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Spatial and vertical biogeography of coral reef sediment bacterial and diazotroph communities

机译：珊瑚礁沉积物细菌和重氮营养菌群落的空间和垂直生物地理学

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Coral reefs are globally important marine ecosystems as sites of high biotic diversity. Reef flat sediments are reasonably homogeneous in composition. This substratum is subject to gradients in water motion, grazing pressure and benthic productivity. This study used DNA fingerprinting techniques, automated rRNA intergenic spacer analysis (ARISA), and terminal restriction fragment length polymorphism (TRFLP) to examine patterns of bacterial assemblage composition within Heron Reef flat sediments, targeting the entire bacterial community (not including Archaea) and nitrogen-fixing bacteria. ARISA fingerprints contained between 51 and 148 operational taxonomic units (OTU) per surface sediment sample. The mean whole-community similarity between adjacent sites along a transect from Heron Island to the reef crest was 0.50 ± 0.03 (mean ± SE) Whittaker Index (comparison of relative abundances) and 0.46 ± 0.03 Jaccard Index (presence/absence only). Comparison of sediment community fingerprints to a water column community fingerprint collected above the reef flat at high tide indicated that sediments contained different assemblages to the water column (mean similarity between sediments and water column assemblage = 0.15 ± 0.01 Jaccard Index); however, assemblage composition did not differ significantly from that expected by random association. Vertical sediment cores showed dissimilarity between surface (0 to 3 cm) and deep (3 to 5 cm) community fingerprints, which was probably related to redox state. Comparison of fingerprints of fecally-derived sediments from the sea cucumber Holothuria atra and surrounding sediments indicated that the impact of metazoan grazing could not be distinguished from ambient small spatial scale variability in sediment assemblage composition. The nifH-TRFLP fingerprints of sediment prokaryotic assemblages (amplified from all samples, but only in sufficient quantities for analysis from 7 locations) indicated the presence of ubiquitous, potentially diverse diazotroph communities, with little assemblage similarity between locations. Our results suggested that while bacterial assemblages (including communities of nitrogen-fixing bacteria) in sediments of a coral reef are diverse, their assemblage composition is not related to grazing pressure but may be influenced by other biotic and abiotic environmental conditions such wave energy and sediment depth.
机译：珊瑚礁是全球重要的海洋生态系统，具有高度生物多样性。礁滩沉积物的成分相当均匀。该底层在水运动，放牧压力和底栖生产力方面受到梯度的影响。这项研究使用DNA指纹技术，自动rRNA基因间隔分析（ARISA）和末端限制性片段长度多态性（TRFLP）来检查鹭鹭礁平坦沉积物中细菌组合组成的模式，目标是整个细菌群落（不包括古细菌）和氮固定细菌。每个表面沉积物样本的ARISA指纹包含51至148个操作生物分类单位（OTU）。从苍鹭岛到礁顶的一条样带的相邻站点之间的平均全社区相似度为0.50±0.03（平均±SE）惠特克指数（相对丰度的比较）和0.46±0.03雅卡德指数（仅存在/不存在）。沉积物群落指纹与涨潮时在礁滩上方收集的水柱群落指纹的比较表明，沉积物与水柱的组合不同（沉积物与水柱组合的平均相似度= 0.15±0.01 Jaccard指数）；但是，组装组成与随机关联所期望的没有显着差异。垂直沉积物核在表面（0至3 cm）和深部（3至5 cm）群落指纹之间显示出差异，这可能与氧化还原状态有关。海参Holothuria atra和周围沉积物粪便来源沉积物指纹图谱的比较表明，后生动物放牧的影响无法与沉积物组成中环境小空间尺度的变化区分开。沉积物原核生物组合的nifH-TRFLP指纹图谱（从所有样品中扩增，但仅从7个位置进行了足够数量的分析）表明存在着普遍存在的，可能具有多样性的重氮营养菌群落，各个位置之间的组合相似性很小。我们的结果表明，尽管珊瑚礁沉积物中的细菌组合（包括固氮细菌群落）是多种多样的，但它们的组合组成与放牧压力无关，但可能受到其他生物和非生物环境条件（例如波浪能和沉积物）的影响深度。

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