ARTICLE IN PRESS Deep Sea Research I 53 2006 48 61 www elsevier com locate dsr Vertical zonation patterns of scavenging amphipods from the Hadal zone of the Tonga and Kermadec Trenches Lesley E Blankenshipa A Aristides Yayanosa Donald B Cadienb Lisa A Levina a Scripps Institution of Oceanography 9500 Gilman Dr 0208 La Jolla CA 92093 0218 USA County Sanitation District of Los Angeles County P O Box 4998 Whittier CA 90607 USA b Received 5 May 2005 received in revised form 19 September 2005 accepted 28 September 2005 Available online 14 November 2005 Abstract Deep sea trenches present an ideal system in which to study vertical zonation though the dif culties inherent in studying these great depths have thus far deterred such research Here we present the rst account of the structure and vertical zonation of the scavenging guild residing in the hadal habitat of the Tonga and Kermadec Trenches SW Paci c Ocean Four species of scavenging amphipod Eurythenes gryllus Scopelocheirus schellenbergi Hirondellea dubia and Uristes sp nov were captured with baited free vehicle traps set 1 m above the sea oor and deployed to bottom depths between 5155 and 10 787 m Each species occupied a distinct vertical zone of 3 5 km or less and the scavenging amphipod assemblage vertically partitioned the hadal zone Scavenging amphipod diversity and evenness sharply declined below 9 km For S schellenbergi and H dubia population structure was strati ed ontogenetically Early instars appeared to reside exclusively in the shallower depths of each species vertical zone and were functionally missing from the median and deeper regions We captured brooding Uristes sp nov females documenting the rst bait attendance event of brooding amphipods in the hadal zone Separation of habitat in conjunction with deviations in reproductive traits behaviors and nutritional strategies may facilitate the coexistence of these four related species in this harsh and con ning habitat r 2005 Elsevier Ltd All rights reserved Keywords Lysianassoidea Hadal Trench Zonation Scavengers Habitat partitioning 1 Introduction With depths exceeding 6000 m the deep sea trenches are characterized by extreme hydrostatic pressures and inhabited by a specialized hadal fauna distinct from shallower deep sea fauna Belyaev 1989 Vinogradova 1997 Since the study of trench communities is both expensive and dif cult the biodiversity and ecological structure of ocean Corresponding author Tel 1 858 534 2935 E mail address lblanken ucsd edu L E Blankenship 0967 0637 see front matter r 2005 Elsevier Ltd All rights reserved doi 10 1016 j dsr 2005 09 006 trenches are poorly understood Angel 1982 Perrone et al 2002 Trenches exhibit topological relief between 51 and 151 Belyaev 1989 and bottom depths can increase by a few thousand meters over a horizontal distance of only tens of kilometers This descent down the trench wall occurs much more rapidly than in non trench settings and has important consequences for resident fauna Fauna inhabiting depths deeper than 7 km often de ned as the true hadal zone Wolff 1960 Kamenskaya 1995 exhibit a high degree of endemism indicating the potential signi cance of ARTICLE IN PRESS L E Blankenship et al Deep Sea Research I 53 2006 48 61 vertical zonation in the abyssal hadal transition zone The abundance and apparent ubiquity of scavenging amphipods in deep sea environments including deep sea trenches suggest that they are important members of these communities Hessler et al 1978 Sainte Marie 1992 Gage and Tyler 1996 Perrone et al 2002 Scavenging amphipods are captured readily with baited traps and there are numerous studies documenting their presence and geographic distribution in deep sea environments Shulenberger and Hessler 1974 Hessler et al 1978 Ingram and Hessler 1983 Charmasson and Calmet 1987 Thurston et al 2002 Deep sea amphipods are adapted to endure a speci c range of hydrostatic pressures Yayanos 1981 This adaptation is re ected in each species vertical distribution which is usually less than a few thousand meters Belyaev 1989 Kamenskaya 1995 Accordingly the vertical range for 85 of all known hadal fauna does not exceed 3 km while 66 of the known fauna are con ned to a 1 2 km vertical range Belyaev 1989 In deep trenches where the hadal zone exceeds 3 km of depth we hypothesize that the hadal amphipod community is vertically strati ed to some degree Belyaev 1989 notes that determining the vertical distributions of hadal amphipods has been problematic because much of the previous hadal sampling employed trawls and grabs amphipods are mobile and easily avoid capture Baited traps circumvent this problem but previous studies on hadal bait attending amphipods are limited to material obtained from traps deployed at a single location within a trench Hessler et al 1978 Perrone et al 2002 Thurston et al 2002 precluding such zonation studies To study the vertical zonation of scavenging amphipods and also to collect specimens for diet analyses we deployed 13 baited free vehicle traps in the abyssal and hadal depths of the Tonga and Kermadec Trenches Traps were deployed at relatively closely spaced depth intervals between 5 1 and 10 8 km bottom depths to address the following questions 1 Do multiple scavenging amphipod species occur in the Tonga and Kermadec Trenches and if so in what vertical zones 2 Is the assemblage similar in both trenches 3 Can we deduce possible mechanisms of ecological habitat partitioning from population size structure sex ratios age at maturity or distribution Speci cally do bait attending amphipods exhibit a speciesspeci c vertical depth zonation b intraspeci c 49 vertical partitioning by size classes or sex and c female size at maturity or brooding correlated with depth or location 2 Materials and methods 2 1 Site description The Tonga and Kermadec Trenches are located in the South West Paci c Ocean and are considered a single province Vinogradova 1979 The trenches are adjacent separated only by a sill the Tonga Platform that rises to approximately 5 5 km in depth Wright et al 2000 The topography of the two trenches and their close proximity to each other allows us to consider depth and also latitude as parameters that might correlate with hadal zonation patterns Both trench axes are roughly parallel to the longitude line the Tonga Trench axis extends from approximately 151S 251S and the Kermadec Trench axis continues from 251S to 351S With maximum depths of 10 882 m and 10 047 m respectively the Tonga and