Meiofauna hotspot in the Atacama Trench,eastern South Pacific Ocean |
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| Affiliation: | 1. Facoltà di Scienze, Istituto Scienze del Mare, Università di Ancona, Via Brecce Bianche, 60131, Ancona, Italy;2. Istituto Scienze Ambientali Marine Università di Genova, Genova, Italy;1. University of Hamburg, Centre of Natural History (CeNak), Zoological Museum, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany;2. A.V. Zhirmunsky Institute of Marine Biology, FEB RAS, Palchevskogo 17, 690041 Vladivostok, Russia;3. Far East Federal University, Oktiabrskaya Str, 29, 690600 Vladivostok, Russia;4. German Centre for Marine Biodiversiy Research, Südstrand 44, D-26382 Wilhelmshaven, Germany;1. German Centre for Marine Biodiversity Research (DZMB), Senckenberg am Meer, Südstrand 44, 26382 Wilhelmshaven, Germany;2. V.I. Il''ichev Pacific Oceanological Institute (POI), Far Eastern Branch of Russian Academy of Sciences (FEBRAS), 43, Baltiyskaya Street, 690041 Vladivostok, Russia;3. Independent Researcher;1. Minderoo UWA Deep-Sea Research Centre, School of Biological Sciences and Oceans Institute, The University of Western Australia, IOMRC Building M470, 35 Stirling Highway, Perth, WA, 6009, Australia;2. British Geological Survey, Lyell Centre, Research Avenue South, Edinburgh, EH14 4AP, UK;3. School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK;4. Caladan Oceanic LLC, 5909 Luther Lane, Dallas, TX, TX 75225, USA;1. Department of Biomolecular Sciences (DiSB), University of Urbino, Italy;2. Department of Pure and Applied Sciences (DiSPeA), University of Urbino, Italy;3. Department of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Genoa, Italy;4. Univ. Lille, CNRS, Univ. Littoral Côte d’Opale, UMR 8187, LOG, Laboratoire d’Océanologie et de Géosciences, F 59000, Lille, France;5. Dipartimento di Scienze e Tecnologie (DiST), CoNISMa, University of Napoli "Parthenope", Napoli, Italy |
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| Abstract: | Meiofaunal assemblages were investigated (in terms of abundance, biomass, individual size and community structure) at bathyal and hadal depths (from 1050 to 7800 m) in the Atacama Trench in the upwelling sector of the eastern South Pacific Ocean, in relation to the distribution and availability of potential food sources (phytopigments, biochemical compounds and bacterial biomass) in this highly productive region. Meiofaunal density and biomass in the Atacama Trench were one to two orders of magnitude higher than values reported in other “oligotrophic” hadal systems. The Atacama Trench presented very high concentrations of nutritionally rich organic matter at 7800-m depth and displayed characteristics typical of eutrophic systems. Surprisingly, despite a decrease in chlorophyll-a and organic matter concentrations of about 50% from bathyal to hadal depths, meiofaunal abundance in hadal sediments was 10-fold higher than at bathyal depths. As indicated by the higher protein to carbohydrate ratio observed in trench sediments, the extraordinarily high meiofaunal density reported in the Atacama Trench was more dependent upon organic matter quality than on its quantity. The trophic richness of the system was reflected by a shift of the size structure of the benthic organisms. In contrast with typical trends of deep-sea systems, the ratio of bacterial to meiofaunal biomass decreased with increasing depth and, in the Atacama Trench, meiofaunal biomass largely dominated total benthic biomass. Nematodes at 7800-m depth accounted for more than 80% of total density and about 50% of total meiofaunal biomass. In hadal sediments a clear meiofaunal dwarfism was observed: the individual body size of nematodes and other taxa was reduced by 30–40% compared to individuals collected at bathyal depths. The peculiarity of this trophic-rich system allows rejection of previous hypotheses, which explained deep-sea dwarfism by the extremely oligotrophic conditions typical of deep-sea regions. |
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