water chemistry

Littoral zones of small water bodies are spatially heterogeneous habitats, harbouring diverse biotic communities. Despite this apparent heterogeneity, many studies have stressed the importance of water chemistry in determining the structure of littoral macroinvertebrate assemblages. The purpose of this study was to consider the relative importance of several spatial and water chemistry variables in explaining the patterns in the structure of macroinvertebrate assemblages in 21 lentic water bodies in northeastern Finland. Water bodies were selected to represent various habitat conditions ranging from small permanent bog ponds to small forest lakes. According to canonical correspondence analysis (CCA), the most important environmental factors related to assemblage composition were water body area, moss cover, total nitrogen and water hardness. In general, species composition in small bog ponds tended to differ from that in larger lakes with forested shoreline. Total species richness was best explained by a composite variable (PCA) describing physical habitat heterogeneity, species richness being lowest in small bog lakes with simple bottom structure and low amount of aquatic plants. Species numbers in dominant functional feeding groups were related to different environmental factors. Shredder species richness was best explained by a regression model incorporating total nitrogen and the amount of organic matter, both of which were negatively related to the number of shredder species. The number of gatherer species increased with mean substratum particle size. Scraper species richness was negatively affected by the abundance of detritus and positively affected by depth, and a model including both variables explained most of the variation. Variation in the number of predatory species was best explained by a regression model including moss cover and lake area.     

Modification of the physical environment by an <Emphasis Type="Italic">Ecklonia radiata</Emphasis> (Laminariales) canopy and implications for associated foliose algae

Macroalgal canopies modify their surrounding environment and thereby influence the structure of associated algal assemblages. Canopies can modify many factors that can be hard to separate and, consequently, the importance of individual factors often remains unknown. Experiments were carried out to test the hypotheses that Ecklonia radiata canopies modify light, sediment cover and water motion, and that each of these physical factors separately influence the assemblage of associated foliose algae. We measured light, sediment cover and water motion across six naturally occurring E. radiata densities and found a reduction in light and sediment cover as kelp density increased. The outcome for water motion was inconclusive. We also manipulated each of these three factors, while controlling for the two others, to determine the separate effects of light, sediment cover and water motion on the assemblage of foliose algae. Reduction in light had a strong effect on the foliose assemblage, reducing species richness and biomass. Reduction in sediment cover and water motion did not cause separate effects at the level of the assemblage, but the biomass of individual species of foliose algae indicated both positive and negative effects. We conclude that E. radiata canopies at Marmion, Western Australia, modify at least two factors of their physical environment, light and sediment cover. However, only light is modified to an extent where it has effects at the assemblage-level because, in contrast to the effects of sediment cover and water motion, the direction of responses are consistent among individual species of algae.     

The impact of climate warming on the diurnal dynamics of the microbial loop: Ice cover vs. lack of ice cover on dystrophic lakes

One of the effects of warming is earlier retreat of the ice cover or a complete lack of ice cover on water bodies in the winter. However, there is still no information on how climate warming affects the 24-hour dynamics of the planktonic microbial loop in winter. The aim of this investigation was to assess the diurnal dynamics of the taxonomic composition and abundance of microbial communities in experimentally reproduced conditions (samples from under the ice, +2, +4 and +8 °C) and to analyse the relationships between components of the microbial loop in relation to physical and chemical parameters. Samples were taken in winter from three dystrophic reservoir. The biological and physicochemical parameters in the water were analysed at the start (day 0), 15 and end of the experiment (day 30) over a 24-hour cycle. The increase in temperature caused an increase in the numbers of predators (particularly testate amoebae and ciliates) and a reduction in the body size of individual populations. During the period with ice cover, marked dominance of mixotrophic testate amoeba (Hyalosphenia papilio) and ciliates (Paramecium bursaria) was observed, while the increase in temperature caused an increase in the proportion of bacterivorous ciliates (Cinetochilum margaritaceum).     

