Data from: Temporal dynamics of encrusting communities during the Late Devonian: a case study from the Central Devonian Field, Russia

In this study we focused on the dynamics of encrusting assemblages preserved on brachiopod hosts collected from upper Frasnian and lower Famennian deposits of the Central Devonian Field, Russia. As the encrusted brachiopods come from deposits bracketing the Frasnian-Famennian (F-F) boundary, the results also shed some light on ecological differences in encrusting communities before and after the F-F event. In order to explore the diversity dynamics of encrusting assemblages, more than one thousand brachiopod valves (substrates) from two localities were analyzed. Taxa accumulation plots and SQS routines indicated that a reasonably small sample of brachiopod host shells (n=50) is sufficient to capture the majority of the encrusting genera recorded at a given site. The richness of encrusters per substrate declined simultaneously with the number of encrusting taxa in the lower Famennian, accompanied by a decrease in epibiont abundance, with a comparable decrease in mean encrustation intensity. Epibiont abundance and occupancy roughly mirror each other. Strikingly, few ecological characteristics are correlated with substrate size, possibly reflecting random settlement of larvae. Evenness, which is negatively correlated with substrate size, shows greater within-stage variability between samples than between Frasnian and Famennian intervals, and may indicate the instability of early Famennian biocenoses following the faunal turnover. The occurrence distribution of encrusters points to non-random co-associations and co-exclusions among several encrusting taxa. However, abundance and occupancy of microconchids remained relatively stable throughout the sampled time interval. The notable decline in abundance (~60%) and relatively minor decline in diversity (~30%) suggest jointly that encrusting communities experienced ecological collapse rather than a major mass extinction event. The differences between the upper Frasnian and lower Famennian encrusting assemblages may thus record a turnover associated with the F-F event.本研究聚焦于俄罗斯中央泥盆纪沉积区弗拉阶上部与法门阶下部沉积地层中，保存在腕足动物宿主壳体上的附生生物组合的动态特征。由于该批附生腕足类标本采自弗拉阶-法门阶（F-F）界线上下的沉积地层，本研究结果亦可为揭示F-F事件前后附生生物群落的生态差异提供参考依据。为探究附生生物组合的多样性动态，研究人员对两处采样点的逾1000件腕足类壳体（附着基质）开展了分析。类群累积曲线图与SQS分析流程结果显示，仅需采集少量腕足类宿主壳体（n=50），即可覆盖某一采样点记录的绝大多数附生生物属类。法门阶下部的单基质附生生物丰富度与附生生物类群数量均同步下降，同时附生生物丰度降低，平均附生强度也出现了相当幅度的下降。附生生物丰度与占据率大致呈镜像相关关系。值得注意的是，几乎无生态特征参数与宿主基质尺寸存在相关性，这或与幼虫的随机附着模式有关。与宿主基质尺寸呈负相关的群落均匀度，其同阶段内样本间的变异性高于弗拉阶与法门阶两个地层区间的变异性，这或许表明经历动物群更替后的法门阶早期生物群落处于不稳定状态。附生生物的出现分布特征表明，多个附生生物类群间存在非随机的共现与互斥关系。但在整个采样时段内，微管虫类的丰度与占据率均保持相对稳定。附生生物丰度显著下降（约60%）而多样性仅小幅降低（约30%），这两项结果共同表明，附生生物群落经历的是生态崩溃而非大规模灭绝事件。因此，弗拉阶上部与法门阶下部的附生生物组合之间的差异，或记录了与F-F事件相关的群落更替过程。