06
May
Study Finds Aquatic Ecosystem Collapse with Neonicotinoid Exposure, Threatening Biodiversity
(Beyond Pesticides, May 6, 2025) A study in Ecology Letters finds “severe degradation of ecosystem functioning in the form of loss of organic matter consumption and dramatic shifts in primary productivity,†the researchers state, after performing an experiment with “36 naturally established freshwater ecosystems exposed to increasing field-realistic concentrations of the neonicotinoid thiacloprid.†Aquatic communities contribute to overall biodiversity and are crucial in maintaining healthy ecosystems; without them, the entire food web and vital ecosystem services, such as nutrient cycling, water filtration, and climate regulation, are threatened.
As the authors reference, there is a current unprecedented decline in biodiversity that can be attributed to anthropogenic impacts. A multitude of studies connect pesticides, and more specifically neonicotinoid insecticides, to impacts on aquatic ecosystems. (See studies here and here.) “Since the community of organisms locally present is responsible for the functioning of the local ecosystems,†the researchers begin, “this begs the question: do neonicotinoid-induced shifts in community composition result in a degradation of ecosystem functioning?â€
Previous research finds that neonicotinoids can “impede several freshwater ecosystem processes such as organic matter (‘OM’) decomposition, primary production or biomass transfer to neighbouring ecosystems,†the authors say. (See studies here, here, and here.) They continue: “However, knowledge is lacking regarding to what extent neonicotinoid concentrations in surface waters actually affect natural freshwater biodiversity and how the functional coherence of the community is affected. To explore this gap, we analysed naturally assembled freshwater communities that were exposed to an environmentally realistic neonicotinoid concentration range.â€
Through a two-tiered network-based approach, the researchers compare aquatic community structures and determine how neonicotinoid-induced stress disrupts ecosystem processes. As a result, they report, “We experimentally show that co-occurrence network approaches can identify the effects of a neonicotinoid at very low concentrations and that co-occurrence network disruption coincides with losses in ecosystem functioning.â€
Assessing species co-occurrence, the pattern of two or more species within the same habitat, and changes to species with the introduction of an environmental stressor provides information on community structure and ecological variables that could cascade to further impacts. This experiment, conducted at an outdoor research facility at Leiden University in the Netherlands called the Living Lab, includes a setup of 36 experimental freshwater ditch ecosystems with a ‘mesocosm’ design to ensure similar habitat structure and conditions.
As the authors describe: “Our setup also allowed natural colonisation: We did not control how and which ecological invertebrate communities developed. This provided a controlled outdoor experimental design to study the effects of the neonicotinoid on naturally-formed communities and their environment.†They allowed species to populate the ditches for five months before closing them off to the adjoining lake, sampling the macroinvertebrates for diversity, and then proceeding with two spikes, two weeks apart, of neonicotinoid exposure in the test groups.
The environmentally relevant concentrations of thiacloprid include 0, 0.1, 1, and 10 μg/L. Before exposure, the researchers confirmed the ditches did not have any significant differences in species abundance or other biotic or abiotic conditions (pH, temperature, etc.). After one month, the macroinvertebrates were sampled and analyzed again to assess impacts on the aquatic communities.
The study considers multiple variables:
- Total abundance (the overall number of individuals),
- Abundance per taxonomic order (the number of individuals within a species or other taxa),
- Species richness (the number of different species), and
- Shannon diversity (a measure of diversity considering species richness and ‘evenness’/uniformity of distribution).
As a result, the authors report:
- “[T]otal invertebrate abundance decreased by 18% at the lowest test concentration and by 36% at the two higher test concentrations. This decrease in total abundance was mostly due to lower abundances in the taxonomic orders Malacostraca and Ostracoda. In contrast, we observed higher abundances with increasing neonicotinoid concentration for the orders of Arachnida and Branchiopoda, likely due to increased reproduction and/or offspring survival of these taxa with relatively short generation times.â€
- “Increasing thiacloprid concentrations induced increasingly significant dissimilarities in species composition… This implies that the dissimilarity can be largely attributed to taxon replacement, which in turn explains the lack of effects on total taxon richness and Shannon diversity.â€
- “At 10 μg/L, we even observed a strong reduction in the number of strong species’ co-occurrences,†which shows 54% fewer correlations when compared to the control community and indicates “a severe impairment of the statistical coherence at high neonicotinoid concentrations.â€
- “The biomass of the combined functional feeding group of ‘Gatherer/Collectors + Shredders’ decreased significantly by 15%, 46% and 85% for the insecticide concentrations 0.1, 1 and 10 μg/L, respectively, relative to the control. This coincided with changes in the ecosystem processes fulfilled by these functional feeding groups; invertebrate organic matter consumption strongly declined by 80% and 100% at the 1 and 10 μg/L treatment relative to the control, respectively.â€
- “Through losses in the ‘Gatherer/Collectors + Shredders’ functional feeding groups, ditches also became dominated by floating algal beds [FLABs] with increases in biomass relative to the control of over 300 and over 1400% at 1 and 10 μg/L, respectively.†The presence of FLABs also cascaded to cause a decline in phytoplankton levels.
