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International audience; The relevance of considering environmental variability for understanding and predicting biological responses to environmental changes has resulted in a recent surge in variability-focused ecological research. However, integration of findings that emerge across studies and identification of remaining knowledge gaps in aquatic ecosystems remain critical. Here, we address these aspects by: (1) summarizing relevant terms of variability research including the components (characteristics) of variability and key interactions when considering multiple environmental factors; (2) identifying conceptual frameworks for understanding the consequences of environmental variability in single and multifactorial scenarios; (3) highlighting challenges for bridging theoretical and experimental studies involving transitioning from simple to more complex scenarios; (4) proposing improved approaches to overcome current mismatches between theoretical predictions and experimental observations; and (5) providing a guide for designing integrated experiments across multiple scales, degrees of control, and complexity in light of their specific strengths and limitations.

Space-for-Time-Substitution surveys (SFTS) are commonly used to describe zooplankton community dynamics and to determine lake ecosystem health. SFTS surveys typically combine single point observations from many lakes to evaluate the response of zooplankton community structure and dynamics (e.g., species abundance and biomass, diversity, demographics and modeled rate processes) to spatial gradients in hypothesized environmental drivers (e.g., temperature, nutrients, predation), in lieu of tracking such responses over long time scales. However, the reliability and reproducibility of SFTS zooplankton surveys have not yet been comprehensively tested against empirically-based community dynamics from longterm monitoring efforts distributed worldwide. We use a recently compiled global data set of more than 100 lake zooplankton time series to test whether SFTS surveys can accurately capture zooplankton diversity, and the hypothesized relationship with temperature, using simulated SFTS surveys of the time series data. Specifically, we asked: (1) to what degree can SFTS surveys capture observed biodiversity dynamics; (2) how does timing and duration of sampling affect detected biodiversity patterns; (3) does biodiversity ubiquitously increase with temperature across lakes, or vary by climate zone or lake type; and (4) do results from SFTS surveys produce comparable biodiversity-temperature relationship(s) to empirical data within and among lakes? Testing biodiversity-ecosystem function (BEF) relationships, and the drivers of such relationships, requires a solid data basis. Our work provides a global perspective on the design and usefulness of (long-term) zooplankton monitoring programs and how much confidence we can place in the zooplankton biodiversity patterns observed from SFTS surveys. info:eu-repo/semantics/publishedVersion

Climate changes cause increased input of dissolved organic carbon (DOC) in shallow lake ecosystems, leading to alterations in physico-chemical factors, composition of zooplankton and food web interactions. Rotifers, as an important component of freshwater plankton, significantly contribute to the carbon transfer from lower to higher trophic levels. In this study in situ mesocosms were used to determine the impact of labile and recalcitrant carbon on lake ecosystems. The main objectives of this study were to assess: (i) structural and functional traits of rotifers ; (ii) the influence of abiotic and biotic factors on composition of rotifers ; and (iii) ecosystem recovery after impact of different sources of DOC. Higher diversity, abundance and biomass of rotifers were observed in the mesocosm with labile carbon compared to the mesocosm with recalcitrant carbon. During the experiment, planktonic nanoalgivor rotifer species (Keratella cochlearis), dominant at the beginning, were replaced by semiplanktonic detritivore species (Lecane, Lepadella) dominant at the end of the experiment with labile and mixed DOC. That shift in the rotifer assemblage was likely caused, first, by higher concentrations of chlorophyll a as well as presumably competition with crustacean algivores at the beginning, and second, higher concentrations of DOC and nutrients at the end of the experiment. The results of this study indicate the possibility of ecosystem recovery after external DOC load, replacement of species which lead to assemblage more adopted to the stressor impact, and the importance of rotifers as indicators in assessing changes on the ecological status of shallow water bodies.

While the climate induced increase of allochthonous dissolved organic carbon ( input to freshwater ecosystems is well studied, however, the effects of different DOC sources and their impact on seston quality, and in turn on the food webs and particularly on zooplankton biomass and composition is poorly understood Accordingly, we tested the effects of recalcitrant and labile DOC pulse disturbances on zooplankton communities via outdoor mesocosm experiments for six weeks We expected that zooplankton community biomass would be enhanced with labile DOC source compared to the recalcitrant, and zooplankton community composition would differ between particular DOC sources Treatments included a single pulse of alder leaf leachate ( labile DOC), Huminfeed ( recalcitrant DOC) and both together ( compared to controls (no DOC) After day 10 of the experiment, relative to the control, zooplankton biomass increased in the L and HFL treatments but did not change in the HF treatment The highest biomass increase was observed in HFL Before the pulse, Ceriodaphnia spp dominated approximately 60 of the total zooplankton biomass At the end of the experiment, the community composition was different for L, HF and HFL Unlike control, Daphnia spp dominated (approx 90 biomass in L and HFL treatments, while Cyclopoid Copepoda and Diaphanosoma spp were together 50 in HF Despite the temporal variation, overall mean seston N P ratio in L ( std 105 5 47 1 and HFL 102 1 35 2 was lower relative to HF 256 8 117 9 and controls 208 4 108 7 Additional seston phosphorus coming from labile DOC source led to lower seston N P ( and in turn, may have favoured Daphnia spp in L and HFL Initial results demonstrated that labile DOC source could have major impacts on zooplankton biomass and composition, especially when it combined with recalcitrant DOC source.

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1105

situ Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.

