Indagini sull\u27evoluzione del popolamento zooplanctonico: confronto con i dati pregressi anche alla luce delle mutate condizioni meteo-climatiche

Not availableRicerche sull\u27evoluzione del Lago Maggiore. Aspetti limnologici. Programma triennale 2013-2015. Campagna 2013. Indagini sull\u27evoluzione del popolamento zooplanctonico: confronto con i dati pregressi anche alla luce delle mutate condizioni meteo-climatich

Not only Cladocera: what we can learn from RRE analysis in deep lake sediment cores

Since early palaeolimnological studies, Cladocera have been largely investigated in lakes of different typologies and from a large variety of sites. Analyses of their subfossil remains provide evidence for changes in trophodynamics, habitat and water level fluctuations and of impact of drivers such as climate change on lake ecosystem functioning. Rotifers are an important component of lacustrine food webs. They are responsible for the largest part of zooplankton diversity. Because of short developmental times and intrinsic rate of increase, they promptly respond to different impacts, such as changes in trophy, pollution and recovery as well as climatedriven changes. Rotifers have been overlooked in palaeolimnological studies because they do not leave subfossil remains. They do produce, however, resting eggs of a variety of morphotypes (MTs), which preserve well in sediments. We report here results of a study in which we applied RRE MTs (Rotifer Resting Eggs MorphoTypes) analyses to a sediment core of Lake Orta on which cladocera and diatoms were analysed along with lake chronic, heavy metal pollution and acidification as well as recovery. We found that RRE abundance increased during pollution. RRE MTs differed substantially before vs. during pollution and along with the different recovery phases. The restored RRE community differed substantially from the pre-pollution one. Unexpectedly, RREs persisted over the full pollution phase, when copper concentration in the water column was as high as 108 ?g/L (in the late fifties) and when lake pH (value at the winter mixing) was of 3.8 (in the middle eighties). The presence of open egg cases also proves attempts of e.g. Brachionus calyciflorus to establish also during pollution phase. Extending RREMTs analyse to other deep subalpine lakes (i.e. Leman, Annecy and Bourget) encourage to further develop this approach to contribute to understanding impact of local vs. global drivers affecting lake ecosystem functioning

Mechanisms underlying recovery of zooplankton in Lake Orta after liming

The goal of this study was to improve the understanding of the large-scale mechanisms underlying the recovery of the zooplankton of Lake Orta from historical contamination, following reduced input of ammonia and metals and the subsequent 1989/90 liming intervention. The industrial pollution had been severe and long-lasting (1929-1990). Zooplankton biodiversity has improved, but most of the new taxa appearing in our counts are rotifers, while many calanoids and the large cladoceran predators (Bythotrephes and Leptodora) that are common in the nearby Lake Maggiore, were still absent from Lake Orta 17 years after liming. To aid understanding of the large-scale mechanisms controlling changes in annual richness, we assessed the annual persistence (P) of Crustacea and Rotifera taxa as an estimator of whether propagules that survived introduction, as result of the natural recolonization process, also thrived. We found that the rate of introduction of zooplankton colonists and their persistence in the water column of Lake Orta changed from 1971 to 2007. New rotifer taxa appeared in the lake after the mid-1980s, when discharge of toxic substances decreased, but their annual persistence was low (P<0.5) until the turn of the century. The numerical values of rotifer and crustacean persistence in Lake Orta were unexpectedly high in 2001 and 2007 (0.55 and 0.72 for rotifers, 0.85 and 0.86 for crustacean, respectively), much higher than in limed lakes in Sudbury, Canada, and in adjacent Lake Maggiore. We hypothesize this could be related to the lack of Cladoceran predators and zooplanktivorous fish in the pelagic waters of Lake Orta

Invasione di specie aliene: comparsa di Polyphemus pediculus (Linnaeus, 1761; Crustacea Cladocera) nel Lago Maggiore

Polyphemus pediculus (Linnaeus, 1761) is a holoarctic cladoceran species typically inhabiting the littoral zone of lakes. It is a voracious predator, hunting its prey by visual predation, able to deplete the zooplankton population. Its detection for the first time in Lake Maggiore, at a sampling station close to the littoral, in which zooplankton was monitored for 20 years is worth of being discussed. First, because it represents a further increase in predatory Cladocera, after Bythotrephes longimanus (Leydig, 1860) have successfully re-emerged in the open water. Second, because it may be regarded as an increasing invasion trend in a lake traditionally considered as a stable, mature environment, in which invasions should be hardly successful.Polyphemus pediculus (Linnaeus, 1761) ? un cladocero oloartico che tipicamente colonizza la zona litorale dei laghi. ? un predatore vorace, che attua una strategia di predazione visiva, in grado di decimare il popolamento zooplanctonico. La presenza di questo organismo, rilevata per la prima volta in campioni provenienti da una stazione del Lago Maggiore, posta vicino alla zona litorale nella quale lo zooplancton viene monitorato da 20 anni, ? meritevole di discussione. Primo, perch? rappresenta un ulteriore aumento della frazione di Cladoceri predatori, dopo l\u27accresciuta presenza numerica di Bythotrephes longimanus (Leydig, 1860) nelle acque pelagiche. Secondo, perch? pu? essere considerato un aumento della tendenza alle invasioni, in un lago tradizionalmente considerato come un ambiente stabile e maturo, nel quale pertanto la probabilit? di successo delle invasioni dovrebbe essere bassa

