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Articles and Plankton Ocean Sci., 15, 1327–1340, 2019 https://doi.org/10.5194/os-15-1327-2019 © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. The Pelagic In situ Observation System (PELAGIOS) to reveal biodiversity, behavior, and ecology of elusive oceanic fauna Henk-Jan Hoving1, Svenja Christiansen2, Eduard Fabrizius1, Helena Hauss1, Rainer Kiko1, Peter Linke1, Philipp Neitzel1, Uwe Piatkowski1, and Arne Körtzinger1,3 1GEOMAR, Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany 2University of Oslo, Blindernveien 31, 0371 Oslo, Norway 3Christian Albrecht University Kiel, Christian-Albrechts-Platz 4, 24118 Kiel, Germany Correspondence: Henk-Jan Hoving ([email protected]) Received: 16 November 2018 – Discussion started: 10 December 2018 Revised: 11 June 2019 – Accepted: 17 June 2019 – Published: 7 October 2019 Abstract. There is a need for cost-efficient tools to explore 1 Introduction deep-ocean ecosystems to collect baseline biological obser- vations on pelagic fauna (zooplankton and nekton) and es- The open-ocean pelagic zones include the largest, yet least tablish the vertical ecological zonation in the deep sea. The explored habitats on the planet (Robison, 2004; Webb et Pelagic In situ Observation System (PELAGIOS) is a 3000 m al., 2010; Ramirez-Llodra et al., 2010). Since the first rated slowly (0.5 m s−1) towed camera system with LED il- oceanographic expeditions, oceanic communities of macro- lumination, an integrated oceanographic sensor set (CTD- zooplankton and micronekton have been sampled using nets O2) and telemetry allowing for online data acquisition and (Wiebe and Benfield, 2003). Such sampling has revealed a video inspection (low definition). The high-definition video community typically consisting of crustaceans, cephalopods, is stored on the camera and later annotated using software fishes, and some sturdy and commonly found gelatinous and related to concomitantly recorded environmental data. fauna (Benfield et al., 1996). Underwater observations in The PELAGIOS is particularly suitable for open-ocean ob- the open ocean via scuba diving (Hamner et al., 1975) and servations of gelatinous fauna, which is notoriously under- later via submersibles (Robison, 1983; Robison and Wish- sampled by nets and/or destroyed by fixatives. In addition ner, 1990) and in situ camera systems (Picheral et al., 2010) to counts, diversity, and distribution data as a function of revealed that a variety of organisms are much more abundant depth and environmental conditions (T, S, O2), in situ ob- in the open ocean than previously estimated from net sam- servations of behavior, orientation, and species interactions pling (Robison, 2004). This was particularly true for frag- are collected. Here, we present an overview of the techni- ile gelatinous zooplankton, a diverse taxonomic group, in- cal setup of the PELAGIOS as well as example observations cluding the ctenophores and cnidarians (Remsen et al., 2004; and analyses from the eastern tropical North Atlantic. Com- Haddock, 2004) as well as polychaetes (Christiansen et al., parisons to data from the Multiple Opening/Closing Net and 2018), Rhizaria (Biard et al., 2016), and pelagic tunicates Environmental Sensing System (MOCNESS) net sampling (Remsen et al., 2004; Neitzel, 2017), which often are too del- and data from the Underwater Vision Profiler (UVP) are pro- icate to be quantified using nets as they are damaged beyond vided and discussed. identification, or they are easily destroyed by the use of com- mon fixatives. Underwater (in situ) observations in the pelagic ocean not only revealed a previously unknown community, they also allowed the collection of fine-scale distribution patterns of plankton in relation to biotic and abiotic factors (e.g., Haslob et al., 2009; Möller et al., 2013; Hauss et al., 2016) as well as information on posture, interactions, and behavior (Ham- Published by Copernicus Publications on behalf of the European Geosciences Union. 1328 H.-J. Hoving et al.: The Pelagic In situ Observation System (PELAGIOS) ner and Robison, 1992; Robison, 2004; Robison, 1999; Hov- ganisms between 1 and 100 cm, it combines a high-resolution ing et al., 2013, 2016). Submersibles have proven to be valu- color digital charge-coupled device (CCD) camera using pro- able instruments to study deep-sea pelagic biology (e.g., Ro- gressive scanning interline-transfer technology with flashing bison, 1987; Bush et al., 2007; Hoving et al., 2017). Us- strobes, and it is towed at 1 knot via a fiber optic wire. LAPIS ing video transecting methodology, pelagic remotely oper- collects still images, illumination is sideways, and organisms ated vehicle (ROV) surveys have been applied to study inter- have to enter an illuminated volume to be visualized. Deploy- and intra-annual variation in mesopelagic zooplankton com- ments in the Southern Ocean enabled the reconstruction of munities (Robison et al., 1998; Hull et al., 2011) and to ex- depth distributions of the pelagic fauna (salps, medusae) but plore deep pelagic communities in different oceans (Young- also allowed some behavior