CNRS, UMR 7144, EPPO, Université Pierre et Marie Curie, Station Biologique de Roscoff - Place Georges Teissier, Roscoff, France.
PLoS One. 2013;8(1):e53598. doi: 10.1371/journal.pone.0053598. Epub 2013 Jan 11.
Marine planktonic organisms that undertake active vertical migrations over their life cycle are important contributors to downward particle flux in the oceans. Acantharia, globally distributed heterotrophic protists that are unique in building skeletons of celestite (strontium sulfate), can produce reproductive cysts covered by a heavy mineral shell that sink rapidly from surface to deep waters. We combined phylogenetic and biogeochemical analyses to explore the ecological and biogeochemical significance of this reproductive strategy. Phylogenetic analysis of the 18S and 28S rRNA genes of different cyst morphotypes collected in different oceans indicated that cyst-forming Acantharia belong to three early diverging and essentially non symbiotic clades from the orders Chaunacanthida and Holacanthida. Environmental high-throughput V9 tag sequences and clone libraries of the 18S rRNA showed that the three clades are widely distributed in the Indian, Atlantic and Pacific Oceans at different latitudes, but appear prominent in regions of higher primary productivity. Moreover, sequences of cyst-forming Acantharia were distributed evenly in both the photic and mesopelagic zone, a vertical distribution that we attribute to their life cycle where flagellated swarmers are released in deep waters from sinking cysts. Bathypelagic sediment traps in the subantarctic and oligotrophic subtropical Atlantic Ocean showed that downward flux of Acantharia was only large at high-latitudes and during a phytoplankton bloom. Their contribution to the total monthly particulate organic matter flux can represent up to 3%. High organic carbon export in cold waters would be a putative nutritional source for juveniles ascending in the water column. This study improves our understanding of the life cycle and biogeochemical contribution of Acantharia, and brings new insights into a remarkable reproductive strategy in marine protists.
海洋浮游生物在其生命周期中进行主动垂直迁移，是海洋中向下颗粒通量的重要贡献者。刺胞动物门是全球分布的异养原生动物，它们的独特之处在于形成天青石（硫酸锶）骨骼，可以产生被重矿物壳覆盖的生殖囊，这些生殖囊会迅速从表面下沉到深海。我们结合系统发育和生物地球化学分析，探索了这种生殖策略的生态和生物地球化学意义。对在不同海洋中收集的不同囊泡形态的 18S 和 28S rRNA 基因进行系统发育分析表明，形成囊泡的刺胞动物门属于三个早期分化的、基本上非共生的进化枝，分别来自 Chaunacanthida 和 Holacanthida 目。环境高通量 V9 标签序列和 18S rRNA 的克隆文库表明，这三个进化枝广泛分布于印度洋、大西洋和太平洋，分布纬度不同，但在初级生产力较高的区域更为突出。此外，形成囊泡的刺胞动物门的序列在透光层和中层水层中均匀分布，这种垂直分布归因于它们的生命周期，其中鞭毛游动孢子从下沉的囊泡中释放到深水中。在亚南极和寡营养亚热带大西洋的深海沉积物陷阱中，只有在高纬度和浮游植物爆发期间，刺胞动物的向下通量才很大。它们对每月总颗粒有机物质通量的贡献可达 3%。冷水的高有机碳输出可能是在水柱中上升的幼体的潜在营养源。这项研究提高了我们对刺胞动物生命周期和生物地球化学贡献的认识，并为海洋原生动物的这种显著生殖策略提供了新的见解。