Contaminanti nello zooplancton

Not availableIndagini su DDT e sostanze pericolose nell\u27ecosistema del Lago Maggiore. Programma 2013-2015. Rapporto annuale 2014 - Contaminanti nello zooplancto

Demographic cost and mechanisms of adaptation to environmental stress in resurrected Daphnia

A characteristic feature of the Daphnia (Crustacea: Cladocera) life cycle are the so-called ephippia, which are fertilised eggs that need to undergo diapause. When they are shed by the female, they sink to the lake bottom, where they may become embedded in the sediment and may remain viable for decades. Extracting and hatching ephippia in the laboratory and subjecting resurrected lineages to conditions representative of historic lake environments allows retrospective investigation of life-history responses to environmental change. Here we reanalyse data from such a resurrection experiment (Piscia et al., 2015: Bull. Environ. Contam. Toxicol. 94:46-51). Contemporary and past lineages of Daphnia galeata Sars 1863 were obtained from Lake Orta (Italy), a deep, subalpine lake with a well-documented history of industrial copper pollution. Experimental Daphnia were subjected to three copper treatments representative of two levels of historic as well as to current (i.e., unpolluted) lake conditions, and life-table data were collected. With these data at hand, we first estimated vital rates (survival, maturation, and reproduction) and used these rates to project the asymptotic population growth rates (?) for each population-by-treatment combination. Next, we performed life-table response experiments (LTRE) to estimate the contributions of the vital rates to observed differences in ?. Finally, we used elasticity analysis to explore the functional relationship between ? and each of the vital rates. We found that survival rates were only compromised at elevated copper levels. Moreover, past, resurrected Daphnia had a higher ? at low copper concentrations compared to unpolluted conditions, but a lower ? when exposed to high copper levels. Contemporary Daphnia, on the other hand, only reproduced successfully in unpolluted water. Under these conditions, however, they had a higher population growth rate than the past Daphnia, suggesting a cost of copper tolerance in the latter. This cost was mainly due to a lower probability of reproduction and reduced fecundity, whereas survival remained largely unaffected. Finally, we found higher elasticity values of ? to survival than to reproductive rates. This suggests that any change in the environment that will affect survival rather than reproductive parameters will have a much larger impact on Lake Orta\u27s current Daphnia population

Evaluation of the Egg Bank of Two Small Himalayan Lakes

High mountain lakes are biodiversity treasures. They host endemic taxa, adapted to live in extreme environments. Among adaptations, production of diapausing eggs allows for overcoming the cold season. These diapausing eggs can rest in the sediments, providing a biotic reservoir known as an egg bank. Here, we estimated changes in abundance of the egg bank in two lakes in the Khumbu Region of the Himalayas, during the last ca. 1100 and 500 years, respectively, by analyzing two sediment cores. We tested viability of the diapausing eggs extracted from different layers of the sediment cores under laboratory conditions. We found that only diapausing eggs of the Monogont rotifer Hexarthra bulgarica nepalensis were able to hatch, thus suggesting that a permanent egg bank is lacking for the other taxa of the lakes, not least for the two Daphnia species described from these sites. Our results confirm previous studies suggesting that in high mountain lakes, the production of diapausing is mainly devoted to seasonal recruitment, therefore leading to a nonpermanent egg bank. The different ability of different taxa to leave viable diapausing eggs in the sediments of high mountain lakes therefore poses serious constraints to capability of buffering risk of biodiversity loss in these extremely fragile environments

Contaminanti nello zooplancton

Not availableContaminanti nello zooplancton nell\u27ambito del progetto di ricerca "Indagini su DDT e sostanze pericolose nell\u27ecosistema del Lago Maggiore"

Contaminanti nello zooplancton

No abstract availabl

Contaminanti nello zooplancton

Not availableIndagini su DDT e sostanze pericolose nell\u27ecosistema del Lago Maggiore. Programma 2013-2015. Rapporto annuale 2013 - Contaminanti nello zooplancto