Research on interactions between marine organisms, and between organisms and their environment is urgently needed to enhance our knowledge on ecosystem resilience in a period of rapid climate change. The most promising approach to enhance our understanding is experimental manipulation in the field. However, whereas controlled field experimentation in marine ecology is well established for shallow water habitats, experimental work in deep waters is still in its infancy. Prerequisite for most experimental approaches at the deep seafloor is the availability of free-falling devices (Bottom-Lander) and Remotely Operated Vehicles (ROV).
Long-term biological experiments at the HAUSGARTEN observatory were already started in 1999 and comprise feeding and starvation experiments, exclusion and colonisation experiments as well as bioturbation and disturbance experiments.
For example, to study the reaction of the small benthic biota to decreasing food availability, which is a common scenario for the changing Arctic Ocean, we installed cages (2 x 2 m in dimension, 50 cm in height) at the deep seafloor (2500 m water depth). The solid lids of these cages prevent the sedimentation of particulate organic matter, representing the main food/energy source for benthic organisms. Since 2009, we repeatedly retrieved sediment samples inside the cages to investigate changes in organism densities and alterations in the community structure of bacteria and meiofaunal organisms (size range 32 - 1000 µm) to reduced food availability.
Smaller cages preventing the access of larger benthic organisms to certain areas at the seafloor were installed to study the reaction of the small benthic biota to decreasing levels of disturbance (sediment perturbation, feeding pressure), while in another experiment, we spread small inert fluorescing microspheres, so-called luminophores, on a defined area at the deep seafloor to start an experiment assessing the perturbation rates (bioturbation) by larger benthic organisms at HAUSGARTEN observatory.
Soltwedel, T., Guilini, K., Sauter, E., Schewe, I., Hasemann, C. (2017): Local effects of large food falls on nematode diversity at an arctic deep-sea site: Results from an in-situ experiment at the LTER observatory HAUSGARTEN , Journal of Experimental Marine Biology and Ecology. doi: 10.1016/j.jembe.2017.03.002
Soltwedel, T., Mokievsky, V., Rabouille, C., Sauter, E., Volkenandt, M., Hasemann, C. (2013): Effects of experimentally increased near bottom flow on meiofauna diversity in the deep Arctic Ocean. Deep-Sea I 73 (3): 31-45. doi: 10.1016/j.dsr.2012.11.008
Freese, D., Schewe, I., Kanzog, C., Soltwedel, T., Klages, M. (2012): Recolonisation of new habitats by meiobenthic organisms in the deep Arctic Ocean: an experimental approach. Polar Biology 35: 1801-1813. doi: 10.1007/s00300-012-1223-2.
Guilini, K., Soltwedel, T., van Oevelen, D., Vanreusel, A. (2011): Deep-sea nematodes actively colonise sediments, irrespective of the presence of a pulse of organic matter: Results from an in-situ experiment. PLOS One 6(4), e18912. doi: 10.1371/journal.pone.0018912.
Kanzog, C., Ramette, A., Quéric, N.V., Klages, M. (2009): Response of benthic microbial communities to chitin enrichment: an in-situ study in the deep Arctic Ocean. Polar Biology 32 (1): 105-112. doi: 10.1007/s00300-008-0510-4.
Gallucci, F., Fonseca, G., Soltwedel, T. (2008): Effects of megafauna exclusion on nematode assemblages at a deep-sea site. Deep-Sea Research I, 55 (3): 332-349. doi: 10.1016/j.dsr.2007.12.001.