Showing papers in "Journal of Limnology in 2004"

Survival strategies of freshwater insects in cold environments

Abstract: At high latitudes and altitudes, ice formation is a major variable affecting survival of freshwater fauna and hence the abundance and composition of invertebrate communities. Freezing, but also desiccation and anoxia, are lethal threats to all life stages of aquatic insects, from the eggs to the adults. During cold periods, the aquatic stages commonly remain in or move to a portion of the water body that will not freeze or dry (e.g., deep waters of lakes, springs and hyporheic zone) where they can remain active. Less frequently they migrate to habitats that will freeze at the onset of winter. Insects have developed a complex of strategies to survive at their physiological temperature minimum, comprising (a) morphological (melanism, reduction in size, hairiness/pubescence, brachyptery and aptery), (b) behavioural (basking in the sun, changes in feeding and mating habit, parthenogenesis, polyploidy, ovoviviparity, habitat selection and cocoon building), (c) ecological (extension of development to several years by quiescence or diapause and reduction of the number of generations per year), (d) physiological and biochemical (freezing tolerance and freezing avoidance) adaptations. Most species develop a combination of these survival strategies that can be different in the aquatic and terrestrial phase. Freezing avoidance and freezing tolerance may be accompanied by diapause. Both cold hardiness and diapause manifest during the unfavourable season and: (i) involve storage of food resources (commonly glycogen and lipids); (ii) are under hormonal control (ecdysone and juvenile hormone); (iii) involve a depression or suppression of the oxidative metabolism with mitochondrial degradation. However, where the growing season is reduced to a few weeks, insects may develop cold hardiness without entering diapause, maintaining in the haemolymph a high concentration of Thermal Hysteris Proteins (THPs) for the entire year and a slow but continuous growth. A synthesis of literature regarding adaptation strategies in aquatic insects is presented, highlighting the scarcity of information on freshwater insects from Alpine regions. Most references are on Diptera Chironomidae from North America and North Europe. Some recent findings on aquatic insects from Italian Alpine streams are also presented.

Fragilaria and Staurosira (Bacillariophyceae) from sediment surfaces of 40 lakes in the Austrian Alps in relation to environmental variables, and their potential for palaeoclimatology

Abstract: The percentage distributions of Fragilaria and Staurosira taxa in surface sediment samples from 40 oligo- to ultra-oligotrophic, pH neutral to alkaline, mountain lakes of the central Austrian Alps (Niedere Tauern) were studied in relation to environmental variables using multivariate statistics. Selected taxa that were of uncertain taxonomy or that might be difficult to distinguish were illustrated in LM or SEM. The same statistics as they were applied to the total diatom data set were run on a Fragilariaceae subset with Fragilaria and Staurosira. These analyses emphasized on the high sensitivity of these genera to climate-driven environmental variables in mountain lakes. Canonical Correspondence Analyses (CCA) indicated that the pH, mean July water temperature (TJuly), length of ice cover, and dissolved organic carbon (DOC) made significant contributions to explain the variation in the diatom assemblages. In addition, water depth affected the distribution of benthic and planktonic taxa. Differences or similarities in ecological preferences of taxa provided suggestions for taxonomy. Correlations between the mean valve length and summer water temperatures increase the overall high potential of Fragilaria and Staurosira for palaeoclimatological reconstructions in mountain lakes.

Trophic conditions of marine coastal waters: experience in applying the Trophic Index TRIX to two areas of the Adriatic and Tyrrhenian seas

Abstract: This paper is an extension of an earlier paper on a Trophic Index TRIX, a linear combination of the log of 4 state variables: ChA, aD%O, minN & TP (Vollenweider et al. 1998), to characterizing succinctly the trophic levels of coastal marine areas, and to discuss questions that since have arisen in applying and developing the index further. This entails in depth review of some procedural aspects such as data processing including transformation of rough data; the statistical distribution of TRIX; comparisons over different spatial and temporal scales; discrimination limits between two contiguous means of TRIX; interrelationships between TRIX and its components, and between TRIX and other water related variables. Further to statistical properties of TRIX, attention is given to integrative features and other implicit functional relationships pertinent to the description of trophic characteristics of coastal systems, among which to mention the term "efficiency". This theoretical framework has been applied to data from two trophically different responding coastal systems, i.e. the Emilia-Romagna coastal area of the Adriatic Sea and the Tuscany coastal area of the Tyrrhenian Sea to illustrate some of the arising interpretative problems in using TRIX. Finally, analyses of the two system are juxtaposed in an alternatively slightly modified reference diagram in which the trophic location and the extent of variability are shown in relation to the N/P ratio and related efficiency.