Potential of restored gravel pits to provide suitable habitats for Eurasian otters in anthropogenic landscapes

In anthropogenic landscapes, which are usually characterized by the existence of highly heterogeneous patchworks of habitats with different conservation status, restored gravel pits have the potential to play a conservation role for semiaquatic species such as Eurasian otters (Lutra lutra). Here, we report an otter habitat suitability analysis on a complex fluvial system in an anthropogenic landscape to understand the role of different artificial water bodies (i.e. irrigation channels and ditches) and natural water bodies (i.e. rivers) related to a restored gravel pit lagoon system as providers of suitable habitats for otters. We implemented seven sampling campaigns during 2016 and 2017 consisting of 19 transects across all existing types of water bodies. We integrated 34 environmental variables with otter habitat use, measured by three spraint marking intensity indicators. We found that otter use of water bodies was not related to the natural or artificial origin of the water. Three key factors influenced habitat suitability: riparian vegetation tree cover, forestland use (either natural or planted) within 100 m from the banks, and the level of human disturbance. Our results suggest that otters' tolerance of human activities might be lower in key areas of their territory compared to areas they pass through or explore. We argue that restored gravel pit lagoon systems can potentially play a role in providing suitable habitats for otters in anthropogenic landscapes.     

Development of Streptococcal L-Form Colonies

The development and architecture of L-form agar colonies produced from protoplasts and L-phase bodies were studied by both light and scanning electron microscopy. Agar blocks containing L-phase microcolonies of group A Streptococcus strains ADA and GL8 and group D Streptococcus strain F24 as well as longitudinal sections of mature colonies were used as samples. Initially, granules of about 0.5 mum in diameter were produced by multiple condensation and fragmentation of protoplasts and large bodies. Surface growth by granules ensued and infiltration into agar occurred only after 10 to 11 hr of incubation at 37 C. Club-shaped granules were noted and division seemed to take place by simple fission. The configuration of large bodies and granules in mature colonies suggested budding as another means of replication. Acellular spaces inside the colonies appeared to have been formed by lysis of large bodies or by the envelopment of space by the extending growth of minute granules. Whereas no significant strain variation was noted in colonies of less than 24 hr of incubation, fully mature colonies were differentiated on uniform media.     

Scanning Electron Microscopy of the Influence of Fixation Vehicle Osmolality on Cell Morphology of Spiroplasma, Acholeplasma, and Mycoplasma spp. grown on Agar

Young Spiroplasma citri, corn stunt spiroplasma, and honey bee spiroplasma colonies fixed in 5% glutaraldehyde in M 199 cell culture medium with 0.25 M sucrose showed elongated mycelium-like cells which were sometimes branched or helical. In older colonies beaded chains and rounded bodies were formed. Fixation in 6 % glutaraldehyde in distilled water resulted in amorphous masses in which rounded bodies were present. The spiroplasma cells did not remain osmotically active after glutaraldehyde fixation. Acholeplasma laidlawii and Mycoplasma hyorhinis colonies fixed in glutaraldehyde with or without M 199 medium with 0.25 M sucrose showed little difference in cell morphology.     

High abundance of Trochospongilla horrida (Porifera, Spongillidae) in the Rhine (Germany) 1992–1995

Trochospongilla horrida (Porifera, Spongillidae) was the dominant freshwater sponge in the Rhine between Karlsruhe and Bonn between 1992 and 1995 are reported. It showed an annual life cycle, with an inactive phase during winter. The life cycle was controlled by temperature. Gemmules were produced in high numbers, and played a significant role as resting bodies. Their role as distribution units was negligible because they were tightly fixed to the substratum. Trochospongilla horrida preferred relatively stable habitats, not affected by fluctuations in water level; it was restricted to habitats with a slightly alkaline pH. Laboratory experiments showed a delayed germination of the gemmules, which explains why the highest abundance of the species occured considerably after the first hatching colonies.     

The combined effect of environmental factors and neighbouring populations on the distribution and abundance of Arvicola terrestris. An approach using rule-based models