This Standard Operating Procedure (SOP) describes methods for sampling, and analysis of phytoplankton from mesocosm experiments carried out in all aquatic environments (fresh and marine waters). It gathers best practice advice with a focus on sampling, counting and other analyses of phytoplankton as well as Quality Assurance/ Quality Control (QA/QC) practices. This SOP is based on EU Water Framework Directive and other related documents. It is designed to be compliant with this EU Directive (2000/06/EC) [1]. Use of this SOP will ensure consistency and compliance in collecting and processing phytoplankton data from mesocosm experiments across the AQUACOSM community, in Europe and beyond. This SOP covers guidance on health, safety and environmental information, best practice advice on materials and methodology and QA/QC procedures to be followed during the sampling, analysis and counting of phytoplankton samples from mesocosm experiments. It applies only to the phytoplankton microscope investigation of the identification, composition, abundance, and biovolume estimation of phytoplankton samples. Published Refereed Current 14.A Phytoplankton biomass and diversity Best Practice Standard Operating Procedure

The likelihood of an ecological system to undergo undesired regime shifts is expected to increase as climate change effects unfold. To understand how regional climate settings can affect resilience, i.e., the ability of an ecosystem to tolerate disturbances without changing its original structure and processes, we used a synchronized mesocosm experiment (representative of shallow lakes) along a latitudinal gradient. We manipulated nutrient concentrations and water levels in a synchronized mesocosm experiment in different climate zones across Europe involving Sweden, Estonia, Germany, the Czech Republic, Turkey and Greece. We assessed attributes of zooplankton communities that might contribute to resilience under different ecological configurations. We assessed four indicator of relative ecological resilience (cross-scale, within-scale structures, aggregation length and gap size) of zooplankton communities, inferred from discontinuity analysis. Similar resilience attributes were found across experimental treatments and countries, except Greece, which experienced severe drought conditions during the experiment. These conditions apparently led to a lower relative resilience in the Greek mesocosms. Our results indicate that zooplankton community resilience in shallow lakes is marginally affected by water level and the studied nutrient range unless extreme drought occurs. In practice, this means that drought mitigation could be especially challenging in semi-arid countries in the future.

The likelihood of an ecological system to undergo undesired regime shifts is expected to increase as climate change effects unfold. To understand how regional climate settings can affect resilience; i.e., the ability of an ecosystem to tolerate disturbances without changing its original structure and processes, we used a synchronized mesocosm experiment (representative of shallow lakes) along a latitudinal gradient. We manipulated nutrient concentrations and water levels in a synchronized mesocosm experiment in different climate zones across Europe involving Sweden, Estonia, Germany, the Czech Republic, Turkey and Greece. We assessed attributes of zooplankton communities that might contribute to resilience under different ecological configurations. We assessed four indicator of relative ecological resilience (cross-scale, within-scale structures, aggregation length and gap size) of zooplankton communities, inferred from discontinuity analysis. Similar resilience attributes were found across experimental treatments and countries, except Greece, which experienced severe drought conditions during the experiment. These conditions apparently led to a lower relative resilience in the Greek mesocosms. Our results indicate that zooplankton community resilience in shallow lakes is marginally affected by water level and the studied nutrient range unless extreme drought occurs. In practice, this means that drought mitigation could be especially challenging in semi-arid countries in the future.

In Little Mere, diurnal sampling of the zooplankton at three different habitats in 1993 provided little evidence to support the data of Timms and Moss (10) that cladocerans move out from refugia at night to graze in open water. The floating-leaved water lily, appeared to be more efficient at providing refuge to D. hyalina in the presence of high planktivore fish predation than the submerged plant beds and the open water. This might be due to unfavourable physical and chemical environmental conditions associated with the water lily bed for fish feeding, a possibility supported by the findings of very low dissolved oxygen and pH values in the water lily beds. Potamogeton berchtoldii beds appeared to be more favourable habitats for submerged plant associated zooplankters than for open water grazers, probably due to the high predation pressure of planktivorous fish on the latter. The findings of this study suggest that it is important to have a better understanding of effectivness of submerged plants at provison of refuges for open water Cladocera against fish predation to combat eutrophication by using biomanipulation., 1993 yılında, Little Mere’de yapılan, üç farklı habitattaki zooplankton günlük örneklemesi, Timms ve Moss’un (10) Cladocera’ların gece sığınak olarak kullandıkları makrofitlerin yoğun bulunduğu habitatlardan açık suya çıkarak fitoplankton üzerinden beslendikleri temeline dayanan ‘sığınak hipotez’ni desteklememektedir. Yüzen yapraklı su nilüferinin D. hyalina’ya planktivor balık avlama baskısına karşı barınak sağlamada sualtı bitkisi olan Potamogeton berchtoldii ye göre daha etkin olduğu bulgulanmıştır. Bu durum su nilüferinin yoğun olarak bulunduğu ortamlarda yarattığı fiziksel ve kimyasal değişmeler sonucu balık beslenmesini olumsuz olarak etkilemisi ile ilgili olabilir. Su nilüferinin yoğun bulunduğu ortamlarda balık beslenmesinin olumsuz etkilenmesi, 1994 yılında yapılan günlük örneklemede gözlenen çok düşük pH ve çözünmüş oksijen ile desteklenmektedir. P. berchtoldii’nin su bitkilerine bağlı yaşayan zooplakton gruplarına (Eurycercus, Sida, Simocephalus vb.) barınak sağlamada pelajik Cladocera’lara göre daha etkin olduğu bulgulanmıştır. Bu durum planktivor balık beslenmesinin sualtı bitkilerinin bulunduğu ortamdan olumsuz etkilenmemesi ile açıklanabilir. Bu çalışmanın bulguları, ötrofikasyonu kontrol etmek için uygulanan biyomanipulasyon tekniğinin daha etkin olarak kullanılabilmesinde, sualtı makrofitlerin pelajik Cladocera’lara planktivor balık avlanma baskısına karşı barınak sağlamadaki rolünün daha iyi anlaşılmasının önemini vurgulamaktadır.