Experiences with dormancy in tardigrades

Abstract: Tardigrades often colonise extreme habitats, in which they survive using both types of dormancy: quiescence and diapause. Together with nematodes and bdelloid rotifers, tardigrades are known to enter quiescence (with several forms of cryptobiosis: anhydrobiosis, cryobiosis, anoxybiosis, osmobiosis) at any stage of their life cycle, from egg to adult. Entering anhydrobiosis, tardigrades contract their body into a so-called tun, loosing most of their free and bound water (>95%), synthesizing cell protectants (e.g., trehalose, glycerol, heat shock proteins) and strongly reducing or suspending their metabolism. Our research on cryptobiosis focused on some ecological and evolutionary aspects. We evaluated: i) the long-term anhydrobiotic survival by comparing quantitative data on recovery from naturally induced desiccation in several species of tardigrades; ii) differences in survival patterns between species and populations by experimentally inducing anhydrobiosis and cryobiosis; iii) phenotypic factors affecting anhydrobiotic survival. As regards diapause, we considered encystment and eggs. Encystment involves at least the synthesis of new cuticular structures. Morphological changes during cyst formation are more complex than those involved in tun formation. We analyzed more in detail encystment processes, comparing a semiterrestrial with a limnic species. Several inter-specific differences have been identified, other than the production of two types of cysts in the semiterrestrial species. Our analysis of life history traits of a laboratory reared strain of a soil tardigrade revealed a particular hatching phenology that involved the production of both subitaneous and resting eggs. The latter need a cue to hatch (dehydration followed by re-hydration). In addition, the evolutionary meaning of dormancy in tardigrades is discussed.

Use of ephippial morphology to assess richness of anomopods: potentials and pitfalls

Abstract: Zooplankton species richness is typically assessed through analysis of active community samples. These samples ought to be collected at many different locations in the lake and at multiple occasions throughout the year so as to cover the spatial and temporal heterogeneity in active community structure. A number of studies have shown that high numbers of species can be retrieved with a limited effort through hatching of dormant eggs isolated from lake sediments. However, dormant eggs of different species differ in their propensities to hatch, resulting in biased assessments of species composition, abundance and richness. In this paper, we explore the potentials and pitfalls of a third method to assess cladoceran species richness. For twenty European lakes, we identified the number of ephippium morphotypes in sediment samples taken on a single occasion. The morphotype richness was well correlated with species richness as assessed through hatching of dormant forms and through analysis of active community samples covering a six month period. However, not all species had a species-specific ephippial morphotype, consequently resulting in an underestimation of true species richness.

Role of diapause in dispersal and invasion success by aquatic invertebrates

Abstract: Review of existing literature shows an important role of diapause in dispersal of aquatic invertebrates. There is evidence that among aquatic invertebrates, the role of diapause in dispersal can be important in crustaceans, specifically for species that produce resting eggs. Analysis of dispersal vectors of diapausing species revealed the increasing role of human-mediated vectors of species dispersal during last century (intentional and unintentional introductions, specifically associated with shipping) in comparison with natural vectors (currents, wind, birds). Generally, the role of human-mediated vectors is most important for species dispersal across geographical barriers and into large aquatic ecosystems affected by shipping. Current human-mediated transport vectors increase rates of aquatic species introductions in many orders of magnitude in comparison with historical nature-driven species dispersal rates. Ability to develop diapausing resting stages facilitates species survival during movement across geographical barriers under extreme conditions, such as in ballast tanks of ships. Case studies for invasive species of Cladocera show that some invaders may possess adaptive life cycles, switching to the early prolonged gamogenetic reproduction, which facilitates their invasion success into novel ecosystems and further dispersal by both natural and human-mediated vectors.

Biomass, composition and size structure of invertebrate communities associated to different types of aquatic vegetation during summer in Lago di Candia (Italy)

Abstract: We compared the biomass, taxonomic composition, and size distribution of invertebrates associated to emergent (Schoenoplectus lacustris), submerged (Myriophyllum spicatum), and floating leaved (Trapa natans) vegetation at two depths (surface and water column) during summer in Lago di Candia, Italy. Invertebrate biomass was positively related to epiphyton biomass (Chl-a). M. spicatum supported higher invertebrate biomass per unit of plant weight than S. lacustris whereas T. natans was somewhat intermediate. Depth did not affect invertebrate biomass significatively. Surface sections of M. spicatum and T. natans supported invertebrate communities with similar taxonomic composition dominated by oligochaetes and ostracods. Large hirudineans and gastropods characterized the communities on the water column sections of M. spicatum. S. lacustris and the water column sections of T. natans (composed of stems and aquatic roots) were supporting invertebrate communities dominated by copepod nauplii and lacking large organisms. Changes in aquatic vegetation in Lago di Candia following harvesting of T. natans and removal of submerged vegetation by the invasion of the rodent coypu (Miocastor coypus) may affect the invertebrate biomass of its littoral zone.

Phototropic sulfur and sulfate-reducing bacteria in the chemocline of meromictic Lake Cadagno, Switzerland

Abstract: Lake Cadagno, a crenogenic meromictic lake located in the catchment area of a dolomite vein rich in gypsum in the Piora Valley in the southern Alps of Switzerland, is characterized by a compact chemocline with high concentrations of sulfate, steep gradients of oxygen, sulfide and light and a turbidity maximum that correlates to large numbers of bacteria (up to 107 cells ml-1). The most abundant taxa in the chemocline are large- and small-celled purple sulfur bacteria, which account for up to 35% of all bacteria, and sulfate- reducing bacteria that represent up to 23% of all bacteria. Depending on the season, as much as 45% of all bacteria in the chemocline are associated in aggregates consisting of different populations of small-celled purple sulfur bacteria of the genus Lamprocystis (up to 35% of all bacteria) and sulfate-reducing bacteria of the family Desulfobulbaceae (up to 12% of all bacteria) that are almost completely represented by bacteria closely related to Desulfocapsa thiozymogenes. Their association in aggregates is restricted to small-celled purple sulfur bacteria of the genus Lamprocystis, but not obligate since non-associated cells of bacteria related to D. thiozymogenes are frequently found, especially under limited light conditions in winter and early summer. Aggregate formation and concomitant growth enhancement of isolates of both partners of this association suggests synergistic interactions that might resemble a sulfide-based source-sink relationship between the sulfate-reducing bacterium that is able to sustain growth by a disproportionation of inorganic sulfur compounds (sulfur, thiosulfate, sulfite), with the purple sulfur bacteria acting as a biotic scavenger. The availability of these isolates opens up the door for future studies considering other facets of potential interactions in aggregates since both types of organisms are metabolically highly versatile and interactions may not be limited to sulfur compounds only.

