Working on a baseline for the Kongsfjorden food web: production and properties of macroalgal particulate organic matter (POM), supplementary material

Macroalgae, in particular kelps, produce a large amount of biomass in Kongsfjorden, which is to a great extent released into the water in an annual cycle. As an example, the brown alga Alaria esculenta loses its blade gradually, 3 ± 0.8 % of the blade area per day (August 2012), thereby adding to the pool of particulate organic matter (POM) in the fjord. Upon release small thallus pieces are “aging” in that they are prone to leaching and serving as substrate for microorganisms, thus turning into palatable food for suspension and bottom feeders. In order to define a macroalgal baseline for the Kongsfjorden food web, stable isotopes d14C and d15N were measured in individuals of A. esculenta, Saccharina latissima and Laminaria digitata directly sampled after collection and in artificially produced POM (aPOM) of A. esculenta that was allowed to age under experimental conditions. In aPOM from this species sampled in August 2012 the C/N ratios decreased between d1 and d8 of a 14-day culture period in parallel to the fading photosynthetic activity of the algal fragments as demonstrated by use of an Imaging-PAM. Microscopic observations of the aPOM in August 2012 and 2013 revealed the frequent occurrence of small brown algal endo- and epiphytes. First feeding experiments with Mysis oculata (Mysids) and Hiatella arctica (Bivalves) showed that these species can ingest macroalgal POM. The importance of kelp-derived POM for the food web is subject of the current research.

大型藻类（尤其是海带类）在孔斯峡湾（Kongsfjorden）中可产生大量生物量，且这些生物量会以年周期为节奏大量释放至水体中。举例来说，褐藻掌状海带（Alaria esculenta）的叶片会逐渐脱落，2012年8月的观测显示其每日脱落的叶片面积占比为3±0.8%，由此为峡湾中的颗粒态有机物（particulate organic matter, POM）库补充了有机质。脱落的小型藻体片段会经历“老化”过程：它们易于发生淋溶，同时可作为微生物的附着基质，最终成为悬浮食性与底栖食性生物适口的食物来源。为构建孔斯峡湾食物网的大型藻类基准数据集，研究人员对采集后即刻取样的掌状海带、长海带（Saccharina latissima）、昆布（Laminaria digitata）个体，以及在实验条件下老化得到的掌状海带人工颗粒态有机物（artificially produced POM, aPOM）样本进行了碳稳定同位素δ¹⁴C与氮稳定同位素δ¹⁵N的测定。在2012年8月采集的该物种aPOM样本中，14天培养周期的第1天至第8天期间，C/N比值随藻体片段光合活性的衰减而下降，这一结果通过成像脉冲振幅调制荧光仪（Imaging-PAM）得到验证。对2012年与2013年的aPOM样本进行显微镜观测后发现，其中频繁出现小型褐藻内生与附生生物。针对眼形糠虾（Mysis oculata，糠虾目）和北极白海螂（Hiatella arctica，双壳类）的首次摄食实验表明，这些生物能够摄食大型藻类来源的POM。目前，海带类来源的POM在食物网中的重要性仍是当前研究的热点议题。