Pelagic primary production is the main input of organic energy for benthic production below the photic zone. In the Baltic Sea, spring phytoplankton blooms are dominated by diatoms that sink out rapidly and export nutritionally favorable matter to benthic secondary production, while the summer blooms have more variable sedimentation rates and nutritional profile. Changes in phytoplankton species composition and bloom dynamics, as a consequence of climate change and eutrophication are reducing high quality diatoms reaching the benthic fauna, while promoting cyanobacteria. Here, we test uptake and assimilation of changing phytoplankton composition for three common benthic invertebrates, a clam, an amphipod and a polychaete under varying degrees of spring‐bloom associated diatoms (Skeletonema costatum) and summer‐bloom associated cyanobacteria (Nodularia spumigena). The phytoplankton were labeled with stable isotopes (¹⁵N and ¹³C, respectively) in order to trace assimilation in consumers' tissues. We found that all three macrofauna species fed on both diatoms and cyanobacteria. A linear pattern was found for all three species in assimilation of carbon and nitrogen from diatoms, with increasing assimilation associated with higher proportion of diatoms. There was no clear pattern found between proportion of cyanobacteria and assimilation of carbon and nitrogen for any of the species. This study shows that the investigated macrofaunal species display a selective feeding behavior with preference for spring‐bloom associated diatoms. Thus, changes in phytoplankton bloom composition are likely affecting benthic species composition and production.

中文翻译：

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浮游植物种类组成的变化对底栖无脊椎动物碳氮吸收的影响

中上层初级生产是在光合带以下底栖生物生产的主要有机能源输入。在波罗的海，春季的浮游植物花藻以硅藻为主，硅藻迅速下沉，将营养上有利的物质输出到底栖次生中，而夏季花藻的沉积速率和营养成分变化更大。气候变化和富营养化导致的浮游植物种类组成和花期动态变化，减少了到达底栖动物的高质量硅藻，同时促进了蓝藻。在这里，我们测试了在不同程度的春花相关硅藻下，三种常见底栖无脊椎动物，蛤，两栖类和多毛类的浮游植物组成变化的吸收和同化（Skeletonema costatum）和夏季开花相关的蓝细菌（Nodularia spumigena）。浮游植物标记有稳定的同位素（¹⁵ N和¹³C分别）以跟踪消费者组织中的同化作用。我们发现所有三种大型动物都以硅藻和蓝细菌为食。在硅藻中碳和氮的同化中，所有这三种物质均具有线性模式，同化率越高，硅藻的比例越高。在任何物种中，蓝细菌的比例与碳和氮的同化之间均未发现明确的模式。这项研究表明，被调查的大型动物物种表现出选择性的觅食行为，并且偏爱春季开花的硅藻。因此，浮游植物开花组成的变化可能会影响底栖生物的种类和产量。