Population density, sexual reproduction and diapause in monogonont rotifers: new data for Brachionus and a review

Abstract: Diapausing, fertilized eggs in monogonont rotifers typically are formed after an environmental signal induces amictic females to produce mictic daughters. Mictic females lay haploid eggs that may develop parthenogenetically into males, or that may be fertilized and develop into diapausing, female embryos called resting eggs. Laboratory experiments demonstrate that crowding is the signal for production of mictic females in strains of Brachionus calyciflorus from Texas, Spain and Germany, and in a strain of Brachionus variabilis from Spain. In these experiments, newborn amictic females were cultured singly in large and small volumes to give lowand high-density treatments. Therefore, the induction of mictic females is due exclusively to population density and cannot be attributed to a grouping effect involving some interaction among individuals. B. variabilis is very sensitive to population density; females had to be cultured in 30 ml to prevent appreciable production of mictic daughters. Crowding is now known to be the signal for initiation of sexuality and diapause in four species of Brachionus, two species of Epiphanes, and Rhinoglena frontalis. The chemical that mediates this response somehow influences oocytes in the maternal body cavity to differentiate into mictic females. Aggregation of individuals in natural systems may facilitate the production of mictic females. In some of these rotifers, the response to crowding is suppressed in early generations from the resting egg, assuring that clonal populations will attain higher population densities before committing to sexual reproduction. Fitness benefits of the mictic-female response to crowding, and to other environmental signals in other rotifers (dietary tocopherol, long photoperiod), are discussed.

Response of alpine lakes and soils to changes in acid deposition: the MAGIC model applied to the Tatra Mountain region, Slovakia-Poland

Abstract: A dynamic process-based model of surface water acidification, MAGIC, was applied to 31 representative alpine lakes in the Tatra Mountains (~50% of all alpine lakes >0.3 ha in the lake-district). The model was calibrated to observed lake chemistry for the period 1980-2002. Surface water and soil chemistry were reconstructed from 1860 to 2002, given estimates of historical acid deposition, and forecast to 2020 based on the reduction in sulphur and nitrogen emissions presupposed by the Gothenburg Protocol. In the 1860s, all lakes were buffered by the carbonate system and only ~6% of lakes had acid neutralising capacity (ANC) 50% of the SAA change) in sensitive lakes with intermediate weathering rates and little soils (low BC exchangeable capacity and elevated terrestrial export of nitrate) and (3) by parallel changes in concentrations of protons and aluminium (each ~20% of the SAA change) in extremely sensitive lakes, with the lowest weathering rates and soil base saturation. The full implementation of the Gothenburg Protocol will not be sufficient to allow recovery of the latter group of lakes, which will remain acidified after 2020.

The chemical and biological response of two remote mountain lakes in the Southern Central Alps (Italy) to twenty years of changing physical and chemical climate

Abstract: Two small high mountain lakes in the Alps were monitored in 1984-2003 to follow their response to changes in human impact, such as deposition of atmospheric pollutants, fish stocking and climate change. The results were compared to occasional samplings performed in the 1940s, and to the remains found in sediment cores. When monitoring started, the most acid-sensitive of them, Lake Paione Superiore, was acidified, with evident effects in its flora and fauna: benthic diatoms assemblage was shifted towards aci- dophilous species, and zooplankton lost the dominant species, Arctodiaptomus alpinus. Palaeolimnological studies outlined that lake acidification paralleled the increasing input of long-range transported industrial pollutants, traced by spherical carbonaceous parti- cles. On the contrary, the biota of Lake Paione Inferiore appeared to be mainly affected by fish stocking. In the last twenty years, de- crease in acid load from the atmosphere led to an improvement in lake water quality, with an increase in both pH and alkalinity. First signs of biological recovery were identified, such as change in diatom flora and appearance of sensitive species among benthic insects. However, climate change and episodic deposition of Saharan dust were important driving factors controlling lake water chemistry. Further monitoring to assess the effects of climate change and of the increasing load of nitrogen and other pollutants is recommended. Key word: atmospheric deposition, acidification, plankton, benthos, diatoms

A consideration of potential confounding factors limiting chemical and biological recovery at Lochnagar, a remote mountain loch in Scotland

