Freshwater Ecology and Management (F.E.M.) Research Group, Department of Evolutionary Biology, Ecology and Environmental Sciences, Universitat de Barcelona, Barcelona, Catalonia, Spain.
PLoS One. 2018 Mar 1;13(3):e0193545. doi: 10.1371/journal.pone.0193545. eCollection 2018.
This study aims to contribute to the understanding of the impact of Didymosphenia geminata massive growths upon river ecosystem communities' composition and functioning. This is the first study to jointly consider the taxonomic composition and functional structure of diatom and macroinvertebrate assemblages in order to determine changes in community structure, and the food web alterations associated with this invasive alga. This study was carried out in the Lumbreras River (Ebro Basin, La Rioja, Northern Spain), which has been affected by a considerable massive growth of D. geminata since 2011. The study shows a profound alteration in both the river community composition and in the food web structure at the sites affected by the massive growth, which is primarily due to the alteration of the environmental conditions, thus demonstrating that D. geminata has an important role as an ecosystem engineer in the river. Thick filamentous mats impede the movement of large invertebrates-especially those that move and feed up on it-and favor small, opportunistic, herbivorous organisms, mainly chironomids, that are capable of moving between filaments and are aided by the absence of large trophic competitors and predators -prey release effect-. Only small predators, such as hydra, are capable of surviving in the new environment, as they are favored by the increase in chironomids, a source of food, and by the reduction in both their own predators and other midge predators -mesopredator release-. This change in the top-down control affects the diatom community, since chironomids may feed on large diatoms, increasing the proportion of small diatoms in the substrate. The survival of small and fast-growing pioneer diatoms is also favored by the mesh of filaments, which offers them a new habitat for colonization. Simultaneously, D. geminata causes a significant reduction in the number of diatoms with similar ecological requirements (those attached to the substrate). Overall, D. geminata creates a community dominated by small organisms that is clearly different from the existing communities in the same stream where there is an absence of massive growths.
本研究旨在深入了解双眉藻大量生长对河流生态系统群落组成和功能的影响。这是首次联合考虑硅藻和大型底栖无脊椎动物组合的分类组成和功能结构，以确定群落结构的变化，以及与这种入侵藻类相关的食物网变化。本研究在卢姆布雷拉斯河（埃布罗流域，拉里奥哈，西班牙北部）进行，自 2011 年以来，该河流受到双眉藻大量生长的严重影响。研究表明，受大量生长影响的地点的河流群落组成和食物网结构发生了深刻变化，这主要是由于环境条件的改变，因此表明双眉藻在河流中作为生态系统工程师具有重要作用。厚厚的丝状垫阻碍了大型无脊椎动物的移动——特别是那些在上面移动和觅食的无脊椎动物——并有利于小型、机会主义、草食性生物，主要是摇蚊，它们能够在丝状垫之间移动，并得益于缺乏大型营养竞争者和捕食者——猎物释放效应。只有小的捕食者，如水螅，能够在新环境中生存，因为它们受益于摇蚊数量的增加，摇蚊是它们的食物来源，并且它们自身的捕食者和其他摇蚊捕食者的数量减少——中型捕食者释放效应。这种自上而下的控制变化影响硅藻群落，因为摇蚊可能以大型硅藻为食，从而增加基质中小硅藻的比例。丝状垫为快速生长的先锋硅藻提供了新的栖息地，也有利于它们的生存。同时，双眉藻大量生长导致具有相似生态需求（附着在基质上的硅藻）的硅藻数量显著减少。总的来说，双眉藻创造了一个以小型生物为主的群落，与同一溪流中不存在大量生长的现有群落明显不同。
