Layout 1 INTRODUCTION Subfossil Cladocera (Crustacea, Branchiopoda) rep- resent one of the most valuable biological proxies pre- served in lake sediments that can be studied for reconstruction purposes (Kohrola and Rautio, 2011). They are widespread in both the pelagic and littoral zones of lakes of different geographical distribution, altitude and typology, where they often represent the dominant com- ponent of zooplankton in terms of biomass. The chitinous parts of their body are well preserved in lake sediments, and the taphonomic taxonomy is well established, thanks to the numerous studies that followed the first pioneer works by Frey (1960). Cladocera play a key ecological role in freshwater ecosystems, as they occupy an intermediate position in the food web between primary producers (phytoplankton) and primary consumers (invertebrates and fish). As a con- sequence, subfossil Cladocera remains have the capability to track long term changes in both bottom-up drivers (such as nutrients, physical and chemical stressors) and top down regulators, such as invertebrate and fish preda- tion (e.g., Jeppesen et al., 2001; Szeroczyńska, 2006; Perga et al., 2015). The changes in taxonomical composition of subfossil Cladocera, which mainly includes Bosminidae and Chy- doridae, and secondly Daphniidae, have been increasingly investigated during the last decades and successfully used to track past environmental changes related to nutrient en- richment (Lotter et al., 1998; Bigler et al. 2007; Manca et al., 2007; Nevalainen and Luoto, in press), acidification and calcium decline (Krause and Dellin, 1986; Paterson, 1994; Jeziorski et al., 2008), chemical contamination (Ko- rosi and Smol, 2012a; Labaj et al., 2016), hydrological changes (Korhola et al., 2005; Nevalainen et al., 2011), submerged macrophytes (Davidson et al., 2011a), and cli- mate change (Lotter et al., 1997; Kamenik et al., 2007; Ko- rponai et al., 2011; Nevalainen et al., 2013; Zawiska et al., 2015). The strong response of Cladocera remains to envi- ronmental variability led to inference methods for quanti- tative reconstruction of past lake water variables, especially phosphorus (Brodersen et al., 1998), lake depth (Davidson et al., 2011b; Nevalainen et al., 2011), and water tempera- ture (Duigan and Birks 2000; Lotter et al., 2000). In addition, subfossil cladoceran remains preserved in lakes sediments have the very valuable capability to allow reconstructing past changes in the lake food-web induced by the predation pressure by planktivorous fish (e.g., Ko- rosi et al., 2013). Information on past fish populations and predation pressure on lacustrine zooplankton is in many case scattered, partial, or controversial, as it often relies on imprecise historical data, or on catch records from sport or commercial fisheries, the latter being biased by temporal changes in the catches of certain species due to their fluctuating commercial value. Within this context, changes in species composition and abundances of Clado- cera remains can support the indirect reconstruction of food web changes in both temperate and high altitude/high latitude lakes (which are mainly naturally fishless, but experienced historical legal or illegal fish in- troductions), thus fostering conservation and restoration actions (e.g., Tiberti et al., 2014). Recent investigations revealed that not only species composition and abundance, but also morphology of clado- ceran remains can be used for ecological reconstructions. It is well established that invertebrate and fish predation can affect body size, morphology and pigmentation of Cladocera (Jeppesen et al., 2002; Hansson, 2004; Guiliz- zoni et al., 2006;). However, pigmentation has been re- cently used also to track changes in underwater UV radiation in relation to solar activity (Nevalainen and Rautio, 2014) and changes in water DOC concentrations, the latter in relation to lake productivity (Nevalainen et al, 2016) or changing land use within the lake catchment (e.g., Advances in Oceanography and Limnology, 2016; 7(2): 125-130 DOI: 10.4081/aiol.2016.6467 This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). Subfossil Cladocera as a powerful tool for paleoecological reconstruction Monica Tolotti,1* Manuela Milan,2 Krystyna Szeroczyńska3 1Sustainable Agro-ecosystems and Bioresources, Research and Innovation Centre (CRI), Fondazione E. Mach, Via E. Mach 1, 38010 San Michele all'Adige, TN, Italy 2Department of Ecology and Environmental Sciences (EMG), Umeå University, Linnaeus väg 6, 90187 Umeå, Sweden 3Institute of Geological Sciences, Polish Academy of Sciences, Research Centre Warsaw, Twarda 51/55, PL 00818 Warsaw, Poland *Corresponding author: monica.tolotti@fmach.it Key words: Cladocera, paleoecology, lakes, sediments, human impact, climate change. Received: December 2016. Accepted: December 2016. No n c om me rci al us e o nly 126 M. Tolotti, M. Milan, and K. Szeroczyńska a-forestation, water regulation). Isotopic composition of cladoceran remains also revealed to be a very time-effective and promising tool for interpreting changes in lake food web and functionality (Perga et al., 2010; Perga, 2011). Nevertheless, a set of factors still hamper the interpre- tation of sedimentary Cladocera results, and, in turn, the exploitation of the great potential of this biological proxy for the reconstruction of past lake evolution. Firstly, tax- onomy of subfossil Cladocera is well established for tem- perate and boreal regions of Europe and North America (Szeroczyńska and Sarmaja-Korionen, 2007; Korosi and Smol, 