Abstract: Lochnagar, a remote loch in the Grampian Mountains of Scotland is one of the most studied freshwater bodies in the UK. It represents a key site in a number of monitoring programmes and has become the UK’s 'flag-ship' mountain lake in various EU funded projects over the last 15 years. Palaeolimnological studies have revealed the extent and diverse provenance of atmospherically deposited pollution at the site and show that the loch began to acidify in the mid-19th century. However, despite abatement strategies dramatically reducing the emission and deposition of non-marine sulphate and trace metals since the 1970s, the loch pH shows little sign of recovery and full basin fluxes of, for example, Pb and Hg show no decline or even a continued increase. It is suggested that the lack of recovery from acidification over the last 15 years of monitoring results from the balancing of the decline in sulphate by increased nitrate, and that this increase is related to winter duration and severity. The lack of response by the sediment record to declines in metal deposition is thought to be due to a continuing input of previously deposited metals from the catchment. Hypotheses for these enhanced catchment inputs involve responses to a changing climate. Site specific climate reconstructions and predictions for the 21st century suggest an accelerated increase in temperature rise and increased winter precipitation and storminess. These predicted changes are likely to exacerbate the input of metals (and other stored pollutants) from the catchment but higher temperatures may also help to promote recovery from acidification.

Horizontal heterogeneity of seston, organic carbon and picoplankton in the photic zone of Lago Maggiore, Northern Italy

Abstract: The horizontal heterogeneity of seston, dissolved (DOC) and particulate (POC) organic matter, Chlorophyll-a (Chl) and of autotrophic (APP) and heterotrophic (HPP) picoplankton was evaluated seasonally during a two-year period in Lago Maggiore, a large deep oligotrophic lake in Northern Italy The dissolved fraction resulted homogeneously distributed in the epilimnion during the whole sampling period The particulate fraction showed the higher heterogeneity in winter 2000 and 2001 For those years, POC and Chl heterogeneity was, respectively, 3-5 and 5-7 times higher than DOC A similar trend was evident for Chl and for APP The spatial heterogeneity of HPP resulted always smaller than the analytical variability, thus preventing any consideration about the spatial distribution of HPP POC and Chl concentration exhibited a recurrent pattern of their spatial heterogeneity, possibly in relation with the location of the part of the drainage basin conveying higher amounts of nutrients to the lake

Lake Bolsena (Central Italy): an updating study on its water chemistry

Abstract: In spite of its importance as regards size (volume 9.2 106 m3, max depth 151 m) and as a source of drinking water, Lake Bolsena has not been studied from a hydrochemical point of view since the second half of the 60s, when a group of researchers from the Istituto Italiano di Idrobiologia co-ordinated a complete study of the limnology of the Latium lakes Bolsena, Albano, Vico, and Bracciano. In the following years analyses were performed sporadically; since the 90s, temperature and oxygen profiles and other studies were made by the Associazione Lago di Bolsena. Based on chemical profiles made in 2001-2003, this paper discusses the present chemical composition of Lake Bolsena waters, and compares them with those of other volcanic lakes in Latium (Bracciano, Albano, Nemi and Vico). The paper briefly considers the main factors influencing the water chemistry of Lake Bolsena, the variations observed from the analyses of the 60s, and the main sources of risk to water quality.

Phenotypic variation and developmental instability of life-history traits: a theory and a case study on within-population variation of resting eggs formation in Daphnia

Abstract: It is commonly accepted that within-population phenotypic variation is caused by genotypic and environmental heterogeneity. Non-genotypic variation is thought to result from diversity of environmental conditions alone. This however contradicts experimental data showing that even when both genetic and environmental sources of phenotypic variation are neglected, residual variation still exists. This residual phenotypic variation is caused by deviations of developmental trajectories from the target trajectory determined for particular genotype and environment, i.e. by developmental instability. This variation is well-known for morphological traits where it is measured most often by fluctuating asymmetry, i.e. random deviations from perfect symmetry, which can be easily separated from the other type of phenotypic variation. In morphological characters which do not possess symmetry or in non-morphological characters this variation cannot usually be separated from other type of non-genotypic variation, caused by environmental heterogeneity. Most researchers still believe that all non-genotypic variation, even under standardised experimental conditions, is caused by insufficient standardization of environment, rather than by other sources of phenotypic variation. When special efforts are undertaken to analyse variation caused by developmental instability, this variation contributes substantially to non-genotypic variation. To exemplify how variation caused by developmental instability can be separated from phenotypic plasticity we analysed phenotypic variation of resting egg formation in Daphnia pulicaria. The proportion of females carrying resting eggs has been shown to depend on the photoperiod of their mothers, revealing transgeneration effects (Alekseev & Lampert 2001). Developmental instability manifests itself in differences between clonemates within an experimental vessel in a standardized environment. Some females produce resting eggs whereas others do not. Our estimations based on results obtained in experimental conditions and extrapolation to conditions in the wild showed that phenotypic plasticity, i.e. phenotypic response to changes of day duration in maternal environment (phenotypic plasticity) explains only 1-2% of phenotypic variation whereas developmental instability explains approximately 98-99% of phenotypic variance of this trait (i.e. producing or not producing resting eggs), if other factors causing phenotypic plasticity are absent. This example demonstrates a major role of developmental instability in variation of the trait under study. The contribution of developmental instability to phenotypic variation should be considered in studying evolutionary patterns of phenotypic traits.

