The paucity of data on non-indigenous marine species is a particular challenge for understanding the ecology of invasions and prioritising conservation and research efforts in marine ecosystems. Marenzelleria spp. are amongst the most successful non-native benthic species in the Baltic Sea during recent decades. We used stable isotope analysis (SIA) to test the hypothesis that the dominance of polychaete worm Marenzelleria arctia in the zoobenthos of the Neva Estuary after its invasion in the late 2000s is related to the position of this species in the benthic food webs. The trend towards a gradual decrease in the biomass of Marenzelleria worms was observed during 2014–2020, probably due to significant negative relationships between the biomass of oligochaetes and polychaetes, both of which, according to SIA, primarily use allochthonous organic carbon for their production. The biomass of benthic crustaceans practically did not change and remained very low. The SIA showed that, in contrast to the native crustacean Monoporeia affinis, polychates are practically not consumed either by the main invertebrate predator Saduria entomon, which preys on M. affinis, oligochaetes and larvae of chironomids or by benthivorous fish that prefer native benthic crustaceans. A hypothetical model for the position and functional role of M. arctia in the bottom food web is presented and discussed. According the model, the invasion of M. arctia has created an offshoot food chain in the Estuary food webs. The former dominant food webs, associated with native crustaceans, are now poorly developed. The lack of top-down control obviously contributes to the significant development of the Marenzelleria food chain, which, unlike native food chains, does not provide energy transfer from autochthonous and allochthonous organic matter to the upper trophic levels. The study showed that an alien species, without displacing native species, can significantly change the structure of food webs, creating blind offshoots of the food chain.

中文翻译：

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Marenzelleria arctia（Spionidae，Polychaeta）入侵后芬兰湾东部的食物网改变

非本土海洋物种数据的缺乏是理解入侵生态和优先考虑海洋生态系统的保护和研究工作的一个特殊挑战。Marenzelleria spp. 是近几十年来波罗的海最成功的非本地底栖物种之一。我们使用稳定同位素分析 (SIA) 来检验多毛类蠕虫 Marenzelleria arctia 在 2000 年代后期入侵后在涅瓦河口底栖动物中的优势地位与该物种在底栖食物网中的位置有关的假设。在 2014-2020 年期间观察到 Marenzelleria 蠕虫的生物量逐渐减少的趋势，这可能是由于寡毛类和多毛类的生物量之间存在显着的负相关关系，根据 SIA 的说法，主要使用外来有机碳进行生产。底栖甲壳类动物的生物量几乎没有变化，而且仍然很低。SIA 表明，与原生甲壳类动物 Monoporeia affinis 相比，主要的无脊椎动物捕食者 Saduria entomon（捕食 M. affinis、寡毛纲动物和摇蚊的幼虫）或喜欢原生底栖甲壳类动物的底栖鱼类几乎不会食用多壳类动物。提出并讨论了 M. arctia 在底部食物网中的位置和功能作用的假设模型。根据该模型，M. arctia 的入侵在河口食物网中创建了一个分支食物链。以前与本地甲壳类动物相关的占主导地位的食物网现在发育不良。缺乏自上而下的控制显然有助于 Marenzelleria 食物链的显着发展，与本地食物链不同，它不提供从本地和外来有机物质到上层营养水平的能量转移。研究表明，外来物种在不取代本地物种的情况下，可以显着改变食物网的结构，造成食物链的盲目分支。