Bathymetric patterns of megafaunal assemblages from the arctic deep-sea observatory HAUSGARTEN Thomas Soltwedel à , Nina Jaeckisch, Nikolaus Ritter 1 , Christiane Hasemann, Melanie Bergmann, Michael Klages Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany article info Article history: Received 4 November 2008 Received in revised form 13 May 2009 Accepted 18 May 2009 Available online 29 May 2009 Keywords: Arctic Deep sea Megafauna Photo/video system Continental margin Zonation abstract Five photographic transects, covering some 830 m 2 of seafloor in total, were analyzed to characterize the megabenthic community along a bathymetric gradient covering water depths from 1200 to 5500 m in the eastern Fram Strait. Megafaunal densities ranged between 11 and 38 ind.m 2 . The highest densities were found at 1650 m and the lowest densities occurred at 3000 m depth. The number of taxa and morphotypes ranged between 4 at 5500 m and 27 at 1650 m water depth. Ophiocten gracilis, a small white unidentified amphipod, Kolga hyalina, and Bathycrinus carpenteri were the dominant and characteristic species on the slope and continental rise. Elpidia heckeri dominated in the Molloy Hole, the deepest depression known in the Arctic Ocean. Megafaunal zonation patterns appeared to be mainly controlled by food availability, as indicated by phytodetrital matter measured at the seafloor, and by benthic biomass in the sediments, as indicated by sediment-bound particulate proteins and phospholipids. By contrast, physical factors, including water depth and seabed properties such as sediment porosity and hard substrata (e.g., dropstones), appear to play a secondary role in determining megabenthic zonation patterns along the bathymetric HAUSGARTEN gradient. & 2009 Elsevier Ltd. All rights reserved. 1. Introduction Deep-sea megafauna, usually characterized as the group of organisms Z1–2 cm (Grassle et al., 1975; Rex, 1981; Ohta, 1983; Smith and Hamilton, 1983), has been studied since the HMS ‘‘Challenger’’ expedition (1873–1876). Megafaunal organisms often contribute considerably to the total benthic biomass (Lampitt et al., 1986) and to remineralization processes (Piepenburg et al., 1995), and have a strong impact on the physical and biogeochemical micro-scale environment (e.g., Hu ¨ ttel and Gust, 1992; Guille ´n et al., 2008). For example, mobile megafauna creates pits, mounds, and traces that enhance habitat heterogeneity, and thus diversity, of smaller sediment-inhabiting biota in otherwise apparently homo- genous environments (Soltwedel and Vopel, 2001; Hase- mann, 2006; Que ´ ric and Soltwedel, 2007). Furthermore, structurally complex organisms such as sponges or cold- water corals enhance three-dimensional habitat complex- ity and provide resting places and shelter from predation (e.g., Collie et al., 1997; Kaiser et al., 1999). Also, megafaunal predators control the population dynamics of their prey and therefore shape benthic food webs and assemblage structure (e.g., Gray, 1981; Feder and Pearson, 1988; Baden et al., 1990; Freire, 1996; Sarda ´ et al., 1998; Gallucci et al., 2008). Although much progress has been made in this field, knowledge about the density, biomass, and dispersion of deep-sea megafauna is still scarce. Reasons for this lack are logistic difficulties involved with sampling in deep Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsri Deep-Sea Research I ARTICLE IN PRESS 0967-0637/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr.2009.05.012 à Corresponding author. Tel.: +49 47148311775; fax: +49 47148311776. E-mail address: Thomas.Soltwedel@awi.de (T. Soltwedel). 1 Present address unknown. Deep-Sea Research I 56 (2009) 1856–1872