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Heterogeneous energetic pathways and carbon sources on deep eastern Mediterranean cold seep communities

机译：地中海东部深部冷渗群落的非均质能量途径和碳源

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摘要

Cold seep communities in the Mediterranean Sea have only been discovered two decades ago, and their trophic ecology has been the subject of very few studies. We investigated the benthic food web of two deep che-mosynthesis-based ecosystems on the Napoli and Amsterdam mud volcanoes (MVs) in the eastern Mediterranean Sea (～2,000 m depth). Seeping methane has been detected at the surface of both MVs during pioneering cruises and has been hypothesised to be assimilated by benthic fauna as observed in other oceans' margins. Given the extreme oligotrophic character of the eastern Mediterranean Sea, we a priori expected that chemosynthetic food sources, especially methane-derived carbon (MDC), played a major trophic role in these deep seep communities relative to what has been observed in other seep systems worldwide. We aimed at unravelling the trophic relationships on Napoli and Amsterdam MVs through the analysis of carbon, nitrogen and sulphur isotopes both in the dominant benthic invertebrates including the small endofaunarn(300 μm < size < 1 cm) and in the sedimented organic matter. In particular, we assessed the fraction of MDC in the tissue of several heterotrophic and symbiotic species. Low mean δ~(34)S and δ~(13)C values (0.4 ± 4.8% and -31.6 ± 5.7‰, respectively) obtained for mega- and macrofauna suggested that the investigated benthic food webs are virtually exclusively fuelled by carbon of chemosynthetic origin. A few grazer invertebrates (δ~(34)S up to 11‰) depart from this trend and could complement their diet with sedimented and decayed phytoplanktonic organic matter. Faunal δ~(13)C values indicated that the oxidation of sulphur is likely the predominant energetic pathway for biosynthesis on both MVs. Nevertheless, mytilid bivalves and small capitellid, ampharetid and spionid polychaetes were ~(13)C-depleted (δ~(13)C < -37‰) in a way indicating they assimilated a significant portion of MDC. For these later heterotrophic species, MDC ranged between 21 and 31% (lower estimates) and 97 and 100% (upper estimates). However, our results highlighted that the origin of assimilated carbon may be complex for some symbiotic species. The vestimentiferan tubeworm Lamellibrachia sp., which exclusively depends on its sulphur-oxidising endo-symbionts, showed a ～20‰ inter-individual δ~(13)C variability on a very small spatial scale (<1 m) at the summit of Napoli MV. This mostly reflects the variable isotopic composition of pore-water-dissolved inorganic carbon (DIC) and evidenced that tubeworms (and subsequently their endosymbionts) uptake DIC derived from multiple methane oxidation processes in varying proportions. The lower and upper MDC estimates for the vestimentum of Napoli's individuals were 11-38 and 21-73%, respectively. Finally, data on trophic ecology of Napoli and Amsterdam MVs clearly corroborate previous geophysical results evidencing the spatial heterogeneity of Mediterranean MV environmental conditions.
机译：地中海的冷渗流群落直到二十年前才被发现，其营养生态一直是很少研究的主题。我们调查了地中海东部那不勒斯和阿姆斯特丹泥火山（MVs）（约2,000 m深度）上两个基于化学合成的深层生态系统的底栖食物网。在开创性航行中，在这两个MV的表面都检测到了甲烷的渗入，并被假想为与其他海洋边缘的底栖动物同化。鉴于地中海东部地区具有极端的贫营养特征，我们先验地期望，化学合成食品来源，尤其是甲烷衍生的碳（MDC），在这些深层渗水群落中起着重要的营养作用，相对于在全球其他渗水系统中所观察到的。我们旨在通过分析主要底栖无脊椎动物中的碳，氮和硫同位素（包括小的内生真菌（300μm<尺寸<1 cm）和沉积的有机物）来揭示那不勒斯和阿姆斯特丹MV的营养关系。特别是，我们评估了几种异养和共生物种的组织中MDC的比例。大型动物和大型动物获得的较低的平均δ〜（34）S和δ〜（13）C值（分别为0.4±4.8％和-31.6±5.7‰）表明，所研究的底栖食物网实际上完全由碳作为燃料。化学合成起源。一些食草无脊椎动物（δ〜（34）S高达11‰）背离了这种趋势，可以通过沉积和腐烂的浮游植物有机质来补充其饮食。动物的δ〜（13）C值表明，硫的氧化可能是两种MV上生物合成的主要能量途径。但是，枯萎的双壳类动物和小头足类，羊栖类和带鞘类的多毛类动物被〜（13）C耗尽（δ〜（13）C <-37‰），这表明它们同化了MDC的大部分。对于这些后来的异养物种，MDC介于21％至31％（较低的估计值）和97％至100％（较高的估计值）之间。但是，我们的结果强调，对于某些共生物种而言，同化碳的起源可能很复杂。在那不勒斯的顶峰处，仅依赖于其硫氧化内共生体的鳞茎tube虫Lamellibrachia sp。在很小的空间尺度（<1 m）上表现出〜20‰的个体δ〜（13）C变异性。 MV这主要反映了溶解在孔隙水中的无机碳（DIC）的同位素组成的变化，并表明结核虫（以及随后的它们的共生共生体）吸收了来自多种甲烷氧化过程的不同比例的DIC。 MDC对那不勒斯个人遗迹的估计的下限和上限分别为11-38％和21-73％。最后，那不勒斯和阿姆斯特丹MV的营养生态学数据清楚地证实了先前的地球物理结果，证明了地中海MV环境条件的空间异质性。

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  • 来源
    《Marine biology》 |2010年第11期|P.2545-2565|共21页
  • 作者

    Antoine Carlier; rnBenedicte Ritt; rnClara F. Rodrigues; rnJozee Sarrazin; rnKarine Olu; rnJacques Grail; Jacques Clavier;

  • 作者单位

    LEMAR-IUEM, UMR 6539 (CNRS-Universite de Bretagne Occidentale-IRD), Technopole Brest Iroise, Place Nicolas Copernic, 29280 Plouzane, France;

    Laboratoire Environnement Profond, Departement Etudes des Ecosystemes Profonds, Centre Ifremer de Brest, BP 71, 29280 Plouzane, France;

    rnCESAM & Biology Department, University of Aveiro, Aveiro, Portugal;

    rnLaboratoire Environnement Profond, Departement Etudes des Ecosystemes Profonds, Centre Ifremer de Brest, BP 71, 29280 Plouzane, France;

    rnLaboratoire Environnement Profond, Departement Etudes des Ecosystemes Profonds, Centre Ifremer de Brest, BP 71, 29280 Plouzane, France;

    rnLEMAR-IUEM, UMR 6539 (CNRS-Universite de Bretagne Occidentale-IRD), Technopole Brest Iroise, Place Nicolas Copernic, 29280 Plouzane, France;

    LEMAR-IUEM, UMR 6539 (CNRS-Universite de Bretagne Occidentale-IRD), Technopole Brest Iroise, Place Nicolas Copernic, 29280 Plouzane, France;

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