Geochemical response of a closed-lake basin to 20th century recurring droughts/wet intervals in the subtropical Pampean Plains of South America

Abstract: Laguna Mar Chiquita is a highly variable closed saline lake located in the Pampean Plains of central Argentina. Presently is the largest saline lake in South America (∼ 6,000 km2) and also one of the largest in the world. During the 20th century the hydrological balance of the region was characterized by contrasting scenarios. Well-defined wet or dry climatic phases had ruled the lake level fluctuations and the rivers discharge, mainly controlling the geochemical composition of sediments. Sediments accumulated during positive hydrological balances (i.e., high lake level) are mainly composed of allogenic mineral due to higher riverine inputs into the lake. This fluvial-dominated lake phases are recorded as sediments enriched in Al2O3, SiO2, K2O, Fe2O3 and TiO2 and in trace elements such as Co, Cr, Cs, Rb, Sc, Hf, Ta, Th as well as rare earth elements (REE). Sediments accumulated during dry phases (i.e., low lake levels and high salinity) are evaporite mineral-rich with elevated concentrations of CaO, MnO, MgO, and P2O5. High contents of As and U are probably due to a co-precitation during high evaporative phases. The calibration of the sediment chemical composition of Laguna Mar Chiquita to well-defined water-level fluctuations of the 20th century shows that elemental geochemistry can be a useful proxy to study former lake-water fluctuations. It may further provide a comparative model to evaluate past environmental conditions in other saline lacustrine basins.

Genetic and morphometric differentiation among sympatric spawning stocks of whitefish (Coregonus lavaretus L.) in Lake Femund, Norway

Abstract: Lake Femund, Norway, contains several sympatric ecotypes of whitefish, Coregonus lavaretus L. Deepwater whitefish, river whitefish, and shallow water whitefish can be easily distinguished by spawning habitat and gillraker number. Variation in morphological and ecological characters and allozyme loci from 11 different spawning sites was analysed to compare the ecological polymorphism with possible genetic sub-structuring of whitefish in the lake. Of the individual morphological and ecological characters, gillraker number best separated the spawning populations, followed by body length. In a hierarchical cluster analysis based on gillraker number, body length and age of fish, the four deepwater sites grouped together as well as the three samples from, or closely related to, inlet rivers. The shallow water sites, however, were more dispersed. In the allozyme analysis, nine of the 38 enzyme loci were polymorphic at the 0.95 level. The amount of genetic variation was quite similar among localities with Hexp = 0.046 - 0.066. Allele frequencies differed significantly among localities at all polymorphic loci indicating distinct reproductive isolation between spawning sites. A consensus tree based on genetic distances grouped samples according to spawning depth and trophic morphology rather than regional proximity. All deepwater spawners grouped together with rather high support while geographically adjacent samples differing by their morphology or behaviour were dispersed. The patterns of differentiation based on allozyme variation and morphology are not fully concordant, but still the association between genetic differentiation and morphological and life history variables was highly significant. Thus, the morphological differences are not due to phenotypic plasticity within single spawning populations as is commonly seen in many other fish species. The possible evolutionary origins of reproductively isolated whitefish forms are discussed. The relatively close association between differences in gillraker counts and genetic difference indicates that the present management of Femund whitefish stocks based on gillraker counts is sensible.

Measured and modelled trends in European mountain lakes: results of fifteen years of cooperative studies

Abstract: Papers included in this Special Issue of the Journal of Limnology present results of long-term ecological research on mountain lakes throughout Europe. Most of these studies were performed over the last 15 years in the framework of some EU-funded projects, namely AL:PE 1 and 2, MOLAR and EMERGE. These projects together considered a high number of remote lakes in different areas or lake districts in Europe. Central to the projects was the idea that mountain lakes, while subject to the same chemical and biological processes controlling lowland lakes, are more sensitive to any input from their surroundings and can be used as earlywarning indicators of atmospheric pollution and climate change. A first section of this special issue deal with the results of long-term monitoring programmes at selected key-sites. A second section focuse on site-specific and regional applications of an acidification model designed to reconstruct and predict long-term changes in the chemistry of mountain lakes.

First record and morphological features of Hemidiaptomus (Occidodiaptomus) ingens (Gurney, 1909) (Copepoda Calanoida) in Italy

Abstract: During a survey, carried out to assess the consistency of microcrustacean fauna inhabiting temporary ponds in Sicily, Hemidiaptomus (Occidodiaptomus) ingens (Gurney, 1909), a large calanoid copepod up to now known only for North-African ponds, Camargue and Corse, was found in the north-western part of the island. Due to its central location in the Mediterranean Sea, Sicily represents a transition zone where several chorological zones of the West Palearctic merge and converge. A brief summary of the existing literature regarding this taxon is given with some morphological considerations on the recently found population which represents the first record for Italy. In particular, the morphological features of the Sicilian population are closely related to those described by Gurney for the specimens collected in the locus typicus (Oued Tindja, Tunisia) and slightly differ from the other European populations.