This study highlights the impacts of neonicotinoid insecticides on freshwater ecosystems, as exhibited by the altered aquatic communities and dramatic decrease in functioning within the results. The researchers note: “These analyses show that increasing levels of disturbance lead to a progressive loss of the number and strength of species co-occurrences within these communities, to the point that almost all strong species correlations are lost… Indeed, the observed progressive loss of species correlations from the co-occurrence networks coincided with increasingly degraded ecosystem functioning.”
Additional research supports this study’s findings. (See Beyond Pesticides’ coverage of neonicotinoids and aquatic impacts here, here, here, here, and here.) Specifically, many studies use the network approach to assess community vitality within ecosystems. (See studies here, here, here, here, and here.) The researchers also share that, “[R]ecent research with thiacloprid at the same test facility showed that short-term toxicity effects can lead to persistent restructuring of the invertebrate community, which coincides with observations in long-term studies on local community changes.†(See studies here, here, and here.)
Through multiple direct and indirect pathways, insecticide exposure can induce stress on ecosystem functioning. These systems rely on a balance of many factors, with changes in any of them causing disruption and further cascading impacts. As the authors say: “While there are few laws in ecology, at least a simple and perhaps trivial consensus is that in ecological systems, ‘organisms interact with one another (…) and their environment.’ Hence, it may not be the species richness of a local community per se, but rather the set of functional links between organisms in a specific community and with their environment that provides the connection between biodiversity and ecosystem functioning.†(See here, here, and here.)
The ability of environmentally relevant levels of thiacloprid to “induce major compositional shifts and degradation of the aquatic food web shortly (i.e., 1 month) after pulse applications†is of great concern. The researchers note: “These effects are well beyond any effects that could be estimated from species-specific effects (as obtained from bioassays) described by standard risk assessment methodology (e.g., OECD 235, 2011; OECD 211, 2012). In addition, we already observed significantly impaired statistical coherence of invertebrate communities at nominal thiacloprid concentrations as low as 0.1 μg/L (actual 0.08 μg/L), which lies well below nearly all recognised toxic concentrations for individual aquatic species.†(See studies here, here, and here.)
This concentration, as the authors reference, is also dangerously close to established values, such as the chronic benchmark from the U.S. Environmental Protection Agency (EPA) for freshwater invertebrates and the European Food Safety Authority’s (EFSA) Maximum Allowable Concentrations – Environmental Quality Standard. “This indicates that these norms are insufficient for the protection of freshwater invertebrate communities,†the researchers maintain.
They continue, “This also strongly suggests that the result of degrading co-occurrence networks is not simply a result of differential thiacloprid-induced mortality between species. Therefore, and because several taxa increased in abundance, the observed degradation is likely a result of both direct and indirect thiacloprid-induced toxicity. The sensitivity of the co-occurrence analysis of the ecological community shows that the current pesticide risk assessment has major shortcomings since it can fail to predict effects on the integrity of natural communities and related ecosystem functioning.†(See more on EPA failures here.)
Neonicotinoid insecticides threaten freshwater life and function, and therefore also threaten overall biodiversity. This study, as the authors conclude, shows how thiacloprid “can strongly disrupt freshwater ecosystem functioning via degradation of the invertebrate food web… Our results also suggest an immediate re-evaluation of the extensive usage of these insecticides is warranted, because both EPA and EFSA thresholds (that are deemed safe for freshwater life) were within our tested environmentally relevant concentrations where we observed degradation of freshwater communities and ecosystem functionality. Importantly, given the hundreds of pesticides that are on the market worldwide and present in the freshwater environment, the ecological networks and ecosystem functioning may be in far more perilous state than we have concluded based on trends in local taxon richness alone.â€
To mitigate these risks, the elimination of not only neonicotinoid insecticides but all petrochemical pesticides and synthetic fertilizers is needed. The availability of organic land management, which safeguards the environment and health for all organisms including humans, provides a holistic solution. To learn more about the health and environmental benefits of organic practices, see here and here. Get engaged by taking action to protect ecosystems, as well as signing up to receive Action of the Week and Weekly News Updates delivered straight to your inbox.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Barmentlo, S. et al. (2025) Networks in Aquatic Communities Collapse Upon Neonicotinoid-Induced Stress, Ecology Letters. Available at: https://onlinelibrary.wiley.com/doi/10.1111/ele.70121.
