Abstract
Abstract. There is a need for cost-efficient tools to explore deep-ocean ecosystems to collect baseline biological observations on pelagic fauna (zooplankton and nekton) and establish the vertical ecological zonation in the deep sea. The Pelagic In situ Observation System (PELAGIOS) is a 3000 m rated slowly (0.5 m s−1) towed camera system with LED illumination, an integrated oceanographic sensor set (CTD-O2) and telemetry allowing for online data acquisition and video inspection (low definition). The high-definition video is stored on the camera and later annotated using software and related to concomitantly recorded environmental data. The PELAGIOS is particularly suitable for open-ocean observations of gelatinous fauna, which is notoriously under-sampled by nets and/or destroyed by fixatives. In addition to counts, diversity, and distribution data as a function of depth and environmental conditions (T, S, O2), in situ observations of behavior, orientation, and species interactions are collected. Here, we present an overview of the technical setup of the PELAGIOS as well as example observations and analyses from the eastern tropical North Atlantic. Comparisons to data from the Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) net sampling and data from the Underwater Vision Profiler (UVP) are provided and discussed.
Highlights
The open-ocean pelagic zones include the largest, yet least explored habitats on the planet (Robison, 2004; Webb et al, 2010; Ramirez-Llodra et al, 2010)
Underwater observations in the open ocean via scuba diving (Hamner et al, 1975) and later via submersibles (Robison, 1983; Robison and Wishner, 1990) and in situ camera systems (Picheral et al, 2010) revealed that a variety of organisms are much more abundant in the open ocean than previously estimated from net sampling (Robison, 2004). This was true for fragile gelatinous zooplankton, a diverse taxonomic group, including the ctenophores and cnidarians (Remsen et al, 2004; Haddock, 2004) as well as polychaetes (Christiansen et al, 2018), Rhizaria (Biard et al, 2016), and pelagic tunicates (Remsen et al, 2004; Neitzel, 2017), which often are too delicate to be quantified using nets as they are damaged beyond identification, or they are destroyed by the use of common fixatives
We present a description of the Pelagic In situ Observation System (PELAGIOS), examples of the kind of biological information it may gather, as well as biological discoveries that have resulted from deployments on research cruises in the eastern tropical North Atlantic
Summary
The open-ocean pelagic zones include the largest, yet least explored habitats on the planet (Robison, 2004; Webb et al, 2010; Ramirez-Llodra et al, 2010). Examples of instruments include the autonomous Underwater Vision Profiler (UVP5; Picheral et al, 2010), the Lightframe On-sight Key species Investigations (LOKI; Schulz et al, 2010) and towed plankton recorders (In Situ Ichthyoplankton Imaging System – ISIIS; Cowen and Guigand, 2008; for a review, see Benfield et al, 2007) These instruments can be deployed from ships of opportunity and collect detailed information on fine-scale distribution and diversity patterns of particles and plankton. Examples are the TowCam (WHOI), the DTIS (Deep Towed Imaging system, NIWA), the WASP vehicle (Wide Angle Seafloor Photography), OFOS (Ocean Floor Observation System, GEOMAR), and the more recent version OFOBS (Ocean Floor Observation and Bathymetry System; Purser et al, 2018) All these instruments are used for video or photo transects of the seafloor, with a downward looking camera and typically a set of lasers for size reference. We present a description of the Pelagic In situ Observation System (PELAGIOS), examples of the kind of biological information it may gather, as well as biological discoveries that have resulted from deployments on research cruises in the eastern tropical North Atlantic
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