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

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.

诸如海藻鞭击扰动（seaweed whiplash）这类生物扰动（biotic disturbances）对底栖群落（benthic communities）多样性的影响，在温带近岸系统中已有充分文献记载，但针对北极底栖生物（Arctic benthos）的相关研究仍付阙如。在北极软底质生境中，巨藻（kelp）的叶状体从岩岸脱落之后，要么持续滞留（如被沉积物困住），要么间歇性地在沉积物表面漂移。为探究巨藻叶状体是否会扰动北极近岸软底质群落的结构与多样性，我们将单株长叶糖海带（Saccharina latissima）的叶状体持续固定于沉积物表面，或每两周将其在沉积物上移动一次，并将两种处理组的效应与未进行人工干预的样方（对照组）进行对比。2013年9月6日（即人工干预73天后），我们从30个样方中各采集1个沉积物岩芯（每个处理组含10个样方，n=10），并记录了其中观测到的45种动物的个体数量。实验中持续固定的巨藻叶状体的存在，使样方内个体总数平均降低27%，差异具有统计学意义。而每两周移动一次巨藻叶状体的处理组，其扰动效应更强，个体总数平均降低49%。同理，当长叶糖海带叶状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，但巨藻处理对群落均匀度（evenness）和生物量（biomass）并无显著影响。本研究结果表明，单株巨藻叶状体的存在及其周期性移动，可促进近岸软底质群落结构与多样性的小型斑块化分布，并印证了岩岸与沉积质近岸生境之间存在显著的生态联系。