Application of MAGIC to Lake Redó (Central Pyrenees): an assessment of the effects of possible climate driven changes in atmospheric precipitation, base cation deposition, and weathering rates on lake water chemistry

Abstract: The process-oriented catchment-scale model MAGIC was used to simulate water chemistry at Lake Redo, a high mountain lake in the Central Pyrenees, Spain. Data on lakewater and atmospheric deposition chemistry for the period 1984-1998 were used to calibrate the model, which was then used to reconstruct past and to provide forecasts for three hypothetical future scenarios of deposition. Forecast scenarios considered several combinations of changes in S and N deposition due to abatement strategies, and in base cation deposition due to climate-induced changes in air-mass trajectories from northern Africa. Scenario 1 assumed constant deposition of base cations at the present level plus the expected decrease in S and N deposition resulting from reduced emissions; scenario 2 (best case) assumed an increase in base cation deposition plus the same decrease in S and N deposition as in scenario 1; scenario 3 (worst case) assumed a decrease in base cation deposition plus no decrease in S and N deposition. The hindcast indicated that during the past 140-year period changes in lake water chemistry have been significant for a remote mountain catchment, although no substantial acidification has occurred. In this regard Lake Redo can be described as a "non-sensitive lake" maintaining a reference condition. The forecasts indicated changes that do not affect this status, but the trends, even if slight, were different between scenarios. A slight decline in the surface water ANC is predicted by Scenario 3. The N budget indicates an unusually low retention in the catchment, which may result in enhanced sensitivity to further increased N deposition. Some of the discrepancy between modelled and measured Ca 2+ in lake water during 1984-98 could be explained by changes in rainfall amounts and by increased weathering rates due to increases in air temperature.

Diapause in Calanoid Copepods: within-clutch hatching patterns

Abstract: Diapause is a major life history feature of many invertebrate organisms. Determining the phenology of diapause is critical for understanding survival and reproductive success of individuals as well as the long-term viability of many populations. The time spent in dormancy by individuals and variability among offspring in the duration of dormancy are two important aspects of invertebrate life histories. Some data are available, especially on duration of diapause, for plants and insects, but little information is available concerning variability among offspring in diapause traits. This is especially true for crustacean zooplankton, where essentially no information has been published on duration of diapause or variability among offspring in diapause timing or dynamics. Here I present data on the duration of diapause, and variability among offspring for diapause characteristics. The freshwater calanoid copepod Onychodiaptomus sanguineus, an obligately sexual species, was collected from Bullhead Pond, Rhode Island, U.S.A., and raised under conditions in the laboratory to induce production of diapausing eggs. One hundred clutches of these diapausing eggs (920 total eggs) were incubated for over two years in a full-factorial experiment testing the effects of temperature and photoperiod cycles on the hatching dynamics and duration of diapause. Overall hatching success was highest (approximately 86%) for eggs exposed to simultaneous temperature and photoperiod cycles mimicking natural changes, and was lowest (approximately 20%) when eggs were incubated at constant temperature (4 °C) and in constant dark conditions. The highest fraction of eggs hatched at approximately 550 days of age, but the age of eggs at hatching was highly variable among clutches. There was also large variability within clutches for hatching patterns, with some clutches containing eggs that all hatched synchronously and others in which eggs hatched more continuously throughout the experiment. Treatment conditions significantly affected within-clutch synchrony of hatching, as well as synchrony of the onset of hatching. These results of high within-clutch variability and differences among clutches in diapause dynamics have important implications for our understanding of reproductive success of individuals producing diapausing eggs, parent-offspring conflict, and the evolution of bet-hedging strategies in invertebrates.

The influence of biological and environmental factors on the stable isotopic composition of ostracods - the Late Pleistocene record from Lake Albano, Central Italy

Abstract: The stable oxygen and carbon isotopic composition of ostracod valves is the result of the interaction of several variables Understanding and identifying the biological and ecological factors influencing the life of these animals improves the interpretation of isotopical data, and leads to better paleoenvironmental reconstructions Ostracod biostratigraphy and determinations of oxygen and carbon stable isotopes on ostracod valves were carried out on a short sequence of the Last Glacial Maximum from Lake Albano (Central Italy) The oxygen isotopic composition of adults of Candona neglecta ranged between 05‰ and 15‰, and in Ilyocypris bradyi between –2‰ and –05‰ Isotopic values from adults of C neglecta fell within the range –15‰ to –08‰ when corrected for vital effect The carbon isotopic signal ranged from 94‰ to 108‰ in adults and juveniles of C neglecta, and from 98‰ to 113‰ in I bradyi Differences between left/right valve and gender were negligible, whereas there appeared to be a marked influence of life stage and species-specific factors related to vital effect and differences in microhabitat and seasonality We combined analyses on carbon and oxygen isotopes with information deriving from ostracod ecology to reconstruct short term oscillations in past lake water level Seasonal changes in either the temperature or the isotopic composition of the lake water were also identified Relatively high δ18O values in ostracod valves were probably associated with the lake location and source of moisture, while high δ13C values were most probably related to the input of volcanic CO2 into the lake

Ecological relations and temporal changes in the pelagial of the high mountain lakes in the Rila Mountains (Bulgaria)

Abstract: The high mountain lakes in the Rila Mountains (Bulgaria) were studied in the years 2000 and 2001 considering the following groups of variables: geography, geology, morphology, hydrology, water chemistry of the pelagial, biomass and size structure of bacterio- phyto- and zooplankton, and occurrence of three fish species. Multivariate analysis (RDA) revealed that the nutrient concentrations in the lakes were significantly influenced by the soil percentage coverage of the catchment area. The explained variation in plankton components (bacterio-, phyto- and zooplankton) and plankton size structure was determined by biological as well as morphometrical and geographical variables. Changes in the Mg2+ and NO3-N concentrations were traced over the period 1993- 2001; the Ca2+ concentration, pH, nutrients, bacterio-, phyto- and zooplankton were monitored in the period 1995-2001. A nutrient decrease accompanied by an increase in size of zooplankton organisms in the period 1995-2001 led to a considerable increase of water transparency in the lakes.