We investigated how the interplay between environmental factors and presence of neighbouring populations determines the distribution and abundance of a small, endangered rodent, the water vole ( Arvicola terrestris ). We studied thriving and non-fragmented populations of water voles in the absence of their main predator, the introduced American mink ( Mustela vison ). A low degree of population fragmentation, such as the one characterizing the studied populations, was probably typical of water voles before their decline started. We found that under these conditions water voles' distribution is mainly determined by three environmental factors: presence of freshwater, adequate food, and cover. Variance in other factors is well tolerated by water voles. We obtained this result by the use of rule-based models in two separate areas. The two models correctly classified 81% and 83% of the observed cases, respectively. When optimised on one area and cross-validated on the other area the performance of the models was still high (73% and 79%) indicating that the models were robust and generalizable. We also found that the density of animals was lower in sub-optimal than in optimal habitat. We then tested the hypothesis that the number of neighbouring colonies determines the probability of finding voles in a given section. We found that the presence of nearby colonies was an important factor in determining the presence of water voles in sub-optimal habitat, while isolated patches of suitable habitat were less likely to host water voles. These observations suggest the possible presence of a source-sink dynamic, where an optimal habitat acts as a source for populating sub-optimal habitats that may be considered a sink habitat. These findings are discussed in the context of water vole conservation.     

Brood pheromone regulates foraging activity of honey bees (Hymenoptera: Apidae)

Brood pheromone modulated the foraging behavior of commercial honey bee, Apis mellifera L., colonies pollinating a 10-ha market garden of cucumber, Cucurbita pepo L., and zucchini, Cucumis saticus L., in Texas in late autumn. Six colonies were randomly selected to receive 2000 larval equivalents of brood pheromone and six received a blank control. The ratio of pollen to nonpollen foragers entering colonies was significantly greater in pheromone-treated colonies 1 h after treatment. Pheromone-treated foragers returned with pollen load weights that were significantly heavier than controls. Pollen returned by pheromone-treated foragers was 43% more likely to originate from the target crop. Number of pollen grains washed from the bodies of nonpollen foragers from pheromone-treated colonies was significantly greater than controls and the pollen was 54% more likely to originate from the target crop. Increasing the foraging stimulus environment with brood pheromone increased colony-level foraging and individual forager efforts. Brood pheromone is a promising technology for increasing the pollination activity and efficiency of commercial honey bee colonies.     

Confirmation of the single-step membrane filtration procedure for estimating Pseudomonas aeruginosa densities in water.

The efficiency of two procedures, membrane filtration and most probable number, to resuscitate and enumerate Pseudomonas aeruginosa have been compared at two temperatures and varying incubation periods. Data indicate that the membrane filtration procedure using mPA or mPA medium B is more efficient than the most-probable-number procedure in estimating P. aeruginosa populations. It was also found that the specificity of the membrane filtration procedure was such that 92 to 99% of the colonies counted as P. aeruginosa were confirmed, whereas only 2.7 to 10% of the nontypical colonies were confirmed as P. aeruginosa. Furthermore, the data indicate that mPA medium B combined with a 3- to 4-day incubation period at 4.15 degrees C is slightly more specific than mPA medium and is a valid single-step procedure for the resuscitation and enumeration of P. aeruginosa from water or sewage effluent.     

Seasonal succession of the travertine‐forming desmid Oocardium stratum

The calcifying Conjugatophyte Oocardium stratum occurs exclusively in spring‐associated limestones (SAL) with active meteogene limestone deposition. The macroscopic colonies of Oocardium stratum form hemispherical, pinhead‐like structures with a diameter of 0.5–2.0 mm. As its autecology is still poorly understood, we focused on the seasonal development of Oocardium stratum and linked environmental factors to its abundance. The study was conducted in a rivulet in Lunz/See (Austria) for 16 months on a weekly (growing season) to monthly (winter season) basis. Oocardium colonies were found throughout the whole year, with maximum abundance during the mid‐summer months July and August. Repeated macro‐mapping of three SAL sites measuring 750 cm² each showed a maximum Oocardium cover of around 30% in August; two smaller peaks developed in early summer and late autumn with ~10% cover. Diatom mats dominated by Cymbella excisiformis occurred in spring, autumn and winter, with more than 75% cover. The seasonal change between Oocardium and diatoms in limestone‐precipitating springs causes a typical sequence pattern of limestone layers. Redundancy analysis revealed water temperature and bicarbonate content as the main structuring factors; these control the occurrence and growth of Oocardium, reflecting season as a background variable. Optimum growth conditions for Oocardium were an alkalinity around 4.7 meq · L^?1 and a water temperature around 13°C. Site openness, nitrate and dissolved carbon dioxide were inversely related to Oocardium biomass, the opposite for diatoms. Other environmental factors such as total ions or soluble reactive phosphorus had no significant influence on Oocardium stratum abundance.