Planktotrons: A novel indoor mesocosm facility for aquatic biodiversity and food web research

Abstract

We established a new indoor mesocosm facility, 12 fully controlled "Planktotrons", designed to conduct marine and freshwater experiments for biodiversity and food web approaches using natural or artificial, benthic or planktonic communities. The Planktotrons are a unique and custom-tailored facility allowing longterm experiments. Wall growth can be inhibited by a rotating gate paddle with silicone lips. Additionally, temperature and light intensity are individually controllable for each Planktotron and the large volume (600 L) enables high-frequency or volume-intense measurements. In a pilot freshwater experiment various trophic levels of a pelagic food web were maintained for up to 90 d. First, an artificially assembled phytoplankton community of 11 species was inoculated in all Planktotrons. After 22 d, two ciliates were added to all, and three Daphnia species were added to six Planktotrons. After 72 d, dissolved organic matter (DOM, an alkaline soil extract) was added as an external disturbance to six of the 12 Planktotrons, involving three Planktotrons stocked with Daphnia and three without, respectively. We demonstrate the suitability of the Planktotrons for food web and biodiversity research. Variation among replicated Planktotrons (n 5 3 minimum) did not differ from other laboratory systems and field experiments. We investigated population dynamics and interactions among the different trophic levels, and found them affected by the sequence of ciliate and Daphnia addition and the disturbance caused by addition of DOM.Enclosed experimental systems provide a highly valuable and widely used approach bridging small-scale laboratory experiments and large-scale field surveys (Petersen et al. 2010). Until now, most small-scale laboratory experiments investigating long-term dynamics or trophic interactions are performed in chemostats or Erlenmeyer flasks with relatively small (sample) volumes (J€ urgens et al. 1997;Fussmann et al. 2000;Huisman et al. 2002;Yoshida et al. 2003;Becks et al. 2010;Hardenbicker et al. 2015). While such highly controlled small-scale systems have the advantage of high replicability, they often suffer from stochastic effects, which arise from small population sizes in small sample volumes (Petersen et al. 2010). Also, the possibility to investigate volume-intense parameters is naturally limited in small-scale setups. This particularly complicates investigations of food webs, where features of the whole community or multiple trophic levels are of interest as predictors and/or responses, often including the necessity to cover dynamic interactions over time by repeated sampling. Over longer time periods (months to years), such dynamics can be resolved by monitoring of real ecosystems in the field and whole-system experiments, with the advantage of increased realism, yet missing opportunities for manipulation, replication, or isolated investigation of mechanisms. Experimental mesocosms, indoor as well as outdoor, offer a good compromise of the two extremes (Petersen et al. 2010). Mesoc...

Warming and oligotrophication cause shifts in freshwater phytoplankton communities

“…The experiment was conducted in 12 custom‐tailored, stainless steel indoor‐mesocosms, the so‐called Planktotrons located at the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany (Gall et al., ). These tanks are 1.2 m high and have an inner diameter of 0.8 m, resulting in a volume of 600 L. Built‐in rotors with silicon lips at the side, top, and bottom, gently rotate in the Planktotrons, to prevent wall growth during the experiment.…”

“…Treatments were chosen based on a field study of small farmland ponds in Belgium (Verbeek et al., ), which revealed a strong decrease in nutrient loading over time (especially for phosphorus) with significant change in phyto‐ and zooplankton biomass and composition. Using an indoor mesocosm facility comprising 12 so‐called Planktotrons (Gall et al., ), we manipulated temperature (either constant at 20°C or increasing by 2°C per week for a total experiment duration of 7 weeks) and nutrient availability (either ambient or gradually decreasing by 20% per week) in a factorial design. The inoculum for the experiment was a natural phytoplankton community from one of the ponds in Belgium.…”

Linking primary producer diversity and food quality effects on herbivores: A biochemical perspective

“…To our knowledge, despite the large interest in understanding the effects of biodiversity on trophic interactions 9 , no study explicitly investigated the links between species diversity, biochemical diversity and consumer performance. Here we used the well- established model system consisting of the freshwater herbivore Daphnia magna and different phytoplankton species 9 , 18 , 22 . Based on the low quality species Synechococcus elongatus (non-toxic, well-ingestible, but lipid-deficient: lack of sterols and PUFA) 17 , included in all experimental setups, we established different phytoplankton communities differing in species diversity and thus evaluated the growth potential of D. magna on these phytoplankton communities focusing on the underlying mechanism between species and biochemical diversity.…”

Streamside mobile mesocosms (MOBICOS): A new modular research infrastructure for hydro‐ecological process studies across catchment‐scale gradients

“…Recently, there have been numerous attempts to develop sophisticated mesocosms for marine experimental ecology (Gall et al, 2017; Pansch, Winde, Asmus, & Asmus, 2016; Wahl et al, 2015). However, freshwater mesocosms largely follow traditional, low‐tech setups.…”

“…Effects of stressors and other environmental drivers are usually tested by specific manipulation of the target parameters in (multi‐)factorial designs, and by comparing the obtained data with a control. For certain parameters such as temperature experimental manipulations on larger scales are highly elaborate, energy consuming and expensive (Gall et al, 2017; Wahl et al, 2015). For other factors such as organic chemicals, law usually prohibits experimental additions in the field, and their elimination, for example, through activated carbon filters, is expensive and requires advanced chemical analysis for elimination control (Elsaesser et al, 2013; Pereda, Acuna, von Schiller, Sabater, & Elosegi, 2019).…”