Pacific oysters Crassostrea (Magallana) gigas have been successfully invading ecosystems worldwide. As an ecosystem engineer, they have the potential to substantially impact on other species and on functional processes of invaded ecosystems. Engineering strength depends on oyster density in space and time. Density has not yet been studied on the extent of reef structural dynamics. This study assessed abundance of naturalized Pacific oysters by shell length (SL) of live individuals and post-mortem shells at six sites over six consecutive years during post-establishment. Individual biomass, i.e. live wet mass (LWM), flesh mass (FM) and live shell mass (SM LIVE), were determined from a total of 1.935 live oysters in order to estimate areal biomass. The generic term density attribute was used for SL-related population categories and the biomass variables LWM, FM, SM LIVE and SM. As the oyster invasion modulated resident Mytilus edulis beds, the study was supplemented by contemporaneously assessed data of mussels and corresponding analyses. Interrelations of abundance and areal biomass revealed distinct linkages between specific density attributes. Most importantly, large individuals were identified as intrinsic drivers for the determination of areal biomass. Additionally, allometry of large oysters differed from small oysters by attenuated scaling relations. This effect was enhanced by oyster density as results showed that crowding forced large individuals into an increasing slender shape. The significant relationship between the density attributes large oyster and biomass enabled a classification of reef types by large oyster abundance. Reef type (simple or complex reef) and oyster size (small or large) were considered by implementing a novel concept of weighted twin functions (TF) for the relationship between SL and individual biomass. This study demonstrates that the interplay of scaling parameters (scalar, exponent) is highly sensitive to the estimation of individual biomass (shape) and that putative similar scaling parameters can exceedingly affect the estimation of areal biomass. For the first time, this study documents the crucial relevance of areal reference, i.e. cluster density (CD) or reef density (RD), when comparing density. RD considers reef areas devoid of oysters and results from CD reduced by reef coverage (RC) as the relative reef area occupied by oysters. A compilation of density attributes at simple and complex reefs shall serve as a density guide. Irrespective of areal reference, oyster structural density attributes were significantly higher at complex than at simple reefs. In contrast, areal reference was of vital importance when evaluating the impact of engineering strength at ecosystem-level. While mussel CD was similar at both reef types, RD at complex reefs supported significantly more large mussels and higher mussel biomass than at simple reefs. Although mussels dominated both reef types by abundance of large individuals, oysters were the keystone engineers by dominating biomass. The prominent status of large oysters for both allometric scaling and density, presumably characteristic for Pacific oyster populations worldwide, should be considered when conducting future investigations. The effort of monitoring will substantially be reduced as only large oysters have to be counted for an empirical characterization of Pacific oyster reefs. The large oyster concept is independent of sampling season, assessment method or ecosystem, and is also applicable to old data sets. Harmonization on the proposed density attributes with a clear specification of areal reference will allow trans-regional comparisons of Pacific oyster reefs and will facilitate evaluations of engineering strength, reef performance and invasional impacts at ecosystem-level.

中文翻译：

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密度有多高？寻求统一的方法来表征非本地太平洋牡蛎的礁石-考虑到本地贻贝

太平洋牡蛎Crassostrea（Magallana）gigas已成功入侵全球生态系统。作为生态系统工程师，它们有可能对其他物种和入侵生态系统的功能过程产生实质性影响。工程强度取决于时空上的牡蛎密度。尚未对礁石结构动力学程度进行密度研究。这项研究在建立后的连续六年中，通过活体个体的壳长（SL）和尸体在六个地点的死后壳的壳长（SL）评估了归化太平洋牡蛎的丰度。从总共1.935个活牡蛎中确定单个生物量，即活湿质量（LWM），肉重（FM）和活壳质量（SM LIVE），以估算面积生物量。通用术语密度属性用于与SL相关的种群类别以及生物量变量LWM，FM，SM LIVE和SM。由于牡蛎入侵调节了常住的Mytilus edulis病床，该研究得到了贻贝同期评估数据和相应分析的补充。丰度和面积生物量的相互关系揭示了特定密度属性之间的独特联系。最重要的是，大型个体被确定为确定区域生物量的内在驱动力。此外，大牡蛎的变构关系与小牡蛎的比例关系有所不同。牡蛎密度增强了这种效果，因为结果表明，拥挤迫使大个体变成越来越细长的形状。密度属性大牡蛎和生物量之间的显着关系使得可以通过大牡蛎丰度对礁石类型进行分类。通过对SL和单个生物量之间的关系实施加权孪生函数（TF）的新概念，可以考虑礁的类型（简单或复杂的礁）和牡蛎大小（大小）。这项研究表明，缩放参数（标量，指数）的相互作用对单个生物量（形状）的估计高度敏感，并且推定的相似缩放参数可能会极大地影响面积生物量的估计。这项研究首次记录了在比较密度时区域参考的关键相关性，即簇密度（CD）或礁石密度（RD）。RD认为没有牡蛎的珊瑚礁区域，CD的结果由于珊瑚礁覆盖率（RC）的减少而减少，这是牡蛎占据的相对珊瑚礁区域。简单和复杂礁石上密度属性的汇编应作为密度指南。不论面积参考如何，复杂结构的牡蛎结构密度属性均明显高于简单礁石。相反，在评估工程实力在生态系统层面的影响时，区域参考至关重要。尽管两种礁石类型的贻贝CD相似，但是复杂礁石的RD支持的大型贻贝和更高的贻贝生物量要比简单礁石支持得多。尽管贻贝以大量个体占据了这两种珊瑚礁的类型，但牡蛎却是控制生物量的主要工程师。在进行将来的调查时，应考虑大牡蛎在异形结垢和密度方面的突出地位，大概是全球太平洋牡蛎种群的特征。监测工作将大大减少，因为只需要对大型牡蛎进行计数就可以对太平洋牡蛎礁进行经验表征。大型牡蛎概念与采样季节，评估方法或生态系统无关，也适用于旧数据集。对拟议的密度属性和区域参考的明确说明进行协调，将可以对跨太平洋的牡蛎礁进行跨区域比较，并且将有助于在生态系统水平上评估工程强度，礁石性能和入侵影响。进行未来调查时应考虑。监测工作将大大减少，因为只需要对大型牡蛎进行计数就可以对太平洋牡蛎礁进行经验表征。大型牡蛎概念与采样季节，评估方法或生态系统无关，也适用于旧数据集。对拟议的密度属性和区域参考的明确说明进行协调，将可以对跨太平洋的牡蛎礁进行跨区域比较，并且将有助于在生态系统水平上评估工程强度，礁石性能和入侵影响。进行未来调查时应考虑。监测工作将大大减少，因为只需要对大型牡蛎进行计数就可以对太平洋牡蛎礁进行经验表征。大型牡蛎概念与采样季节，评估方法或生态系统无关，也适用于旧数据集。对拟议的密度属性和区域参考的明确说明进行协调，将可以对跨太平洋的牡蛎礁进行跨区域比较，并且将有助于在生态系统水平上评估工程强度，礁石性能和入侵影响。大牡蛎的概念与采样季节，评估方法或生态系统无关，并且也适用于旧数据集。对拟议的密度属性和区域参考的明确说明进行协调，将可以对跨太平洋的牡蛎礁进行跨区域比较，并且将有助于在生态系统水平上评估工程强度，礁石性能和入侵影响。大牡蛎的概念与采样季节，评估方法或生态系统无关，并且也适用于旧数据集。对拟议的密度属性和区域参考的明确说明进行协调，将可以对跨太平洋的牡蛎礁进行跨区域比较，并且将有助于在生态系统水平上评估工程强度，礁石性能和入侵影响。