Department Aquatic Ecology

The use of biodegradable plastics as an alternative to conventional non-degradable synthetic polymers is gaining market to reduce plastic pollution, however, their biodegradability is not unconditional. In this study, we hypothesized that planktonic protists (nanoflagellates and ciliates) increase the degradation of the biodegradable PLGA (poly(lactic-co-glycolic) acid) due to particle uptake. We conducted uptake and degradation experiments using PLGA microspheres of 4.9 ± 2.8 μm diameter and the microbial planktonic community from the Baltic Sea. We found that planktonic protists ingested PLGA of different sizes, with ciliates displaying higher clearance rates and ingesting larger particles compared to nanoflagellates. In addition, we observed a more pronounced decrease in PLGA concentration and particle size over time in the presence of seawater containing microbial plankton compared to a control with only ultrapure water, suggesting that the presence of these organisms increases the rate of degradation of PLGA in marine ecosystems. Altogether, these results indicate that microbial plankton enhances the degradation of biodegradable microplastics like PLGA, specifically through rapid uptake by planktonic protists. These findings highlight the role of particle ingestion by planktonic protists in the fate of the so-called biodegradable plastics when they enter aquatic ecosystems.

Heatwaves and increasing average temperatures associated with climate change pose severe stress on nature, including freshwater ecosystems. As these thermal stressors do not act in isolation over temporal or spatial scales, interactions with other stressors, like pesticides, may lead to unpredictable combined effects. Empirical studies investigating multiple stressor effects across different trophic levels are scarce and often lack environmental realism. Here, we performed a multiple stressor experiment using outdoor freshwater mesocosms and realistic pond assemblages including microbes, phytoplankton, macrophytes, and invertebrates. The effects of the pesticide imidacloprid at three dosings (0, 1, 10 μg/L) were examined in combination with three temperature scenarios comprising natural ambient, elevated temperatures (+4 °C), and repeated heatwaves (+8 °C). Our results reveal fast imidacloprid dissipation for all temperature treatments with the lowest average dissipation half-lives (DT₅₀: 6 days) in the heatwave treatment. Imidacloprid induced a series of significant effects on the macroinvertebrate community at 10 μg/L across the temperature treatments. Significant declines in abundance appeared throughout the experiment for the most sensitive taxa Cloeon dipterum, Caenis sp., Chironomini, and Dero sp., whereas significant imidacloprid effects on Tanytarsini, Chironomus, and Gammarus pulex occurred only after each dosing. Only Zygoptera showed an imidacloprid-related increase in abundance, whereas significantly adverse time-cumulative effects on abundance occurred for Asellus aquaticus. The zooplankton community showed imidacloprid tolerance (10 μg/L) with increasing abundances of Chydorus sphaericus, Acroperus harpae, and Ascomorpha. Heatwaves induced significantly meliorating effects on Dero sp. and adverse effects on Caenis sp., Tanytarsini, G. pulex, and A. harpae. The macroinvertebrate community demonstrated faster post-exposure recovery dynamics in the highest imidacloprid treatment when previously exposed to heatwaves and elevated temperatures compared to ambient conditions. Overall, heatwaves amplified the effects of imidacloprid on the invertebrate community, manifesting in manifold effects that adversely impacted multiple trophic levels.

Urban blue and green spaces, like ponds and parks, can mitigate the negative effects of urbanization on biodiversity by providing diverse, connected habitats and enabling resource flows between ecosystems. While studies have evaluated these spaces for terrestrial and aquatic communities individually, few have examined shared factors influencing both communities simultaneously. Consequently, it is unclear how these spaces should be conceived and maintained to support the diversity of both aquatic and terrestrial species, as well as their interactions. Here, we use environmental DNA (eDNA) metabarcoding to identify shared drivers and assess if and how aquatic and terrestrial invertebrate communities are coupled across 54 paired aquatic and terrestrial habitats along an urbanization gradient in the city of Zurich, Switzerland. Contrary to general expectations, we find no significant correlation in aquatic and terrestrial community structure, which we attribute to distinct drivers identified for both communities. Aquatic communities were primarily influenced by local factors related to habitat quality, while terrestrial communities were associated to landscape drivers pertaining to habitat quantity, suggesting that different processes at different spatial scales need to be considered to support both communities. Furthermore, with increasing urbanization, aquatic and terrestrial communities exhibited signs of decoupling driven by the filtering of organisms straddling ecosystem boundaries. We conclude that increasing levels of urbanization weaken resource flow between aquatic and terrestrial environments. By employing eDNA across ecosystem boundaries, our study highlights the critical importance of both the quality and quantity of urban habitats in conserving aquatic and terrestrial communities, as well as their linkages.