PAST AND ONGOING PROJECTS
Areas of interest: aquatic ecology | restoration | plant-animal interactions | multiple stressors | biological invasions
biodiversity | ecosystem functioning and services
SUBMERGED AQUATIC VEGETATION SHIFTS IN OLIGO-MESOTROPHIC LAKES
2024 - 2025
Shifts in dominance between charophytes and submerged vascular plants are a key feature of ecological change in oligo-mesotrophic hardwater lakes and have important implications for biodiversity, ecosystem functioning, and lake management, conservation, and restoration. Despite their ecological importance, charophytes have declined across many European lakes and are often replaced by vascular plants, even in systems where external nutrient loading has ceased, indicating that the mechanisms driving these shifts remain poorly understood. This project aims to understand how light and nutrient availability influence plant and periphyton growth, plant tissue stoichiometry, and the decomposition of charophytes and submerged vascular plants, thereby identifying the critical conditions that drive shifts in species dominance and their effects on nutrient immobilization. To improve mechanistic understanding of these macrophyte community shifts, two consecutive enclosure experiments were conducted at the IGB LakeLab facility at Lake Stechlin in Germany. Establishing critical conditions for charophyte dominance is essential for achieving restoration goals.
ACHIEVING THE GOAL "MORE NATIVES, LESS INVASIVES": PRIORITY EFFECTS AS A POTENTIAL TOOL FOR RESTORATION
2020 - 2023
Invasive plant species are a major threat to biodiversity, negatively impacting ecosystem structure and functioning. Although their removal is often seen as beneficial, ecosystems do not always recover, and native plant communities may fail to re-establish. Active restoration of native plant communities is recognized as a strategy to limit invasions. However, restoration attempts which most commonly add species at the same time in a single seed mix or propagules have shown only moderate success. These unsatisfying results are often due to a failure to account for priority effects. Early-arriving species can either reduce resource availability (niche pre-emption) or alter environmental conditions (niche modification). However, early arrival does not guarantee success, as outcomes depend on factors like resource overlap and species’ impacts on ecosystems. This project evaluates how priority effects of native plants influence restoration success in freshwater systems. Using a whole-pond manipulation experiment, it also monitors multiple biological communities and water quality to understand ecosystem responses and improve strategies to prevent reinvasion.
BIODIVERSITY RECOVERY FOLLOWING INVASIVE FREE-FLOATING AQUATIC PLANT CONTROL
2021 - 2023
Invasions of freshwater systems by floating plants such as Salvinia molesta threaten biodiversity worldwide. Dense mats reduce light and nutrient availability, alter pH and water quality, and release allelopathic compounds that suppress other primary producers. This loss of aquatic vegetation decreases habitat complexity, ultimately affecting higher trophic levels. Biological control using host-specific natural enemies, such as the weevil Cyrtobagous salviniae, is widely used to manage these invasions and is often assumed to facilitate ecosystem recovery. However, post-control outcomes are rarely assessed beyond invader reduction, leaving broader ecological responses poorly understood. This study examines the recovery of aquatic plants and associated communities following biological control of S. molesta across freshwater systems in South Africa. The findings will improve understanding of ecosystem resilience and inform more effective restoration and management strategies.
MADMACS: MASS DEVELOPMENT OF AQUATIC MACROPHYTES - CAUSES AND CONSEQUENCES OF MACROPHYTE REMOVAL FOR ECOSYSTEM STRUCTURE, FUNCTION, AND SERVICES
2020 - 2022
Mass development of aquatic macrophytes in rivers and lakes is a global issue, prompting costly and recurring removal efforts. However, this approach is unsustainable, as it fails to address underlying causes and can trigger new problems, such as algal or cyanobacterial blooms. While dense macrophyte stands can have negative impacts, they also provide key ecosystem services, including nutrient and carbon retention and habitat for diverse organisms. These benefits are often overlooked, leading to management decisions driven by negative perceptions rather than evidence. The causes of nuisance growth are poorly understood, as they typically involve multiple interacting pressures. This project investigates the drivers of macrophyte overgrowth and the ecological consequences of their removal. Using coordinated before–after–control–impact (BACI) experiments across six case studies in five countries (Norway, Germany (2), France, South Africa, Brazil), this project aims to inform more sustainable, evidence-based management strategies.
BIOTIC RESISTANCE TO ALIEN PLANT INVASIONS IN TROPICAL AND TEMPERATE FRESHWATER ECOSYSTEMS
2015 - 2019
In my PhD project, I focus on biotic resistance or the role of species interactions in reducing the success (colonisation and performance) of alien species invasions. The main aim is to assess whether native freshwater communities from tropical and temperate regions can resist invasions and to identify the mechanisms underlying this resistance. Using submerged plant species and a generalist aquatic herbivore as a model system, the project combines mesocosm experiments, evidence from the literature and modelling approaches. It addresses two key questions: (I) Can native communities provide biotic resistance to alien plant invasions? and (II) Which mechanisms underlie this resistance? The project considers both community-level susceptibility to invasion (invasibility) and traits of alien plants that promote establishment and spread (invasiveness), contributing to a better understanding of invasion dynamics and informing management strategies.
INFLUENCE OF HERBIVORE DAMAGE ON METHANE EMISSIONS FROM EMERGENT AQUATIC MACROPHYTES
2013 - 2015
Wetlands are the largest natural source of methane (CH₄), with vegetated littoral zones playing a key role in emissions. While herbivores are known to affect macrophyte biomass and growth, their influence on plant-mediated CH₄ fluxes, particularly by insects, remains poorly understood. We conducted a mesocosm experiment simulating insect herbivory on Eleocharis equisetoides, manipulating the proportion of damaged culms (0, 20, 50, and 100%) and measuring CH₄ emissions, sediment concentrations, and production potential. CH₄ fluxes increased significantly only under high herbivory pressure: mesocosms with 50% and 100% damaged culms showed emissions 3.5 times higher than those with little or no damage. These results suggest that physical damage enhances gas transport through plant tissues. Field observations indicated low overall biomass consumption, highlighting that even minor but widespread damage can disproportionately increase CH₄ emissions. This study reveals an overlooked role of herbivory in methane dynamics and carbon cycling.