Meiofauna and nematode abundances from cold seep related habitats along the Norwegian coast@en

Cold-seep environments and their associated symbiont-bearing megafaunal communities create islands of primary production for macro- and meiofauna in the otherwise monotonous and nutrient-poor deep-sea environment. To examine the spatial variation and distribution patterns of metazoan meiobenthos in different seepage-related habitats, samples were collected in two regions off Norway: several pockmarks associated with the Storegga Slide including the Nyegga pockmark area (730 m; 64°N), and the active, methane-venting Håkon Mosby Mud Volcano (HMMV) west of the Barents Sea (1280 m; 72°N). Based on sediment geochemistry and associated epifauna, three different habitat types were distinguished across the two regions: (1) reduced sediment with suboxic conditions, sometimes covered by bacterial mats, (2) sediment colonised by chemosynthetic, siboglinid tubeworms, and (3) sediment outside the influence of seepage and without a large chemosynthetic fauna. Meiofaunal communities varied strongly in terms of generic diversity and dominance among the different habitat types. Control sites and Siboglinidae polychaete fields both supported high nematode genus richness similar to normal deep-sea sediments, whereas the reduced sediments yielded a genus-poor nematode community dominated by one or two successful species. Meiofaunal densities in the different habitats were negatively correlated with macrobenthic densities. An extremely dense (>11,000 ind. 10 cm**2), mono-specific nematode population appeared to be restricted to the bacterial mats at HMMV. It consisted of a new cryptic species of the Halomonhystera disjuncta complex, which has been described from intertidal habitats in the North Sea. The reduced seep sediments at Nyegga did not yield H. disjuncta but were dominated by Terschellingia longicaudata, another cosmopolitan nematode species known to be abundant in organic-rich, oxygen-poor, shallow-water environments. These observations point to a past or recent connection between margins and shallow-water habitats.

冷泉环境（cold-seep environments）及其携带有共生体的大型底栖动物群落，在单调贫瘠的深海生境中为大型和小型底栖生物构建了初级生产的“岛屿生境”。为探究不同渗液相关生境中后生动物小型底栖生物（metazoan meiobenthos）的空间变异与分布格局，研究团队在挪威外海的两个区域采集了样本：一是与Storegga滑坡相关的多个麻点（pockmark）区域，包括Nyegga麻点区（水深730米，北纬64°）；二是巴伦支海西侧活跃的甲烷喷溢哈康莫斯比泥火山（Håkon Mosby Mud Volcano, HMMV）（水深1280米，北纬72°）。基于沉积物地球化学特征与伴生的底表动物（epifauna），研究人员在两个区域中区分出三类生境类型：(1) 处于次氧环境的还原沉积物，部分区域被细菌席（bacterial mats）覆盖；(2) 定植化能合成类群的管栖蠕虫（siboglinid tubeworms）沉积物；(3) 不受渗液影响且无大型化能合成动物的沉积物。小型底栖生物群落在不同生境类型间的属级多样性与优势类群组成存在显著差异。对照站点与管栖蠕虫科（Siboglinidae）多毛类群落生境均支持较高的线虫（nematode）属丰富度，与正常深海沉积物的线虫属丰富度相近；而还原沉积物中的线虫群落属数匮乏，由1~2个优势物种主导。不同生境中的小型底栖生物密度与大型底栖生物密度呈负相关关系。在哈康莫斯比泥火山的细菌席生境中，存在一个密度极高（>11000个个体/10cm²）的单一种类线虫种群。该种群属于Halomonhystera disjuncta复合群中的一个新隐存物种，该复合群此前曾在北海潮间带生境中被报道。Nyegga区域的还原渗液沉积物中未检出H. disjuncta，而是以Terschellingia longicaudata为优势类群；该物种为广布性线虫，已知在富含有机质、低氧的浅水环境中大量繁衍。上述观测结果表明，深海陆缘与浅水生境之间存在过去或近期的物种交流关联。