Invasions and re-emergences: an analysis of the success of Bythotrephes in Lago Maggiore (Italy)

Bythotrephes was first seen in North America in 1982 (single individual, Lake Ontario) and noticed elsewhere in the Laurentian Great Lakes in abundance in 1985. Starting from 1987 it sharply increased in the open-water zooplankton of Lago Maggiore, reaching values never recorded in the past 40 years. Despite being native, the species\u27 impact on Lago Maggiore was somewhat comparable to that observed in invaded North American lakes. The re-emergence led to an overall increase in invertebrate predation which became permanent five years after Bythotrephes\u27 establishment, causing direct and indirect effects on the food web. Changes included a sharp decrease in the large filter-feeder Daphnia, whose mortality rate increased, and consequently an increase in phytoplankton cell density; an increase in abundance and size of colonial rotifers with a decline in Leptodora abundance, and an overall decrease in zooplankton biomass were also observed. The increase of Bythotrephes in Lago Maggiore, however, was related to a shift in population phenology, which resulted in seasonal growth starting earlier and lasting longer. Daphnia phenology changed only later, suggesting that the impact was consequent to a temporary decoupling between Bythotrephes and its preferred prey. The shift in density and phenology became permanent. Over the long-term, however, potential competitors and prey were able to recover, reaching levels of abundance comparable to those recorded before the Bythotrephes\u27 re-emergence. Such a response is likely attributable to behavioural adaptation mechanisms resulting in temporal and spatial displacement of potential competitors, predators and prey

In memory of Oscar Ravera

Oscar Ravera was one of the most lively and active protagonists in the field of ecology. A man of great culture, Oscar had a genuine interest in knowledge, an interest fed by his insatiable childlike curiosity. Arriving young, at Pallanza, he found fertile ground to develop his passion for aquatic ecology, a passion that led both to important scientific achievements, and to very large-scale initiatives..

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

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

What have we learned about ecological recovery from liming interventions of acid lakes in Canada and Italy?

The idea of launching another special issue of the Journal of limnology on Lake Orta was born in 2014, on the 25th anniversary of its liming intervention, during an International symposium on Lake Orta organized and hosted by the Pallanza Institute (http://www.ise.cnr.it/vb). The conference did not simply celebrate the past. While the liming of Lake Orta was undoubtedly a great national and international success, the speakers at the conference, instead sought to enlarge and deepen knowledge of patterns and mechanisms of lake ecosystem responses to the water quality improvements, or chemical recovery, that accompanied Lake Orta\u27s liming

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

Sedimentary Record of Cladoceran Functionality under Eutrophication and Re-Oligotrophication in Lake Maggiore, Northern Italy

We examined fossil Cladocera (Crustacea) communities and their functional assemblages in a similar to 60-year sediment record from Lake Maggiore, northern Italy. Our main objective was to document the response of aquatic community functioning to environmental stress during eutrophication (1960-1985) and recovery (post-1985), and to identify environmental controls on cladoceran functionality. Of the functional groups, large filter feeders and oval epibenthos thrived prior to eutrophication (reference conditions pre-1960) and globular epibenthos and small filter feeders increased during eutrophication and as the lake recovered. Multivariate analyses suggested that bottom-up controls (i.e., total phosphorus) were important for shaping functional assemblages but taxonomic community changes were likely related to top-down control by predators, particularly the predaceous cladoceran Bythotrephes longimanus. Functional diversity (FD) was higher and Daphnia ephippia length (DEL) larger during the reference and early eutrophication periods and decreased during eutrophication and recovery. Both FD (high) and DEL (large) were distinct during reference period, but were similar (FD low, DEL small) between the eutrophication and recovery periods. The functional attributes and the assemblages did not recover post-eutrophication, suggesting that the system exhibited a clear shift to low FD and dominance of small filterers. Cladoceran functionality appears to be related to fundamental ecosystem functions, such as productivity, and may thus provide insights for long-term changes in ecological resilience.Peer reviewe

Unusual median pores of Alona head shields recovered from recent and pre-industrial sediments of alpine lakes

We report the finding of Alona (affinis-quadrangularis) - type headshields with atypical median pores, recovered from the sediments of high-mountain lakes. Subfossil Cladocera remains were analyzed in the framework of the European Project EMERGE (2000-2002, European Mountain lakes Ecosystem: Regionalisation, diaGnostic & socioeconomic Evaluation), to evaluate changes in their assemblages consequent to industrial pollution. Observed response includes an increase in A. affinis with respect to A. quadrangularis after industrialization. According to the literature, the atypical head shields are most probably attributable to A. affinis. However, being detected in high mountain lakes, these remains may be interpreted as a result of mutations, as the intensity of UV radiation is high in these environments. In this sense, they might be interpreted as the abnormal Daphnia?s and Chydorus? ephippia, which were also detected in the sediments of these lakes

Indagini sullo zooplancton e sulla rete trofica pelagica attraverso analisi d\u27isotopi stabili di carbonio e azoto. Analisi di isotopi stabili di carbonio e azoto e rete trofica pelagica

No abstract availableCaratterizzazione del fingerprint isotopico dei principali organismi zooplanctonici (Copepodi e Cladoceri) e relative interazioni nel lago Maggiore nei quattro momenti stagionali

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