Effects of thallus disturbance on abundance and biomass of soft-bottom species in Kongsfjorden in summer 2013@en

The effects of biotic disturbances, like seaweed whiplash, on the diversity of benthic communities are well documented for temperate coastal systems, yet missing for Arctic benthos. In Arctic soft-bottom habitats, kelp thalli occur either continuously (e.g. trapped by sediment) or sporadically (by drifting on the sediment) after detachment from rocky shores. To explore whether a kelp thallus can disturb the structure and diversity of a coastal Arctic soft-bottom assemblage, we continuously fixed a single thallus of the kelp Saccharina latissima to or sporadically (i.e. biweekly) moved it on the sediment and compared treatment effects to unmanipulated plots (= controls). On 6 September 2013 (i.e. after 73 days of manipulation), one sediment core was taken from each of the 30 plots (n = 10), from which the number of individuals of each of the 45 encountered animal species were recorded. The continuous presence of an experimentally fixed kelp thallus significantly reduced the number of individuals on average by 27 %. This disturbance effect was even stronger, on average 49 %, where a kelp thallus was biweekly moved on the sediment. Likewise, taxon richness was lowered by an average of 19 and 36 % where a S. latissima thallus was continuously or sporadically present, respectively. While the composition of taxa was also significantly different among all treatment groups, evenness and biomass were unaffected by kelp treatments. We conclude that the presence and already movements of a single kelp thallus can promote small scale patchiness in near-shore soft-bottom assemblage structure and diversity and exemplify a significant connection between rocky and sedimentary coastal habitats.温带近岸系统中，诸如海藻鞭甩（seaweed whiplash）这类生物扰动（biotic disturbances）对底栖生物群落（benthic communities）多样性的影响已有充分记载，但针对北极底栖生物（Arctic benthos）的相关研究仍属空白。在北极软底质栖息地（soft-bottom habitats）中，海带藻体（kelp thalli）从岩岸脱离后，要么持续滞留于沉积物中（如被沉积物困住），要么间歇性随沉积物漂移。为探究单条海带藻体是否会干扰北极近岸软底质群落的结构与多样性，我们将单条宽叶海带（Saccharina latissima）藻体持续固定于沉积物表面，或每隔两周（双周）将其在沉积物上移位一次，并以未施加人为操控的样方作为对照，对比不同处理的效应差异。2013年9月6日（即开展73天操控实验后），我们从30个样方中各采集1个沉积物岩芯（sediment core，每组10个样方，n=10），统计其中共记录到的45种动物的个体数量。实验设置的持续固定海带藻体处理，使样方内总个体数平均显著减少27%；若采用每隔两周移位藻体的处理，该扰动效应更为显著，平均个体数降幅达49%。同样，当宽叶海带藻体持续存在或间歇性存在时，类群丰富度（taxon richness）分别平均降低19%和36%。尽管所有处理组的类群组成均存在显著差异，但海带处理对群落均匀度（evenness）与生物量（biomass）无显著影响。本研究结论认为，单条海带藻体的存在及其周期性移动，可驱动近岸软底质群落结构与多样性形成小型斑块格局，并揭示了岩岸生境与沉积质近岸生境之间的重要生态关联。