Data from: Evaluating fish scale preservation in sediment records from the oxygen minimum zone off Peru

Fish scales accumulating in marine laminated sediments can provide a record of population variability of small pelagic fishes. Although some studies have noted signs of scale degradation that could affect estimates of population variability, there are presently no well-developed means to evaluate degradation. We developed several indices as indicators of fish scale preservation in two box-cores that we collected off Pisco (14ºS), one at 301 m near the center of the oxygen minimum zone (OMZ), and the other at 201 m near the upper limit of the OMZ. These indices include (1) an index of fish scale integrity (estimate of scale wholeness relative to fragmentation), (2) the fungi-free area of fish scales and vertebrae, (3) the ratio of fish scales to vertebrae (as well as fish scales to vertebrae and bones), and (4) the ratio of whole scales to fragments. We address whether lower numbers of anchovy scales occurring in association with reduced total organic carbon fluxes and higher bottom-water oxygen concentrations are due entirely to lower abundances of anchovy or whether differential preservation of the fish scales in the sediments plays an important role in reduced scale abundances. Comparison of temporal sequences between the two cores provides the means to assess whether there are differences in the preservation of fish scales. The combined indices indicate that the lower numbers of fish scales in the earliest period have been affected by degradation, and to a greater degree in the box-core from 201 meters, which can be subject to higher oxygen concentrations. On the other hand, decadal-scale variations in fish scale abundance within the period of better preservation are unlikely to be caused by degradation. We discuss the utility and drawbacks of different indices of preservation for reconstructing past changes in fish population sizes with fluxes of fish debris and also briefly discuss the utility of these indices to other paleobiological systems.海洋纹层沉积物中赋存的鱼鳞，可作为小型中上层鱼类种群动态变化的历史档案。尽管已有研究指出鱼鳞降解会对种群动态估算造成干扰，但目前尚无成熟方法可用于评估这类降解程度。本研究针对在皮斯科（14°S）海域采集的两个箱式岩芯（box-core），建立了若干表征鱼鳞保存状况的指标体系：其中一处岩芯站位水深301米，位于氧最低带（OMZ）中心附近；另一处站位水深201米，紧邻氧最低带上限。这些指标具体包括：(1) 鱼鳞完整度指数（即完整鱼鳞与碎裂残片的相对占比估算）；(2) 鱼鳞与脊椎骨的无真菌附着面积；(3) 鱼鳞与脊椎骨的数量比值（以及鱼鳞与脊椎骨、骨骼的数量比值）；(4) 完整鱼鳞与残片的数量比值。本研究旨在厘清：与总有机碳通量降低、底层水氧浓度升高相伴出现的鳀鱼鳞片数量减少，究竟是完全由鳀鱼种群丰度下降所致，还是沉积物中鱼鳞的差异保存对鳞片丰度降低起到了关键作用。通过对比两处岩芯的时间序列，可评估不同站位间鱼鳞保存状况是否存在差异。综合各项指标结果显示，最早沉积阶段的鱼鳞数量偏低，曾受到降解作用的影响，其中水深201米的箱式岩芯受影响程度更高——该站位的底层水氧浓度相对更高。另一方面，在保存状况较好的沉积阶段内，鱼鳞丰度的年代际波动则不太可能由降解作用导致。本研究还讨论了利用鱼类碎屑通量重建史前鱼类种群规模变化时，各类保存指标的适用性与局限性，并简要探讨了这些指标在其他古生物研究体系中的应用潜力。