Harmful algal blooms (HABs) are globally increasing in number and spatial extent. However, their propagation dynamics along environmental gradients and the associated interplay of abiotic factors and biotic interactions are still poorly understood. In this study, a nutrient gradient was established in a linear meta-ecosystem setup of five interconnected flasks containing an artificially assembled phytoplankton community. The harmful dinoflagellate Alexandrium catenella was introduced into different positions along the nutrient gradient to investigate dispersal and spatial community dynamics. Overall, total algal biovolume increased, while community evenness decreased with increasing nutrient concentrations along the gradient. Alexandrium was able to disperse through all flasks. On the regional scale, diatoms dominated the community, whereas on the local scale the dinoflagellate showed higher contributions at low nutrient concentrations and dominated the community at the lowest nutrient concentration, but only when initiated into this flask. A control treatment without dispersal revealed an even stronger dominance of Alexandrium at the lowest nutrient concentration, indicating that dispersal and the associated nutrient exchange may weaken dinoflagellate dominance under low nutrient conditions. This study presents a first approach to experimentally investigate spatial dynamics and ecological interactions of a harmful dinoflagellate along an environmental gradient in a meta-ecosystem setup, which has the potential to substantially enhance our understanding of the relevance of dispersal for HAB formation and propagation in combination with local environmental factors.

中文翻译：

---

扩散、开花开始的位置和营养条件决定了有害的甲藻亚历山大藻的优势：元生态系统研究

有害藻华 (HAB) 在数量和空间范围上都在全球范围内增加。然而，它们沿环境梯度的传播动力学以及非生物因素和生物相互作用的相关相互作用仍然知之甚少。在这项研究中，在包含人工组装的浮游植物群落的五个相互连接的烧瓶的线性元生态系统设置中建立了营养梯度。将有害的甲藻亚历山大藻沿营养梯度引入不同位置，以研究散布和空间群落动态。总体而言，总藻类生物量增加，而群落均匀度随着梯度营养浓度的增加而降低。亚历山大能够分散通过所有烧瓶。在区域尺度上，硅藻在群落中占主导地位，而在局部尺度上，甲藻在低营养浓度下表现出更高的贡献，并在最低营养浓度下支配着群落，但仅当开始进入这个烧瓶时。没有扩散的对照处理揭示了亚历山大藻的更强优势在最低养分浓度下，表明在低养分条件下，传播和相关的养分交换可能会削弱甲藻的优势。本研究提出了第一种方法，在元生态系统设置中沿着环境梯度实验研究有害甲藻的空间动态和生态相互作用，这有可能大大增强我们对散布与 HAB 形成和传播相关性的理解。与当地环境因素有关。