Environmental plasticity of fish avoidance diapause response in Daphnia magna

Abstract: Organisms cope with harsh environmental conditions in various ways: either by tolerating environmental stress (through physiological adaptations), or by avoiding it in space (through migration) or time (diapause). Some species rely on a single strategy while others may choose from an array of options when facing different environmental stressors. Planktonic crustaceans may utilise different active (morphological, behavioural, life-history) or passive (diapause) defences to survive periods of high risk of fish predation. Recent evidence has indicated that resting egg production could be induced in Daphnia magna by chemical cues associated with fish predation. This suggests that contrary to most known cases of diapause, which are triggered well in advance of catastrophic events (here termed "predictive diapause"), fish avoidance diapause in D. magna may exhibit a "responsive nature" and be initiated only after intensive predation appears. Experimental evidence discussed here indicates that the reaction of D. magna to chemical signals of fish predation could be conditional and determined by key environmental conditions, which in nature affect relative gains of activity vs dormancy. At high risk of fish predation, the decision of Daphnia to produce resting eggs was disfavoured by high food concentration. This reaction was claimed adaptive since high food allows for higher reproductive rates and better survival of offspring. All this may assure higher benefits due to activity despite some risk of predation (once predation pressure is not fatal to all active descendants) and disfavour resting eggs production. Moreover, at moderate food conditions the decision of Daphnia to produce resting eggs was disfavoured by the availability of a dark refuge from fish visual predators and thus likely lowering the risk of being preyed upon. Furthermore, when food was at a moderate level and a dark refuge was not present the decision of Daphnia to produce resting eggs was favoured by low water temperature. This could be explained as an adaptive reaction again, once low water temperature (due to its effect on a rate of metabolism) should have affected the gains derived from active life and reproduction more seriously than ones of inactive stages. The evidence presented here indicates that a responsive diapause allows D. magna to maximise reproductive output by taking advantage of opportunities presented by an unpredictable environment.

Effects of diel vertical migration on ephippia production in Daphnia

Abstract: Fish presence in experimentally simulated temperature conditions (limno-towers) led to diel vertical migration and resulted in a decrease of ephippia production in Daphnia pulicaria. Diel fluctuation of food, temperature and day length similar to those experienced by migrating Daphnia were tested in laboratory experiments with flow-through-systems. Daphnids were kept under these conditions for 15 days and the proportions of females producing an ephippium were determined. In addition, maturation time, survival to maturation, size of the first clutch and female dry weight (without eggs) on day 15 were traced. The most important factor affecting ephippia production in migrating Daphnia was photoperiod change, and when mother and embryo are exposed to alternating light conditions, these are thought to have the effect on the mother of acting as a signal to stop ephippia production. Such effects might be explained by the different sensitiveness to light intensity in females carrying an embryo and an embryo itself in broods. Fish presence forced Daphnia to stay in low-light conditions during daytime hours, to avoid attacks by fish. The Daphnia were able to check light intensity constantly by short vertical jumps above a light-threshold that was confirmed experimentally in limno-towers. The dim conditions were possibly light enough for adults to check day length, but were too dark for embryos shaded by the mother's body. Food conditions played a relatively small role in the process, and no effects of temperature on ephippia production were found. As expected, food affected the size of the first clutch, and temperature controlled the time to maturation. Photoperiod had a marginally significant influence on the time to maturation in Daphnia. A hypothesis on the role of photoperiod as the key factor for Daphnia life cyclic recurrence and other seasonal adaptations is proposed.

Population dynamics of the pioneer population of Daphnia parvula, Fordyce during the invasion of Lake Candia (Northern Italy)

Abstract: Since the 1970s Daphnia parvula, Fordyce, originally distributed in the New World, has been invading Europe. In Italy D. parvula first appeared in the shallow, eutrophic Lake Candia (Piedmont, Northern Italy) during September 2002. Although several studies have documented D. parvula dispersal in European habitats, little is known about the life cycle and ecology of this invader in its new habitats. Invasion success depends on the ability of the invader population to perform well in the new ecosystem, which in turn results from the interaction between the characteristics of the invader and those of the invaded environment and its resident community. Early detection of D. parvula in the intensively studied Lake Candia offered an excellent opportunity to study the performance of the pioneer population and to document the early phases of invasion. Following the dynamics of the pioneer D. parvula population provided evidence of a high level of gamogenetic reproduction during most periods of population development. The production of males started at the onset of population growth prior to ephippia formation. The sex ratio ranged from 0.1 to 0.33 males per female with a maximum in October when males accounted for up to 24% of the total population density. The percentage of ephippia (free ephippia + ephippial females) out of the total population density ranged from 3 to 23%. The large pool of resting eggs produced by the pioneer population of D. parvula in Lake Candia might reflect a strategy for increasing the probability of survival and establishment in the new environment.