2012b), whereas only a few works has been pub- lished for tropical regions (Cuna et al., 2014; Sinev and Zawisza, 2013; Szeroczyńska et al., 2015). Much work remains to be done also to evaluate how well taphonomic Cladocera represent the living communities (Kattel et al., 2007; Alric and Perga, 2011; Kirillova et al., 2016), and how preservation of remain type and species in the sedi- ment can be affected by water characteristics, such as oxy- genation, pH and chemical composition. Sedimentation dynamics can also affect spatial distribution of remains in the lake sediments (Alric and Perga, 2011). Finally, the interpretation of sediment records is complicated by the reciprocal interactions between multiple drivers, such as climate and nutrients, which can produce additive, com- petitive or synergic effects (Battarbee et al., 2012). Al- though the multi-proxy paleoecological approach and the comparison of sediment records with limnological data (e.g. Manca et al., 2007; Bennion et al., 2015) can help disentangling the effects of multiple drivers, more studies are still necessary to make the interpretation of the Clado- cera sediment records more straightforward. The first Subfossil Cladocera Workshop was initiated by Prof. Atte Korhola in 1999 (Helsinki) with the aim of getting together specialists, young researchers and stu- dents working on various aspects of Cladocera remains in lake sediments in order to share knowledge, to foster dis- cussion on new ecological findings and ideas, and to prac- tice species identification at the microscope under the guidance of expert taxonomists. The XIV Subfossil Cladocera Workshop was organized within this same spirit and held at Levico Terme (Italy) from 5th to 8th April 2016. The 30 participants (Fig. 1) from 9 countries (Czech Republic, Finland, France, Germany, Hungary, Italy, Poland, Russia, UK) were almost equally distributed between senior, young scientists and students, what promoted the transfer of knowledge and experience among generations. One special objective of this workshop was to stimulate the discussion on possible future develop- ments of Cladocera-based paleoecological reconstructions based on relatively new approaches, such as the “resurrec- tion ecology” techniques, the study of isotopic signatures in body and ephippia remains, and the statistical treatment of multiproxy sediment data. THEMATIC PAPERS The thematic papers grouped in this volume represent the outcome of presentations and discussions held at the XIV Subfossil Cladocera Workshop. The contributions focus on taxonomy, diversity, distribution of Cladocera remains in lake sediments in Europe and America, as well as on the subfossil Cladocera capability to track past changes in both bottom-up and top-down drivers of lake ecological dynamics. Several papers aimed at reconstructing the environ- mental evolution of temperate European lakes at secular (Milan et al., 2016) or millennial (Niska, 2016; Sze- roczyńska, 2016; Zawisza et al., 2016) scales. The con- tribution by Milan et al., (2016) showed how the multiproxy approach, and in particular the combination of biological proxies and geochemical analyses, could im- prove the understanding of the relation between clado- ceran communities and hydrological variability. The paleolimnological studies at millennial scale investigated the relations between Cladocera and environmental driv- ers in stages where human impact was still absent or neg- ligible, thus allowing the discrimination of climate related effects. Korponai et al. (2016) used subfossil Cladocera to distinguish lentic and lotic stages in oxbow lakes along the River Tisza (Hungary), thus demonstrating the poten- tial of cladoceran remains to reconstruct changes in the hydrological regimen of transitional water ecosystems. The thematic section of this volume tackled also the taxonomic issue. Wojewódka et al. (2016) presented a first description of Cladocera diversity in superficial sed- iments of 29 lakes of different altitude and size in Central America, thus contributing to the improvement of the cladoceran taxonomy within this still scarcely investi- gated region. On the other side, Zawiska et al. (2016) de- scribed a time and cost effective method to prepare subfossil Cladocera for SEM analysis, which allows the observation of taxonomically important details of the structure and ornamentation of carapace and spines. Finally, several contributions studied the importance of morphological variability of Cladocera remains in track- ing long term environmental and ecological changes. Lep- pänen and Weckström (2016) explored the potential use of changes in size and preservation level of Daphnia caudal spines to track fishing and forestry activities, as well as changes in water pH. Milan et al. (2016) analyzed changes in Bosminidae and Daphniidae body size and appendages length to reconstruct major changes in the lake food-web, outlining nutrient enrichment and appearance of predator Cladocera species as the major drivers of size changes. Szeroczyńska (2016) related the presence of extreme Eu- bosmina morphs, observed in a German lake, to stages of particularly pronounced water turbulence and turbidity. Fi- nally, Bérubé Tellier et al. (2016) demonstrated as varia- No n c om me rci al us e o nly Subfossil Cladocera for paleoecology 127 tions in resting eggs (ephippia) pigmentation can be used to track changes in predation pressure by fish and changes in water DOC concentration in relation to catchment land use. 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