Invasive macroalgae shape chemical and microbial waterscapes on coral reefs

Over the past decades, human impacts have changed the structure of tropical benthic reef communities towards coral depletion and macroalgal proliferation. However, how these changes have modified chemical and microbial waterscapes is poorly known. Here, we assessed how the experimental removal of macroalgal assemblages influences the chemical and microbial composition of two reef boundary layers, the benthic and the momentum. Chemical and microbial waterscapes were spatially structured, both horizontally and vertically, according to macroalgal dominance and boundary layers. Microbes associated with reef degradation were enriched in the boundary layers surrounding macroalgal-dominated substrata. Dominant macroalgae were surrounded by a distinct chemical pool of diverse lipid classes (e.g., diterpenoids and glycerolipids) and labile organic matter (e.g., organooxygen compounds), which diffused from algal tissues to boundary layers according to their polarity. Finally, our results highlighted strong co-variations between specific algal-derived metabolites and planktonic microbes, giving insight into their roles in coral reef functioning and resilience.近数十年来，人类活动干扰已改变热带底栖珊瑚礁群落结构，使其呈现珊瑚覆盖率下降、大型藻类（macroalgae）大量增殖的态势。然而，目前人们对这类变化如何改变化学与微生物水域景观仍知之甚少。本研究通过实验移除大型藻类群落，探究其对两种珊瑚礁边界层——底栖边界层与动量边界层（momentum boundary layer）——的化学与微生物组成的影响。化学与微生物水域景观的空间结构兼具水平与垂直分异特征，其分布格局与大型藻类优势度及所处边界层类型紧密相关。与珊瑚礁退化相关的微生物，在大型藻类占主导的基质周边的边界层中显著富集。优势大型藻类周围存在独特的化学物质库，涵盖多种脂类组分（如二萜类化合物（diterpenoids）与甘油脂类（glycerolipids））以及活性有机物（labile organic matter，如有机含氧化合物（organooxygen compounds））；此类物质可依据自身极性从藻类组织扩散至周边边界层。本研究结果最终揭示了特定藻类来源代谢物与浮游微生物之间存在显著的共变关系，为阐明二者在珊瑚礁生态功能与恢复力中的作用提供了重要见解。