Seasonal phenotypes of Daphnia: post-diapause and directly developing offspring

Abstract: Life-history and physiology of post-diapause and directly developing offspring in Daphnia were compared to determine differences in life-history pattern between offspring origins, identify the basic traits effecting pattern distinction, assess the consequencies of differing life-history for relative fitness, and qualify this seasonal phenomenon. Although the size of ex-ephippial hatchlings was positively correlated with maternal size, ephippia produced by differently sized females of D. magna yielded neonates which body size and it’s variation were similar to those for the first-clutch parthenogenetic neonates produced under high food conditions. Otherwise, post-diapause neonates of D. pulex were larger than first-clutch parthenogenetic neonates and varied in size close to that for neonates from the later clutches. Ex-ephippial offspring showed elevated metabolic activity. Under rich food, they grew faster during juvenile development and were larger at maturation than parthenogenetic females. Post-diapause offspring of D. magna showed higher juvenile growth rates also at limited food availability. Female origins during early maturity differed in resource allocation strategy. A greater allocation to progeny in offspring exiting diapause, however, resulted in increased progeny numbers and higher relative fitness only under rich food environments. Whereas, parthenogenetic females of D. magna exhibited a trend for higher fitness across limited food concentrations. For D. pulex, variability of fitness across differing nutritional environments was lower in directly developing females than that for ex-ephippial offspring. Higher metabolic activity in combination with small initial size resulted in lower resistance to starvation of post-diapause offspring of D. magna. Descendants of female origins in this species showed similar fitness. We conclude that although some traits of ex-ephippial offspring in comparison to parthenogenetic ones may differ across Daphnia species, the life-history strategy of post-diapause females in Daphnia is the same. Ex-ephippial females are adapted to predictable optimal conditions, whereas parthenogenetic females are adapted to unpredictably varying environment. Daphnia have evolved two alternative seasonal phenotypes matching environmental conditions in which they occur, and perform in accordance with predictions of seasonal polyphenism. Due to higher metabolic activity, which must lead to increased resource acquisition and probably is associated to larger allocation to progeny, post-diapause females are superior to directly developing offspring under high food conditions, which are expected during early season, but inferior under limiting food environments, which frequently occur later in the season. In seasonal climate, the adjustment of resource acquisition with respect to resource availability may be a general evolutionary trend for multivoltine organisms resulting in a seasonal polyphenism.

Recovery of acidified mountain lakes in Norway as predicted by the MAGIC model

Abstract: As part of the EU project EMERGE the biogeochemical model MAGIC was used to reconstruct acidification history and predict future recovery for mountain lakes in two regions of Norway. Central Norway (19 lakes) receives low levels of acid deposition, most of the lakes have undergone only minor amounts of acidification, and all are predicted to recover in the future. Central Norway thus represents a reference area for more polluted regions in southern Norway and elsewhere in Europe. Southern Norway (23 lakes), on the other hand, receives higher levels of acid deposition, nearly all the studied lakes were acidified and had lost fish populations, and although some recovery has occurred during the period 1980-2000 and additional recovery is predicted for the next decades, the model simulations indicated that the majority of the lakes will not achieve water quality sufficient to support trout populations. Uncertainties in these predictions include possible future N saturation and the exacerbating effects of climate change. The mountain lakes of southern Norway are among the most sensitive in Europe. For southern Norway additional measures such as stricter controls of emissions of air pollutants will be required to obtain satisfactory water quality in the future.

Intraspecific differences in hatching phenology of the fairy shrimp Chirocephalus diaphanus Prévost, 1803 (Crustacea, Anostraca) in relation to habitat duration

Abstract: The influence of environmental characteristics on hatching phenology in the fairy shrimp Chirocephalus diaphanus Prevost, 1803 was investigated by comparing the hatching behaviour of two populations living in mountain pasture pools differing in size and in duration of filling. Significant differences observed at population level confirmed that an influence of the environment in determining hatching pattern does actually exist. C. diaphanus seems to be able to adjust the cyst reactiveness to the stochastic nature of its habitat. The cysts laid by females adapted to a predictable and relatively constant environment are characterized by higher hatching percentages with respect to those produced in a temporary pool having erratic hydrocycles.

Acidification and recovery at mountain lakes in Central Alps assessed by the MAGIC model

Abstract: The dynamic model MAGIC was calibrated and applied to 84 lakes in Central Alps to predict the response of water chemistry to different scenarios of atmospheric deposition of S and N compounds. Selected lakes were representative of a wide range of chemical characteristics and of sensitivity to acidification. The most sensitive lakes have already shown in the latest years signs of recovery in terms of pH and ANC. The model well captured the main trends in lake chemical data. According to the model forecast, recovery at sensitive lakes will continue in the next decades under the hypothesis of a further decrease of acidic input from the atmosphere. Results clearly demonstrated the benefits of achieving the emission reductions in both S and N compounds agreed under the Gothenburg Protocol. Nevertheless, besides the achieved reduction of SO4 2- deposition from the peak levels of the 80s, also N deposition should be reduced in the near future to protect alpine lakes from further acidification. The condition of lake catchments with regard to N saturation will probably be the dominant factor driving recovery extent. Beside atmospheric deposition, other factors proved to be important in determining long-term changes in surface water chemistry. Climate warming in particular affects weathering processes in lake catchments and dynamics of the N cycle. Including other factors specific to the alpine area, such as dust deposition and climate change, may improve the fit of experimental data by the model and the reliability of model forecast.