Data_Sheet_1_Seasonal Variability in Benthic–Pelagic Coupling: Quantifying Organic Matter Inputs to the Seafloor and Benthic Macrofauna Using a Multi-Marker Approach.docx

The exchange between the water column and the seafloor is a complex process, and is particularly intensive in the shallow waters of highly productive coastal areas, where the temporal variability in the inputs of pelagic organic matter will determine many aspects of the benthic community structure. However, few studies have focused on the seasonality of inputs of organic matter to the seafloor, and on the consequent dynamics and time scales of response of benthic consumers. We conducted a 1-year study where we repeatedly sampled multiple organic compounds traditionally used as markers to study the link between the pelagic organic matter inputs and the seafloor, and the potential response of benthic macrofauna to seasonal trends in phytoplankton biomass. We simultaneously quantified the particulate organic matter in the water column, the sinking material and different seafloor compartments, and analyzed it for pigments, organic carbon and nitrogen content, C/N ratio, and stable isotopes. Seafloor sediment was also analyzed for total lipids, and the dominant macrobenthic species for isotopic signatures. Results showed a major deposition of fresh organic matter during the spring bloom followed by more degraded organic matter inputs during the late summer bloom and even lower quality of the organic matter reaching the seafloor during winter. Strong positive relationships between water column and sedimentary pigments suggest that phytoplankton was the main source of carbon to the seafloor. The isotopic signatures of the dominant macrobenthic species suggest a fast response to the organic matter inputs from the water column. However, different species responded differently to the deposition of organic matter. Macoma balthica and Marenzelleria spp. fed on more reworked and degraded sedimentary material, while Monoporeia affinis showed a shift in the feeding habits according to its life stage, with adult individuals feeding on fresher material than juveniles did. Our study highlights the seasonal variability of the benthic–pelagic coupling and the utility of a multi-marker approach to follow the temporal inputs of organic matter from the water column to the seafloor and benthic organisms.

水柱与海底之间的物质交换是一个复杂的过程，在高生产力海岸带的浅水区尤为剧烈。在此区域，浮游有机物质（pelagic organic matter）输入的时间变异性将决定底栖群落（benthic community）结构的诸多特征。然而，目前鲜有研究聚焦于输入至海底的有机物质的季节动态，以及由此引发的底栖消费者（benthic consumers）响应过程与时间尺度。本研究开展了为期1年的野外调查，多次采集传统用作示踪标记物的多种有机化合物，以探究浮游有机物质输入与海底之间的关联，以及大型底栖动物（benthic macrofauna）对浮游植物生物量（phytoplankton biomass）季节变化的潜在响应。研究同时对水柱中的颗粒有机物质（particulate organic matter）、沉降颗粒物以及不同海底圈层进行定量分析，并检测其中的色素、有机碳与氮含量、碳氮比（C/N）以及稳定同位素（stable isotopes）组成。本研究还对海底沉积物中的总脂类进行了检测，并分析了优势大型底栖物种（macrobenthic species）的同位素信号。研究结果显示，春季水华（spring bloom）期间会有大量新鲜有机物质沉降，随后夏季晚期水华（late summer bloom）期间输入的有机物质降解程度更高，而冬季抵达海底的有机物质质量则更低。水柱与沉积色素（sedimentary pigments）之间存在显著正相关关系，这表明浮游植物是海底有机碳的主要来源。优势大型底栖物种的同位素信号表明，它们对水柱输入的有机物质存在快速响应。然而，不同物种对有机物质沉降的响应模式存在差异。白樱蛤（Macoma balthica）和马泽蚓属（Marenzelleria spp.）以经再改造且降解程度较高的沉积物质为食，而独钩虾（Monoporeia affinis）的摄食习性会随生活史阶段发生变化：成体相较于幼体，会摄食更新鲜的有机物质。本研究凸显了底栖-浮游耦合（benthic-pelagic coupling）的季节变异性，以及采用多示踪标记物方法追踪有机物质从水柱向海底及底栖生物的时间输入过程的实用性。