Data from: Submerged macrophytes mitigate direct and indirect insecticide effects in freshwater communities

Understanding how ecological interactions mitigate the impacts of perturbations such as pesticides in biological communities is an important basic and applied question for ecologists. In aquatic ecosystems, new evidence from microcosm experiments suggests that submerged macrophytes can buffer cladocerans from pulse exposures to the widely used insecticide malathion, and that mitigation increases with macrophyte density. However, whether these results scale up to more complex aquatic communities where ecological interactions such as competition can alter toxicity is unknown. Further, macrophyte abilities to mitigate different insecticide exposure scenarios (i.e. single versus repeated pulses) have never been tested. To address these gaps, we performed a factorial mesocosm experiment examining the influence of four macrophyte treatments (0, 10, 50, or 100 Elodea Canadensis shoots planted per mesocosm) crossed with three malathion exposure scenarios (no insecticide, single pulse, repeated pulses) on aquatic communities containing zooplankton, phytoplankton, periphyton, two snail species, and larval amphibians. In the absence of macrophytes, single malathion pulses caused short-term declines in cladoceran abundance followed by their rapid recovery, which precluded any indirect effects (i.e. trophic cascades). However, repeated malathion pulses caused cladoceran extinctions, resulting in persistent phytoplankton blooms and reduced abundance of one snail species. In contrast, with macrophytes present, even at low density, malathion had no effect on any taxa. We also discovered novel effects of macrophytes on the benthic food web. In the two highest macrophyte treatments, we observed trends of reduced periphyton biomass, decreased abundance of one snail species, and decreased amphibian time to and mass at metamorphosis. To our knowledge, this is the first evidence of negative submerged macrophyte effects on amphibians, a taxa of global conservation concern. Our findings suggest that facilitating macrophytes could be an important strategy for buffering freshwater communities from insecticides, though consideration of their impacts on animal species is necessary.

解析生态交互如何缓解扰动对生物群落的影响，是生态学家关注的重要基础与应用研究课题。在水生生态系统中，微宇宙实验（microcosm）的最新证据表明，沉水植物（submerged macrophytes）可帮助枝角类动物（cladocerans）抵御广泛使用的杀虫剂马拉硫磷（malathion）的脉冲暴露，且这种缓冲效应随沉水植物密度升高而增强。然而，这类效应能否外推至存在竞争等生态交互、可改变毒物毒性的更复杂水生群落，目前尚不明确。此外，沉水植物对不同杀虫剂暴露场景（即单次脉冲与重复脉冲暴露）的缓解能力，尚未得到实验验证。为填补这些研究空白，我们开展了析因中宇宙实验（mesocosm），设置4组沉水植物处理（每个中宇宙分别种植0、10、50或100株加拿大伊乐藻（Elodea Canadensis）茎枝），并与3种马拉硫磷暴露场景（无杀虫剂、单次脉冲暴露、重复脉冲暴露）进行交叉设计，探究其对包含浮游动物（zooplankton）、浮游植物（phytoplankton）、周丛生物（periphyton）、两种螺类以及两栖类幼体的水生群落的影响。在无沉水植物的处理组中，单次马拉硫磷脉冲暴露会导致枝角类丰度短期下降，随后迅速恢复，因此未产生任何间接效应（如营养级联效应（trophic cascades））。但重复马拉硫磷脉冲暴露会导致枝角类完全灭绝，进而引发持续性浮游植物水华，并降低其中一种螺类的丰度。与之相反，只要存在沉水植物（即便密度较低），马拉硫磷对所有类群均无显著影响。我们还发现了沉水植物对底栖食物网（benthic food web）的全新调控效应。在沉水植物密度最高的两组处理中，我们观察到周丛生物生物量下降、其中一种螺类丰度降低，以及两栖类变态发育（metamorphosis）所需时间缩短、变态时体重降低的趋势。据我们所知，这是首次发现沉水植物对两栖类的负面效应，而两栖类是受到全球保护关注的类群。本研究结果表明，培育沉水植物可作为缓解淡水群落遭受杀虫剂威胁的重要策略，但同时也需兼顾其对各类动物类群的潜在影响。