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.

哥鲁姆海槽与惠塔德峡谷（东北大西洋）是两个接收来自真光层大量有机质与植物碎屑输入的海域，但二者的营养动力学与水动力条件存在显著差异。本研究分析了沉积物生物地球化学特征，并结合线虫群落的结构与多样性，对研究区域、水深（700 m与1000 m）、采样站位以及沉积物层之间的差异开展了显著性检验。

哥鲁姆海槽与惠塔德峡谷栖息着较高丰度的小型底栖生物（1054–1426 个/10 cm²）以及较高的线虫多样性（共计181个属）。除小型底栖生物丰度与线虫生物量提升外，研究区域还存在大量有机质沉积的迹象，形成了沉积物还原环境，进而塑造了线虫群落的结构。在此方面尤为引人注目的是，大量‘化能合成（chemosynthetic）’型阿氏线虫属（Astomonema）线虫的存在，包括南方阿氏线虫（Astomonema southwardorum），隶属于单宫目（Monhysterida）、吸管咽科（Siphonolaimidae）。该属线虫缺乏口器、口囊与咽部，拥有退化的肠道，肠道内共生有已被鉴定为硫氧化细菌（sulphur-oxidising bacteria）的原核生物。阿氏线虫属的优势类群占比，可能指示研究区域存在还原环境，这一推论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物层差异及伴随的营养动力学条件影响，而非与研究区域、水深或采样站位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便越显著。类似地，本研究还表明，线虫群落的结构多样性可与营养动力学条件呈正相关，且当水动力扰动越强时，这一关联便越紧密。