observations, e.g., the molting of bluth et al., 2008; Hosia et al., 2017; Robison et al., 2010). krill (Madin et al., 2006). More publications of data collected However, due to high costs as well as technological and lo- with LAPIS are unavailable to our knowledge. In addition to gistical challenges, regular submersible operations are still LAPIS, we wanted to develop a towed pelagic observation restricted to very few institutes and geographical locations. system that collects video during horizontal transects (with Hence, there is a need for the development of additional more forward projected light), in a similar way to pelagic ROV cost-effective methodologies to explore and document deep- video transects, in order to document behavior in addition to sea communities via in situ observations. diversity, species-specific distribution, and abundance data of In the last decades, a variety of optical instruments has pelagic fauna. been developed to image and quantify plankton in situ (Ben- The functional requirements for the instrument were (1) field et al., 2007). The factors that typically differentiate the the ability to visualize organisms >1 cm in waters down to available plankton imaging technologies are the size fraction 1000 m with high-definition video, (2) the possibility of de- of the observed organisms, illumination type, resolution of ploying the instrument from ships of opportunity in an au- collected images or video, depth rating, deployment mode tonomous or transmitting mode, (3) for it to be lightweight (e.g., autonomous, towed, CTD-mounted), and towing speed. and practical so it can be deployed easily and safely with two Examples of instruments include the autonomous Underwa- deck persons and a winch operator, (4) to enable the corre- ter Vision Profiler (UVP5; Picheral et al., 2010), the Light- lation of observations with environmental parameters (S, T, frame On-sight Key species Investigations (LOKI; Schulz O2) and other sensor data, and (5) to make observations com- et al., 2010) and towed plankton recorders (In Situ Ichthy- parable to ROV video transects in other reference areas. We oplankton Imaging System – ISIIS; Cowen and Guigand, present a description of the Pelagic In situ Observation Sys- 2008; for a review, see Benfield et al., 2007). These instru- tem (PELAGIOS), examples of the kind of biological infor- ments can be deployed from ships of opportunity and collect mation it may gather, as well as biological discoveries that detailed information on fine-scale distribution and diversity have resulted from deployments on research cruises in the patterns of particles and plankton. The data reveal biological eastern tropical North Atlantic. patterns on a global scale (Kiko et al., 2017) and of previ- ously underappreciated plankton species (Biard et al., 2016). More recently, optical (and acoustic) instruments have been 2 Pelagic In Situ Observation System combined with autonomous gliders, rapidly increasing spa- tial resolution (Ohman et al., 2019). 2.1 Technical specifications Various towed camera platforms have been developed that can obtain video transect observations above the deep sea The PELAGIOS consists of an aluminum frame (length: 2 m) floor. Examples are the TowCam (WHOI), the DTIS (Deep that carries the oceanographic equipment (Fig. 1). White Towed Imaging system, NIWA), the WASP vehicle (Wide light LED arrays (four LEDs produced at GEOMAR, two Angle Seafloor Photography), OFOS (Ocean Floor Obser- LED arrays of the type LightSphere of Deep-Sea Power and vation System, GEOMAR), and the more recent version Light ©), which illuminate the water in front of the sys- OFOBS (Ocean Floor Observation and Bathymetry System; tem, are mounted on an aluminum ring (diameter: 1.2 m). Purser et al., 2018). All these instruments are used for video Power is provided by two lithium batteries (24 V; 32 Ah) in or photo transects of the seafloor, with a downward looking a deep-sea housing. High-definition video is collected con- camera and typically a set of lasers for size reference. How- tinuously by a forward-viewing deep-sea camera (1Cam Al- ever, published descriptions of optical systems, other than pha, SubC Imaging ©), which is mounted in the center of ROVs and submersibles that visualize macrozooplankton and the ring. We used the maximum frame rate of 50 frames s−1 micronekton (>1 cm) in the water column undisturbed by a but a lower frame rate is possible. A CTD (SBE 19 Sea- filtering device or cuvette are, to the best of our knowledge, CAT, Sea-Bird Scientific ©) with an oxygen sensor (SBE 43, restricted to one (Madin et al., 2006). The Large Area Plank- Sea-Bird Scientific ©) records environmental data. A deep- ton Imaging System (LAPIS) is the only towed system that sea telemetry (DST-6, Sea and Sun Technology ©; Linke et was developed for the documentation of larger organisms in al., 2015) transmits video and CTD data to a deck unit on the water column (Madin et al., 2006). LAPIS visualizes or- board allowing a low-resolution preview (600 × 480 lines) Ocean Sci., 15, 1327–1340, 2019 www.ocean-sci.net/15/1327/2019/ H.-J.
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