(Appendix A) Pigment content, microbial biomass and activity, and grain size characteristics in caged and control sites of the Arctic long-term observatory HAUSGARTEN@en

Present theories of deep-sea community organization recognize the importance of small-scale biological disturbances, originated partly from the activities of epibenthic megafaunal organisms, in maintaining high benthic biodiversity in the deep sea. However, due to technical difficulties, in situ experimental studies to test hypotheses in the deep sea are lacking. The objective of the present study was to evaluate the potential of cages as tools for studying the importance of epibenthic megafauna for deep-sea benthic communities. Using the deep-diving Remotely Operated Vehicle (ROV) \"VICTOR 6000\", six experimental cages were deployed at the sea floor at 2500 m water depth and sampled after 2 years (2y) and 4 years (4y) for a variety of sediment parameters in order to test for caging artefacts. Photo and video footage from both experiments showed that the cages were efficient at excluding the targeted fauna. The cage also proved to be appropriate to deep-sea studies considering the fact that there was no fouling on the cages and no evidence of any organism establishing residence on or adjacent to it. Environmental changes inside the cages were dependent on the experimental period analysed. In the 4y experiment, chlorophyll a concentrations were higher in the uppermost centimeter of sediment inside cages whereas in the 2y experiment, it did not differ between inside and outside. Although the cages caused some changes to the sedimentary regime, they are relatively minor compared to similar studies in shallow water. The only parameter that was significantly higher under cages at both experiments was the concentration of phaeopigments. Since the epibenthic megafauna at our study site can potentially affect phytodetritus distribution and availability at the seafloor (e.g. via consumption, disaggregation and burial), we suggest that their exclusion was, at least in part, responsible for the increases in pigment concentrations. Cages might be suitable tools to study the long-term effects of disturbances caused by megafaunal organisms on the diversity and community structure of smaller-sized organisms in the deep sea, although further work employing partial cage controls, greater replication, and evaluating faunal components will be essential to unequivocally establish their utility.当前关于深海群落组织的理论已认识到，小型尺度生物扰动（部分源自底上大型巨型动物（epibenthic megafauna）的活动）对维持深海高底栖生物多样性具有重要意义。然而受限于技术难题，目前缺乏针对深海相关假说的原位实验研究。本研究旨在评估网箱作为研究工具的潜力，以探究底上大型巨型动物对深海底栖群落的重要性。本研究使用深潜遥控水下机器人（Remotely Operated Vehicle，ROV）"VICTOR 6000"，在2500米水深的海底部署了6个实验网箱，并分别在部署2年（2y）和4年（4y）后采集多种沉积物参数样本，以检测网箱实验伪影（caging artefacts）。两次实验获取的影像资料显示，网箱可有效排斥目标大型动物。此外，网箱表面及周边未出现生物附着或定居的迹象，表明其适用于深海研究。网箱内部的环境变化与实验周期相关：在4年实验中，网箱内部沉积物表层1厘米的叶绿素a浓度高于箱外；而在2年实验中，箱内外的叶绿素a浓度无显著差异。尽管网箱会对沉积环境造成一定改变，但相较于浅水同类研究，其影响相对微弱。两次实验中，仅脱镁色素（phaeopigments）浓度在网箱下方显著升高。由于研究区域的底上大型巨型动物可通过摄食、分解和埋藏等方式影响海底植物碎屑的分布与可获得性，因此我们推测，网箱对这类动物的排斥作用至少部分导致了箱内脱镁色素浓度的升高。尽管后续需通过设置部分网箱对照组、增加重复样本量以及评估动物群落组成等工作，才能明确验证网箱的应用价值，但本研究表明，网箱或可作为研究工具，用于探究大型巨型动物造成的扰动对深海小型生物多样性及群落结构的长期影响。