Meiofauna in the Gollum Channels and the Whittard Canyon, Celtic Margin—How Local Environmental Conditions Shape Nematode Structure and Function

The Gollum Channels and Whittard Canyon (NE Atlantic) are two areas that receive high input of organic matter and phytodetritus from euphotic layers, but they are typified by different trophic and hydrodynamic conditions. Sediment biogeochemistry was analysed in conjunction with structure and diversity of the nematode community and differences were tested between study areas, water depths (700 m vs 1000 m), stations, and sediment layers. The Gollum Channels and Whittard Canyon harboured high meiofauna abundances (1054–1426 ind. 10 cm−2) and high nematode diversity (total of 181 genera). Next to enhanced meiofauna abundance and nematode biomass, there were signs of high levels of organic matter deposition leading to reduced sedimentary conditions, which in turn structured the nematode community. Striking in this respect was the presence of large numbers of ‘chemosynthetic’ Astomonema nematodes (Astomonema southwardorum, Order Monhysterida, Family Siphonolaimidae). This genus lacks a mouth, buccal cavity and pharynx and possesses a rudimentary gut containing internal, symbiotic prokaryotes which have been recognised as sulphur-oxidising bacteria. Dominance of Astomonema may indicate the presence of reduced environments in the study areas, which is partially confirmed by the local biogeochemical environment. The nematode communities were mostly affected by sediment layer differences and concomitant trophic conditions rather than other spatial gradients related to study area, water depth or station differences, pointing to small-scale heterogeneity as the main source of variation in nematode structure and function. Furthermore, the positive relation between nematode standing stocks, and quantity and quality of the organic matter was stronger when hydrodynamic disturbance was greater. Analogically, this study also suggests that structural diversity can be positively correlated with trophic conditions and that this relation is tighter when hydrodynamic disturbance is greater.

哥鲁姆海槽（Gollum Channels）与惠塔德峡谷（Whittard Canyon，东北大西洋）均接收来自透光层（euphotic layers）的大量有机质与植物碎屑输入，但二者的营养动力学与水动力条件存在显著差异。本研究结合沉积物生物地球化学特征，分析了线虫群落的结构与多样性，并针对研究区域、水深（700米与1000米）、站位以及沉积层之间的差异开展检验。哥鲁姆海槽与惠塔德峡谷的小型底栖动物（meiofauna）丰度较高（1054~1426 个/10 cm²），线虫群落多样性亦十分丰富，共涵盖181个属。除小型底栖动物丰度与线虫生物量提升外，研究区域还存在有机质大量沉积的迹象，进而导致沉积环境还原化，而这一过程又塑造了线虫群落结构。值得注意的是，该区域存在大量“化能合成”型的Astomonema属线虫（Astomonema southwardorum，单殖线虫目（Monhysterida），管咽线虫科（Siphonolaimidae））。该属线虫无口器、口咽腔与咽，仅具退化的肠道，肠道内共生有被鉴定为硫氧化细菌的原核生物。Astomonema属的优势地位或表明研究区域存在还原环境，这一点得到了当地生物地球化学环境的部分验证。线虫群落主要受沉积层差异及其伴随的营养动力学条件影响，而非与研究区域、水深或站位差异相关的其他空间梯度，这表明小型空间异质性是线虫群落结构与功能变异的主要来源。此外，当水动力扰动越强时，线虫现存量与有机质的数量、质量之间的正相关关系就越显著。类似地，本研究还表明，线虫群落结构多样性与营养动力学条件呈正相关，且该相关关系在水动力扰动更强时更为紧密。